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 Chemistry, meteorology, and 
 the function of digestion 
 
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THE BRIDGEWATER TREATISES, 
 
 ON THE POWER, WISDOM, AND GOODNESS OF GOD, AS 
 MANIFESTED IN THE CREATION. 
 
 TREATISE VIII. 
 
 CHEMISTRY, METEOROLOGY, AND THE FUNCTION OF DIGESTION, 
 ^Y WILLIAM PROUT, M.D. F.R.S. 
 
OVK aV iJ'yvXTO ^VVU/UiV iTl KXKZs i^OVTA Tot iyKiK0(rfX3L/UiV*. 
 
 HIPPODAMUS DE FELICITATE. 
 
CHEMISTRY, METEOROLOGY, 
 
 AND 
 
 THE FUNCTION OF DIGESTION 
 
 CONSIDERED WITH 
 
 REFERENCE TO NATURAL THEOLOGY. 
 
 BY 
 
 WILLIAM PROUT, M.D. F.R.S 
 
 FELLOW OF THE ROYAL COLLEGE OF PHYSICIANS. 
 
 PHILADELPHIA: 
 CAREY, LEA & BLANCHaRD. 
 
 1834. 
 
TO 
 
 DAVIES GILBERT, ESQ. 
 
 LATE PRESIDENT OF THE ROYAL SOCIETY, 
 
 ^f^in Volntat 
 
 IS 
 
 RESPECTFULLY LVSCRIBED. 
 
NOTICE. 
 
 The series of Treatises, of which the present is one, is published 
 under the followinir circumstances : 
 
 The Right Honourable and Reverend Francis Henry, Earl of 
 Bridgewater, died in the month of February, 1829; and by his last 
 Will and Testament, bearing date the 25th of February, 1825, he di- 
 rected certain Trustees therein named to invest in the public funds the 
 sum of Eight thousand pounds sterling; this sum, with the accruing 
 dividends ihereon, to be held at the disposal of the President, for the 
 time being, of the Royal Society of London, to be paid to the person 
 or persons nominated by him. The Testator further directed, that the 
 person or persons selected by the said President should be appointed 
 to write, print, and publish one thousand copies of a work On the 
 Power, fVisdom, and Goodness of God, as manifested in the Creation; 
 illustrating such work by all reasonable arguments, as for instance the va- 
 riety and formation of God's creatures in the animal, vegetable, and mi- 
 neral kingdoms,- the effect of digestion, and thereby of conversion ,- the 
 construction of the hand of man, and an infinite variety of other arguments ; 
 as also by discoveries ancient and modern, in arts, sciences, and the whole 
 extent of literature. He desired, moreover, that the profits arising from 
 the sale of the works so published should be paid to the authors of the 
 works. 
 
 The late President of the Royal Society, Davies Gilbert, Esq. re- 
 quested the assistance of his Grace the Archbishop of Canterbury and 
 of the Bishop of London, in determining upon the best mode of carry- 
 ing into effect the intentions of the Testator. Acting with tlieir advice, 
 and with the concurrence of a nobleman immediately connected with 
 the deceased, Mr. Davies Gilbert appointed the following eight gentle- 
 men to write separate Treatises on the different branches of the subject 
 as here stated : 
 
 THE REV. THOMAS CHALMERS, D. D. 
 
 Professor of Divinity in the University of Edinburgh. 
 
 ON THE POWER, WISDOM, AND GOODNESS OF GOD AS MANIFESTED IN THE 
 
 ADAPTATION OF EXTERNAL NATURE TO THE MORAL AND 
 
 INTELLECTUAL CONSTITUTION OF MAN. 
 
 JOHN KIDD, M. D. F. R. S. 
 
 Regius Professor of 3Iedicine in the University of Oxford. 
 
 ON THE ADAPTATION OF EXTERNAL NATURE TO THE PHYSICAL CONDITION 
 
 OF MAN. 
 1* 
 
VI 
 
 THE REV. WILLIAM WHEWELL, M.A. F.R.S. 
 
 Fellow of Trinity College, Cambridge. 
 
 ASTRONOMY AND GENERAL PHYSICS CONSIDERED WITH REFERENCE TO 
 
 NATURAL THEOLOGY. 
 
 SIR CHARLES BELL, K. G. H. F.R.S. L.&E. 
 
 THE HAND : ITS MECHANISM AND VITAL ENDOWMENTS AS EVINCING DESIGN. 
 
 PETER MARK ROGET, M. D. 
 
 Fellow of and Secretary to the Royal Society. 
 ON ANIMAL AND VEGETABLE PHYSIOLOGY. 
 
 THE REV. WILLIAM BUCKLAND, D.D. F.R.S. 
 
 Canon of Christ Church, and Professor of Geology in the University of Oxford. 
 ON GEOLOGY AND MINERALOGY. 
 
 THE REV. WILLIAM KIRBY, M.A. F.R.S. 
 
 ON THE HISTORY, HABITS, AND INSTINCTS OF ANIMALS. 
 
 WILLIAM PROUT, M.D. F.R.S. 
 
 CKEMISTRY, METEOROLOGY, AND THE FUNCTION OF DIGESTION, CONSIDERED 
 WITH REFERENCE TO NATURAL THEOLOGY. 
 
 His Royal Highness the Duke of Sussex, President of the Royal 
 Society, having- desired tiiat no unnecessary delay should take place in 
 the publication of the above mentioned treatises, they will appear at 
 short intervals, as they are ready for publication. 
 
TO THE READER. 
 
 Chemistry has not hitherto been considered in detail with 
 reference to Natural Theology: the difficulties, therefore, 
 incidental to a first attempt, added to those arising from the 
 nature of Chemistry itself as a science, must be the apology 
 of the author for numerous imperfections in this treatise. 
 
 The peculiar chemical opinions advanced, would never 
 have appeared in their present form ; had not the author 
 been strongly impressed with the belief that they are calcu- 
 lated, sooner or later, to bring chemical action under the 
 dominion of the laws of quantity ; and had he not despaired, 
 under his professional engagements, of being himself able to 
 submit them to experimental proof These opinions, how- 
 ever, have been always introduced as mere illustrations. 
 
 The argument of design is necessarily cumulative ; that 
 is to say, is made up of many similar arguments. To avoid 
 repetitions therefore, the illustration of principles rather than 
 of details, has been studied ; and the application of particular 
 facts to the argument, has been often left to the Reader. 
 
 LONDO?:, 
 
 February 3, 1834. 
 
CONTENTS. 
 
 iNTnoDtrcTioif. 
 
 Of the Leading Argument of Natural Theology ; that Design, or the 
 
 Adaptation of Means to an End exists in Nature. 23 
 
 BOOK 1. 
 
 CHEMISTRY. 
 
 Preliminary Observations on the Rank of Chemistry as a Science ; 
 and on the Apphcation of Chemistry to the Argument of De- 
 sign. 25 
 Chapter T. — Of the Mutual Operation of Physical Agents and of Mat- 
 ter, and of the Laws which they obey. 32 
 Chapter II. — Of the Inertia and Activity of Matter. 33 
 Chapter III. — Of Molecular or Polarizing Forces, etc. 35 
 Section I. Of the Divisibility of Matter. 35 
 Section II. Of the Forms of Aggregation of the ultimate Mole- 
 cules of Matter. o7 
 Section III. Of the solid Form of Bodies. Crystallization. 38 
 Of Electricity. 42 
 Of Magnetism. 44 
 Of Polarity. 46 
 Section IV. Of the Liquid Form of Bodies. Of Heat. 48 
 Of the Latency of Heat. 51 
 Section V. Of the Gaseous Form of Bodies. 53 
 Of the Diffusion of Gaseous Bodies. 55 
 Of the equal Expansion of Gaseous Bodies ; and of their simi- 
 lar Capacit}^ for Heat. 56 
 Section VT. Of the other Properties of Heat. Of Heat in Motion. 
 
 Of the Radiation, Conduction, and Convection of Heat. 57 
 Section VII. Of Light. 59 
 Of the Radiation of Light. 59 
 Of the Reflection and Refraction of Light. . 60 
 Of the Polarization of Light. 61 
 Of the Decomposition of Light. 63 
 Section VIII. Of the Sources of Heat and Light. 65 
 Section IX. Recapitulation and General Observations on the Sub- 
 jects treated of in the preceding Chapters. 66 
 Arguments in Proof of design, Deducible from the Divisibility 
 
 and Molecular constitution of Matter 68 
 Chapter IV — Of Chemical Elementary Principles, and of the Laws 
 
 of their Combination. 71 
 
 Section I. Of Chemical Elementary Principles, ' 72 
 Of the Five Elementary Supporters of Combustion j Oxygen, 
 
 Chlorine, Bromine, Iodine, and Fluorine. 73 
 
X CONTENTS. 
 
 Of Elements, wliich instead of Supporting- Combustion, are 
 
 for the most part themselves Combustible. 76 
 
 Of the Eig-ht Elements not Metallic, generally termed Acidifia- 
 ble Bases, most of which are Combustible ; Hydrog-en, Car- 
 bon, Azote, Boron, Silicon, Phosphorus, Sulphur, Selenium 76 
 Of the Ten Metalloids, Arsenic, Antimony, Tellurium, Cliro- 
 mium. Uranium, Vanadium, Molybdaenum, Tungsten, Tita- 
 nium, Columbium. 80 
 Of the Twelve Metallic Bases of the Alkalies and Earths ; Po- 
 tassium, Sodium, Lithium, Calcium, Magnesium, Stron- 
 tium, Barium, Aluminum, Glucinum, Yttrium, Zirconium, 
 and Thorinum, 80 
 Of the Nineteen Metals Proper ; Iron, Manganese, Nickel, Co- 
 balt,Cerium, Zinc, Cadmium, Lead,Tin, Bismuth, Copper, 
 Mercury, Silver, Gold, Platinum, Palladium, Rhodium, 
 Iridium, Osmium. 83 
 Section- II. Of the Laws of Chemical Combination. 86 
 Of the Atomic Theory. 93 
 Of the Representation of the Combining Molecules of Bodies 
 
 by Numerical series. 95 
 
 Section III. General Remarks upon Chemical Compounds. 95 
 
 Of Primary Compounds. 96 
 
 Of Acids. 96 
 
 Of Alkalies and Bases. 97 
 
 Of Neutral Compounds. 98 
 
 Of Secondary Compounds ; Salts. 98 
 
 Section IV. Recapitulation. General reflections on the Subjects 
 
 treated of in the preceding Chapters. 99 
 
 Statement of the P'acts on which the Atomic Theory is Founded. 99 
 Of the Adaptation of Subordinate to Primordial Agents and Ele- 
 ments, and of the Means by which these Adaptations have 
 been effected. 100 
 
 Of Adaptations produced by adjustments of quality and quantity 103 
 of the Tendency in Nature to a state of Repose or Equilibrium 105 
 Of the Creation of the Elements with the Properties essential 
 
 to produce perfect Compounds. 108 
 
 Of the wonderful Nature of the most simple Chemical Processes 110 
 Brief Examination of certain Objections to the Argument of De- 
 sign. Ill 
 
 BOOK II. 
 
 Of METEOnOLOGY ; COMPREHEKrniNG A GENERAL SkETCII OF THE CoX- 
 STITUTION OF THE GlOHE ; AND OF THE DlSTRIlirTION AND MUTUAL 
 
 Influence of the Agents and elements of Chemistry in the 
 Economy of Nature. 
 
 Preliminary Observations. 114 
 
 Chapter I — Of the General Structui'e of the Earth ; particularly 
 with reference to the Distribution of its Surface into Land and 
 Water ; and witli respect to its Atmosphere. 115 
 
 Section I. Of the General Relations of the Sea and Land to each 
 
 other. • 115 
 
 Section II. Of the Ocean. 116 
 
 Section III. Of the Atmosphere. 118 
 
CONTENTS. XI 
 
 Chapter II. — Of Heat and Light : the Modes of Estimating- their De- 
 gree, and the Ways in which they are Propag'ated. Of the Gene- 
 ral Temperature of the Celestial Reg-ions, and of the Earth inde- 
 pendently of the Sun. 122 
 Section I. Of Heat and Lig-ht, and the Modes of estimating' their 
 
 deg-ree. 122 
 
 Section- II. Of the Propag-ation of Heat and Lig-ht. 123 
 
 Section III. Of the Temperature of the Celestial Regions. 124 
 
 Section- IV. Of the Temperature of tlie Interior of the Earth. 124 
 
 Chapteu III. Of the Temperature of the Earth at its Surface, as de- 
 pendent on the Sun. 127 
 Section I. Of Mean Temperature. 128 
 Section II. Of tlie actual Distribution of Temperature over the 
 
 Globe. Of Isothermal Lines, &.C. Climate. 129 
 
 Of the Temperature of the Poles and of the Polar Regions. 129 
 Of the mean annual Temperature of the Equator. 150 
 
 Of tlie Temperature of the intermediate Regions of the 
 
 Globe. Of Isothermal Lines, 8<c. 130 
 
 Climate. 134 
 
 CtiAPTEn IV. — Of the Primary Constituents of Climate : or of the Tem- 
 perature of the Earth, as dependent on its Globular Form •, and 
 on its Annual and Diurnal Motions. _. 134 
 
 Chaptku V. Of the secondary or subsidiary Constituents of Climate ; 
 comprehending a Sketch of those Circumstances capable of In- 
 fluencing Climate, which are the more immediately connected 
 ^vith the Surface of the Earth, as consisting of Land or Water ; 
 or which are connected with the Atmosphere. 136 
 
 Section I. Of the secondary Constituents of Climate, Immediately 
 connected with the Surface of the Earth; and depending- on 
 the Nature of that Surface of the Earth ; and depending on the 
 Nature of that Surface as composed of Land or Water. 137 
 
 1. Of the Proportion of Solar Heat and Light that actually 
 arrives at tlie Surface of the Earth. 137 
 
 2. Of the Distribution of Heat and Light over the Earth's 
 Surface in the latent and Decomposed Forms. 138 
 Of tlie General Distribution of Electricity and Magnetism 
 
 over the Earth. 139 
 
 Of the Distribution of Light in the decomposed Form 
 over the Earth. 141 
 
 3. Of the Laws of Absorption, Radiation, and Reflection of 
 Heat and Light. 142 
 
 4. Of the Conduction of Heat below the Earth's Sui'face on 
 Land. 145 
 
 5. Of the Propagation of Heat and Light below the Earth's 
 Surface in Water. 146 
 Of tlie Temperature of the Waters of the Ocean at great 
 
 Depths. 150 
 Of the under Currents of the Ocean existing between the 
 
 Equatorial and the Polar Regions. 150 
 
 Temperatiu-e on Land and at Sea. 151 
 
 Temperature of Natural Springs. 152 
 Section II. Of the Secondary Constituents of Climate immediately 
 
 connected with the Atmosphere. 153 
 1. Of the Distribution of heat and of light through the At- 
 mosphere, and of the Consequences. 153 
 
Xll CONTENTS. 
 
 Of the Limits of Perpetual Snow. 154 
 
 Of the Distribution of Heat and Light through the Atmo- 
 sphere in their Latent and Decomposed Forms. 156 
 Of the Propagation of Sensible Heat through the Atmo- 
 sphere. 156 
 Of Atmospheric Currents. The Trade Winds. 158 
 2. Of the Presence of Water in the Atmosphere. 160 
 Of the Relations of the Water in the Atmosphere to Tem- 
 perature. 160 
 Of the General Relations of Evaporation and Conden- 
 sation. 167 
 Of the Actual Quantity of Water that is evaporated and 
 
 condensed over the Eartli. 176 
 
 Of Dew and Hoar Frost. 178 
 
 Of Mists and Fogs. 180 
 
 Of Clouds. 181 
 
 Of Snow and Sleet. 185 
 
 Of Rain. 186 
 
 Of Hail. 189 
 
 Of the Distribution of Heat and Light in their latent and 
 decomposed Forms througli the Vapour of the Atmo- 
 sphere ; and of the Effects of that Distribution. 190 
 Of the Relations of Electricity to the Vapour of the At- 
 mosphere. 190 
 Of the Aurora Borealis. 192 
 Of the Phenomena depending upon the Decomposition, 
 Refraction, and Reflection of Light by the Vapour of 
 the Atmosphere. The Mirage. The Fata Morgana. 
 Halos. The Rainbow. 192 
 3. Of the Occasional Presence of Foreign Bodies in the Atmo- 
 sphere ; and of their Effects. 194 
 Of Matter suspended in the Atmosphere in a state of Mix- 
 ture. Coloured Rain and Snow. Aerolites. Dr}' Fogs. 194 
 Of Matters v.'hich pervade the Atmosphere in a state of So- 
 lution. Malaria. 197 
 Recapitulation. The Arrangements of Climate demonstra- 
 tive of Design. 198 
 Ckapter VI. — Of the Adaptation of Organized Beings to Climate ; 
 comprehending a General Sketch of the Distribution of Plants 
 and Animals over the Earth, and of the Present Position and Fu- 
 ture Prospects of Man. 203 
 Of the Formation and Ingredients of the Soil. 203 
 Sf.ctiox I. Of the Distribution of Plants over the Earth. 204 
 
 1. Of the Differences of Vegetation, as Hable to be influenced 
 
 by Soil, and by other minor Local Circumstances, in the 
 same Climate. 204 
 
 2. Of the Influence of Climate on Vegetation. Distribution 
 
 of Plants. 206 
 
 Profusion of Vegetable Productions. 210 
 
 Sectiox II. Of the Distribution of Animals over the Eartli. 212 
 
 1. Of the Difterences existing among Animals in similar Cli- 
 
 mates. 213 
 
 2. Of the Effects of Diversity of Climate on the Distribution 
 
 of Animals. 215 
 
 Migration and Hybernation. 220 
 
 Coverings of Animals. 220 
 
CONTENTS. Xlll 
 
 Section III. Of the present Position and future Prospects of Man. 222 
 
 BOOK III. 
 
 Of the Chemistrx of Organizatiok : PAnxrcuLAULT of the Che- 
 MiCAi, Process of Digestion : and of the suBSEauENT Pro- 
 cesses, BY WHICH various AlIMENTART SuBSTANCES ARE ASSIMI- 
 LATED TO AND BECOME COMPONENT PaRTS OF, A LiVING BoDY. 228 
 
 Chapter I, — Of the Nature and Composition of Organized Bodies in 
 
 general, as compared with Inorg-anic Matter. 228 
 
 1. Of Organic Bodies considered as Chemical Compounds. 229 
 
 Of the Chemical Composition of Sugar, Vinegar, Starch, 
 and Wood. 232 
 
 2. Of the Cause of the Differences in the Sensible Proper- 
 
 ties of Substances nearly allied in their Chemical Composi- 
 tion. 233 
 Of the Peculiarity of the Composition of Organic Sub- 
 stances. 233 
 Of the Nature of the Agents by which Organic Substances 
 are Produced. 235 
 
 3. Of the Modes of Operation of Organic Agents. 237 
 
 Reflections on the Mutual Adaptation of the Elements 
 and the Agents of Organic Nature. 241 
 
 Chapter II. — Of the Modes of Nutrition ; comprehending a Sketch 
 of the Alimentary Apparatus ; and of Alimentary Substances 
 in Plants and in Animals. 243 
 
 Section I. Of the Modes of the Nutrition of Plants ; and of the Na- 
 ture of those Matters by wliich their Nutrition is effected. 243 
 Section II. Of the Modes of Nutrition in Animals ; and of the Ali- 
 mentary Substances by which they are nourished. 246 
 1. Of the Organs of Digestion in Animals. 247 
 Of the mouth and its Appendages. 247 
 Of the Oesophagus, the Stomach, and the Intestinal Canal. 249 
 Of the Liver, the Pancreas, and the Spleen. 253 
 Of the Circulation of the Blood, and of the Distribution 
 
 of the Nerves in the Organs of Digestion. 254 
 
 Of Alinientary Substances composed of the Saccharine, 
 the Oily, and the Albuminous Principles. ■ 256 
 
 Chapter III. — Of the Digestive Process ; and of the General Action 
 
 of the Stomach and the Duodenum. 261 
 
 Of the Influence of Water as an Essential, and as an Acci- 
 dental Ingredient of Alimentary Substances. 261 
 Of the Powers exerted by the Stomach in the Digestion of 
 
 the Food. 265 
 
 1. Of the Reducing Powers of the Stomach. 265 
 
 2. Of the Powers of Conversion possessed by the Sto- 
 
 mach. 269 
 
 3. Of the Organizing and Vitalizing Powers of the Sto- 
 
 mach. 271 
 
 Of the Changes the Food undergoes in the Duode- 
 num, 721 
 Of the Functions of the Alimentary Canal, beyond the 
 Duodenum. 273 
 Observations on tlie Choice and the Preparation of Aliment. 274 
 Observations on the General Character of the Assimilating 
 
 Agency. 275 
 
 2 
 
XIV CONTENTS. 
 
 Chapter IV. — Of the Processes of Assimilation subsequent to those in 
 the Stomach and Alimentary Canal ; particularly of the Conver- 
 sion of the Chyle into Blood, Of Respiration and its Uses. Of 
 the Final Decomposition of Organized Bodies. General Reflec- 
 tions and Conclusion. 277 
 
 1. Of the Passage of the Chyle from the Alimentary Canal 
 
 into the Sanguiferous System ; and of the Function of 
 Absorption generally. 277 
 
 Process similar to Digestion carried on in all Parts of the 
 Body. 279 
 
 2. Of the Blood. 279 
 
 Of the Constituents of the Blood. 279 
 
 Of the Organization of the Blood. 280 
 
 3. Of Respiration. 280 
 
 Of the different Colours of Arterial and of Venous Blood. 282 
 Of tlie Source of the Carbonic Acid in Venous Blood, and 
 of the Gaseous Vapour that is expelled from tlie 
 Lungs. 282 
 
 Of the Use of the continual Extraction of Carbonic Acid 
 
 from Living Animals, 282 
 
 4. Of Secretion. 283 
 
 5. Of the Spontaneous Decay of Organized Bodies. 284 
 Recapitulation of the Mechanical Arrangements of the Di- 
 gestive Organs, and of the Chemical Changes by which 
 the Food is adapted for Assimilation. 285 
 
 Reflections on the Mutual Dependence of Plants and Ani- 
 mals. On the Subserviency of their Mechanism to the 
 Chemical Properties of Matter ; and on the beneficial 
 Effects of their Renovation and Decay. 288 
 
 Conclusion. Of the Future Progress of Chemistry ; of the 
 Application of Chemistry to Physiological Research ; 
 and of the Tendency of Physical Knowledge to elevate 
 the Mind by Displaying the Attributes of the Deity and 
 the Immensity of His Works. 291 
 
 Appendix.— Contahnng Additional Notes and Emendations. 297 
 
INTRODUCTION. 
 
 OF THE LEADING ARGUMENT OF NATURAL THEOLOGY; THAT DESIGN, OR 
 THE ADAPTATION OF MEANS TO AN END, EXISTS IN NATURE. 
 
 With the view of illustrating the argument of design, we shall 
 commence with a statement of that argument in its simplest form. 
 
 Animals in cold climates have been provided with a covering 
 of fur. Men in such climates cover themselves with that fur. In 
 both cases, whatever may have been the end or object, no one 
 can deny that the effect^ at least, is precisely the same : the ani- 
 mal and the man are alike protected from the cold. Now, since 
 the animal did not clothe itself, but must have been clothed by 
 another ; it follows, that whoever clothed the animal, must have 
 known what the man knows, and must have reasoned like the 
 man ; that is to say, the clother of the animal must have known 
 that the climate in which the animal is placed, is a cold climate ; 
 and that a covering of fur, is one of the best means of warding off 
 the cold ; he therefore clothed his creature in this very appropriate 
 material. 
 
 The man who clothes himself in fur to keep off the cold, per- 
 forms an act directed to a certain end ; in short, an act of design. 
 So, whoever, directly or indirectly, caused the animal to be clothed 
 with fur to keep off the cold, must likewise have performed an 
 act of design. 
 
 But, under the circumstances, the clother of the animal, must 
 be admitted to have been also the Creator of the animal ; and by 
 extending the argument ; the Creator of man himself — of the uni- 
 verse. Moreover, the reasoning the Creator has displayed in 
 clothing the animal, He has designed to impart to man, who is 
 thus enabled to recognize his Creator's design. 
 
 Such is an instance of those varied adaptations of means to ends 
 around him, which man by his reasoning, appreciates ; and which 
 demonstrate to him, the existence of an intelligent Creator. Com- 
 pared, however, with the extent of creation, the instances, nu^ 
 
24 INTRODUCTION. 
 
 merous as lliey appear, in which man is thus able to trace the 
 designs of his Creator, are really few. Man not only sees means 
 directed to certain ends ; but ends accomplished by means, which 
 he is totally unable to understand. He also sees, every where, 
 things, the nature, and the end of which are utterly beyond his 
 comprehension; and respecting which, he is obliged to content 
 himself with simply inferring the existence of design. 
 
 The argument of design, therefore, in its general sense, em- 
 braces at least three classes of objects : — 
 
 1. Those objects, regarding which, the reasoning of man coin- 
 cides with the reasoning evinced by his Creator ; as in the sim- 
 ple adaptation of clothing above mentioned : or those objects, in 
 which, man is able to trace, to a certain extent, his Creator's de- 
 signs ; as in various phenomena amenable to the laws of quantity ; 
 viz. mechanics, &:c. 
 
 2. Those objects, in which, man sees no more than the pre- 
 liminaries and the results, or the end and design accomplished ; 
 without being able to trace through their details, the means of that 
 accomplishment ; as in all the phenomena and operations of 
 chemistry. 
 
 3. Those objects, in which, design is inferred, but in which 
 the design, as well as the means by which it is accomplished, are 
 alike concealed ; as in the existence of fixed stars, of comets, of 
 organized life ; and indeed in all the great and more recondite 
 phenomena of nature. 
 
 The intention of these Treatises, is to point out the various evi- 
 dences of design, among the objects of creation ; and to deduce 
 from them, the existence, and the attributes, of the Creator. The 
 following pages are occupied more particularly, with the illustra- 
 tion of the evidences of design, in objects belonging to the second 
 of the three classes above mentioned ; with those, namely, in 
 which design is obvious, though we cannot trace the means by 
 which that design is accomplished. 
 
BOOK I. 
 
 OF CHEMISTRY. 
 
 PRELIMINARY OBSERVATIONS ON THE RANK OF CHEMISTRY AS A SCIENCE; 
 AND ON ITS APPLICATION TO THE ARGUMENT OF DESIGN. 
 
 " Chemistry does not afford the same species of argument (in 
 favour of design) that mechanism affords, and yet may afford an 
 argument in a high degree satisfactory." * This remark of the 
 excellent Paley has been made by him with reference only to a 
 particular subject, but the following sketch, pointing out the 
 grounds upon which chemistry as a science is foundei!, and the 
 rank which it holds among the departments of human knowledge, 
 will at the same time show the general truth of the remark. 
 
 An elaborate inquiry into the origin and nature of human know- 
 ledge would be quite misplaced here. We shall content ourselves 
 with simply considering it as of two kinds, viz : a knowledge of 
 what must be ; that is to say of what we cannot conceive eitiier 
 not to exist, or to exist otherwise than as it is, and which is there- 
 fore founded upon reason ; and a knowledge of what simply is, 
 but how or why we know not, and for the existence of which, 
 therefore, we can assign no reason but our experience alone. 
 
 Of these, the only instance of the first kind which particularly 
 concerns us at present, is the knowledge of quantity and its rela- 
 tions in general; of the second, that of certain natural phenomena, 
 the consideration of which constitutes the principal object of the 
 present volume. 
 
 The fundamental differences between these two great branches 
 of human knowledge, as well as their consequences, cannot per- 
 haps be more strikingly illustrated than in the following familiar 
 exposition by a celebrated writer. " A clever man," says Sir J. 
 Herschel, "shut up alone and allowed unlimited time, might 
 reason out for himself all the truths of mathematics, by proceed- 
 ing from those simple notions of space and number of which he 
 cannot divest himself without ceasing to think ; but he would never 
 tell by any effort of reasoning what would become of a lump of 
 sugar, if immersed in water, or what impression would be pro- 
 
 * Natural Theolog-y, chap. vii. 
 3 
 
26 INTRODUCTION. 
 
 duced on his eye by mixing the colours yellow and blue,"* results 
 which can be learnt only from experience. 
 
 Thus then the extremes of human kno\vledo;e mav be considered 
 as founded on the one hand purely upon reason, and on the other 
 purely upon sense. Now, a very large portion of our knowledge, 
 and what in fact may be considered as the most important part of 
 it, lies between these two extremes, and results from a union or 
 mixture of them, that is to say, consists of the application of ra- 
 tional principles to the phenomena presented by the objects of 
 nature. 
 
 With respect to knowledge founded upon reason.^ we are so 
 constituted, that whether we contemplate those primary notions 
 of space, time, force, &c. above alluded to in the abstract, or 
 whether we view them in connexion v/ith the objects of sense 
 around us, we cannot divest them of quantity, which seems to 
 be involved in their very essence. Quantity and its relations, 
 therefore, in some shape or other, enter as a necessary element 
 into by fiir the greater portion of humrai knowledge. Now the 
 primary relations of quantity are exceedingly simple ; one quantity 
 may be equal to anothef, or it may be greater or less, but we can 
 conceive no other relation. Hence all the operations of the ma- 
 thematics — the science of quantity and its relations — however 
 abstruse and complicated they appear, can be ultimately resolved 
 into addition and subtraction. 
 
 It is principally then through the medium of the relations of 
 quantity that we are enabled to reason in a satisfactory manner 
 upon the objects of sense. For as everything in nature, or what 
 is the same thing to us, every sensation produced by one natural 
 object, as compared with that produced by another, must be either 
 equal or similar, or unequal or dissimilar ; the whole are capable 
 of being subjected, more or less perfectly, to the laws of quantity. 
 This is effected in various ways and by various artifices, but 
 chiefly through the intervention of certain natural or assumed 
 units, or standards of resemblance, as a second in time, a foot in 
 space, &LC., and in proportion to the definite character of these 
 units, or standards, and as they can be more or less satisfactorily 
 applied, so will the resulting branch of knowledge be more or less 
 of a mathematical character, or be more or less rational and per- 
 fect. 
 
 By contemplating, in the abstract, the boundless relations of 
 time and of space, where no end can be conceived to addition and 
 subtraction, we arrive at the only notions of infinity of which our 
 nature seems capable. These once obtained, the obvious and ne- 
 
 * Discourse on the Study of Natural Philosophy, p. 76, 
 
INTRODUCTION. 27 
 
 cessary existence of cause within the narrow sphere of our ob- 
 servation naturally leads us to inquire, can this cause be infinite ? 
 And thus we are led by degrees, but irresistibly, to the sublimest 
 of all conclusions, that a Cause or Agent in every way commen- 
 surate with infinity — omniscient and omnipresent, eternal and 
 omnipotent must exist — in other words, a God. 
 
 Compared with infinity, however, and even with the objects of 
 nature as they visibly exist around us, our actual knowledge of 
 time and of space is exceedingly limited. Like travellers on an 
 extended plain, we see what is going on around us at the present 
 moment, but the distant and the very near, the past and the future, 
 are alike unknown to us. A few millions of miles, for example, 
 or a few thousand years, comprise the utmost that we know of 
 space and of time. On the other hand, beyond the fraction of an 
 inch, or of a second, everything belonging to space and to time is 
 inappreciable by our senses. Yet beyond these limits w^e know 
 that myriads of portions of space and of time must exist, too vast 
 or too minute to be referred to our imperfect standards. Let us, 
 for instance, take the distance of the nearest fixed star. This we 
 are assured by astronomers is so great that the utmost measure 
 we can apply to it — the diameter of the earth's orbit — a space of 
 no less than 192,000,000 of miles is absolutely too little to measure 
 it by — is in fact contained within it so many times that the num- 
 ber cannot at present be counted ! On the other hand, we shall 
 presently find, that the molecules of matter of which the objects 
 we see around us are composed are so minute, that a measure 
 scarcely appreciable by the unassisted sight, the thousandth part 
 of an inch for example, is vastly too large to compare them with, 
 and may in fact comprise millions of them ! 
 
 Experience, the great and ultimate source of all the knowledge 
 we possess of those portions of nature to which our faculties are 
 limited may be acquired in two ways ; by simple observation, 
 and by experiment ; that is to say, either " by noticing facts as 
 they occur without any attempt to influence the frequency of their 
 occurrence, or to vary the circumstances under which they oc- 
 cur ;" or " by putting in action causes and agents over which we 
 have control, and purposely varying these combinations, and no- 
 ticing what efTects take place."* Now in all the higher depart- 
 ments of knowledge the objects of which are principally matter, 
 and its motions in the aggregate, the information we can acquire 
 by one or both these means is so complete, and at the same time 
 so favourable to the application of the relations of quantitj^ that 
 the resulting sciences have all the certainty of abstract truths 
 
 * Herschel*s Discourse on the Study of Natural Philosophy, p. 76. 
 
38 INTRODUCTION, 
 
 themselves. But when the knowledge we possess of objects is 
 wholly sensible, and in no way commensurate, or only very im- 
 perfectly so with their quantity, here it is that uncertainty begins ; 
 for though we may be able to trace the apparent cause and eff'ect 
 of a particular phenomenon, the most minute and careful obser- 
 vation and experiment, often give us but little insight into the 
 connexion between the two, and generally fail us altogether. The 
 reason of this is to be sought for in the limited nature of our fa- 
 culties, and particularly in our complete ignorance of the nature 
 of that mysterious communication wliich we maintain with the 
 external world through the medium of sensation. In two of the 
 senses indeed, seeing and hearing, we are able to trace the inter- 
 mediate train of phenomena between the external object producing 
 the sensation and the sensation itself, and even to form some idea of 
 the remote cause of the sensation ; but in the other tv/o senses, 
 tasting and smelling, the whole is involved in mystery from be- 
 ginning to end. 
 
 Thus w^hen a bell is struck, philosophers have satisfactorily 
 demonstrated that a vibratory motion, excited in the bell, and de- 
 pending upon its elasticity, is communicated to the air in contact 
 with it, and through this medium is propagated to the ear, in which 
 organ, we know not why, the sensation of sound is excited. Cir- 
 cumstances very similar have been supposed to take place with 
 respect to light, and undulse (or something obeying the laws of 
 undidse) have been demonstrated to exist and to be propagated 
 from the luminous body to the eye, and thus the remote cause of 
 sound, and probably of light, is proved to be motion. But in the 
 cases of tasting and smelling the circumstances are altogether 
 dissimilar ; here the sapid and odoriferous matters are brought at 
 once into actual contact with the sentient organs, and the sensa- 
 tions are the consequence \vithout any intermediate train of pheno- 
 mena, at least any that we can appreciate. What it is therefore 
 in an acid or a rose for example, analogous to motion in the bell, 
 and which produces the sensations we call sour and siveet we 
 know not, and probably never shall know, and simply because 
 the laws and relations of quantity are here either totally inappli- 
 cable, or can be only indirectly and most imperfectly applied. 
 
 These observations are principally introduced with reference to 
 the department of knowledge we have at present to consider. Al- 
 most all of M'hatare denominated the chemical properties of bodies, 
 are objects of taste and of smell, rather than of sight and of hear- 
 ing. Hence they admit only of the indirect application of the 
 laws of quantity, and are the result, not of reason but solely of 
 experience. Indeed, so much is chemistry the creature of actual 
 experimental research, that its simplest truths have seldom, been 
 
INTRODUCTION. 29 
 
 anticipated a priori. Thousands of years of observation and ex- 
 perience for example had not taught mankind that water is com- 
 posed of two elementary gaseous principles, much less the pro- 
 portions in which those principals combine to form water. 
 Nay, even now the fact has been established upon the clearest 
 evidence, we are unable to explain why it is so, or even to com- 
 prehend the nature of the union or its result. Hence, to use the 
 language of Paley, in all chemical operations — " our situation is 
 precisely like that of an unmechanical looker-on, Avho stands by 
 a machine, the fabric of which is hidden from his sight by the 
 outside case, or if seen, would be too complicated for his unin- 
 formed understanding to comprehend. And what," continues 
 this energetic writer, " is that situation ? Ignorant as he is, he 
 does not fail to see that certain materials, in passing through the 
 machine, undergo remarkable changes ; and what is more, changes 
 manifestly adapted for future use. Is it necessary that this man, 
 in order to be convinced that design, that intention, that contri- 
 vance, have been employed about the machine, should be allowed 
 to pull it to pieces to study its construction ? He may indeed 
 wish to do this for many reasons, but for all the purposes of as- 
 certaining the existence of counsel and design in the formation of 
 the machine, he wants no such intromission or privity. What 
 he sees is sufficient. The effect upon the material, the change 
 produced in it, the utility of that change for farther applications 
 abundantly testify, be the concealed part of the machine, or of its 
 construction what it will, the hand and agency of a contriver."* 
 
 We have thus attempted to point out the rank which chemistry 
 holds among human knowledge, and the kind of evidence which 
 it furnishes in favour of design ; and the whole argument may be 
 briefly recapitulated as follows : chemistry is a branch of know- 
 ledge founded solely on experience, for the phenomena of which 
 we can assign no reason. i3ut although the intimate nature of its 
 changes be unknown to us, we see them manifestly directed to 
 certain ends ; hence as objects directed to certain ends, where the 
 whole of the intermediate phenomena can be traced and understood, 
 always imply design, we naturally infer design in others obvious- 
 ly so directed, even although we may not be able to understand 
 their intimate nature. 
 
 Such is the state in which Paley has left the argument, and 
 while we admit that even in its most perfect form, it is less sa- 
 tisfactory than that founded upon mechanism, we have always 
 thought that our excellent author has not made quite so much of 
 his subject as he might have done, and that the very imperfections 
 
 * Natural Theology, chap. vii. condensed slig-htly, but the argument 
 strictly adhered to. 
 
 3* 
 
30 INTRODUCTION. 
 
 and difficulties of chemistry and of the allied branches of know- 
 ledge give them some advantages over mechanism itself. When 
 a series of wheels or of levers are arranged in a certain order, they 
 must move in a certain way, and produce a certain effect which 
 can be foretold exactly. In such a case, we may admire the skill 
 and ingenuity of the Contriver, or perhaps feel astonished at his 
 power, but we scarcely do more, and much of the effect is lost in 
 the apparent necessity of the result, and the consciousness that 
 under the circumstances nothing else could have happened. When 
 the Deity, therefore, operates through the medium of mechanism, 
 he appears almost too obviously to limit his powers within the 
 trammels of necessity ; but when he operates through the me- 
 dium of chemistry, the laws of which are less obvious, and indeed 
 for the most part unknown to us, his operations have much more 
 the character of those of a free agent, and, in many instances also, 
 appear of a higher order, and are more striking and wonderful. 
 Do not, for instance, those extraordinary and mysterious changes 
 constantly going on around us, beneath us, within us, derive no 
 small additional interest from the very circumstance of their not 
 being understood ? Just such an interest, to revert to the argument 
 of Paley, as the unmechanical looker-on feels in the operations 
 of a corn-mill, a carding-machine, or a threshing machine, and 
 to which he who is well acquainted with the mechanism is a 
 stranger. Certainly this is the case. Obvious mechanism, though 
 well suited to display the intelligence and design of the Contriver, 
 is not always so well adapted for arresting the attention of the ob- 
 server ; its very obviousness in some measure depriving it of its 
 interest. But when we see the same Contriver, besides the most 
 beautiful and complicated mechanism, employ other means utterly 
 above our comprehension, though evidently most familiar to hhn^ 
 the circumstance is not only calculated to arrest our attention more 
 forcibly, but at the same time to impress us with more exalted 
 notions of his wisdom and power. 
 
 There yet remain one or two other points to be briefly consi- 
 dered before we proceed to our subject. In the first place it may 
 be asked, do those extraordinary changes which appear to be 
 constantly going on in bodies around us, indicate real and sub- 
 stantial changes in the bodies themselves, or are they mere phan- 
 tasms and creations of the organs of sense, through which we be- 
 come acquainted with them? The discussion of this question 
 will probably be considered by most as superfluous, but for the 
 sake of those (if there be any) who entertain doubts upon the 
 point, it may be remarked, that the sensations, though admitted 
 to be mere signals or indications, bearing little or no analogy with 
 the causes producing them, and therefore throwing little light up- 
 
INTRODUCTION. 31 
 
 on their nature, do nevertheless represent real and substantial ope- 
 rations of some sort in the bodies themselves. This miffht be 
 proved were it necessary by a variety of arguments, but one or 
 two only will be sufficient for our present purpose. In the first 
 place it may be stated, that changes in the chemical constitution 
 of bodies are usually accompanied by corresponding changes in 
 weight. Now weight is a modification oi force ^ one of those 
 self-evident existences which we cannot doubt without doubting 
 our own. Another, and perhaps indeed the most striking argu- 
 ment in favour of the reality of chemical changes, may be de- 
 duced from the subserviency to them of those mechanical contri- 
 vances and operations everywhere existing in organized^ beings. 
 At least, half the mechanism in a living animal is subservient to 
 the chemical changes constantly going on in it, and necessary to 
 its existence. Take, for instance, the circulation of the blood : 
 what a complicated apparatus is here employed for the simple 
 purpose of exposing the blood to the action of the air in the lungs, 
 in order that it may there undergo some chemical change. Now, 
 surely no one can reasonably doubt that this chemical change is 
 as much a reality as the mechanism by which it has been accom- 
 plished ; and if one chemical change be admitted to be a reality, 
 why may not all others ? 
 
 Lastly, if there be any one who denies the existence of design, 
 and sees nothing in all the more obvious arrangements and order 
 around him but the necessary results of what he chooses to de- 
 nominate " the laws of nature," let him calmly and deliberately 
 consider the facts brought forward in the following pages ; and if 
 he can witness unconvinced all the numerous instances of pro- 
 spective arrangement obviously made with reference to things 
 not yet in existence ; all the beautiful adjustments and adapta- 
 tions of noxious and conflicting elements most wonderfully con- 
 spiring together for good ; and, lastly, the subversion of even his 
 favourite " laws of nature" themselves, when a particidar purpose 
 requires it ; if, we say, he can witness all these and still remain 
 incredulous of the evidences of design, we can only observe, 
 that his mind must be most singularly constituted, and appa- 
 rently beyond the reach of conviction. 
 
32 CHEMISTRY. 
 
 CHAPTER I. 
 
 OF THE MUTUAL OPERATION OF PHYSICAL AGENTS AND OF MATTER, AND 
 
 OF THE LAWS WHICH THEY OBEY. 
 
 " God has been pleased to prescribe limits to his own power, 
 and to work his ends within those limits. The general laws of 
 matter have perhaps the nature of these limits ; its inertia, its re- 
 action, the laws which govern the communication of motion, of 
 light, of heat, of magnetism and electricity, and probably of 
 others yet undiscovered. These are general laws, and when a 
 particular purpose is to be effected, it is not by making them 
 wind and bend and yield to the occasion, (for nature with great 
 steadiness adheres to and supports them,) but it is, as we have 
 seen in the eye, by the interposition of an apparatus correspond- 
 ing with these laws, and suited to the exigency which results 
 from them, that the purpose is at length attained. As we have 
 said, therefore, God prescribes limits to his power, that he may 
 let in the exercise, and thereby exhibit demonstrations of his wis- 
 dom. For then, i. e. such laws and limitations being laid down, 
 it is as though one Being should have fixed certain rules ; and, 
 if we may so speak, provided certain materials ; and afterwards 
 have committed to another Being, out of these materials, and 
 in subordination to these rules, the task of drawing forth a crea- 
 tion : a supposition which evidently leaves room, and induces 
 indeed a necessity for contrivance. Nay, there may be many 
 such agents, and many ranks of these."* This admirable pas- 
 sage from Paley is so much in point, and so exactly expresses 
 our views upon the subject, that we have chosen it as a text, as 
 in a former instance, for illustration. We shall proceed, there- 
 fore, to take a summary view of " the limits within w'hicli the 
 Deity has confined his operations ;" that is to say, of the laws 
 by which matter, and these subordinate agents by which it is 
 capable of being influenced, have been made to mutually act and 
 react upon each other. 
 
 The principles of activity which operate as subordinate agen- 
 cies in nature may be considered as of two kinds ; those which 
 operate universally upon every individual atom of matter without 
 reference to its sensible properties, as the forces producing the 
 phenomena of gravitation, &lc. ; and those which operate among 
 the different constituent molecules of which all bodies are com- 
 posed, and which are denominated molecular or polarizing 
 forces, Slc. Of each of these we siiajl in the first place endeavour 
 to convey some idea to the general reader. 
 
 • Nuturtil Theology, chap. iii. 
 
INERTIA AND ACTIVITY OF MATTER. 33 
 
 CHAPTER IL 
 
 ON THE INERTIA AND ACTIVITY OE MATTER. 
 
 To form a notion of what is termed the inertia or inactivity 
 of matter, let us imagine a portion of it, as for example, a ball of 
 lead A detached from all other matter, and existing absolutely un- 
 influenced in space. Such a mass of matter, if supposed to be at 
 rest, must obviously remain so, for it cannot move itself; on the 
 other hand, if it be supposed to be in motion, it must continue in 
 motion, for it cannot be conceived to be able to stop itself any 
 more than it could be conceived to be able to set itself in 
 motion ; in short, a mass of matter under such circumstances of 
 isolation must be considered as perfectly passive and unable to 
 change its state, whatever that may happen to be, whether of 
 motion or- of rest. Now let us suppose another portion of mat- 
 ter, as for example, another ball of lead b exactly of the same size 
 as A, placed in free space at any moderate distance from a, and 
 away from all other influences, \vhat will happen ? We know 
 from general experience that under these circumstances, the two 
 balls will mutually approach each other with an accelerated mo- 
 tion, till they meet at a point exactly intermediate from those at 
 which they first started; and the inference from this experience 
 is, that the two balls exert a mutual and equal attractive force, 
 which causes them to move towards each other. If the ball b be 
 twice the size of the ball a, the two balls will mutually approach 
 each other as before, but, in this instance, instead of moving with 
 equal velocity, while the ball a moves two feet, the ball b will 
 only move one foot ; or taking an extreme case, and supposing 
 the ball b to be indefinitely larger, say a million times larger, than 
 the ball a, they will mutually influence and mutually move to- 
 wards each other as before, but the motion of the ball b will be 
 so minute as to be insensible, while that of the ball a will be the 
 greatest possible. Here we have instances of the inertia (inacti- 
 vity, opposing force, &c.) and of the activity (force of attraction, 
 force of gravitation, &c.) which all matter exerts reciprocally and 
 mutually towards all other m.atter, and the laws of which, as de- 
 ducible from the circumstances stated, and from others, which it 
 would be foreign to our present purpose to enter upon, may, in 
 general terms, be given as follows : " The mutual attraction of 
 two bodies increases in the same proportion as their masses are 
 increased, and as the square of their distance is decreased, and it 
 decreases in proportion as their masses are decreased and as the 
 
34 CHEMISTRY. 
 
 square of their distance is increased." These laws, and those of 
 the motions connected with them, are absolutely general, and not 
 only extend to tlie utmost limits of the universe hitherto explored 
 by man, but to every form and condition of matter, without ex- 
 ception and without reference to its other properties. They, 
 therefore, constitute, probably, the most comprehensive " limits 
 which the Deity has been pleased to prescribe to His power," 
 and within which He operates with the most unceasing and unde- 
 viating regularity and certainty ; they have also the remarkable 
 property of being so amenable to the laws of quantity and ma- 
 thematics, as to be in most instances as firmly established upon 
 reason as abstract truths themselves. The mind of a Newton 
 was chosen to reveal these laws to man, and man's acquaintance 
 with them may be justly considered as one of his noblest privi- 
 leges. To point out their wonders in detail, and the sublime 
 conclusions to which they lead, is the business of a colleague ; 
 at present we have to consider them in their more general form 
 only, and, except in a single point of view, as objects of compa- 
 rison merely with those more immediately connected with our 
 own subject. 
 
 The point of view to which we allude is that peculiar case, or 
 instance of gravitating force, termed iveight. In our illustration 
 of the attractive forces of matter above given w^e supposed a case 
 in which one ball was very much larger than the otlier: now this 
 precisely corresponds with the case of the globe of the Earth, and 
 of all common bodies near its surface. The earth is more than 
 1,000,000,000,000,000 times the mass of any body which is ob- 
 served to fall on its surface, and therefore if even the largest body 
 which can come under observation M^ere to fall tlirouijh a height 
 of 500 feet, the corresponding motion of the Earth would be 
 through a space less than the 1,000,000,000,000,000th part of 
 500 feet, which is less than the 100,000,000,000th part of an inch, 
 and therefore quite inappreciable.* Now the attractive force ex- 
 erted between the earth and detached bodies is denominated 
 weight. Hence the weight of a body, at the earth's surface, is 
 proportionate to its mass, or to the quantity of matter it may con- 
 tain, whatever its form or qualities may be — a most important 
 fact for the chemist, who, by employing the chemical properties 
 of bodies as indications of identity or of change, is by these means 
 enabled to apply to them the more certain measure of U'eight, 
 and thus in some degree to bring them under the dominion of the 
 laws of quantity. 
 
 * Lardner's Cabinet Cyclopaedia, Art. Mechanics, p. 79. 
 
POLARIZING FORCES. 35 
 
 CHAPTER III. 
 
 OF MOLECULAR OR POLARIZING FORCES, ETC. 
 
 In all chemical operations, as already observed, we only wit- 
 ness the beginning and the end, the cause and the effect, while 
 the whole of the intermediate chancres elude our senses. Never- 
 theless, by a careful observation of the phenomena we are enabled 
 to form some notion upon the subject, and that amply sufficient 
 to convince us of their wonderful nature. With a view therefore 
 of arresting the attention of those who may be unconscious of 
 these wonders, or too apt to overlook them, we have thought it 
 proper to premise a sketch of what may be supposed to take 
 place among the ultimate particles of which all bodies are consti- 
 tuted, during those remarkable changes which they are constantly 
 undergoing. And here it may be remarked, once for all, that 
 many of the views commonly entertained on these points have 
 always appeared to us to be so imperfect and unsatisfactory, that 
 so far from elucidating the subject, they have only served to ren- 
 der it the more obscure. In the following sketch, therefore, as 
 better adapted for our purpose, we have endeavoured to give that 
 view of the subject, which, after twenty years of close attention 
 and no ordinary labour, we have been induced to consider as the 
 most simple and consistent with the phenomena. The general 
 reader, who feels no interest in these inquiries, and who at the 
 same time wishes to be apprized of the nature of the arguments 
 deducible from the divisibility and molecular constitution of 
 matter, is referred to the end of the present and of the following 
 chapters for a summary of these arguments. 
 
 SECTION I. 
 
 Of the Divisibility of Matter, 
 
 The first point which naturally claims our attention in the 
 consideration of molecular operations, is the size of these mole- 
 cules ; a subject usually discussed under the head of the divisi- 
 bility of matter. Matter, or rather space, may be conceived to 
 be divisible ad infinitum ; at least no limits can be assigned be- 
 yond which its subdivision cannot necessarily proceed. As how- 
 ever, it exists in the world around us, there cannot be the least 
 doubt that it is composed of ultimate particles or molecules inca- 
 
36 CHEMISTRY. 
 
 pable of further division or change, at least by ordinary agents : 
 the reasons for these assertions will appear hereafter, at present 
 it is our object to convey to the general reader some idea of the 
 magnitude of these particles, with the view, principally, of show- 
 ing how infinitely they surpass the limited powers not only of 
 our senses, but almost of our conception. The subject, however, 
 has so much attracted the attention of philosophers, that most of 
 our readers must be already familiar with it ; we shall therefore 
 content ourselves with merely selecting a single instance from 
 each of the kingdoms of nature. As an instance from the mine- 
 ral kingdom, we may quote from Dr. Thomson, who has shown 
 that an ultimate molecule of lead cannot weigh more than the 
 Troo"ooWoFo 0" ^'^' ^^^^ ^^ ultimate molecule of sulphur more 
 than foTJ'oo^o ^^ ^^ ^ grain, and probably a great deal less; 
 and that ihe size of the molecule of lead cannot surpass, and is 
 probably much less than the ^-s^-x-gro-gooooooo ^^ of a cubic 
 inch !* The vegetable kingdom presents us with innumerable 
 instances, not only of the extraordinary divisibility of matter, but 
 of its activity, in the almost incredibly rapid developement of cel- 
 lular structure in certain plants. Thus the Bovista glgantcum 
 (a species of fungus), has been known to acquire the size of a 
 gourd in one night. Now supposing, with Professor Lindley, 
 that the cellules of this plant are not less than the -j-g-oth of an inch 
 in diameter, a plant of the above size will contain no less than 
 47,000,000,000 cellules ; so that, supposing it to have grown in 
 the course of twelve hours, its cellules must have been developed 
 at the rate of nearly 4,000,000,000 per hour, or of more than 
 sixty -six millions in a minute !t and when we consider that every 
 one of these cellules must be composed of innumerable molecules, 
 each one of which is again composed of others, we are perfectly 
 overwhelmed with the minuteness and number of the parts em- 
 ployed in this single production of nature. Rut the animal king- 
 dom perhaps presents us with still more striking instances than 
 these. Tiius animalcules have been discovered whoso magni- 
 tude is such that a million of them does not exceed a grain of 
 sand ; and yet each of these creatures is composed of members as 
 curiously organized as those of the largest species; they have life 
 and spontaneous motion, and are endowed with feeling and in- 
 stinct. In the liquids in whicii thev live thev are observed to 
 move with astonishing speed and activity, nor are their motions 
 blind and fortuitous, but evidently governed by choice and di- 
 rected to an end. They use food and drink, from w^hich they 
 
 • System of Inorg-anic Chemistry, I. 7. 
 f Introduction to Botany page 7. 
 
DIVISIBILITY OF MATTER. 37 
 
 derive nutrition, and are therefore provided with a digestive ap- 
 paratus. They have great muscular power, and are provided 
 with limbs and muscles of strength and flexibility. They are 
 susceptible of the same appetites and obnoxious to the same pas- 
 sions. Must we not conclude that these creatures have hearts, 
 arteries, veins, muscles, sinews, tendons, nerves, circulating 
 fluids, and all the ' concomitant apparatus of a living organized 
 body ? and if so, how inconceivably minute must these parts be ? 
 If a globule of their blood bears the same proportion to their 
 whole bulk, as a globule of our blood bears to our magnitude, 
 what power of calculation can give an adequate notion of its mi- 
 nuteness ?* 
 
 We have thus endeavoured to convey some idea of the mag- 
 nitude of the ultimate molecules of which bodies are composed; 
 but though we have succeeded in showing that they cannot ex- 
 ceed a certain magnitude, we are by no means certain that they 
 are not in reality much lesS'— indeed a great deal less than the 
 least magnitude of which we have endeavoured above to convey 
 a conception: yet notwithstanding this inapproachable minute- 
 ness, they retain all the characters of matter in the highest de- 
 gree, and moreover possess certain remarkable properties in com- 
 mon, upon the nature of which, in the next place, we have to 
 make a few remarks. 
 
 Section II. 
 
 Of the Forms of ^Aggregation of the ultimate Molecules of 
 
 Matter. 
 
 Matter in the aggregate, and as it appears to exist in the 
 world around us, is known to us principally in three forms or 
 conditions :— the Solid, the Liquid, and the Gaseous (the latter 
 including the state of vapour and the etheriform condition of 
 matter) ; these in their well marked states are sufficiently distinct, 
 though the whole graduall}^ run into each other ; the solid into 
 the liquid, and the liquid into the gaseous, by such imperceptible 
 grades, that in many instances it is not easy to say where one 
 ends and the other begins.t The notions, which the mechanician 
 or natural philosopher employs in reasoning on these forms 
 of bodies are — of a solid, that all its parts are indissolubly and 
 
 * Lardner's Cyclopedia, Art. Mechanics, p. 13. 
 
 f It may be proper here to observe that some bodies, as water, for in- 
 stance, are capable of existing- in that perfectly g-aseous form denomi- 
 nated vapour, under all ordinary circumstances ; thus even ice gives off 
 vapour rapidly, as we shall find hereafter. 
 
 4 
 
38 CHEMISTRY. 
 
 unalterably connected, and impenetrable, so that the relative situ- 
 ation of the parts among one another, cannot be changed, or one 
 part be set in motion without all the rest ; of a liquid, that all its 
 parts are freely moveable among one another, but that it is not 
 dilatable or compressible by mechanical means ; of a gas or aeri- 
 form body, that all its parts are not only freely moveable among 
 one another, but that it is compressible and dilatable without 
 limits. Strictly speaking, however, there are no objects in nature 
 actually existing which completely conform to these definitions : 
 no solid, for instance, absolutely hard and impenetrable, no fluid 
 not compressible and dilatable, no gas compressible or dilatable 
 without limits : and these circumstances are evidently the natural 
 result of their being composed of aggregations of the minute mole- 
 cules we have been considering. Thus solids composed of such 
 molecules must necessarily have innumerable interstices or pores ; 
 hence, when submitted to pressure, they are liable to undergo 
 more or less of condensation, and apparently occupy less space 
 than before : the same remarks may be made with respect to 
 liquids ; while gaseous bodies, supposed to be composed of such 
 molecules, of course cannot be intinilely compressible. 
 
 Section III. 
 Of the solid Form of Bodies, Crystallization, 
 
 Natural solids present us with a variety of properties usually 
 termed secondary^ many of which are of the utmost importance : 
 such are hardness and softness, elasticity, toughness, mallea- 
 bility, tenacity, ductility, &lc., all too well understood to require 
 definition here. These properties evidently depend in a great 
 degree upon original differences in the properties of the compo- 
 nent molecules themselves ; but there is no doubt that many of 
 them are also intimately connected with the modes in which the 
 molecules are arranged. Of these modes we can form no pre- 
 cise idea in a great many instances : there is, however, one form 
 of solid aggregation, the regidar crystalline form, which has 
 occupied much more attention than the rest, and upon this we 
 shall proceed to offer a few remarks. 
 
 As an object of illustration we shall select the familiar one of 
 water, which from its well known properties of existing either 
 as a solid, a liquid, a vapour, or a gas, by a slight variation of 
 circumstances, is well adapted for our purpose, as we are thus 
 enabled to employ the same object of illustration throughout. At 
 present we have to consider it in its solid form of ice. 
 
SOLID FORM OF MATTER. 39 
 
 Every one must have remarked that water in the act of freez- 
 ing assumes various symmetrical forms, shooting into speculae, 
 &;c., as may be beautifully seen on our windows on a frosty 
 morning. Now this affords a familiar instance of what is termed 
 crystallization, a property apparendy possessed by all pondera- 
 ble matter, and readily exhibited by it when under favourable 
 circumstances : and it has been remarked that the form assumed 
 by the same matter is usually similar, or easily deducible from 
 some common form according to well-ascertained and obvious 
 laws. Let us now briefly inquire into the properties which the 
 ultimate molecules of water must be supposed to possess to enable 
 them to form these symmetrical aggregations. In the first place 
 it is evident that the simple supposition of mutually attractive 
 forces between these molecules, analogous or identical with the 
 forces of gravitation, is inadequate to explain the phenomena. 
 Possessed of such properties alone the ultimate molecules of 
 bodies might indeed be imagined to adhere together, and their 
 aggregations might even exhibit something like regularity, but 
 this regularity would in a great measure be accidental, and proba- 
 bly never twice alike ; hence the utmost latitude of assumption 
 would never enable us to explain upon such principles alone that 
 sameness of figure above alluded to as always assumed by 
 the same matter. It is obvious, therefore, that the ultimate 
 molecules of bodies are influenced by other powers than those of 
 simple inertia and attraction : what is the nature of these powers ? 
 On this point there have been various opinions. Some have 
 supposed the ultimate particles of bodies to possess shapes iden- 
 tical with those of the aggregates which they form ; that a crystal, 
 for example, whose shape is a cube, is formed by the aggregation of 
 a number of infinitely little cubes, &c. But to others this supposition 
 has appeared so improbable, and so unlike the usual simplicity of 
 nature's operations, that they have rejected it, and have formed the 
 more feasible hypothesis, that the ultimate molecules of bodies 
 are either spheres, or spheroidal, that is to say, more or less, virtu- 
 ally globular.* Let us take it for granted then that the ultimate 
 
 • Strictly speaking", perhaps tliis observation is applicable to the forms 
 supposed to be assumed by the influences surrounding' the molecules, 
 and by which all then' operations are directed, rather than to the abso- 
 lute forms of the molecules themselves, which, thoug'h in all instances 
 virtually exerting" spheroidal influences, must, in different instances, 
 have ve-ry different forms. Those who wish to study the principles upon 
 which spheroidal molecules may be supposed to ag"gregate into crystal- 
 line forms, are referred to Dr. WoUaston's interesting" paper on the sub- 
 ject in the Philos. Trans. 1813, p. 51. It may be noticed, however, that 
 the principles here advanced differ materially in other respects from those 
 referred to. 
 
40 
 
 CHEMISTRY. 
 
 Fig. 1. 
 
 i 
 
 T7 
 
 molecules of bodies are spheres, with what powers is it necessary 
 to suppose these little spheres to be invested in order to enable 
 them to cohere and form the symmetrical figures we observe 
 among natural bodies? The existence of simple, mutual and ge- 
 neral attractive powers among such a set of molecules, has been 
 already observed to be inadequate to explain the phenomena ; 
 there must be some specific powers determining similar parti- 
 cles, to combine in similar ways, otherwise the same resulting 
 
 forms could not be supposed to take 
 place. In the tliree small spheres,* 
 (Fig. 1.) let us suppose the points 
 Ec^ Ee, Ee. on their superficies to 
 be endowed with the following pro- 
 perties, viz. that the similar points, 
 E, E, E, and c, c, e, have the pro- 
 perty of mutually repelling each other, while the 
 dissimilar Ee, Ee, Ee, have the properly of mutual 
 attraction. In such a case the three molecules will 
 readily combine E to e, as in Fig. 2, but in no other 
 
 way. Now let us 
 suppose the same 
 three spheres to be 
 endowed with pro- 
 perties at the points 
 31 m. Mm, Mm, 
 as in Fig. 3, very 
 similar to those at E e. Spheres so 
 endowed will aggregate readily, as in 
 Fig. 4:, E io e and M \.o m, but in no 
 other way ; and thus instead of a sin- 
 gle line wc obtain a plate of molecules 
 one in thickness.t To form th.e third 
 dimension, or to constitute a solid, it 
 is necessary to assume the molecules 
 as in fig. 5, to be possessed not only 
 of the attractive points E e, E e, E e, 
 
 ( 
 
 
 * Or rather sections of .spiieres, .and the same is to be understood of 
 all the subsequent figures. 
 
 t Here it is to be observed tliat tlie similar poles E E, e e, of each 
 pair of molecules being- supposed lo be repellent within certain limits, as 
 will hereafter be explained, their absolute contact is prevented, and the 
 two molecules are l)alanccd, as it were, between the two opposing- and the 
 two attracting forces, 'I^he consideration of forces operating in these and 
 in the otlicr modes, suhsequcntl}' mentioned, present some highly in- 
 teresting and novel objects of researcli for the mathematician. 
 
CRYSTALLIZATION. 
 
 41 
 
 
 L^X2^^ 
 
 3Imy Mm, Mm, but also of 
 M' m\ M' m'y M' m', (the 
 point m', being supposed to be 
 opposite to the point M', and 
 out of sight.) Molecules so 
 endowed will readily combine 
 as in Fig. 6, and form a cube 
 or some figure obviously dedu- 
 cible from it, but in no other 
 manner ; and in this way by 
 assuming certain attractive and 
 repulsive points upon our 
 spheres at appropriate parts of 
 their superficies, it is not difl[i- 
 cult to conceive them capable, 
 in different instances, of form- 
 ing aggregates of any shape whatever. The next point to be 
 considered is, how far are we authorized in making such appa- 
 rently complicated and gratuitous assumptions respecting the pro- 
 perties of the ultimate molecules of matter; are there any pheno- 
 mena in nature justifying such conclusions, and what are they ? 
 And this leads us to inquire further, but as briefly as possible, 
 into the phenomena of aggregation, as we see them constantly 
 going on around us. 
 
 Aggregation is usually considered as of two distinct kinds, viz. 
 that depending upon the simple cohesion of similar molecules of 
 matter, as of water, and which for the present may be svipposed 
 to undergo no change by the combination ; and that depending 
 upon the union of dissimilar molecules of matter, capable of ex- 
 erting a mutual chemical change upon each other, in which case 
 the aggregate is a teriium quid, or third something differing alto- 
 gether from either of the original molecules composing it. Now both 
 these kinds of aggregation obviously exist in the same substance, 
 at least when in the solid form. In the first place the chemical 
 aggregation is exerted between the heterogeneous molecules, 
 (hydrogen and oxygen in the present case of water) which uniting, 
 form compound homogeneous molecules, (of water) ; while in the 
 next place, the molecules of water uniting chemiccdly in one di- 
 rection and cohesively in the other, form the solid crystal (of 
 ice). Hence chemical aggregation and cohesive aggregation are 
 as distinct as the polarities themselves upon which they depend ; 
 and if the one existed alone without the other, no such thing as a 
 regular crystalline solid would probably be formed in nature. 
 From the above views, of molecular forces, it follows as a 
 
 consequence that every molecule, and crystalline aggregate of 
 
 4« 
 
42 CHEMISTRY. 
 
 molecules, must possess one axis (as lliat, for instance, joining the 
 polarities E e in tlie preceding figures,) having totally different 
 powers and properties from the other two axes and polarities. 
 This axis, by way of distinction, may be called the chemical axis 
 and polarities. The other two axes (and indeed every other axis 
 that can be supposed to be drawn, through the centre, from oppo- 
 site points of the superficies of the molecule) probably possess 
 common properties, and may be called the cohesive axes and po- 
 larities. Here then the existence of two forces is indicated, — the 
 one axial, the other equatorial, if we may be allowed the expres- 
 sions. The next question is, do such forces actvially exist in na- 
 ture on the large scale, and what are these forces ? Now late ob- 
 servations have proved, beyond a doubt, that the electric and 
 magnetic are such forces. We proceed, therefore, to take a short 
 view of electricity and magnetism.* 
 
 Electricity. — It would be foreign to our present purpose to 
 enter into details respecting this or any other department of 
 science we may have occasion to allude to : hence we shall con- 
 tent ourselves with a short summary of its general principles. It 
 seems to be satisfactorily proved that the phenomena of electrici- 
 ty depend upon two energies, usually existing throughout nature 
 in a state of equilibrium, in which slate their peculiar powers are 
 not perceptible ; that this equilibrium is capable of being destroy- 
 ed by a variety of causes, as friction, &c. ; and that owing to the 
 different capacities possessed by different bodies, for conducting 
 and retaining them, these energies can be partially separated and 
 kept asunder, in which state they are capable of exhibiting their 
 peculiar powers. These powers are such, that if two bodies 
 charged in excess with the same energy be brought into the vicini- 
 ty of each other, they mutually repel each other ; while two 
 bodies charged with the two different energies mutually attract 
 each other. In this disturbance of the equilibrium of the two 
 energies, it is to be remarked, that in no instance do we suppose 
 that the two energies are, or ran be, entirely separated, so as to 
 reside each,y;er se, in different bodies ; but that a portion of the 
 energy of the one body goes to the other body, which at the same 
 
 * It may be rcmnrkcd, tliat as all parts of the superficies of our mole- 
 cules, except the cJiemicul poles, are supposed to be more or less capable 
 of cohesion, their ag'g-ret^'ation in the form of common crystallized solids 
 may be readily conceived. With respect to the cohesion (if we may be 
 allowed the expression) of the diflerent chemical poles E c, of similar 
 molecules with each otlier, such coliesion seems to be proved by several 
 circumstances, which it would be foreign to our purpose at present to 
 inquire into ; hut of wliicli, perhaps, the optical ];)i-o])erties of crj'stuls 
 will hereafter form one of the most striking illustrations. 
 
ELECTRICITY. 43 
 
 time returns a corresponding portion of its antagonist energy; 
 hence, other tilings being equal, eacli body contains the same total 
 quantity of the two electricities as before the equilibrium was de- 
 stroyed. For the sake of the general reader, the matter, in short, 
 may be represented numerically as follows : — Let us suppose 
 that 2000 balls, all exactly of the same size, Slc, but one half 
 black and the other half white, are divided into two equal groups, 
 A and B, of 1000 balls each, but in such a way that the group a 
 shall contain 200 black and 800 white balls, and the group b 800 
 black and 200 white balls. In this case th.e two groups will cor- 
 respond exacdy with two bodies in different states of electricity ; 
 and (supposing them to be possessed of similar powers), if a third 
 group, c, containing 200 black and 800 white balls be brought into 
 the neighbourhood of the group a, which is similarly constituted, 
 the two will be found mutually to repel each other, till they ap- 
 proach within a certain distance, that is to say, till the 200 ijlack 
 balls of each group come into action, and unite each with 200 
 white balls. At this distance they will no longer repel but attract 
 each other; although, instead of forming a state of equilibrium, 
 the white balls (or one of the electric energies,) will predominate. 
 The same thing precisely may be supposed to happen if a fourth 
 group, D, composed of 800 black and 200 white balls, be brought 
 into the neighbourhood of the group b. But if the group a, con- 
 taining 200 black and 800 white be brought into the neighbour- 
 hood of tlie group b, containing 800 black and 200 white, the two 
 will attract each other, and combine to form the original group of 
 2000 balls, consisting of 1000 of each kind, as at first supposed. 
 
 Such are, we believe, the fundamental laws of action and equi- 
 librium of the two electric energies. There is one circumstance 
 immediately arising out of them, which, as it is the most frequent 
 and important of all the causes disturbing the natural equilibrium 
 of the two energies in diflerent bodies, we shall briefly explain : 
 we allude to what are usually called the phenomena oi inductio7i. 
 Suppose an electrified body a, (that is to say, a body having the 
 equilibrium of its electric energies destroyed, as above mention- 
 ed,) be brought into the neighbourhood of another body, b, in its 
 natural state, what takes place ? The electricity e, of the body 
 A, acting upon the corresponding electricity e, in the body b, 
 repels it to the furthest extremity of the body b ; and at the same 
 time attracts to that end of the body b whicli is nearest to the 
 body A, the other and opposite electricity e. The body b, there- 
 fore, while under the influence of the body a, will exhibit all the 
 phenomena of electricity, and is said to be electrified by induc- 
 tion ; but remove this body b from the neighbourhood of the 
 body a, and immediately the natural equilibrium of the energies 
 
44 CHEMISTRY. 
 
 of the body b will be restored, and all signs of electricity will 
 vanish. In this experiment neither of the bodies gains or loses 
 anything. As these phenomena are constantly occurring in nature, 
 and as we shall have frequent occasion to use the term induction^ 
 we have endeavoured to convey an idea of the nature of the sub- 
 ject to the general reader. 
 
 Of Galvanism. — >While we are upon the subject of electricity, 
 we may briefly notice that important modification of it termed 
 galvanism. This form of electricity, instead of being evolved by 
 friction, is usually obtained by the mutual action of various metals 
 and chemical agents upon each other. Late experiments, how- 
 ever, have shown that the energies thus developed, differ in no 
 respect from those of common electricity, but that they are ob- 
 tained in this way in much greater quantity only, though in a 
 lower state of intensity than by the common machine ; and that 
 many of the supposed peculiar eflects of galvanism are the con- 
 sequence of the motion of such large quantities of these energies, 
 through bodies of various conducting powers. Galvanism has 
 recently attracted much more attention than ordinary electricity, 
 from the facility with which it may be applied to the purposes of 
 the chemist, and from the extraordinary light it has thrown upon 
 many chemical phenomena. Indeed, the chemist has been more 
 indebted to the energies of galvanism than to any other; and he 
 will probably be still further indebted to them than he yet has 
 been. With respect to the phenomena of galvanism, these in 
 most respects, so closely resemble the phenomena of electricity, 
 that they do not require further illustration here. 
 
 Of Magnetism. — The general phenomena and laws of magnet- 
 ism are very analogous to those of electricity. There are evi- 
 dently two antagonist energies, which, while in a stale of equi- 
 librium, are not cognizable ; but when separated, each one is 
 mutually repellant of its similar, and mutually attractive of its op- 
 posite or antagonist. Thus the two north or two south poles of 
 two magnetic needles mutually repel each other (with the same 
 exceptions as the two electric poles), but the north pole of one 
 needle and the south pole of another, mutually attract each other. 
 Bodies are also rendered magnetic by induction when in the vici- 
 nity of another magnet, precisely as happens with respect to elec- 
 tricity. Magnetism principally differs from electricity in being 
 apparently limited to a few bodies, as iron, and two or three others ; 
 but late observations have thrown an entirely new light on this 
 part of the subject, which we have next to consider. Before we 
 proceed, however, we may make a few remarks upon the obvi- 
 ous questions : — What becomes of the two electric and two mag- 
 netic energies when in a state of equilibrium ? Do the electric and 
 
/:i c 
 
 M< — 
 
 -m 
 
 ELECTRICITY AND MAGNETISM. 45 
 
 magnetic energies combine to yield the same, or a diflerent re- 
 sult, and what is the nature of this result or results, and in what 
 form do they exist around us? On these points difrtrcnt opinions 
 have been lield : some supposing that by their union, both tlie elec- 
 tric and the mngnetic energies alike constitute heat ; others some- 
 thing else. That both are most intimately connected with heat 
 and light, is evidewt ; but at present we decline to give a decided 
 opinion on the subject. 
 
 We come now to consider the relations of electricity and of 
 magnetism to one another — a discovery which we owe to Oer- 
 sted, and one of the most important that has been made in the pre- 
 sent age. The following is a summary of these relations. Let 
 Fig-. 7. lis suppose, in the annexed figure, E e, to repre- 
 
 sent the wire connecting the zinc and the cop- 
 per terminating plates of a galvanic battery in 
 action. From what has been said, it may be 
 conceived that under these circumstances there 
 will be two currents moving through this wire 
 in opposite directions ; (from the copper to the 
 
 _._ zinc, usually called positive electricity, which 
 
 oappi^r I p-jj^y j^g supposed to be represented by our black 
 
 balls in the previous illustration ; and from the zinc to the cop- 
 per, usually termed negative electricity, which may be represented 
 by our white bails). Now in this state of things it has been sa- 
 tisfactorily established by experiment, that besides these two cur- 
 rents, there are two others having totally different properties, 
 indeed all the properties of the magnetic energies, moving, not in 
 the direction of the wire, but in circles, or rather spirals, 
 round it. The energy corresponding to the north pole of the 
 magnetic needle moves from right to left, round the wire, as 
 above posited, while the energy corresponding to the south pole 
 of the magnet moves in the opposite direction, or from left to 
 right. Hence when a delicate magnetic needle M "tn, is placed 
 above the wire E e, its north pole M, will be attracted by the 
 current moving from left to right, with which it comes first in 
 contact ; and its south pole, for similar reasons, will be attracted 
 by the opposite current. A needle so placed will consequently 
 assume the direction represented in the figure, with its north 
 pole M to the left ; and if it be carried round the wire by its 
 point of suspension, it will be always found to keep the same 
 relative position with respect to the wire. Thus when below the 
 wire, the needle will apparently point in the opposite direction ; 
 when on the same level, on the left hand, vertically downwards; 
 w^hen on the right, upwards. 
 
 Bearing in mind these relative positions of the currents and 
 
46 
 
 CHEMISTRY. 
 
 needles, in what follows we may neglect the currents and judge 
 from the posiiion of the needles alone. Let us consider the case 
 of two connecting wires placed by the side of each other, as in 
 the figures annexed, and which wires may be supposed to repre- 
 
 M< — 
 
 c 
 
 j Copp&r 
 
 Fig. 8. 
 
 I Zf'iic I 
 
 Zffic \ 
 
 -TTl 3K- 
 
 E 
 
 -VI 
 
 Cupper I 
 
 Fig-. 9. 
 
 Ziri c 
 
 \E 
 
 M- 
 
 u^ 
 
 -VI 
 
 VI- 
 
 Coppci^ 
 
 Copper 
 
 E 
 
 Zinc i 
 
 sent the chemical axis of our molecules. Now these wires, in 
 consequence of the magnetic energies circulating round them, 
 will mutually attract or repel each other, according to tiieir posi- 
 tion. If as in fig. 8, they are both in the same relative position, 
 they will mutudly attract each other, as may be inferred from the 
 position of the needles, Mrn^ Mm, the north pole of one of 
 which corresponds wiih the south pole of the other ; but if one 
 of the wires be reversed, as in fig. 9, they will mutually repel 
 each other, the two similar poles of the needles in this case 
 being contiguous. These relations hold universally, and what is 
 most important, recent observations have shown them to be re- 
 ciprocal ; that is to say, if the magnetic energies be made to 
 move in straight lines, the galvanic energies are found to circu- 
 late round them precisely in the way, and according to the laws 
 above described as happening to magnetism round electricity. 
 Hence electric sparks, and indeed all the phenomena of electri- 
 city can now be obtained from a common maornet. 
 
 Whether electricity and magnetism be different forms of the 
 snme energies resulting from the difierent directions of their mo- 
 tions — whether they be distinct energies — whether they be the 
 cause or tlie effect of Polarity, we shall not stay to inquire ; it is 
 sufficient for our present purpose to know that they are insepara- 
 bly associated with one another in the manner stated, and are al- 
 ways present at least in, if they be not the immediate cause of, 
 all molecular actions among ponderable bodies. And this brings 
 us back to the point, where we digressed to consider the subjects 
 of electricity and magnetism. 
 
 We attempted to show that the ultimate molecules of matter 
 must possess two kinds of Polarity ; one which we have deno- 
 minated Chemical Polarity, of a binary character, and existing 
 
POLARIZATION, ELECTRICITY, ETC. 47 
 
 between molecule and molecule, cliiefly when of different kinds ; 
 and another denominated cohesive polarity, determining, under 
 certain circumstances, molecules of the same matter to cohere. 
 We further attempted to explain how these polarities (each sup- 
 posed to be connected by its own proper axis) must exist or be 
 distributed in our molecules so as to fulfil the offices assigned to 
 them, and which they evidently fultil in nature. Lastly, we have 
 shown that the electric and magnetic polarities or energies are 
 actually related to one another, precisely in the same way that 
 we supposed the chemical and cohesive polarities to be. The 
 question then at once arises, — are these forces identical ? Do the 
 electric polarities correspond with the supposed chemical polari- 
 ties, and the magnetic with the cohesive polarities of our mole- 
 cule ? 
 
 To us, we have no hesitation in saying, this conclusion seems 
 very probable, nay, almost inevitable, not only for the reasons 
 stated, but for others equally striking, that we shall have occasion 
 to refer to hereafter. In the mean time we may briefly consider 
 the subject with a little more attention, and principally with refer- 
 ence to some apparent objections that may be raised against it. 
 In the first place it may be objected that it is difficult, from what 
 we know of the varying and capricious character of the electric 
 energies, to suppose that they can ever exist in that definite and 
 permanent form in which they must exist if they be really iden- 
 tical with the cause of chemical affinity. To this objection, it 
 may be replied, that magnetism can and does exist permanently 
 in bodies for ages, and as electricity is an inseparable attendant 
 upon magnetism, this energy must also have equal permanence. 
 Again, a portion of zinc and a portion of copper placed in con- 
 tact produce electrical effects as constant and enduring as the me- 
 tals themselves. The argument, therefore, founded upon the 
 want of permanence, and uniformity of the electric and magnetic 
 energies, cannot, if duly considered, be supposed to have any 
 weight; for the molecule may be conceived to be composed of 
 two parts analogous to the copper and zinc in contact, and the elec- 
 tricity and accompanying magnetism evolved may be supposed 
 to be as permanent in their character as the parts of the mole- 
 cule evolving them. To the argument that electricity and mag- 
 netism, as we are acquainted with these energies, are inadequate 
 to produce the effects and explain the phenomena of chemical 
 affinity and cohesion, it may be replied, that they may be so : 
 but that these energies, as we are acquainted with them, are pro- 
 bably merely accidental and peculiar modifications of the real en- 
 ergies, which in their elementary form, may be something alto- 
 gether difierent, and quite unknown to us. In proof of this no- 
 
48 CHEMISTRY. 
 
 tion, it may be observed, that the electricities of the common 
 machina and of the galvanic machine apparendy differ material- 
 ly ; while that existing in certain animals appears to differ from 
 both. The magnetism evolved by electricity differs also slighUy 
 from common magnetism, yet no one now doubts that these dif- 
 ferences arise from varieties in the quantity and intensity of the 
 same energies, whicli in their elementary form, therefore, may, 
 and probably do, differ from all these varieties. At any rate, we 
 are unable to say that one of these varieties is more elementary 
 than another, and consequently we have no right to assume that 
 either of them is elementary, much less to found any argument 
 upon the assumption. 
 
 Before we quit this subject of polarities and polarizing forces, 
 it may not be amiss, in the last place, to make a few general re- 
 marks on tlie points in which they resemble or difi'er from those 
 of gravitation. 
 
 The forces of gravitation, inertia and attraction, appear to be 
 associated, and to reside in every individual atom of matter in the 
 universe ; hence every atom mutually attracts and is attracted by 
 every other atom. The polarizing forces, on the other hand, are 
 evidently disassociated, and reside in different parts of the same 
 mass ; hence this mass can in no instance be a mathematical point, 
 (or atom ?), but must consist of at least two parts ; hence, also, as 
 all matter appears to possess polarity, matter must exist in the 
 state of mass or molecule^ each of which molecules must occupy 
 actual space. Thus the forces of gravitation and those of polari- 
 zation are quite distinct. The forces of gravitation are primordial, 
 and probably co-existent with matter ; while the forces of polari- 
 zation have more of a derivative or resultant cliaracter, and are 
 evidendy subordinate to those of gravitation. The question here 
 naturally arises, — Are these difl^erent forces related to one another ? 
 Do the forces of polarization consist of the forces of gravitation 
 in a state of separation, (if we may be allowed the expression,) or 
 do they result from the motion of the molecules upon their axes? 
 These are questions quite beyond our powders, — indeed we have 
 nothing to do with them, — our present objectbeing merely to point 
 out the apparent limits within which the Deity has chosen to con- 
 fine his operations. 
 
 Section IV. 
 
 Of the Liquid Form of Bodies. Of Heat. 
 
 Hitherto we liave spoken of tlie a^-orregation of molecules in 
 the solid form only ; we have next to consider their arrangement 
 
OF HEAT. 49 
 
 in that state in which they constitute a liquid. Our notion of a 
 fluid, generally speakino^, is, tiiat all its parts or molecules, instead 
 of being fixed, are perfectly moveable among one another ; our 
 notion of a liquid (the least perfect form of fluidity) is, that its 
 molecules are incompressible. Now, still retaining water as our 
 example of a liquid, let us consider what must happen to its mole- 
 cules situated, as we suppose them to be, in the form of ice, be- 
 fore they can be so arranged as to constitute the liquid water. A 
 moment's reflection teaches us that they must be loosened or se- 
 parated from each other; and, as they cannot separate themselves, 
 that some new agency is requisite for this purpose. It need scarcely 
 be mentioned that this agent is heat ; on the general phenomena 
 and laws of which most important principle we now proceed to 
 make a few remarks. 
 
 The sensations termed hcaf.mvl cold are too well known to re- 
 quire explanation. These sensations, however, like all others, 
 are merely the effects of some external cause or causes, operating 
 on and through our organs, in a manner totally unknown to us. 
 Various opinions have been entertained on the subject; some con- 
 sidering the cause of heat (caloric) to be an existent and material 
 fluid, though of such extreme tenuity and imponderability as to 
 escape our observation, and to become manifest to us only by its 
 effects upon our sensations, and upon all ttie ponderable forms of 
 matter ; others considering it not as material, but as a property or 
 principle of motion, which by exciting a certain species of vibra- 
 tion among the particles of bodies causes the sensations and effects 
 of heat. Such are the most usual opinions, and the probability 
 is, that they are neither of them literally correct, but that heat, and 
 we may add light, are substances, the molecules of which are in- 
 fluenced by polarizing forces precisely similar in all respects to 
 those which influence common matter ; that is to say, that the 
 molecules of heat and of light obey laws, similar in all respects to 
 those which govern the molecules of ponderable bodies.* We 
 have already alluded to the opinion maintained by some, that heat 
 is a compound principle (like water for instance), consisting of a 
 union of the two forms of electricity. We now draw the attention 
 of the reader to this hypothesis, in order to state, that whatever 
 heat may consist of besides, it is almost impossible to explain its 
 
 * We are aware trial this opinion is opposed to that of most mathema- 
 ticians, who favour the undulatory theory of light, and with good reason, 
 so far as they have occasion to consider it ; but we are decidedly of opi- 
 nion that the chemical action of lig'lit can be explained only upon chemical 
 principles, whatever these may be. Whether these chemical principles 
 will hereafter explain what is now st happily illustrated by undulse, time 
 must determine. 
 
 5 
 
50 
 
 CHEMISTRY. 
 
 effects upon the polarizing forces, without supposing that it at 
 least involves, if it do not pass into the electric forces, upon which 
 the polarizing forces apj^ear to us to depend. We have said ap- 
 pear, for as has been already stated, though it is convenient to 
 consider the polarizing forces under the forms of electricity and 
 magnetism, in which they are most usually and palpably mani- 
 fested to us among ponderable bodies, yet, in their elementary 
 form these forces may in reality be something very different, not 
 only from those of electricity and magnetism, but from all others 
 with which we are acquainted ; while electricity and magnetism, 
 themselves, may be nothing more than the effects of these element- 
 ary forces upon the subtle matters of which the electric and mag- 
 netic molecules are composed. 
 
 One of the most general effects of heat is the increase of volume 
 which it produces in all bodies in which it is accumulated. There 
 are a few exceptions to this law, and one of so curious and im- 
 portant a character as to require especial notice hereafter. In the 
 mean time, however, the generality of the law may be taken for 
 granted, and an attentive comparison of what has preceded and 
 follows, will perhaps throw some light upon the nature of this 
 phenomenon. 
 
 Let us suppose Fig. 10, to represent, 
 as in our former illustrations, two mole- 
 cules of ice, with the chemical axes E e, E e, 
 parallel and similar. In this state their co- 
 hesive polarities will be dissimilar, and the 
 molecules, of course, will cohere as repre- 
 sented. Let us now suppose, from some external source, a cer- 
 tain quantity of heat to be communicated to these molecules. The 
 natural tendency of heat is usually considered to be to arrange 
 
 itself in the form of an atmosphere, around 
 the molecules as in Fig. 11 ; the consequence 
 of which is, that their apparent temperature 
 is raised a certain quantity, and they will 
 be separated from each other in some slight 
 degree ; they will thus occupy more space 
 than in Fig. 10, before the addition of heat; the cohesion between 
 the parts Mm will also at the same time be diminished. And 
 here it may be proper to notice an important fact, that the same 
 quantity of heat when introduced into different bodies produces 
 very difierent apparent temperatures and effects, and that this con- 
 stitutes what is called by chemists their capacity for heat, or their 
 specific heat. Thus if the same quantity of heat, which we sup- 
 posed to have been introduced into two molecules of ice, had been 
 introduced into two molecules of silver, their apparent temperature 
 would have been raised more than ten times as much as that of 
 
CAPACITY FO?^ HEAT, ETC. 51 
 
 the molecules of ice ; hence in the case of the ice some of the heat 
 must have disappeared, or become, in the language of chemists, 
 latent^ a most important property of heat which we have next 
 briefly to inquire into. Previously, however, it may not be amiss 
 to observe, that the molecules of heat are supposed to be vastly 
 less than those of any ponderable substance ; and that they may 
 thus, without any incongruity, be supposed capable of forming an 
 atmosphere around the ponderable molecules, which they could 
 not otherwise of course be imagined to do. 
 
 The latency of heat appears to depend upon two totally differ- 
 ent phenomena, or rather, properly speaking, is of two distinct 
 kinds, as may be thus illustrated. Let us take the two bodies 
 above alluded to — ice and silver ; these under the same volume 
 contain very unequal portions of matter, the silver being ten times 
 as heavy as the ice. The vacuities in the ice, therefore, must be 
 very much greater than those in the silver; hence, when the same 
 quantity of any principle, capable of occupying such vacuities, as 
 heat may be supposed to be, is introduced equally into both, very 
 dissimilar apparent eflects must be produced. The more porous 
 body will absorb and condense within its vacuities the added prin- 
 ciple, and leave but little external and sensible ; while the less 
 porous body, having less room among its pores, will exhibit a 
 larger quantity external and sensible. The more porous body, 
 therefore, may be said to have a greater capacity for heat than the 
 less porous body, from its greater power of absorbing heat, and ren- 
 dering it latent.* This, we believe, is the usual explanation of the 
 phenomenon under the assumed circumstances, and it is probably 
 correct to a certain extent : but there is obviously another form of 
 latent heat, totally different from the above, and which evidently 
 cannot be explained on the same principles, and this we have now 
 to consider. Let us suppose that into a mass of ice, cooled con- 
 siderably below the freezing point, a uniform and regular flow of 
 heat be determined from some external source ; the temperature 
 of the ice, of course, will gradually go on increasing till it rise up 
 to the freezing point ; it will then suddenly stop, and remain sta- 
 tionary till a quantity of heat, equal to 140 degrees of the ther- 
 mometer, have flowed into the ice. The ice has now become 
 water ; but up to that point the water still retains the original tem- 
 perature of the ice ; after that point, however, if the heat continue 
 
 * This union of heat with ponderable bodies may, perhaps, be consi- 
 dered as analog-ous to the condensation of gaseous bodies by porous sub- 
 stances — a very remarkable set of phenomena, which deserve to be much 
 more carefully studied than they have been. The absorption of light is 
 probabl)^ of a similar nature ; and the whole apparently depend upon che- 
 mical principles, and probably, if studied in connexion, would mutually 
 illustrate each other. 
 
52 CHEMISTRY. 
 
 to be applied, the water acquires apparent temperature as before. 
 Now in this experiment a quantity of heat equal to 140 degrees 
 of the thermometer has actually disappeared ; but this disappear- 
 ance cannot be explained in the same manner as that above men- 
 tioned ; for the water, instead of being greater in volume, and 
 consequently having greater vacuities than the ice from which it 
 was formed, is actually less, and must therefore contain fewer va- 
 cuities. How then are the plienomena to be explained ? We 
 commenced our observations upon heat, by alluding to the hypo- 
 thesis that this principle is capable of being decomposed into two 
 energies, if not identical Avith, at least operating in the same way 
 as those of electricity. In the above experiment, therefore, we 
 consider that the 140 degrees of heat which have disappeared, are 
 decomposed and converted into the two polarizing energies ; and 
 that these energies thus produced are superadded to the energies 
 already existing attached to the molecules of water, and in this 
 way increase their total quantity or intensity. The changes in- 
 duced in the relative position of the molecules of water, by this 
 increase of intensity in their energies, may be illustrated as fol- 
 lows : — Let Fig. 12, as before, represent 
 the position of two molecules in the state of 
 ice. Here the similar poles E E and e e, 
 are of course mutually repellent, while co- 
 hesion takes place between the dissimilar 
 polarities, as shown in the figure. Now 
 suppose the polarities, E E, e e, to be suddenly much increased 
 in intensity, so as to extend beyond the semi-diameter of the 
 spheres ; they will of course repel each other, and in such a way 
 that the two sp.heres will revolve on the common axis of adhesion 
 Mm, and the axes E e, E e, instead of remaining parallel, will 
 become at right angles to each other, as in Fig. 13 ; or rather as 
 
 FiP- 11 Fie- 14 '" ^^^' ^^- ^^" ^'?- ^^' ^ ^'^^^^ 
 
 ^ IS supposed n\ the direction or 
 
 the common axes, 31 m M m^ 
 
 of Fig 13. in which view, of 
 
 course, E e,E e, are supposed to 
 
 represent the chemical axes of 
 
 the two spheres at right angles to each other. Hence in the liquid 
 
 state of bodies the position of the axes of adjoining molecules may 
 
 be supposed to be at right angles, or in some position less than right 
 
 angles and approaching parallelism. At exact right angles the 
 
 cohesive polarities are balanced and neutralized, so that the points 
 
 Afm have neither a tendency to unite nor to separate, but remain 
 
 simply in contact. Hence the molecules of such a body v.-ill be 
 
 all disassociated and free to move among one another ; and if we 
 
 suppose each molecule at the same time to be surrounded by its 
 
GASEOUS FORM OF BODIES. 53 
 
 atmosphere of caloric, so thin as not ahogether to remove mecha- 
 nically the molecules beyond one another's influence, we have 
 probably as clear an idea of the nature of a liquid as we are ca- 
 pable of forming. 
 
 Section V. 
 
 Of the Third or Gaseous Form of Bodies. 
 
 We have next to consider the most perfect form of fluidity, 
 that of gas, or (adhering to our former example), steam ; and we 
 shall, in the first place, take a short view of the molecular arrange- 
 ment of bodies existing in the gaseous form, which will enable us 
 still further to elucidate the subject of latent heat. 
 
 Let us suppose as before, the same constant stream of heat to 
 be flowing into a portion of water that we supposed to be flow- 
 ing into the ice : the w^ater continues to increase in temperature 
 and capacity for heat till it arrives at the boiling point ; at this 
 moment the temperature ceases to be augmented, however much 
 we may urge the apphcation of heat, and the water is converted 
 into a transparent gas, well known by the name of steam ; to ef- 
 fect this latter purpose, however, under the ordinary circumstances 
 of atmospheric pressure, it has been found that nearly 1000 de- 
 grees of heat are necessary, which large quantity of heat actually 
 becomes latent or disappears, since the temperature of the steam 
 formed never exceeds 212°, that of the water at the boiling point. 
 What becomes of these 1000 degrees of heat ? We may suppose 
 one portion of it to become latent in the first of the tw^o ways 
 described above ; that is to say the water in the act of being con- 
 verted into vapour, is much augmented in volume, and into this 
 augmented volume, as into a sort of vacuum, a portion of the heat 
 may be supposed to rush and become insensible ; but another por- 
 tion of heat is obviously decomposed, and goes to augment the 
 molecular polarities of the water, which, in the case of steam 
 (and in all gases), may be imagined to be arranged in some such 
 way as the following : — 
 
 In Fig. 15, we have represented as before, 
 ''^' ' though in a different manner, the chemical 
 
 axes at right angles to each other ; at which 
 angle the cohesive polarities are balanced 
 and neutralized. This angle, therefore, may 
 ^^ -.^g^ 1^^ considered as the point at which liquidity 
 
 terminates and perfect fluidity begins. The next augmentation of 
 heat increases the chemical polaric intensities still further, so as 
 to induce them to repel (or rather to attract) each other's axes into 
 
 5* 
 
54 CHEMISTRY. 
 
 the parallel position, Fig. 16; where the 
 chemical polarities are quite reversed, and 
 of course, the contiguous cohesive polari- 
 ties m and m are brought into the maxi- 
 mum state of repulsion. Now such position, 
 or some angle greater than a right angle, 
 may be supposed to be that assumed by the chemical axes of the 
 molecules of all bodies when in the gaseous state. Hence, as 
 there are two kinds of attraction, so there must likewise be two 
 kinds of repulsion, viz. heterogeneous or chemical repulsion ; 
 and homogeneous, or self-repulsion, opposed to cohesion, upon 
 which the gaseous form of bodies principally depends. 
 
 But here a question arises : in what state are the molecules of 
 bodies in the condition of vapour, as those of water at all tempe- 
 ratures below 212° ; for instance at 32° ? According to an hy- 
 pothesis to be presently mentioned, a given volume of steam, at 
 212°, contains the same number of self-repulsive molecules as a 
 similar volume of air under the same temperature and pressure, 
 and therefore has the same elasticity. But the elasticity of the 
 vapour of water at 32° is only equal to about l-5th of an inch of 
 mercury ;* hence the same given volume of that vapour at 32° 
 will only weigh about 1-1 50th of what steam ought to weigh, sup- 
 posing it could exist as a permanent gas at 32°, and under a pres- 
 sure of thirty inches of mercury. The molecules of the vapour, 
 consequently, will be five or six times further apart than in per- 
 fectly gaseous bodies under a similar temperature and pressure.! 
 Let us now, in the last place, inquire how the above supposi- 
 tions respecting gaseous bodies accord wilii their common leading 
 properties, viz., with their self-repulsive or diffusive properties ; 
 their equable expansion by heat ; their increase in volume in the 
 inverse proportion of the force with which they are compressed; 
 and with their similar capacities for heat. 
 
 * Tl)e elastic force of vajiours increases with their temperatures ; that 
 is to say, accordhig- to oui- h} polhesis, increases with the angle formed by 
 the chemical axes of their molecules. At exact rij^ht ansjles the elastic 
 force is ; at 180° it is equal to that of air under similar pressure and tem- 
 perature. Hence all intermediate elasticities lie between these two points. 
 
 f Supposing' ii were possible for steam to exist at 32°, of course at this 
 temperature its weiglit would bear to thtit of air, the same proportion it 
 bears at 212°, that is to sa}', as 5 to 8. Hence 100 cubic inches of steam 
 at 32°, ought to weig-h 20.49375 grains ; or 5-8ths of 32-79 grains, which 
 is the weight of 100 cubic inches of air at 32°. But the Aveight of 100 
 cubic inches of steam at 32° is only .13C6 grain, or l-150ththat of air. Ti;e 
 number of molecules in steam at 32° is consequently only l-150th of those 
 in air at 32°. Hence this diminution of the number of molecules, if we 
 suppose them to be diffused equally throughout the same space of 100 
 cubic inches, must of coin-sc, as stated in tlie text, cause them to be be- 
 tween five and six times further apart. 
 
PROPERTIES OF GASES. 55 
 
 Of the diffusion of Gaseous Bodies. — For the facts connected 
 with this most important subject we are principally indebted to 
 Dr. Daltoa and to Mr. Graham ; the latter of whom has shown 
 that when any gas or air is confined in a vessel furnished with a 
 very narrow aperture or with a porous plug, an interchange between 
 the confined and the external airs immediately begins to take place 
 through the communicating aperture ; and that this interchange 
 continues to go on to a certain point, which, with respect to the 
 same gas, appears to be uniform, but differs in difl'erent gases ac- 
 cording to a certain law. Two gases also, whatever may be their 
 specific gravities, and however they may be introduced into the 
 same vessel, speedily become mixed uniformly throughout. These 
 facts evidently indicate a species of self-repulsive influence among 
 the molecules of the same gas, which appears to be satisfactorily 
 accounted for by our hypothesis. The argument is very simple 
 and obvious : Two molecules of the same matter have a tendency 
 to cohere and to form a solid, when the chemical polarities of 
 these molecules are similarly arranged, and do not extend beyond 
 the semi-diameters of the molecules ; but two molecules of differ- 
 ent matter, under circumstances precisely alike, remain passive, 
 and have no tendency to cohere. Hence, while two molecules 
 of the same matter, having the intensity of their polarities much 
 increased, and their chemical poles, consequently, reversed, repel 
 each other, or become se^-repulsive ; two molecules of different 
 matter, still retaining their mutual passiveuess, do not repel each 
 other. 
 
 There is reason to believe that these phenomena are not con- 
 fined to bodies perfectly gaseous, but exist also in that less per- 
 fect gaseous condition termed vapour, of which the vapour of 
 water may be considered as the most familiar example. On this 
 supposition, and particularly that the above law of diffusion holds 
 among vapours, (which is probably the case, though in a modified 
 form) the lower the specific gravity of the vapour, that is to say 
 the lower the temperature, the greater the diffusive power ; and 
 consequently the more rapid the evaporation : a most important 
 inference that will enable us to explain many meteorological phe- 
 nomena at present quite inexplicable. Something very similar, 
 if not identical with the above phenomena, also exists in liquids 
 and perhaps in solids. Thus the molecules of certain matters dif- 
 fused through a liquid, as water, may be supposed to exert in some 
 cases a self-repulsive influence on each other, by which supposi- 
 tion only do their equal diffusion through a large mass of liquid 
 seem explicable. Even in the solid slate, as above observed, some- 
 thing of the kind appears to exist, especially among organized 
 bodies, which apparently owe some of their most remarkable pro- 
 
56 CHEMISTRY. 
 
 perties to the diffusion of active self-repulsive molecules through- 
 out their substance. 
 
 Of the equal Expansion of Gaseous Bodies by Heat. — With 
 respect to the second important property of gaseous bodies, that 
 under the same temperature and pressure they all undergo equal 
 expansion by an equal increase of lieat ; this seems to be expli- 
 cable only on the supposition that all gaseous bodies, lender the 
 same pressure and temperature, contain equal numbers of self- 
 repulsive molecules : a most important conclusion, as we shall see 
 hereafter, and one, which at present we are anxious a little further 
 to illustrate. Supposing the fact to be, as it is, undeniable, that 
 within the ordinary limits of experiment, all perfectly gaseous 
 bodies expand equally by similar increments of heat, z/' different 
 gases contain unequal iwixnhe^is, of self-repulsive molecules, those 
 gases which contain the least number of molecules, must exert 
 the greatest power, and consequently have the greatest disposition 
 to expand; in other words, the expansive power of the molecules 
 of a gas, must increase as their number diminishes ; and not only 
 so, but in order to produce the effect stated, the expansive power 
 must increase, neither more nor less, but exactly as the number 
 diminishes — a law which when applied to extreme cases becomes 
 obviously absurd. Further it may be observed, in corroboration 
 of the hypothesis advanced, that in the gaseous state the molecules 
 of bodies may be considered as having undergone the utmost ef- 
 fects, that any increase of heat can produce upon them. All their 
 interstitial vacuities may be supposed to be already saturated with 
 it; while an atmosphere may be supposed to surround each mole- 
 cule, keeping them individually at a considerable distance from 
 each other : their polarities also may be supposed to have under- 
 gone their ultimate change, so that no more heat can be rendered 
 latent by inducing further changes, except in degree, which degree 
 may be supposed to be common to all gases. Hence every mole- 
 cule of matter, when in the gaseous state, and subjected to similar 
 pressure and temperature, may, without reference to its other pro- 
 perties, be supposed to be in circumstances exactly similar, and 
 consequently liable to be affected in an exactly similar manner by 
 all further increments of heat. 
 
 Of the inverse Relation of the J\ilume to the Compressive 
 lorce. — Nearly the same remarks apply to this law as to the pre- 
 ceiling; for were the numbers of molecules in each gas supposed 
 to be unequal, the diminution of volume under similar pressure 
 ought to vary also, which is not the case, at least in the more per- 
 fect gaseous bodies, and neither this observation, nor those in the 
 former para<rraph apply to vapours. 
 
 Of the similar capacity of Gaseous Bodies for Heat. — The 
 begt experiments seem to show that under the same pressure the 
 
HEAT IN MOTION. 57 
 
 same volumes of all gases have ihe same capacity for heat — a cir- 
 cumstance quite according with the other phenomena. Hence, 
 for the above and other reasons which might be mentioned, we 
 have been induced to adopt the hypothesis already stated, that, 
 tinder the same pressure and temperature, all bodies in a per- 
 fectly gaseous state contain equal iiuinbers of self-repulsive mo- 
 lecules.^ 
 
 Section VI. 
 
 Other Properties of Heat. Of Heat in Motion. 
 
 Heat appears to be in a constant state of motion and of inter- 
 change between different bodies, among which it finally settles 
 into a state of equilibrium. If accumulated in any body, this ac- 
 cumulation cannot be preserved ; but the excess will fly off in 
 spite of all we can do to the contrary, and sooner or later the equi- 
 librium will be restored. This motion of heat takes place in three 
 ways, which a common fire-place very well illustrates. If, for 
 instance, we place a thermometer directly before a fire, it soon 
 begins to rise, indicating an increase of temperature. In this case 
 the heat has made its way through the space between the fire and 
 the thermometer, by the process termed radiation. If we place 
 a second thermometer in contact with any part of the grate, and 
 awav from the direct influence of the fire, we shall find that this 
 thermometer also denotes an increase of temperature ; but here the 
 heat must have travelled through the metal of the grate, by what 
 is iexmeA conduction. Lastly, a third thermometer placed in the 
 chimney, away from the direct influence of the fire, will also in- 
 dicate a considerable increase of temperature ; in this case a por- 
 tion of the air, passing through and near the fire, has become 
 heated, and has carried up the chimney the temperature acquired 
 from the fire. There is at present no single term in our language 
 employed to denote this third mode of the propagation of heat ; 
 but we venture to propose for that purpose, the term convection,'^ 
 
 • It is proper to observe tliat these views were adopted by the author 
 long' before he was aware of the existence of the essays on the subject by 
 Messrs. Avog-adro, Ampere, and Dumas. Indeed he was unacquainted 
 with those of Dumas, which most nearly resemble his own, till he saw them 
 alluded to in Mr. Johnston's recent report on chemistry in the Transactions 
 of tlie British Association. Mr. Donovan seems to consider the above hy- 
 pothesis as untenable ; but we think his arguments entirely inconclusive. 
 See Giornale di Fisica, sec. ii. tom. viii. p 1. ; Annates de Chimie, torn, 
 xc. p. 43 ; a Treatise on Chemistry, by Mr. Donovan, in Lardner's Cabinet 
 Cyclopaedia, p. 379 ; and the Introduction to Dumas's Traite de Chimie 
 appliquee aux Arts, which excellent work the author had been prevented 
 from perusing by the nature of the title. 
 
 f Convedio, a carrying or conveying. 
 
58 CHEMISTRY. 
 
 which not only expresses the leading fact, but also accords very 
 well with the two other terms. Each of tliese modes of the pro- 
 pagation of heat possesses certain peculiarities, on which we pro- 
 ceed to make a few remarks. 
 
 Radiation of Heat. — Heat radiates in vacuo in all directions 
 equally, and with immeasurable velocity. Heat radiates also through 
 all gaseous bodies, and more or less through transparent media. 
 Radiation goes on at all temperatures ; but the quantity of heat 
 radiated in a given time bears some proportion to the excess of 
 the temperature of the radiating body a'30ve that of the surround- 
 ing medium. Radiant heat is capable of being rejected like light, 
 (to be presently noticed,) and, indeed, obeys altogether somewhat 
 similar laws. Those surfaces, however, that reflect light most 
 perfectly, are not equally adapted to the reflection of heat. Metals 
 in general, and particularly when highly polished, are the best 
 reflectors of heat, while glass, which reflects light most perfectly, 
 reflects comparatively little heat; thus tin-plate reflects about eight 
 times as much heat as a glass mirror. The radiation of heat is 
 much influenced by the nature and state of the surfaces of bodies. 
 Thus a surface coated with lamp-black radiates eight or nine times 
 as much heat as a polished surface of tin or silver; and in general 
 polished surfaces, particularly of metal, radiate much less than 
 other surfaces. As might be expected, this diflTerence of radiating 
 power exerts great influence in the cooling of bodies ; thus warm 
 water retains its heat much longer in a bright tin vessel, than in 
 the same vessel coated with linen, paint, or particularly lamp-black. 
 Radiant heat is absorbed with different facilities by difTerent sur- 
 faces. The absorbing power of surfaces seems, indeed, to vary 
 directly as their radiating power, and inversely as their reflecting 
 power. That is to say, surfaces receive heat by radiation nearly 
 with the same degree of facility as they give it off; while those 
 that reflect most, of course, must absorb least ; a surface covered 
 with lamp-black, for example, receives in a given time eight or 
 nine times as much heat by radiation as a polished tin surface re- 
 ceives. From these remarks, it will be readily inferred, that the 
 colours of bodies may have considerable influence in the radiation 
 and absorption of heat; now this is found to be the case, "and the 
 darker tlie colour of a body, the more readily it gives off, and ab- 
 sorbs radiant heat. Radiant heat has the power of passing through 
 transparent bodies, as glass. This power, however, varies accord- 
 ing to the thickness of the glass, its relative position to the radia- 
 ting body, and a variety of other circumstances not well under- 
 stood ; but generally speaking heat seems to obey laws, more or 
 less, analogous to those of light under similar circumstances. 
 Conduction of Heat. — The conduction of heat is chiefly con- 
 
OF LIGHT. 59 
 
 fined to solid bodies ; and as solids exist of every degree of con- 
 sistency and density, from perfect fluidity up to perfect hardness, 
 the conducting power varies in like manner. Hence the laws of 
 conduction and those of radiation have a mutual dependance ; and, 
 in fact, the laws of conduction may be considered as only extreme 
 cases of the laws of radiation. The conduction of heat through 
 bodies seems to take place equally in all directions. In general 
 the densest bodies, as metals, stones, hard woods, &c., have the 
 greatest conducting power, though these differ exceedingly among 
 one another. Porous bodies in general are bad conductors ; and 
 of such bodies charcoal may be considered as one of the worst 
 conductors. Among substances employed as articles of dress, 
 hare's fur and eider down are the worst conductors, and flax the 
 best. The relative conducting powers of substances of this class 
 seem to depend much upon the quantity of air enclosed within 
 their interstices, and the power of attraction by which this air is 
 retained or confined. The conducting power of liquids and of 
 gases is very limited, though under certain circumstances they ajo- 
 pear to possess this power in a high degree. But this power is 
 only apparent, and heat is chiefly communicated through liquids, 
 and also through gases by the third process above alluded to, viz. 
 convection. By convection however, heat is only propagated in 
 one direction, namely, upwards ; hence almost any degree of heat 
 may be applied to the upper surface of a liquid or gas without 
 aflfecting the lower. 
 
 Such are the principal phenomena connected with the motion 
 of heat ; but before we proceed to speak of the sources of this 
 wonderful agent, we have yet to consider another imponderable 
 principle of the utmost importance, and intimately connected with 
 heat ; viz., Light, 
 
 Section VII. 
 
 Of Light, 
 
 The laws of the motion of light, of its reflection, refraction, 
 polarization, (fee, properly belong to another department ; we 
 shall, therefore, only briefly describe them here, and endeavour 
 to point out the general connexion and analogy they bear to the 
 phenomena of chemistry, and more especially to the phenomena 
 of heat and electricity. 
 
 Radiation or Motion of Light. — Light radiates or moves in 
 straight lines with such inconceivable velocity, that it occupies only 
 about eight minutes in travelling from the sun to our earth, so 
 that it must move at the rate of nearly 200,000 miles in a second ! 
 At the same rate it would occupy about four hours to travel to us 
 
60 
 
 CHEMISTRY. 
 
 from Ihe planet Uranus, the present ultima Tlnde of our system ; 
 hence if this planet were at any given instant suddenly annihilated, 
 we should not miss it for four hours afterwards ; and when we 
 look at it, we do not see it where it actually is at this instant, but 
 where it was four hours previously. A cannon ball, when first 
 shot from the cannon, moves with a velocity of between 2000 
 and 3000 feet per second ; supposing-, therefore, it could retain its 
 initial velocity, it would scarcely move in a year as much as light 
 moves in a single second ! The utmost velocities of the earth and 
 other planets, in their orbits or on their axes, scarcely exceed 
 30 or 40 miles in a second. Hence the utmost velocity that we 
 are acquainted with as possessed by ordinary matter, and therefore 
 the utmost perhaps of which such matter is capable, only amounts 
 to the l-5000th or l-6000lh of that of light! These striking facts 
 are mentioned with the view of conveying some notion of the im- 
 mensity of space, and of the wonderful velocity with which it is 
 in every direction penetrated by light. They seem also to show, 
 that if light be matter, it must exist in a state of tenuity, totally 
 diflierent from the ponderable matter we are acquainted with, 
 which actually seems incapable of such velocity.* 
 
 If we consider heat and light to consist of polarized molecules 
 in the self-repulsive state, and to obey the same laws that ponde- 
 rable matters in the gaseous state obey, which is exceedingly 
 probable ; the radiation of these imponderable bodies will be ana- 
 logous to the diflusion of gaseous bodies, and by knowing their 
 velocity and applying the same law, we may deduce their 
 comparative gravities. 
 
 Hfflection and Refraction of Light. — In free space, as before 
 observed, light moves in straight lines; but when a ray, 7?, Fig. 
 
 Fig. 17. 
 
 17, falls upon a polished 
 surface, as of glass, a portion 
 of it is reflected in the direc- 
 tion e E, and the angle, R e 
 P, called the angle of inci- 
 dence, is always equal to the 
 angle, P e £, called the 
 angle of reflection. Another 
 portion, e m, passes through 
 the glass, but instead of con- 
 tinuing to move in the same 
 straight line, is bent consi- 
 derably out of that direction 
 towards the perpendicular P 
 
 Pouillet, Elemcns de Physique et de Meteorolog-'ie torn. iii. p. 216. 
 
POLARIZATION OF LIGHT. 
 
 61 
 
 Q ; it then makes its exit at m, and goes on in the direction m ikf, 
 parallel to its original direction, Re. This portion of the ray is 
 said to have undergone refraction ; a term indicating that its na- 
 tural course has been broken. Such are the general facts ; and 
 the study of their laws, varieties, and peculiarities, as modified 
 by different media, constitutes the science of optics, a branch of 
 knowledge not f;illing within our present design. In connection 
 with this part of our subject, it only remains to observe, that in 
 passing through the most transparent bodies much light is lost, 
 by absorption and in other ways. So also when light falls upon 
 metallic bodies, such as polished silver, about one-half only is 
 reflected, while the other half is absorbed and lost. Different 
 substances, however, differ materially in these respects, and from 
 the experiments of M. Bouguer and M. Lambert, it appears that 
 in fluids, transparent solids and metals, the quantity of light re- 
 flected, increases with the angle of incidence reckoned from the 
 perpendicular ; whereas in white opaque bodies the quantity of 
 light reflected, decreases with the angle of incidence.* We shall 
 hereafter have occasion to revert to these curious facts. 
 
 Polarization of Light. — The next property we have to 
 notice is what is called the polarization of light. Let us sup- 
 ply. iq ,, poseFig. 18,torepre- 
 ^'^• ■^^- ^ sent a bundle of plates 
 
 of thin window-glass, 
 bound together in the 
 manner indicated. Let 
 ^ e be a ray of light 
 falling on the upper 
 plate, at an angle 
 of incidence of about 
 56° ; a portion of the 
 ray will be reflected, 
 and will move in the 
 direction e JS, while 
 another portion of the 
 ray e m, will pass through the bundle of glass plates onwards to 
 M, according to the laws of reflection and refraction already stated. 
 Now these two rays e E and m M, possess remarkable properties, 
 similar to one another in most respects, but directly opposed 
 in another. Of these properties we shall endeavour to give a 
 general idea. 
 
 • See article Optics, p. 67, and 68, in the Library of Useful Knowledge. 
 Where the orig-inal observations are to be found, which are there referred 
 to, we do not at present know. 
 
 6 
 
62 CHEMISTRY. 
 
 If the ray of light R Jl^ after failing upon the vertical glass A^ 
 Fig. 19, at an angle of incidence of 56°, be received on a plate 
 
 Fig. 19. 
 
 of glass, C, placed at the same angle of incidence, and be then 
 reflected from C to E ; in the position intended to be shown in 
 the figure, when the ray B is first reflected in a horizontal plane, 
 R A C, and then in a vertical plane, ACE, the ray C E be- 
 comes so weak as to be scarcely visible, the whole of it having 
 passed through the glass C. But if the glass C be turned round 
 90°, (the ray A C being supposed to be the axis of motion) so 
 that the ray C E he reflected horizontally ; instead of passing 
 through the glass C as before, the whole of the ray C E will be 
 reflected. If we continue to turn the plate Cupon the axis A C, round 
 the entire circle, these alternations of transmission and reflection will 
 be found to take place in the same manner at the two other quadrants 
 180° and 270°. Hence the xzj RA, by reflection, has acquired pro- 
 perties altogether new ; it is said in short, to have acquired polarity, 
 or to have become polarized. Now recurring to Fig. 18, the ray 
 R e, in that figure will of course follow the same laws as the ray 
 R A in Fig. 19, that is to say, the ray e E will have acquired 
 polarity by reflection. Let us now consider what has happened 
 to the refracted ray m 31 m the same Fig. 18. This ray m M 
 will also be found to be polarized ; but if we receive it on a glass 
 plate, F G, at the polarizing angle of 56°, we shall find that it 
 will refuse to be reflected ; whereas the reflected ray e E does 
 not refuse to be again reflected, unless the plate E G he turned 
 round 90°, or into a plane at right angles to that plane in which 
 the refracted ray m Af had refused to be reflected. Hence we 
 conclude that when a ray of light is incident at the polarizing 
 angle upon a transparent body, the whole of the reflected light is 
 polarized ; while the whole of the transmitted light is also polar- 
 ized, but in a plane at right angles to that in which the reflected 
 ray is polarized. 
 
 Such is the general law, and it may not be amiss to allude 
 briefly to another familiar illustration of it. Every one is ac- 
 
DECOMPOSITION OF LIGHT. 
 
 63 
 
 quainted with the mineral called Iceland spar, and with the sin- 
 gular property which this mineral possesses of forming a double 
 image of objects seen through it, or its property of double refrac- 
 tion ; that is to say when a ray of light falls on a crystal of such 
 spar in a particular direction, the ray is separated into two. Now 
 it is a remarkable fact that if these two rays be examined in the 
 way before directed, when speaking of reflected and transmitted 
 light, it will be found that both are polarized, but that the two 
 rays are polarized in planes at right angles to each other ; that is 
 to say, the ordinary transmitted ray is polarized like the ordi- 
 nary ray transmitted, through the bundle of glass plates ; while 
 the extraordinary transmitted ray is polarized like the ray re- 
 flected from these plates. Many bodies are similarly constituted ; 
 while others have two or more planes or axes of double refrac- 
 tion, giving origin to a variety of curious and beautiful properties, 
 which it would be quite foreign to our present purpose to detail 
 further. 
 
 Decomposition of light. — When a ray of light, R^ Fig. 20, 
 traverses a prism, CD F, instead of passing onward in the direc- 
 
 Fig. 20. 
 
 Violet 
 
 Indigo 
 
 Blue 
 
 Orecn 
 
 Yellow 
 
 Orange 
 
 Red 
 
 White 
 
 X.' 
 O'- 
 
 tion Y, it is refracted into the spectrum E e; which spectrum 
 when received upon the screen, A B, will be found to consist of 
 seven different colours, in the order and of the kind described, 
 each having, of course, different refractive powers ; the red being 
 the least, and the violet the most refracted from the original direc- 
 tion R y, of the solar beam. This oblong image is called the 
 solar, or sometimes, the prismatic spectrum, and Sir Isaac New- 
 ton found that each colour consists of light no longer separable, 
 like white light, into others, but having uniform refractive pro- 
 perties : hence he called all the seven colours simple or homo- 
 geneous, in opposition to white light, which he called compound 
 or heterogeneous.* This important fact presents a clue to, and 
 
 * Sir David Brewster has lately shown that there are, in fact, but three 
 simple colours, the redf the yellow and the blue, and that each of these 
 
64 CHEMISTRY. 
 
 exhibits the general law which regulates the endless variety and 
 change of colours ; as bodies appear to have this or that colour, 
 according as they have the power of reflecting or transmitting 
 this or that colour, and of absorbing or reflecting the rest ; while 
 wliite bodies reflect all, and black absorb all. Besides colour, 
 it has been likewise noticed that different portions of the prismatic 
 spectrum possesses difl^erent heutimi; and chemical or electrical 
 properties. These vary in some respects, according to the na- 
 ture of the prism employed. In general the heating power in- 
 creases towards the red ray ; while the chemical power seems to 
 be regulated in some degree by the nature of the colour, but is 
 greater (though of opposite character) at the two extremities than 
 in the centre of the spectrum, where it appears to be nearly null. 
 The chemical properties of light, however, are by no means 
 well understood, and have not received the attention which they 
 merit. 
 
 Upon an attentive consideration of the phenomena of heat and 
 of light, and a careful comparison of them with the general phe- 
 nomena of polarizing forces, it is impossible not to be struck with 
 the close analogy tliat prevails throughout the whole. The phe- 
 nomena of heat have hitherto been very imperfectly studied, and 
 in consequence we are much less able to trace the analogy ; but 
 the phenomena of light from their obvious and striking characters 
 have attracted more attention, are much better understood. To 
 enter further upon the inquiry here would be quite foreign to 
 the object of this treatise ; we cannot however, in concluding 
 these remarks, refrain from repeating an opinion already express- 
 ed, that the molecules both of heat and of light possess polari- 
 ties precisely similar to those of ponderable bodies ; and that not 
 only the chemical agencies of these principles, but those pheno- 
 mena of light also at present so beautifully illustrated l3y the 
 hypothesis of undulse, will be hereafter found to admit of explana- 
 tion on the more probable supposition of molecular polarity.! 
 
 colours exists throughout the spectrum. Hence, probably, like the dif- 
 ferent electric and mae^'netic cnerg'ies, these elementary colours, or, at 
 least, the red and the blue (tlie yellow being probably merely resultant), 
 can never be entirely sepai'ated from eacli otlier. 
 
 + In the Newtonian hypothesis of Jits of easy transmission and of easy 
 rejlectiony the molecules of light may be regarded as little magnets re- 
 volving rapidly round their centres \\'hile tliey advance in their course, 
 and thus presenting alternately their attractive and repulsive poles. (See 
 Discourse on the Study of Natural Philosophy, by Sir J. Ilerschel, p. 253.) 
 In our hypothesis, tlie chemical poles of all self-repvdsive molecules are 
 supposed to be ari-angcd positive and negative alternately ; (see Fig. 16, 
 page 54) by which arrangement the contiguous cohesive polarities are 
 rendered of the same kind, and consequently repulsive. Hence when a 
 scries of self-repulsive molecules move onwards in virtue of their self-re- 
 
OF THE SOURCES OF HEAT AND LIGHT. 65 
 
 Section VIII. 
 
 Of the Sources of Heat and Light. 
 
 The principal and obvious sources of heat and light are the 
 sun, electricity, mechanical action ; change of physical con- 
 dition, change of chemical condition ; and organic action. 
 
 The sun is the most obvious and unvarying source from which 
 both heat and light are communicated to our earth. The nature 
 of the sun, however, and the mode in which that wonderful sup- 
 ply of heat and light is maintained are quite unknown to us, and 
 will probably always remain so. Electricity is another source 
 of heat and light which are developed at the moment of the equi- 
 librium of the two energies ; and some of the most intense de- 
 grees of heat and light that have been produced have sprung from 
 a galvanic apparatus. The sudden condensation of air is likewise 
 a source from which heat and light are often both extricated, on 
 principles that it will not perhaps be difficult to understand from 
 what has been stated. The extrication of heat by percussion and 
 condensation appear to be limited, but its extrication by friction 
 seems to be boundless ; that is to say, so long as friction is kept 
 up, will heat continue to be extricated, but whence the heat is 
 derived does not appear to be capable of satisfactory explanation, 
 unless we suppose a perpetual decomposition and recomposition 
 to take place, which is not improbable. Another fertile source 
 from which heat is derived, is the physical change of condition 
 which bodies are constantly undergoing in nature, as for example, 
 the conversion of gases into liquids, of liquids into solids, &;c. 
 by taking advantage of which conversions we can accumulate 
 heat at will, as for instance by the condensation of steam. When 
 these physical changes however are associated with chemical 
 changes, as is very often the case, the most striking effects are 
 produced. Of this kind are all the phenomena of combustion, 
 
 pulsive powers, (as in the radiation of light, &c.) the cohesive axes of 
 the molecules will always be in the line of motion, and each successive 
 molecule will present alternately an opposite polarity ; while the chemi- 
 cal axes of course will be all in the same plane, and transverse to the line 
 of motion. Such will be the order in a single series of molecules in mo- 
 tion ; but when a number of series move onward together, as in homo- 
 geneous light, there is reason to conclude that the molecules of conti- 
 guous series have a tendency to arrange themselves thus •.•.•.••• with the 
 chemical axes at right angles to each other. Those who are interested 
 in these subjects will perhaps readily conceive how such arrangements 
 may be applied to explain the various phenomena we have been consi, 
 dering. 
 
G6 CHEMISTRY. 
 
 the most common source of artificial heat ; and which consists of 
 nothing more than the rapid chemical union of certain bodies 
 with others, and generally with the principle termed oxygen. 
 Nearly allied to chemical action, and perhaps identical with it, 
 is the extrication of heat by organic changes, or what is termed 
 animal heat ; a subject we shall have to consider in a future part 
 of this volume. 
 
 We have thus endeavoured to give a summary view of the 
 phenomena, and laws of motion of heat, and of light. In conclu- 
 sion it only remains to observe that these phenomena and laws 
 are all of the utmost importance in the economy of nature, as 
 constituting limitations and principles of action, to which the 
 Great Author of nature most rigidly adheres in his operations. 
 Hence, whether we view the distribution of heat and of light on 
 the large scale, as regulating climate ; or whether we view them 
 with reference to the most trifling particular, as the clothing of a 
 bud or of an insect; we find the same beautiful adaptation and con- 
 trivance, everywhere exemplified, to ensure or to evade the 
 agency of these all-important principles. The wonderful ar- 
 rangements connected with heat and light will however fall more 
 naturally to be considered' hereafter ; we shall therefore defer 
 what we have to say on these subjects till we come to speak of 
 meteorology. 
 
 Section IX. 
 
 Recapitulation and General Observations on the Subjects treated 
 
 of in the preceding Chapters. 
 
 In the preceding observations we have endeavoured to give a 
 connected sketch of the nature and operation of molecular forces ; 
 and perhaps it will still further facilitate the understanding of the 
 subject, if we recapitulate briefly the leading facts, so as to point 
 out to those who may not be inclined to peruse the foregoing de- 
 tails, the analogy that prevails throughout the whole. 
 
 1. In the first place we attempted to show that the forces 
 which determine molecular union can scarcely be those of mere 
 gravitation, in their ordinary forms at least; but that some other 
 modification of force is necessary to account for the phenomena. 
 
RECAPITULATION. 67 
 
 2. By assuming the molecules of bodies to be virtually sphe- 
 roidal, and endowed with two kinds of polarizing forces, the one 
 operating axially, and the other equutoriulhj, we attempted to 
 show how the phenomena of simple crystaUization might be ex- 
 plained ; and we corroborated our argument by demonstrating 
 that the electric and magnetic forces are actually related to each 
 other, precisely as we assumed the energies of our molecules to 
 be. Hence we ventured to draw the conclusion, that electricity 
 and magnetism, if not identical with, at least represent, or are 
 analogous to those forces, the existence of which among ponde- 
 rable bodies we assumed as necessary to account for the pheno- 
 mena of crystallization. Further we attempted to render it pro- 
 bable, that the molecules of the imponderable principles, heat and 
 light, possess polarities precisely analogous to those of pondera- 
 ble bodies, and that many of their peculiar phenomena depend 
 upon these polarities. 
 
 3. In attempting to account for the different forms assumed by 
 bodies, we- supposed that in the solid form, the molecules are so 
 arranged as to attract each other according to certain laws ; that 
 in the liquid form, they are so arranged as neither to attract nor 
 repel each other; and that in the gaseous form, the arrangement 
 of the energies of the molecules is such as to render them mutu- 
 ally repulsive. Further, by assuming that those molecules which 
 possess the property of attracting each other in the solid form in 
 preference to others, retain a similar relation in the gaseous form, 
 and repel each other in preference to others, we attempted to ac- 
 count for many of the well known phenomena of gaseous bodies. 
 
 4. Lastly, we attempted to show that the phenomena of radia' 
 tion among the molecules of imponderable bodies, are precisely 
 analogous to the phenomena of diffusion and mixture among the 
 molecules of ponderable bodies when in the liquid and gaseous 
 states ; and that consequently the same laws are strictly applica- 
 ble to both. 
 
 With respect to the reasons which have induced us thus to 
 enter into the dry details of molecular action, and which may 
 seem to require some apology to our readers, they are chiefly 
 two-fold : In the first place, as connected with the particular 
 business of the present tieatise, it has been our object to convey 
 to the general reader some idea of the wonderful operations which 
 are constantly taking place in every particle of matter which he 
 sees around him, or to use the language of Paley, some notion of 
 the " concealed and internal operations of the machine." These 
 operations may not be as we have represented them ; they may 
 in fact be altogether different ; but be this as it will, a perusal 
 however cursory, of what has been stated, can hardly fail to ac- 
 
68 CHEMISTRY. 
 
 complish one purpose we had in view, viz: to show to the most 
 incurious and superficial reader that in the minutest fragment of 
 matter, and in the commonest and simplest operations w^hich take 
 place in nature, and which he is altogether too apt to overlook, 
 the most wonderful and extraordinary arrangements, must take 
 place; arrangements which, if duly considered, are calculated 
 fully as much, if not more, than those connected with the more 
 striking and obvious phenomena, to excite his wonder, and at 
 the same time to display the wisdom and power of the great 
 Creator. Tiie second object we aimed at, was, as just stated, to 
 give a connected and popular sketch of molecular forces and ope- 
 rations ; and by placing them in a point of view in which we 
 believe they have not hitherto been considered, to display the 
 beautiful simplicity and analogy that prevail throughout the 
 whole. 
 
 Finally, it remains, before we close, to state briefly the argu- 
 ments deducible from the divisibility and molecular constitution 
 of matter, with reference to our present subject. These arguments 
 may be considered under the three following heads ; first, that 
 matter has not always existed in its present form ; secondly, it 
 could not have existed in its present form by chance ; and thirdly, 
 and consequently, that it must have been the work of a voluntary 
 and intelligent Being. Other deductions might doubtless be made 
 from what has been stated, but these we purposely avoid, and 
 confine our arguments as much as possible to grounds admitting 
 of no controversy. 
 
 In the first place, the divisibility and molecular constitution of 
 matter seem to prove beyond a doubt that it cannot have eternally 
 existed in its present state. 
 
 Although we can form no idea of what matter would be with- 
 out its molecular properties, there is yet nothing in these properties 
 which can induce us to believe that tliey are necessary to the mere 
 existence of matter. On the contrary, we have seen that matter 
 possesses qualities (those of gravitation) of a more primordial kind, 
 to which its molecular properties are apparently secondary or sub- 
 ordinate. But if these subordinate properties be not necessary to 
 the existence of matter, matter m\g\\i possibly at some time have 
 existed without them. Now this very possibility is incompatible 
 with eternal existence; for eternal (passive) existence necessarily 
 involves incapability of change. Hence the molecular constitution 
 of matter, even in this point of view, must be supposed to have 
 had a beginning; and when we consider the leading and charac- 
 teristic property of matter in the molecular state, viz. the endless 
 repetition of exactly similar parts, the difiiculty of arriving at 
 
GENERAL ARGUMENTS. 69 
 
 any other conclusion is exceedino;ly increased. It is to be observed 
 also that the above remarks apply to the supposition of only one 
 form of matter ; but we shall see hereafter that chemists recognize 
 upwards o^ fifty forms of matter, all of an elementary character ; 
 at least we cannot at present say that one of these forms is more 
 elementary than another. Again, the number of molecules in each 
 of these elementary principles, great as it is, is limited ; the pro- 
 perties of the molecules also are fixed and definite, all which cir- 
 cumstances throw further insurmountable difficulties in the way 
 of the supposition, that the whole have existed, as they now ex- 
 ist, from eternity. For how has it happeued, it may be asked, 
 that the number and properties of the elements, and the molecules 
 of which they consist, are just what the economy of nature re- 
 quires, and neither greater, nor less, nor different ? How has it 
 happened, that what is supposed to be infinite in some respects, 
 should be finite and limited in those respects in which we are 
 actually able to trace them ; and what is more, most luckily finite 
 and limited just M'here they appear to be required to be so? He 
 who can satisfactorily answer these questions may contend with 
 some prospect of success for the eternity of matter and its pro- 
 perties ill their present form. In the mean time we assert with- 
 out fear of contradiction, that the molecular constitution of matter 
 is decidedly artificial ; or to use the words of a celebrated writer, 
 that the molecules of matter have all " the essential characters of 
 a manufactured article,"* and consequently are not eternal. 
 
 Secondly, if the present molecular constitution of matter has 
 not always existed, it must have been produced at some time» by 
 some cause superior to itself. Now this cause must have ope- 
 rated either accidentally and by chance ; or voluntarily and under 
 the influence of a ivill. 
 
 With respect to the first of these alternatives, viz. chance ; the 
 endless repetition of similar parts presented by the molecular 
 constitution of matter seems absolutely to preclude this supposition. 
 Do we not consider it a subject of wonder to see even two or 
 three things by chance alike, as for example two or three human 
 faces? Should we not consider the man absolutely mad, who 
 would attribute the uniform and manosuvres of a regiment of sol- 
 diers to chance ? and can we then resist the argument in the in- 
 finitely stronger shape in which it is here presented to us ! Thus, 
 as the idea of chance seems too monstrous to be entertained for 
 a moment by any rational being we are driven irresistibly to the 
 other conclusion, viz. that the cause or agent who formed the 
 molecular constitution of matter was a voluntary agent or Being ; 
 
 * Sir J. Herschel on the Study of Natural Philosophy, p. 38. 
 
70 CHEMISTRY, 
 
 and moreover that this Being possessed a power commensurate 
 with his will. 
 
 Thirdly ; tlie agent or Being who constructed the wonderful 
 system we have been considering must have been as intelligent 
 as he was powerful. 
 
 We infer intelligence in an agent from the fitness and adapta- 
 tion to certain ends exemplified in his works. Thus, when we 
 see a machine admirably fitted for the office it perfi)rms, we infer 
 that the maker of that machine must have possessed intelligence. 
 Now if we judge of the molecular constitution of matter by this 
 rule, we shall find that there is not only the most extraordinary 
 fitness and adaptation to circumstances displayed in its arrange- 
 ments, as far as we can understand them, but evidently much 
 further ; that is to say, the maker of this system must not only 
 have possessed intelligence, but intelligence infinitely surpassing 
 our own. Thus at the very beginning, the selection of the 
 molecular form of matter out of the many possible forms which 
 might be supposed to exist, may be considered as an instance of 
 intelligence of the highest kind ; for this alone, of all the forms 
 that can be conceived, seems best adapted to the purposes of 
 creation. Indeed, on what other supposition, than that of the 
 subdivision of matter into minute similar pcn'ts, could all those 
 endless operations which we see constantly going on in the world, 
 be imagined to take place ? Moreover, the nature of the powers 
 with which the molecules of matter are endowed is truly asto- 
 nishing, and calculated in the highest degree to impress us with 
 exalted notions of the intelligence and power of their conti-iver. 
 Thus, what can be more wonderful, than that the self-same 
 chemical forces differently directed should produce, not only all 
 that endless change of property, of form, and of condition wdiich 
 we see around us, and which are so beneficial and even necessary 
 to our existence ; but likewise some of the most terrible displays 
 of power in nature ; as for instance, the utmost intensities of heat, 
 of cold, and of light; the terrors of the thunderbolt, and the irre- 
 sistible energies of the earthquake ! Nor on the other hand, are 
 the cohesive aflinities existing among the molecules of matter 
 much less wonderful or important ; for if similar molecules had 
 not been constituted with self-attractive and self-repulsive powers, 
 there would have been no aggregation of the same matter into 
 symmetrical groups, no order or regularity, no separation or pu- 
 rity ; in short there would have been no common bond of union, 
 and the whole would have been dispersed throughout nature, as 
 accident or other circumstances might determine. Hence the 
 present order of things could not have existed unless the mole- 
 cules of matter had been endowed with both these properties ; 
 
ELEMENTARY PRINCIPLES. 71 
 
 one of which the chemical^ as it were, goes before and imperi- 
 ously determines what molecules shall be combined or separated; 
 while the other, the cohesive, silent and unobtrusive, follows in 
 its train, and industriously assorting and arranging its predeces- 
 sors' labours, here perhaps forms a diamond, or there superin- 
 tends the integrity of the atmosphere ! 
 
 Such are molecular forces as they obviously appear to us, and 
 such the arguments deducible from them. But when w^e attempt 
 to go further, and inquire into the intimate nature of these forces, 
 we not only find much that is unknown to us, but much that ap- 
 parently surpasses our utmost conception ! And what a still 
 more sublime idea is this calculated to convey to us of the wisdom 
 and power of tliat Being who contrived and made tiie whole ! 
 When and where, do we naturally exclaim, did this Being exist? 
 whence his wisdom, and whence his power? There is, there 
 can be, but one answer to these inquiries. The Being who con- 
 trived and made all these things must have pre-existed from 
 eternity — must have been omniscient — must have been omnipo- 
 tent MUST HAVE BEEN GoD ! 
 
 CHAPTER IV. 
 
 OF CHEMICAL ELEMENTARY PRINCIPLES, AND OF THE LAWS OF THEIR 
 
 COMBINATION. 
 
 In the preceding chapter we have endeavoured to show that 
 the minutest fragment of homogeneous matter cognizable by our 
 senses is composed of innumerable molecules, all of which are 
 exactly alike in size, in shape, in properties, in short, of every 
 kind ; and we argued that these facts incontestibly prove that 
 these molecules could not always have existed in their present 
 form, nor have been formed by chance, but that they must have 
 had a beginning, and have been the work of a Creator. Now 
 when we consider the prodigious quantity of matter composing 
 our globe (to go no further) or even composing a portion of it, 
 as for example, the mass of water existing in the ocean, and re- 
 flect that every individual molecule of this water possesses pro- 
 perties exactly like those of the drop we formerly contemplated, 
 our argument, already sufliciendy convincing, actually over- 
 whelms us with its force. Still however it admits of further 
 corroboration ; and we proceed now to show that all this vast as- 
 semblage of molecules, so numerous, so diversified, so extraordi- 
 nary as they are, may be reduced to a very {qwv elementary 
 
72 CHEMISTRY. 
 
 groups, upon the endless combinations and separations of which 
 all the phenomena of chemistry depend. 
 
 Section I. 
 Of Chemical Elementary Principles. 
 
 The substances at present considered as elementary amount to 
 about fifty-four. Of these several possess certain properties in 
 common, though they all differ from one another in subordinate 
 particulars, or in other words, are specifically different. Of the 
 whole number not above two or three exist in any great quantity 
 in an uncombined state, at least in those parts of our globe to 
 which we have access, but the whole are wrapped up as it were 
 and have their properties concealed in compounds. Under ordi- 
 nary circumstances most elementary principles exist as solids, but 
 some of the more important occur in a gaseous form, and one or 
 two as fluids. A few of them are apparently of so little conse- 
 quence in the world, that if they were annihilated they would 
 scarcely be missed; while others of them, on the other hand, are 
 so obviously necessary to the existence of the present order of 
 things, that the least derangement or alteration in their proportion 
 or quantity would be fatal to the whole. Some of these element- 
 ary substances exist in such enormous quantities as to constitute a 
 large proportion of the whole visible bulk of our globe, while others 
 again, occur in such minute proportion, at least within our reach, 
 as to be obtained with difficulty and not without elaborate research. 
 With respect to the facility with which they enter into combina- 
 tion, and the obstinacy with which they unite, they differ also 
 very remarkably ; a few of them combining readily in a variety 
 of proportions with almost all the rest, while some of the others 
 can be scarcely made to combine under any circumstances. Lastly, 
 with respect to the influences which different elementary sub- 
 stances are capable of exerting upon organic life, these are equally 
 striking. A large majority of them indeed may in their simple 
 state, be considered of a deleterious nature : while three or four 
 of them, on the other hand, make organized beings what they are, 
 and are necessary to their very existence. 
 
 Such are a few of the leading properties of the elementary prin- 
 ciples as we are at present acquainted willi tliem ; in the following 
 table from Dr. Thomson they are arranged, as far perhaps as is 
 practicable, according to their chemical characters. 
 
ELEMENTARY PRINCIPLES. 
 
 73 
 
 TABLE. 
 
 1 Oxygen. 
 
 2 Chlorine. 
 
 3 Bromine. 
 
 4 Iodine. 
 
 5 Fluorine. 
 
 6 
 7 
 8 
 9 
 10 
 
 Hydrogen. 
 Carbon. 
 Azote. 
 Boron. 
 Silicon. 
 
 11 Phosphorus. 
 
 12 Sulphur. 
 
 13 Selenium. 
 
 14 Arsenic. 
 
 15 Antimony. 
 
 16 Tellurium. 
 
 17 Chromium. 
 
 18 Uranium. 
 
 19 Vanadium. 
 
 20 Molybdaenum. 
 
 21 Tungsten. 
 
 22 Titanium. 
 
 23 Columbium. 
 
 24 Potassium. 
 
 25 Sodium. 
 
 26 Litliium. 
 
 27 Calcium. 
 
 28 Magnesium. 
 
 29 Strontium. 
 
 30 Baryum. 
 
 31 Aluminum. 
 
 32 Clucinum. 
 
 33 Yttrium. 
 
 34 Zirconium. 
 25 Thorinum. 
 
 36 Iron. 
 
 37 Manganese. 
 
 38 Nickel. 
 
 39 Cobalt. 
 
 40 Cerium. 
 
 41 Zinc. 
 
 42 Cadmium. 
 
 43 Lead. 
 
 44 Tin. 
 
 45 Bismuth. 
 
 46 Copper. 
 
 47 Mercury. 
 
 48 Silver. 
 
 49 Gold. 
 
 50 Platinum. 
 
 51 Palladium. 
 
 52 Rhodium. 
 
 53 Iridium. 
 
 54 Osmium. 
 
 It is foreign to the object of this work to enter into a minute 
 description of these bodies ; we shall therefore content ourselves 
 with such a view of them as may enable the general reader 
 to form some idea of their properties, and to follow us without 
 much difficulty in our subsequent remarks. 
 
 The five first bodies, Oxygen, Chlorine, Bromine, Iodine, and 
 Fluorine, are usually termed supporters of combustion. They 
 have some properties in common, though in other respects, and 
 particularly in their apparent relative importance in the economy 
 of nature they differ exceedingly. Tbey are remarkable for the 
 tendency they have, not only to combine with one another, but 
 with almost all the bodies below them in the table ; and their union, 
 particularly that of oxygen, is usually accompanied with the ex- 
 trication of more or less of heat and light, and constitutes the well- 
 known phenomena termed combustion. 
 
 (1) Oxygen is one of the very few elementary substances that 
 occur naturally in the gaseous form, in which form it constitutes 
 about one fifth part of common air. As the world at present ex- 
 ists, oxygen, perhaps, may be fairly considered as one of the 
 
 1. Oxygen, from o^vc, acid, and yivvdco, to generate ; from its property 
 of forming acids. 2. Ciilorine, from x^u^c;, green ; so called from its 
 colour. 3 Bromine, from 0^Z/uoc, fetid; so called from its strong odour. 
 4. Iodine, from ^JqhS}]; violet ; from the colour it assumes in the gaseous 
 state. 6. Hydrogen, from vSce^, water, and yivvdai, to generate. 8. Azote, 
 from a privative and ^an), life ; from its bein^ incapable of supporting life. 
 13. Selenium, from ^ihhvn, the moon. 17. Chromium, from ;;^^J:^ot colour ; 
 so called from the beautiful colours of some of its salts. 18. Uranium, 
 from ciu^tfvo?, the heavens. 19. Vanadium, from vanadis, a Scandinavian 
 deity. 20. Molybdaenum, from Mo\v^Su.iv<t., lead. 22. Titanium, from T/ravof, 
 calx. 23. Columbium, from Columbia, in America, where it was first 
 found. 26. Lithium, from A/6oc, a stone. 29. Strontium, from Strontian, 
 the name of a place in Scotland, where first found. 50. Baryum, from 
 
74 CHEMISTRY. 
 
 most important, if not the most important substance in it. From 
 its proneness to enter into composition it is constantly operating 
 upon, and modifying everything. By far the greater proportion 
 of mineral bodies forming the crust of the earth, contain more or 
 less of it; and in all plants and animals it actually exists as a con- 
 stituent elementary principle. In short, the properties of oxygen 
 stamp it as an element and subordinate agent of the most important 
 kind; while the numberless contrivances which are observable in 
 nature, to secure, or evade, or modify its operations, are most ex- 
 traordinary, and exhibit some of the m.ost marked and unequivocal 
 evidences of design on the part of their great Contriver, that we 
 meet with among his works. Several of the most important of 
 these contrivances we shall have occasion to allude to hereafter ; 
 but there is one of so curious and interesting a character that it 
 may be mcrrtioned here as an illustration of the above remarks. 
 The nature and mechanism of the function of respiration will be 
 explained elsewhere, and it is sufficient for our present purpose 
 to state that, by means of a complicated apparatus, the blood is 
 made to circulate through the lungs, in order that it may be there 
 exposed to the oxygen of the atmosphere. For purposes beyond 
 our comprehension, but probably in part at least with a view to 
 the future creation of organized beings, the great Architect of the 
 universe had willed that this principle should exist upon the sur- 
 face of our globe in a gaseous state ; when he created animals he 
 chose also to render them dependent upon oxygen for their ex- 
 istence ; and he effects his object, not by bending this principle 
 to his purpose, by altering its physical or other properties ; not 
 by obtaining it from v/ater, or any of the innumerable compounds 
 into which it enters, wiiich according to our imperfect notions he 
 might have more easily done ; but, as if on purpose to display 
 his power and design, he rigidly adheres to the properties, both 
 mechanical and chemical, imparted to oxygen, and to these pro- 
 perties accommodates his future labours ! The whole therefore 
 of the complicated and beautiful apparatus, connected with the 
 respiration of animals, is most obviously designed and constructed 
 with reference to the properties of the oxygen of the atmosphere, 
 and altogether they afford one of the most striking evidences of 
 adaptation and design presented to us in nature. 
 
 (2) Chlorine in its elementary state is a gas, having all the 
 
 Bstg t^f, heavy. Aluminum, from Alumen, alum. 32, Glucinum, from 
 Ykvku;^ sweet ; from the taste of some of its saUs. 52. Rhodium, from 
 'PoSov, a rose ; from the colour of some of its compounds. 53. Iridium, 
 from ipii; the rainbow ; froin the variety of colours assumed by some of 
 its salts. 54. Osmium, from 'Oa-fA)), odour 5 from the strong smell emitted 
 by some of its compounds. 
 
CHLORINE. BROMINE, IODINE. FLUORINE. 75 
 
 mechanical properties of common air, but in this form it never 
 occurs naturally. It exists however in great abundance in a state 
 of combination, from which it may be readily obtained by easy 
 chemical processes. One of the most abundant sources of chlo- 
 rine is common salt, into which it enters in the proportion of 
 about 60 per cent. As compared with oxygen chlorine is much 
 less abundant and perhaps important; yet it is doubtful if with- 
 out chlorine the present order of things could proceed. Take 
 for example the familiar instance of common salt above referred 
 to. Let us consider the universal diffusion of this substance 
 throughout nature — what the sea would be, or how animals 
 could exist, without it— let us consider these and the numberless 
 other operations which this valuable compound more or less 
 enters into, or influences, and we shall be able to form some 
 notion of the part chlorine bears in the economy of nature. On 
 the other hand, when we reflect that were chlorine to be extri- 
 cated from its state of combination, and made to exist, like oxy- 
 gen, in a gaseous form, that it would instantly prove fatal to 
 organized beings ; can we fail to be struck with the very obvious 
 design thus displayed in rendering its quantity and combining 
 powers such as to keep it in a state of union, and by these means 
 to secure all its useful without its deleterious properties? 
 
 (3) (4) Bromine and Iodine, the next two substances, are 
 found principally in sea-water and in marine productions. They 
 appear to exist in very minute proportion, and always in a state 
 of combination. Bro7nine exists under ordinary circumstances 
 as a deep-coloured red fluid, having a very strong and offensive 
 odour ; Iodine is a crystallized solid, volatile by a slight increase 
 of temperature, and forming a beautiful violet vapour. Bromine 
 and Iodine more nearly resemble chlorine than oxygen in their 
 properties, though they differ materially from both, and their use 
 in the economy of nature is absolutely unknown. It may how- 
 ever be observed that Iodine has lately been much celebrated for 
 its medicinal properties."*^ 
 
 (5) Fluorine has been rather inferred than demonstrated to 
 exist. It occurs principally in the mineral called Fluor spar, in 
 
 * It may not be amiss to observe here that the author of the present 
 volume first employed the hydriodate of potash, as a reinedy for g-oitre, 
 in the year 1816, after having" previously ascertained, by experiments 
 upon himself, that it was not poisonous in small doses as had been repre- 
 sented. Some time before the period stated, this substance had been found 
 in certain marine productions ; and it struck the author that burnt sponge 
 (a well knov/n remedy for g-oitre) might owe its properties to the pre- 
 sence of Iodine, and this was his motive for making- the trial. He lost 
 sig-ht of the case in which the remedy was employed, before any visible 
 
76 CHEMISTRY. 
 
 a state of combination with lime, and in this state it would seem 
 lo be harmless; but in a state of purity it is exceedingly delete- 
 rious. One of its most remarkable properties is that of corroding 
 glass. 
 
 We pass on now to a very different class of substances, and 
 which instead of having the power of supporting combustion in 
 other substances, are for the most part themselves combustible. Of 
 these, the first and perhaps the most important we have to no- 
 tice is 
 
 (6) Hydrogen. This principle in its elementary state exists 
 as a gas, having all the mechanical properties of common air. In 
 this state it is exceedingly inflammable; and if mixed v.'ith oxy- 
 gen, and if the mixture be exposed to heat, the two gases unite 
 suddenly and violently with a loud explosion ; while the result 
 of the combustion is water. Hydrogen is the lightest body 
 known, and under the same bulk therefore contains less matter 
 than any otlier body. It does not exist naturally in a separate 
 state, but always in combination ; and by far most generally and 
 abundantly in combination with oxygen in the form of water. 
 Hydrogen ranks perhaps next to oxygen in importance ; at least 
 as far as organized beings are concerned ; since like oxygen it 
 constitutes one of the elementary principles of which they are 
 formed. It differs however remarkably from oxygen, in not 
 being in its elementary state necessary to the existence of or- 
 ganized beings ; indeed hydrogen is actually incompatible with 
 the existence of animals, if not of vegetables ; and its properties 
 as an element have evidently been sacrificed to its properties as 
 a compound, that is to say, to its properties as ivater. Hence 
 we have to admire tlie happy adjustment of the quantities of the 
 two elements to each other, so that the oxygen shall predominate ; 
 an adjustment that can scarcely be explained upon any other 
 supposition than that of design ; for any other cause, as chance, 
 would have been quite as likely to have produced an excess of 
 hydrogen as of oxygen, or at least anything but the exact pro- 
 j)ortions required. Lastly, it may be remarked, that to the rela- 
 tive proportions of oxygen and hydrogen existing on our globe, 
 more than perhaps to any other subordinate cause, the present 
 order of things owes its stability. For the proportions of these 
 principles are so happily adjusted and balanced, and all the nu- 
 merous operations dependent upon them are, in consequence, so 
 
 alteration was made in the state of the disease ; but not before some 
 of the most strikinjij cfTccts of the remedy were observed. The above 
 employment of the compounds of Iodine in medicine was at the time 
 made no secret; and so early as 1819, the remedy was adopted in St. 
 Thomas's Hospital, by Dr. Elliotson, at the author's' sug-g-estion. 
 
CARBON. 77 
 
 firmly establislied, that no material change can possibly happen 
 to any part from an internal cause, but if changed at all, the whole 
 must be changed from without. 
 
 (7) Carbon, or charcoal, is a substance too well known in its 
 ordinary state to require description ; in its crystallized and pure 
 state it is found to constitute the diamond, the hardest and most 
 brilliant body in nature ; a circumstance that certainly could not 
 have been anticipated, but which affords a most striking instance 
 of the effects produced by the different modes in which molecules 
 of the same matter may be aggregated. Carbon perhaps more 
 than any other principle may be considered as constituting the 
 slaminal or fundamental element entering into the composition of 
 organized beings. This is particularly the case in principles 
 from the vegetable kingdom, which owe their peculiar character 
 essentially to carbon, and their endless varieties to differences in 
 its quantity, and to the modifying influence of the hydrogen and 
 oxygen with which it is associated. In animal substances, car- 
 bon exerts a similar influence, but its effects are materially modi- 
 -fied by the presence of another staminal principle to be presently 
 considered. Carbon, in some state or other, exists in considera- 
 ble quantities upon the surface of our globe, but apparently by no 
 means in so large a proportion as oxygen and hydrogen. Ex- 
 clusively of that actually involved in the composition of organized 
 beings, carbon is met with nearly pure in large quantities in par- 
 ticular districts in the well-known form oi fossil coals; but it 
 occurs in far greater proportion in combination with oxygen in 
 i\\e iouTi oi carbonic acid; which carbonic acid in union with 
 lime, constitutes common chalk and limestone, two of the most 
 abundant minerals in nature.* Carbon in its elementary slate, is 
 a very inert substance, and is scarcely liable to be affected by, or 
 to affect organized beings ; but with hydrogen and oxygen it 
 forms gaseous compounds of great activity, and capable of proving 
 instantly fatal to animals respiring them. Such effects, however, 
 appear to be obviated by a beautiful expedient which we shall 
 have occasion more particularly to notice hereafter. In the mean 
 time it may be observed, that though the compound of carbon 
 and oxygen {carbonic acid) is by innumerable processes con- 
 stantly forming around us in enormous quantities ; by some 
 compensating means it disappears as fast as it is formed ; so that 
 
 * In order to give some idea of the proportion in which carbon exists 
 in different common substances, it may be observed that a pound of char- 
 coal is equal to, and is contained in rather more than, two pounds of su- 
 gar or flour, and eight of potatoes or limestone; so that a mountain of 
 limestone contains the essential element of at least an equal bulk of 
 potatoes, and of a forest that would amply cover manv such mountains. 
 
 7* 
 
78 CHE3IISTRY. 
 
 the atmosphere, which wuhout this provision wouUl probably 
 before now have become contaminated by carbonic acid to an ex- 
 tent fatal to animal life, barely contains traces of it. 
 
 (8) Azote or nitrogen is one of the very few elementary prin- 
 ciples which exist naturally in an uncombined state. It constitutes 
 about 4-5ths or 80 per cent, of common air, the rest being princi- 
 pally oxygen. The great bulk of this principle in existence is 
 confined to the atmosphere, and to animal substances, of which 
 it forms a constituent element ; and it enters very little into natural 
 mineral productions. In its pure state, azote is remarkable for 
 its negative properties, that is to say, for the difficulty with which 
 it enters into combination with other matters. Thus it is neither 
 combustible nor a supporter of combustion ; is neither acid nor 
 alkaline ; possesses neither taste nor smell ; nor does it directly 
 combine with any other known substance. Yet when made by pe- 
 culiar management to unite with oxygen, hydrogen, or carbon, azote 
 forms some of the most energetic compounds we possess : thus, 
 inixed with oxygen it forms atmospheric air, as before observed ; 
 united with oxygen it forms aquafortis, tlie most corrosive of 
 liquids ; united with hydrogen it forms the volatile alkali or am- 
 monia, likewise an energetic compound, but of an opposite nature; 
 while united with carbon and hj'drogen, it ionns prussic acid, the 
 most virulent poison in existence ! Azote may be considered as 
 constituting the characteristic element of animal substances, and 
 as imparting to them their peculiar properties ; in this j)oint of 
 view therefore it is a principle of very great importance. More- 
 over, the above mentioned negative properties of azote are evi- 
 dently of a primordial kind, and seem to have been formed with 
 reference to future creations, which have all been most carefully 
 and rigidly adapted to them. Thus had the properties of azote 
 not been negative, those of its most important compound, atmo- 
 spheric ai r could not have been negative ; and atmospheric air might 
 have been acid or alkaline, or have possessed odour or colour; 
 either of which circumstances would have been incompatible with 
 the present order of things. 
 
 (9) (10) Boron and Silicon. The next two substances obtain 
 their names from borax and silex, the natural productions in which 
 they exist in a state of combination. Borax is a saline production 
 chiefly found in certain lakes in Thibet and China. Boron, the 
 elementary substance obtainable from it, is a deep brown powder 
 possessing neither taste nor smell, but highly inflammable at a 
 temperature below a red heat. Silicon is the elementary basis of 
 silex or common (lint, one of the most abundant minerals in nature. 
 Silicon is a brown powder very similar to boron in appearance, 
 and like it inflammable under certain circumstances. 'I'hese two 
 
PHOSPHORUS. 79 
 
 elementary principles do not exist naturally, but have been formed 
 by elaborate chemical processes in small quantities only. They 
 seem to be more nearly allied to carbon, in their properties, than 
 to any other elementary product. Borax exists in very small 
 quantities, and its use in the economy of nature is not apparent. 
 Silex on the other hand is a most important production, and in 
 its hardness, insolubiUty, and other refractory properties, we re- 
 cognize a substance admirably adapted for the purpose to which 
 it has evidently been designed, viz. that of constituting the stamina 
 or ground-work, as it M'ere, of our globe, and which could not 
 be withdrawn without subverting the whole. Silex is found in 
 small quantities both in plants and in animals, but does not, like 
 hydrogen, oxygen, carbon, and azote, form a constituent element 
 of organized beings. 
 
 (11) Pliosphorus, under ordinary circumstances, is a pale am- 
 ber-coloured substance, very like wax in appearance, but so ex- 
 ceedingly combustible that it cannot be heated, much less melted 
 in the open air, without immediately taking fire. Under these 
 circumstances, as may be supposed, it does not exist naturally, 
 but is obtained by an elaborate process from various compounds 
 into which it enters ; as for example, from hone earth, or the 
 earthy basis of the bones of animals ; and also from certain salts. 
 It exists also in the mineral kingdom in certain districts in con- 
 siderable quantities, but upon the whole, it is not an abundant 
 principle. Phosphorus affords another beautiful instance in which 
 the design has been directed to the properties of the compound, 
 rather than to the element itself. The phosphate of lime or bone 
 earth was apparently the thing wanted to constitute the bony 
 skeleton of animals, and accordingly, to this compound the pro- 
 perties of the element itself seem to have been sacrificed. Neither 
 lime itself in mass, nor any of its mineral compounds, appear to 
 be adapted for forming a constituent principle of a living organized 
 being. It was necessary therefore to have a connecting medium, 
 or link, that should unite organization with the mineral constitu- 
 ent, and phosphorus admirably accomplishes this ol)ject. Accord- 
 ingly, we see that organization goes on in conjunction with lime 
 in the bones of animals, through the medium of this element, quite 
 as readily as in other parts of their system ; whereas when phos- 
 phorus is absent, as in shells, and in other deposits of carbonp.te 
 of lime, the carbonate of lime is extravascular, and seems to form 
 no part of the living system. There are also other important of- 
 fices which this principle evidently performs in the animal econo- 
 my, some of which we shall have occasion to refer to hereafter. 
 
 (12) Sulphur. This well known substance is one of the Aery 
 few that exist naturally in an elementary state. It is a very abun- 
 
80 CHEMISTRY. 
 
 dant and probably important principle in the economy of nature, 
 as it not only exists in large quantities in the mineral kingdom, 
 but in a greater or less proportion in almost all animal, and in 
 many vegetable products. Its uses, however, at present, are very 
 imperfectly understood. Sulphur combines with hydrogen, and 
 forms a very deleterious gaseous compound. Its combinations 
 with oxygen are generally acid, and very active in their concen- 
 trated form, but not poisonous. 
 
 (13) Selenium^ the next substance, is found in very minute 
 quantities generally associated with sulphur, which in its properties 
 it somewhat resembles ; or rather, perhaps it appears to consti- 
 tute the connecting link between sulphur and the metals. The uses 
 of selenium in the economy of nature are unknown , but we shall 
 have occasion hereafter to refer to its compound with hydrogen, 
 which is even more deleterious than the compound of sulphur with 
 this element. 
 
 (14) ^6lr.senic in its pure state is a metalloid, or imperfectly 
 metallic substance, having much the appearance of polished steel. 
 In the form in which it is popularly known, as ichife arsenic, it 
 is combined with oxygen, and constitutes one of the most virulent 
 of poisons. Arsenic exists in certain minerals in considerable quan- 
 tities, and seems in every form, to be incompatible with organic life. 
 
 (15) Antimony is usually found in nature associated with sul- 
 phur, the compound it forms with which, was for along time con- 
 sidered as the metal itself. In its pure state, antimony has a bluish- 
 grey colour, and possesses considerable metallic splendour, but 
 in this form it seldom occurs in nature. The compounds of anti- 
 mony are active medicinal agents, and some of them are much 
 employed for that purpose. 
 
 (16) (17) (18) (19) (20) (21) (22) (23) TeUurium, Chromium, 
 Uraniiwi, Vanadium, Molybdsenum, Tungsten , Titanium and 
 Columbiurn, the next eight substances, are metals, for the most 
 part obtained by elaborate processes i>om rare mineral productions. 
 The most important, as well perhaps as the most abundant of 
 these substances, is chromium, the compounds of which, from the 
 splendour of their colours, have been lately much employed in 
 the arts. It may be remarked of all these substances, that at pre- 
 sent their use in the economy of nature is quite unknown to us. 
 
 (24) (2.5) Potassium and Sodium are the metallic bases of the 
 two well-known alkaline substances, potash and soda, which are 
 compounds of these metals with oxygen. Such, however, are 
 the powerful aflinities of the metallic bases for oxygen, that they 
 nowhere exist naturally upon the surface of our globe. The same 
 may be also remarked of potash and soda, the powerful alkaline 
 properties of which prevent them from existing separately. In 
 
LITHIUM. CxVLCIUM. 81 
 
 this respect, tlie compounds these metals form with oxygen, pre- 
 sent a striking confrnst with the compounds they form with the 
 analogous principle, chlorine ; the compounds of potassium and 
 sodium with chlorine (the latter of which constitutes common 
 salt,) are remarkable for their fixed and permanent character, and 
 for the little tendency in general which they have, to enter into 
 a further state of combination. Besides their remarkable avidity 
 for oxygen, potassium and sodium possess some other unusual 
 properties. Potassium, for example, is so light, that were it com- 
 patible with water, it would swim on the surface of that fluid ; a 
 circumstance we can hardly imagine to happen with a metal. Pot- 
 ash and soda in all their forms are most important principles, and 
 evidently are necessary to the existence of the present order of things, 
 both mineral and organized ; for there are few organized beings that 
 do not contain more or less of them, especially of soda. Potash is 
 found more particularly in plants, but exists also in animals ; while 
 the universal presence of soda in animals, in the form of common 
 salt, has been already referred to, and is generally known. These 
 alkalies present us with a beautiful instance of adaptation, for the 
 purposes which they seem destined to fulfil in the operations of 
 nature. Had they been solids, or had they formed solid com- 
 pounds, like many of the preceding principles, they would have 
 been totally unfitted for their peculiar office, that is to say, for 
 forming a constituent element of the fluids of organized beings. 
 
 (26) Lithium is the metallic basis odilhia, a substance recently 
 discovered, and intermediate in its properties between the alkalies 
 and the earths to be next considered. It has hitherto been met 
 with, in some rare minerals, in small quantities only. 
 
 (27) Calcium, the metallic bases of /ime, can be obtained only 
 by a troublesome and difficult process, and of course does not 
 exist naturally. It is a white metal like silver, and by union with 
 oxygen is readily convertible into lime. This well known prin- 
 ciple exists in the greatest abundance in nature, not as quick-lime, 
 but united with carbon and oxygen, in the form of common lime- 
 stone, marble, &c. The great importance of lime in the economy 
 of nature is too obvious to require notice, and it is only necessary 
 to revert to the fact that this earth is one of the very few mineral 
 productions capable of forming a part of a living organized being; 
 at least in any quantity. This earth, as formerly noticed, con- 
 stitutes \\\\\\ phosphorus and oxygen, the basis of the bones of ani- 
 mals ; and with carbon and oxygen, all the endless variety of shells 
 and similar products. Thus the properties of lime furnish another 
 striking instance of adaptation to a particular purpose. The com' 
 pounds of potash and soda are all very soluble in water, and hence 
 are chiefly confined to x\\ejluids of animals, in which their pre- 
 
82 CHEMISTRY. 
 
 sence is indispensable. But a solid frame-work or skeleton was 
 necessary to the existence of the more perfect animals, and as this 
 could not be formed from the soluble potash or soda, the intro- 
 duction of another mineral substance possessed of the requisite 
 properties was necessary. Now lime, some of the compounds 
 of which are solid and some/Iuld, is admirably adapted for the 
 purpose ; and lime accordingly has been chosen : the lime is car- 
 ried, in a state of solution, to the spot where it is required, and is 
 there converted into a solid ; while by the same agency, when 
 necessary, this solid is a^ain converted into a fluid and removed ! 
 It seems impossible to conceive arrangements to present more 
 striking evidences of adaptation than these ; and the more we con- 
 sider the subject in all its bearings, the more wonderful does it 
 appear. 
 
 (28) Magnesium is the metallic basis of the well-known earth 
 called magnesia. It is said to resemble calcium in its properties, 
 and like that principle does not exist naturally, at least upon the 
 surface of our globe. Magnesia, though occurring most abun- 
 dantly in nature, and entering' very largely into the composition 
 of rocks, does not, like lime, constitute masses of great extent in 
 the same simple state of combination; that is to say, there are 
 no mountains of magnesia, as there are of chalk and of limestone. 
 Magnesia, even more decidedly than the three preceding mine- 
 ral substances, seems to be necessary to the existence of orga- 
 nized beings ; as there does not appear to be one, in which traces 
 of this earth are not met with, generally associated with phos- 
 phorus. Its uses, however, are less obvious than those of the 
 three other substances, and indeed may be said to be unknown ; 
 though there is reason to believe that it is most intimately con- 
 nected with the vital operations of organized beings. 
 
 (29) (30) Sfrontiiim, and Ban/wn, the metallic bases of the 
 two earthy bodies strontla and barijfa, arc allied to calcium and 
 magnesium in some of their properties, but differ exceedingly 
 from them in others. Their combination with oxygen exhibit 
 still more decidedly alkaline powers than those of either calcium 
 or magnesium, and in consequence, like them, they only exist 
 in various states of combination ; and most usually with carbon 
 and oxygen, or with sulphur and oxygen. Compared with lime 
 and magnesia, strontia and baryta exist but sparingly, and neither 
 of them has anything to do with organization ; indeed many of 
 the combinations of baryuni are virulent poisons. 
 
 (.31) Miiminum is the metallic basis of the earth alumina, the 
 characteristic ingredient of the well known salt called «/i/m. The 
 metallic basis, like the preceding, nowhere exists ; but alumina, 
 the compound of aluminum and oxygen, is one of the most abun- 
 
GLUCINUM, YTTRIUM, ETC. IRON. 83 
 
 dant productions of nature, and constitutes an ingredient in by 
 far the greater number of rocks and soils upon the surface of the 
 globe. The difierent kinds of clay, also, of which bricks, earth- 
 enware, &c., are formed, consist chiefly of this earth in difierent 
 states of purity ; so that it is a substance of great utility and im- 
 portance. Alumina appears to have nothing to do with organi- 
 zation ; at least it is not known to form a necessary constituent 
 of any organized being, either vegetable or animal ; though it is 
 in constant communication with organized beings, and appears 
 to be almost necessary, in some indirect way, to their existence. 
 This fact is very remarkable ; for as the earth does not appear 
 to be poisonous, it could scarcely have been so completely ex- 
 cluded from living bodies, except by some design beyond our 
 comprehension. 
 
 (32) (33) (34) (35) Glucinum, Yttrium, Zirconium, and 
 Thorinum, the four next elementary principles are the metallic 
 bases of substances, usually considered as possessing the charac- 
 ters of earthy bodies, and denominated Glucina, Ittria, ZirconiOj 
 and Tlioriaa. They all appear to exist very sparingly in nature, 
 and are only met with in some rare minerals. Glucina has been 
 hitherto met with only in the precious stones denominated the 
 emerald, the beryl, and the euclase; yttria and thorina in some rare 
 Swedish and Norwegian minerals ; and zirconia in the jargon 
 or zircon from Ceylon, and in the hyaci?ith. These earths more 
 nearly resemble alumina than any other substance. 
 
 (36) /ron, one of the most important, is also one of the most 
 abundant principles in nature. It is met with occasionally in the 
 metallic state, but most generally it is found mineralized in vari- 
 ous ways, and can only be obtained pure by an elaborate process. 
 Iron exists in minute quantities in almost all vegetable and animal 
 products, particularly in the blood; though its mode of combi- 
 nation, as well as its precise use, are quite unknown. Iron may 
 justly be considered as the most useful of all the metals, and the 
 one that has perhaps contributed more towards the civilization of 
 mankind than any other. To form some idea of its use, we have 
 only to reflect what would happen if it were annihilated. What 
 substitute could be found for it in all the numerous instances in 
 which it contributes to the wants or to the comforts of mankind; 
 particularly through the medium of tools, of almost every one of 
 which it constitutes the essential material. In short, when we 
 contemplate all the circumstances connected with this metal, its 
 abundance, the manner in which it is mineralized, and the occa- 
 sion which it thus gives to human ingenuity to extract it from its 
 ores ; its wholesomeness (for many of the metals are poisonous) ; 
 its properties, particularly its extraordinary tenacity ; its strength, 
 
84 CHEMISTRY. 
 
 its property of welding, of being converted into steel, and in this 
 form of being tempered to any degree of hardness we choose ; 
 its magnetic properties, &:c., — when we contemplate all these 
 circumstances, it is impossible not to be struck with such varied 
 usefulness, and to consider iron, not only as an article evidently 
 designed for the benefit of man, but as the instrument by which 
 he should conquer and govern the world ; and thus be enabled to 
 place himself, where it was evidently intended he should be, at 
 the head of the creation. 
 
 (37) Manganese somewhat resembles iron in a few of its pro- 
 perties. It may be obtained from its ores by an elaborate process, 
 but in this form it is little known or used. Mangfanese exists in 
 minute quantities in certain mineral waters, and in a few animal 
 products ; and its combinations with oxygen, are not only em- 
 ployed in the arts, but by the die mist, who frequently procures 
 oxygen for his experiments from the ores of manganese. Though 
 much diffused, manganese is not a very abundant metal, at least 
 compared with iron, and its uses in the economy of nature are 
 apparently much less important. 
 
 (38) (39) Nickel and Cobalt, are two metals somewhat re- 
 sembling each other in a few of their properties, and their ores 
 are often associated in nature. It is remarkable also that they 
 are both generally found combined with iron in those bodies, 
 which occasionally fall from the atmosphere, and which are con- 
 sidered as of meteoric origin. Like iron also both these metals 
 are capable of becoming magnetic. Cobalt is used in the arts, 
 and is the basis of the blue colour upon our earthenware ; but 
 neither this metal nor nickel are to be compared with iron in 
 point of utility, nor are they very abundant productions. 
 
 (40) Cerium is a metal very little known, and has hitherto 
 been obtained, in minute quantities only, from some rare minerals 
 occurring in Sweden and in Greenland. 
 
 (41) (42) Zinc, Cadmium. These two metals are generally 
 associated in nature, and somewhat resemble each other in eitrh 
 properties ; but the last is comparatively much less abundant, and 
 has been only recently discovered. Zinc is a metal easily fusible, 
 of a bluish white colour, and of a lamellated brittle texture; 
 though by peculiar management it may be rendered malleable. 
 It is an ingredient in the well-known compound metal, brass, 
 and in this form is much used and is of considerable impor- 
 tance. 
 
 (43) Lead. This well-known metal is not found in its metal- 
 lic state, but its ores are very abundant, and most of the lead of 
 commerce is extracted from the mineral called galena, which is 
 a compound of lead and sulphur. The general properties of lead 
 
TIN. BISMUTH. COPPER. MERCURY. SILVER, GOLD. 85 
 
 and of its compounds render it of considerable importance ; but 
 its poisonous properties are a considerable draw-back to its use- 
 fulness. Why lead, and other mineral matters, should have been 
 constituted poisonous is a question beyond our reach ; and all 
 we can at present venture to state on this and on similar points is, 
 that it is not actually necessary that man should employ lead or 
 other poisons, and that he may, if he chooses, avoid their dele- 
 terious properties. 
 
 (44) Tin. This useful metal has been employed by man from 
 the most remote antiquity, though it nowhere exists naturally 
 in its metallic state, but usually in conjunction with oxygen. Tin 
 is not a very abundant metal, being apparendy confined to a few 
 localities only, one of the most noted of which is Cornwall. It 
 is much used in the arts, and hence is of considerable importance. 
 
 (45) Bismuth occurs in nature both in the metallic state and 
 in various states of combination. It has a reddish white colour 
 and a lamellated brittle texture, and is easily fusible. Bismuth is 
 not a very abundant metal, and is not much employed. 
 
 (46) Copper occurs in nature in the metallic state, but much 
 more frequently mineralized, especially with sulphur. The valua- 
 ble properties of copper, both in its pure and mixed state, render 
 it of considerable importance ; and it is in consequence much em- 
 ployed in the arts. With zinc it constitutes brass ; with tin bell- 
 metal ; hoi\\ well-known compounds. Copper has been lately 
 said to exist in very minute quantities in organic nature, but whe- 
 ther as an accidental, or as an essential ingredient is not known. 
 The compounds of copper are poisonous, but these poisonous pro- 
 perties, like those of lead, can be easily obviated and guarded 
 against. 
 
 (47) Mercury. This well-known fluid metal occurs in the 
 metallic state, but more frequently mineralized, especially with 
 sulphur. Its importance in the arts, and as a medicinal agent, are 
 too well known to require mention here. The fluidity of mercury 
 presents a beautiful instance of the endless diversity of nature, and 
 adds much to its importance and usefulness. Mercury exists in 
 considerable abundance, though much less so than many of the 
 preceding elementary principles. 
 
 (48) (49) Silver and Gold, and their uses, are too familiar to 
 require enumeration. Tiiey are both met wiUi in the metallic 
 state, but silver also occurs mineralized. So unimportant a part 
 do they seem to perform in the economy of nature, that if they 
 were annihilated, it is probable that the world would go on just 
 as well without them. How different in these respects from iron, 
 and how much less therefore intrinsically valuable ! Indepen- 
 dently of their beauty, the only really valuable properties of silver 
 
 8 
 
86 CHEMISTRY. 
 
 and gold are the difficulty with which they are acted on by heat 
 and other extraneous agents, properties, which if they were more 
 abundant, would render them well adapted for a great many use- 
 ful purposes. 
 
 (50) (51) (52) (53) (54) Platinum, Palladimn, FJiodium, Iri- 
 dium, and Osmium, are metallic substances usually found asso- 
 ciated in small quantities, chiefly in certain districts of South 
 America, but recently also in the old world. Platinum, the most 
 abundant and important of them, is the heaviest body in nature. 
 It is scarcely acted on by any ordinary agents, but it may be 
 welded by heat ; properties which render it exceedingly valuable 
 for many purposes, and make us regret that it is not more abun- 
 dant. Palladium somewhat resembles platinum in its i^roperties, 
 but occurs in less quantity. The other three metals exist in very 
 minute quantities, and their properties are very little known. 
 
 We have thus taken a summary view of the different elementary 
 principles met with upon the surface of our globe, and of their 
 leading compounds ; and we are now to consider the laws which 
 regulate the union of these principles with one another. 
 
 Section II. 
 Of the Laws of Chemical Combination. 
 
 As the following remarks upon the laws of chemical combination 
 can scarcely be so given as to prove a source of interest to the 
 general reader, he is desired to pass them over and to turn to the 
 last section of the present chapter, where he will find a brief re- 
 capitulation of the leading facts, and of the arguments which they 
 furnish in favour of design, and of the wisdom and power of the 
 Creator. 
 
 In the preceding chapter we advanced a few of the leading ar- 
 guments which induce us to adopt the hypothesis that all gaseotis 
 bodies under the same pressure and temperature, contain an 
 equal number of self-repulsive molecules ; and we have now to 
 consider, very briefly, some of the important consequences to 
 which this hypotliesis naturally leads. 
 
 It seems to be satisfactorily establislied that bodies, in their ga- 
 seous state, combine both chemicallij and coheslveli/ with refer- 
 ence to their volumes ; that is to say, that the same volume of a 
 gas always combines with either precisely a similar volume of the 
 same or of another gas, or with some multiple or submultiple of 
 that gas (in other words with twice, or thrice, or half, or a quarter 
 as much, &;c.) but not with any intermediate proportion ; and 
 
LAWS OF CHEMICAL COMBINATION. 87 
 
 further, that the resulthig compound always has reference by vo- 
 lume to the original volumes of its constituent elements. Let us 
 take water for example. Water has been shown to consist of one 
 volume of oxygen gas, and two volumes of hydrogen gas ; and so 
 invariably, that we cannot suppose water to be formed of any other 
 proportions of these elements. It has been also shown that the 
 resulting water, if in the state of steam, occupies exactly the space 
 of two volumes, so that one volume has disappeared. Now let 
 us consider attentively what must have happened during these 
 changes. One volume of oxygen gas has contributed to form two 
 volumes of water, which two volumes of water, according to our 
 hypothesis, must consist of twice the number of self-repulsive 
 molecules contained in the one volume of oxygen ; yet every one 
 of these molecules must contain oxygen, because oxygen is an es- 
 sential element of water : it follows, therefore, irresistibly, that 
 every self-repulsive molecule of oxy gen has been divided into two, 
 and consequently must have originally consisted of at least two 
 elementary molecules, somehow or other associated, so as to have 
 formed only one self-repulsive molecule. This conclusion, which 
 seems to flow naturally from our premises, is most important, 
 as we shall see immediately, and enables us to throw no small 
 light upon many points deemed obscure. In the mean time let us 
 consider briefly the nature of the compound self-repulsive mole- 
 cule of oxygen. 
 
 We endeavoured to show in the previous chapter, that every 
 ultimate molecule of matter must possess two kinds of polarity, 
 which, for want of better terms, we denominated the chemical and 
 the cohesive ; and that these polarities bear the same relations to 
 each other as electricity and magnetism ; in other words that, like 
 these forces, the polarities exist at right angles to each other. 
 Hence if a and b be supposed to be two molecules of oxygen, of 
 which Ee Ee represent the chemical poles and axis, and mm, mm the 
 cohesive, it is evident that these two molecules may be supposed 
 to combine in two ways, either e to e chemically, or m to m co^ 
 hesively ; but the latter form of course is most probable yVom the 
 sitnilar nature of the molecules.* Every self-repulsive molecule 
 
 • The general and strong' analogy, if not identity, in all respects except 
 direction, between the axial and the equatorial forces, has been already 
 alluded to, and is exemplified by the striking resemblance between elec- 
 tricity and magnetism. We have seen also that in the crystallized state, 
 similar molecules probably combine chemically. Hence, although the rule 
 stated in the text be true, that similar molecules only combine cohesively ; 
 yet there may be, and probabl}^ are, instances in which they combine che- 
 mically. For the same reasons, dissimilar molecules may also occasionally 
 combine cohesively. It is probable that such states of combination might 
 be readily detected by the optical properties, or by some other peculiarity 
 
88 CHEMISTRY. 
 
 of oxygen, therefore, as it exists in a state of gas, must consist 
 oi at least two molecules, united to each oiher cohesively, and 
 acting as a single one ; and the same may be sliown with respect 
 to other gaseous bodies, as, for instance, hydrogen. It cannot, 
 indeed, be inferred from the composition of water, as above stated, 
 whether the self-repulsive molecule of hydrogen be double or not; 
 but this may be demonstrated from other compounds into which 
 hydrogen enters. Tlius muriatic acid gas is composed of one vo- 
 lume of chlorine and one volume of hydrogen, which unite with- 
 out any condensation, and form two volumes of muriatic acid gas ; 
 now in this case, it is evident that not only the self-repulsive mole- 
 cule of hydrogen, but also that of the chlorine, must be double at 
 least, like the molecule of oxygen above mentioned ; and the same 
 might be shown with respect to the other gaseous bodies. 
 
 We have said above that the self-repulsive molecules of oxygen 
 and of hydrogen are at least double; but the probability is that 
 they are in reality much more compounded, as the following ob- 
 servations will show. The self-repulsive molecule of water, on 
 entering into combination, is often found to be divided into two 
 or three (perhaps more) parts. Now as we cannot admit the di- 
 vision of an ultimate molecule or atom, we must of course con- 
 clude that the molecules of oxygen and of hydrogen are much 
 more compounded than as above represented, and must each of 
 them contain at least three component or sub-molecules. Hence 
 the self-repulsive molecules of water will consist of at least nine 
 component sub-molecules (viz. three of oxygen and six of hydro- 
 gen) which we may suppose to be associated, — in the first place 
 the hydrogen with the oxygen, chemically ; and afterwards the 
 three sub-molecules of water with one another cohesively, so as 
 to constitute one spheroidal molecule ; in a manner that with a 
 little ingenuity it would, perhaps, not be difficult to represent 
 mechanically.* 
 
 Precisely the same laws of union may be supposed to prevail 
 among the molecules of bodies themselves, as they actually exist 
 around us, Tiuis let us take the crystal of oxahc acid as an in- 
 stance for illustration. This acid is composed, according to the 
 present language of chemists, of two molecules of carbon, and 
 
 in the physical properties of bodies, if in a crystalline form ; but by no 
 other known means. Do not some of the phenomena of Isomerism, that 
 is to say, the property wliich the same body occasionally possesses of as- 
 suming" different forms, dejjend upon tliese cliang^es ? 
 
 • When bodies, as, for example, water, arc subjected to intense degrees 
 of heat, it is not improbable that in many instances the self-rcpulslvc mole- 
 cules are more or less separated into their constituent sub-molecules ; 
 in whicli case of course the bodies may be supposed to exhibit altogether 
 different clastic powers and laws of expansion. 
 
LAWS OF CHEMICAL COMBINATION. 89 
 
 three of oxygen, which by combining, form the acid ; while, to 
 complete the compound molecule, and to adapt it for crystallization, 
 three molecules of water are required to be somehow associated 
 with each of the molecules of the acid. Now in this case, we 
 suppose, that the two molecules of carbon (each of which is per- 
 haps already made up of several sub-molecules) are associated 
 together into one symmetrical super-molecule ; that the three 
 molecules of oxygen are arranged in a similar manner, and then 
 associated chemically with the super-molecule of carbon, and thus 
 form by their union a molecule of oxalic acid ; finally, that the 
 three molecules of water are united into one super-molecule, which 
 combines chemically with the molecule of oxalic acid, and thus 
 completes the molecule of the acid as it actually exists in the 
 crystalline form. 
 
 Such are the vieM^s we have been induced to take of the nature 
 of chemical combination, and whether right or wrong, they have 
 the merit of being exceedingly simple and consistent with them- 
 selves throughout, which can hardly be said of any others with 
 which we are acquainted. Indeed much reflection upon the sub- 
 ject, for many years past, has satisfied us that chemical combina- 
 tions can be rationally explained only in some such manner as 
 we have supposed. Any lengthened argument, however, upon 
 the laws of chemical combination here, would be quite out of 
 place ; we shall therefore confine ourselves to the following ob- 
 servations. 
 
 1. The above view of the molecular constitution of bodies na- 
 turally suggests the important question : do the sub-molecules, 
 which we suppose to unite together cohesively and form the self- 
 repulsive molecule, of oxygen and hydrogen for instance, possess 
 the same properties as those of oxygen and hydrogen, or do they 
 possess different properties ? This question, in most instances, 
 cannot, in the present state of our knowledge, be satisfactorily 
 answered ; though there is every reason to believe that the pro- 
 perties both of the sub-molecule and of the super-molecule gene- 
 rally differ from those of the molecule itself, but that the differences 
 are rather of a specific than of a generic character.* Thus che- 
 mists have shown that different volumes of the same gaseous 
 body, termed carburetted hydrogen, combine together and form 
 various compounds : we have, for example, a gas, one volume 
 
 * What we term the sensible properties of bodies are, of course, in all 
 instances, the result of a g-reat number of molecules acting" tog-ether at 
 the same time ; hence below a certain point, mere difference of numbers 
 may be supposed to produce a change in sensible properties, not only in 
 degree, but in kind : of the sensible properties of a single molecule we 
 can form no conception. 
 
 8* 
 
90 CHEMISTRY. 
 
 of which contains two volumes of carburetted hydrogen ; another, 
 one vohime of which contains three, and another four, of the 
 same gaseous body. Now the sensible properties of all these 
 compounds, though resembling each other in some respects, are 
 yet specifically different; and as they are all composed of the 
 same gaseous body in different proportions, these differences 
 must be considered rather as the result of cohesive than of che- 
 mical union. Thus the supposition, that both the sub-molecules 
 and the super-molecules of bodies may possess properties differ- 
 ent from one another and from the standard molecule, is rendered 
 exceedingly probable by the above f\icts ; and if our space ad- 
 mitted, it would not perhaps be difficult to bring forward other 
 facts of the same kind. This however, would be foreign to our 
 purpose ; and we shall only remark, that a great many curious 
 circumstances, at present but very imperfectly understood, evi- 
 dently appear to be referrible to a similar principle. 
 
 2. Although we have thus rendered it exceedingly probable that 
 the molecules of bodies considered at present as elementary, are 
 immediately compounded of many others more or less resembling 
 them; yet it is obvious that there must be a point at which these 
 and other elements exist in a primary or ultimate form, and be- 
 yond which, if they can be supposed to be subdivided, they must 
 become something altogether different. In this respect, therefore, 
 the views we have advanced accord generally with those at pre- 
 sent entertained ; and the only point in which they differ, is in sup- 
 posing that the self-repulsive molecule, as it exists in the gaseous 
 form, does not represent the ultimate molecule, but is composed 
 of many of them. With respect to the nature of the ultimate sub- 
 molecules of those bodies which we consider at present as ele- 
 ments, as, for instance, of oxygen, they may naturally be supposed 
 to possess the most intense properties or polarities. Indeed such 
 sub-molecules may be imagined to resemble in some degree the 
 imponderable matters, heat, &;c., not only by their extreme te- 
 nuity, but in otlier characters also; and this very intensity of pro- 
 perly and cliaracter may be reasonably considered as one, if not the 
 principal reason, why they are incapable of existing in a detached 
 form. Lastly, are not these ultimate and refined forms of matter 
 extensively employed in many of the operations of nature, and 
 particularly in many of the processes of organization? 
 
 3. By supposing that these laws of combination are not con- 
 fined to elementary bodies, but extend to all others throughout na- 
 ture; and that ])0(lies, however complicated they may be, always 
 combine with reference to their volume in the gaseous slate, and 
 always act as simple molecules; we are enabled in some de- 
 gree to explain that endless variety of property and condition 
 
LAWS OF CHEMICAL COMBINATION. 91 
 
 which we see around us. For no sooner is a new compound 
 molecule formed by an assemblage of similar molecules, than it 
 may be supposed to be capable of combining witli other molecules 
 chemically^ and of thus entering into a long and novel series of 
 combinations; while these combinations again in their turn may 
 be imagined to lead to others, and so on, till the variety becomes 
 extreme. Indeed v/ere not such combinations limited by the very 
 nature of things themselves, no two substances would probably 
 possess the same properties. As it is, most of these compounds 
 are incapable of separate existence; thus the compound super- 
 molecules of water in the crystal of oxalic acid before referred to, 
 are incapable of separate existence : if they could exist separately, 
 would they assume the form of water? 
 
 4. It would not be diflicult, though perhaps not very safe or 
 prudent in the present state of our knowledge, to speculate on the 
 crystalline forms assumed by different bodies, with reference to 
 the principles we have advanced. We shall therefore not touch 
 upon this part of the subject, further than by observing that the 
 cohesive force, though supposed to possess some peculiarity as 
 existing among the molecules of different bodies, is nevertheless 
 essentially but of one kind. When therefore the molecules of 
 different bodies are of the same size (or rather of the same weight,) 
 they may be naturally supposed capable of associating themselves 
 into the same form ; and if they happen to be mixed together, they 
 may even enter indiscriminately into the same crystal. Hence 
 arises what has been termed the isomorphism of bodies ; while if 
 there be a near approximation, but not an exact coincidence in the 
 above relations, they may upon the same principles be supposed 
 to give origin to plesiomorphism, that is to say, to a near ap- 
 proach to a similarity of form. 
 
 5. With respect to the nature of the circumstances which deter- 
 mine the peculiar characters and modes of existence of bodies we 
 know very little. We are almost equally ignorant also of the na- 
 ture of the causes which determine the cohesion of the molecules 
 of bodies into the crystalline form. A variety of arguments might, 
 however, be brought forward which appear to show that the size 
 and shape of tlie molecules have a great deal to do with crystalli- 
 zation ; certainly, at least, the molecules must be supposed to have 
 a size and shape somehow or other adapted for the modes in which 
 they are arranged, otherwise they could not be capable of such 
 an arrangement. The cause of this similarity of size and shape 
 is unknown, but it most probably depends upon the similarity of 
 iveight [fsobarism) of the molecule; that is to say, upon the re- 
 lation or identity of the absolute quantify of matter which the 
 molecule contains ; which relation, as far as we can perceive, is 
 
92 CHEMISTRY. 
 
 not only the sole circumstance common to the molecules of dif- 
 ferent bodies, but that which of all others is the most likely to 
 produce identity in the size and shape of these molecules. 
 
 6. When the molecules of bodies in solution do not happen to 
 possess the requisite size and shape for cohesion, there is from 
 the phenomena every reason to believe, that they occasionally 
 possess the power, as it were, of making up the necessary form, 
 by attaching to themselves the molecules of other bodies. Now, 
 bodies so attached may be considered as acting a sort of comple- 
 mentary part ; that is to say, they may be supposed to complete 
 the figure or size of the molecule, so as to adapt it for combining 
 in a certain manner. Thus the water of crystallization (and per- 
 haps occasionally other matters) appears in the greater number of 
 instances to perform an office of this kind, and to be in fact strictly 
 complementary to that particular figure and size of the molecules, 
 which may be supposed to be requisite for enabling them, not 
 only to combine the more readily with each other, but at the 
 same time, to form a symmetrical solid or crystal.^ 
 
 One or two other circumstances connected with this part of 
 our subject will be better understood after we have considered a 
 little more in detail, the combinations of bodies with reference 
 to their iveights, and the absolute quantity of matter which they 
 contain. To this most interesting inquiry, therefore, we shall 
 in the next place proceed, confining ourselves, however, as before, 
 principally to tlie elements of water, hydrogen and oxygen. 
 
 It has been found by experiment that the same volumes of dif- 
 ferent bodies in the gaseous state have very different weights. 
 Thus for instance a volume of oxygen weighs sixteen times as 
 much as the same volume of hydrogen. Hence as the number 
 of self-repulsive molecules in each of these gases is presumed to 
 be the same, the weight of the self-repulsive molecule of oxygen 
 must of course be sixteen times greater tlian that of hydrogen; 
 and GENERALLY, the loeights of the self-repulsive molecules of 
 all bodies ivill be as the specific gravities of these bodies in the 
 gaseous state, or ivill bear certain simple relations to these spe- 
 cific gravities. 'J'his relation in weight among the molecules of 
 
 * There is every reason to befieve that one variety of isomorpliism is 
 effected on the principles here stated ; and that the molecules of different 
 substances, by atlructin.^- to themselves different quantities of v/atcr, or of 
 other matters, may ultimately make up compound molecules similar to 
 those of the bodies with which they may happen to be mixed, and may 
 thus enter indiscriminately with these bodies into the crystalline form. 
 Such a stiite of things is calculated to baffle the mere chemist, however 
 expert ; thoug-h it is probable, that if carefully examined and understood, 
 an intermixture of this kind might be detected by the optical properties 
 of the crystal. 
 
LAWS OF CHEMICAL COMBINATION. 93 
 
 bodies constitutes the basis of what is called the Jiiomic theory^ 
 proposed, some years ago by Dr. Dalton, who established the 
 most important fact, that bodies do not, as formerly supposed, 
 combine at random, but in definite proportions by weight ; and 
 if the preceding doctrines be well founded, it is evident they can- 
 not combine otherwise.* As however water is composed of one 
 volume of oxygen united with two volumes of hydrogen, the re- 
 lative weights of the hydrogen and oxygen in water will be, not 
 as 1 to 16, but as 1 to 8 only ; while the weight of tlie self-re- 
 pulsive molecule of steam will be 9. Hence, as one of the other 
 of the elements of water is usually made the basis of the atomic 
 numbers, this difference between the volumes and the combining 
 weights of its elements has produced considerable confusion, and 
 has given rise to much needless discussion. As a mere matter 
 of convenience it is certainly preferable to consider the two vol- 
 umes of hydrogen as one atom,, (to use the language of Dr. Dal- 
 ton), in which case oxygen will be 8, and water 9 ; but a strictly 
 philosophical arrangement, supposing the principles we have 
 advanced be well founded, would require that the volume in all 
 instances should be tnade the molecular unit ; in which case, 
 the relative weights of the self-repulsive molecules of hydrogen 
 and oxygen, as above mentioned, will be as 1 to IG. 
 
 In this country two volumes of hydrogen, as we have said, are 
 usually considered as one atom., or unity, in which case oxygen 
 is 8 ; but some have chosen instead of hydrogen, to make oxy- 
 gen unity or 10, in which case hydrogen of course will be the 
 one-eighth of 1 or of 10, that is to say, .125 or 1.25 ; and water, 
 instead of 9, will be 1.125 or 11.25. It matters not which of 
 these series of numbers, or whether any other be employed, so 
 that the same relative proportions be observed among them ; but 
 the first series is that most generally adopted, and is upon the 
 whole the most convenient. In the above manner the atomic 
 iveightSy as they are termed, of all bodies capable of assuming 
 the gaseous form can be easily obtained ; but in those bodies that 
 do not assume the gaseous form, in their simple state, but in some 
 state of combination only, we are obliged to deduce the weight 
 of the primary molecule from that of the compound. Thus car- 
 bon in its elementary state is incapable of assuming the gaseous 
 form ; but combined with oxygen it forms carbonic acid gas, one 
 volume of which weighs 22 times as much as our standard two 
 volumes of hydrogen. Now it has been found by other experi- 
 ments, that of these 22 parts, 16 are oxygen. The remaining 6 
 
 * The reader is referred lO *' An Introduction to the Atomic Theory," 
 recently published by Dr. Daubenv, Professor of Chemistry, at Oxford, 
 for an interesting- and able inquiry into the principles of this theory. 
 
94 CHEMISTRY. 
 
 must therefore be carbon ; and accordingly 6 is the number upon 
 our scale representing carbon, and the proportion, with reference 
 to which, this body always enters into composition. In the case 
 of bodies, as for instance, lime, which are incapable of assuming 
 a gaseous form either alone or in combination, we are obliged to 
 trust solely to analysis ; thus common marble or carbonate of lime, 
 as it is termed by chemists, is found to be composed of 22 parts 
 of carbonic acid, and 28 parts of lime ; 28 therefore represents 
 upon our scale the atomic weight of lime, and so of all others. 
 
 It may be observed that we have spoken as if the atomic weights 
 of bodies were related to one another by multiple ; that is to say, 
 were all multiples of some common unit. Now this opinion has 
 been maintained by somiC, while it has been denied l3y others ; 
 who admitting that multiples in weight are necessary to the union 
 of the same body, both chemically and cohesively^ will not admit 
 that they are necessary to the union of different bodies. The 
 matter is one that in the present imperfect state of chemistry can 
 hardly be determined by experiment; for what with the difhculty, 
 or rather impossibility, of procuring bodies in a perfecdy isolated 
 form, and the unavoidable imperfections of all chemical processes, 
 we can scarcely hope to arrive within the necessary limits of pre- 
 cision. If the above views of molecular relations however, be well 
 founded, it seems almost impossible to arrive at any other conclu- 
 sion, than that the combining weights of all bodies are intimately 
 related by multiple; though to enter further upon the subject here 
 would be quite foreign to our present purpose.* 
 
 Lastly, it may be remarked that the numbers at present con- 
 
 * For the sake of those who are interested in such matters, one or two 
 of the leading- arg-umcnts may be briefly stated. We have rendered it 
 probable that when two or more molecules of the same bod}' combine co- 
 hesivelij, they form a compound, wliich thoug'h having properties in some 
 degree allied to those of the original molecule, nevertlieless usually pos- 
 sesses a s])ecific difference, (that is to say, the chemical polarities of the 
 compound molecule as modified by the union, will be different from those 
 of the simple molecule). But a body possessing a specific difference, may 
 be supposed to be a new body, and thus capable of combining in future, 
 not cohesively, but chemically with our original molecule. Now in such 
 a case it is evident that the weight of the original molecule and that of the 
 new compound molecule must have a certain relation to one another by 
 multiple. If our space admitted, it would not, we believe, be difficult to 
 point out instances of such combination among chemical phenomena ; but 
 we shall merely observe, that many of the substances at present considered 
 as elementary, appear to be constituted upon the above principles from 
 some common molecule of a still more elementary character. Moreover 
 this law seems to hold universally throughout nature ; and those substances 
 related to the same molecule, in general constitute a natural group or fa- 
 mily, having certain properties in common. 
 
LAWS OF CHEMICAL COMBINATION. 95 
 
 ventionally employed by chemists, to represent what have been 
 called the atomic weights of bodies, are so convenient that they 
 will not readily, nor indeed ought lightly, to be set aside ; though 
 there is reason to believe that many of them require revision, and 
 are destined to undergo material alterations, even as the subject 
 is at present understood. If the views however which we have 
 advanced be correct, these numbers certainly do not represent na- 
 ture ; for as we have already stated, a strictly philosophical arrange- 
 ment can be rationally founded only upon the volumes of bodies 
 in the gaseous state, in which state some common volume in all in- 
 stances should be considered as the molecular unity. Now, as 
 in most instances, this molecular unity seems capable of subdi- 
 vision, of course the number made to represent it can hardly ever 
 be supposed to be a prime number. Hence, as combining mole- 
 cules of bodies exist both below and above the molecular unity, 
 they may often (perhaps always) be represented by a series. Thus 
 suppose 9 to represent the molecular unity or volume of water, 
 and that this be subdivided into three (which it is at least, and 
 probably into a much greater number) ; the molecular combina- 
 tions of water may be represented by the series, 3, 6, 9, 12, 15, 
 18, (fee. We mean to say, the molecules of water as they actu- 
 ally enter into a combination in different bodies, may be supposed 
 to be represented by these numbers ; while, by way of distin- 
 guishing the different molecules, those below 9, may be desig- 
 nated generally st<6-molecules, and those above sz</?er-molecules ; 
 and the molecular unity itself may be simply called the molecule^ 
 or in the gaseous state the self -repulsive molecule; distinctions, 
 which for the sake of convenience, we have adhered to throughout 
 these remarks, and which we have thought it thus necessary to 
 explain.* 
 
 Section III. 
 
 General Bemarks upon Chem^ical Compounds, 
 
 The number of chemical compounds is so great that an attempt 
 to enumerate them here would be quite out of place ; we shall 
 therefore content ourselves with stating, as briefly as possible, the 
 general principles upon which these compounds are formed. 
 
 We have already pointed out many of the more remarkable 
 compounds, when speaking of simple bodies ; and in subsequent 
 parts of this volume we shall have occasion to allude to others. In 
 
 * The above terms are to be considered as a temporary expedient only. 
 If these views be established it will not perliaps be difficult to devise here- 
 after both a notation and a nomenclature founded upon them. At present 
 such an attempt would be ridiculous. 
 
96 CHEMISTRY. 
 
 speaking of simple bodies we showed that by far the greater num- 
 ber of ihem occur in the metallic state, and are incapable of ex- 
 istence upon the surface of our globe, on account of the tendency 
 they possess to enter into combination, particularly with oxygen. 
 It would seem also, from the intensity of the properties and the 
 general incompatibility of the simple bodies with the present order 
 of things, tiiat their compounds, rather than themselves, were the 
 objects the Autlior of nature had in view. Hence perhaps we are 
 more immediately interested in the character of the compounds 
 than in that of the elements themselves. Of the general nature 
 of these compounds, the following observations, taken chiefly from 
 Dr. Thomson's work on chemistry, will serve to convey some 
 idea to the general reader. 
 
 The COMPOUNDS which bodies form with one another are either 
 PRIMARY OR SECONDARY. By PRIMARY COMPOUNDS are usually un- 
 derstood tho^^e which are formed by the combination of two or 
 more simple boilies with each other ; while by secondary com- 
 pounds are meant the compounds formed by the union of the pri- 
 mary compounds with each other. 
 
 The PRIMARY COMPOUNDS naturally divide themselves into three 
 grand classes, viz. acids, alkalies or bases, and neutrals ; on each 
 of which we shall make a few remarks. 
 
 Of Jicids. Formerly it was considered as requisite that bo- 
 dies, in order to belong to the class of acids, should have a sour 
 taste, should be soluble in water, and should have the property of 
 reddening vegetable blue colours ; and these properties do indeed 
 belong to some of the most common and powerful acids. But 
 there are various acids which have no taste, which are not soluble 
 in water, and some which are incapable of altering the colour of 
 the most delicate vegetable blues ; hence the term acid, as at pre- 
 sent employed by chemists, is understood to denote a substance 
 which has the property of combining with, and neutralizing, al- 
 kalies or bases. The celebrated Lavoisier endeavoured to prove 
 that oxygen constitutes an essential ingredient of all the acids ; 
 but later observations have shown that not only oxygen, but the 
 analogous principles, chlorine, bromine, iodine, and fluorine, are 
 also capable of forming acids by uniting with several of the acidi- 
 fiable bases. Still more recently, certain compounds of cyanogen, 
 (a primary compound of carbon and azote), of sulpliur, of se- 
 lenium, and of tellurium with the aciditiable bases, have been 
 ranked among the acids ; so that the acids at present known may 
 be divided into nine classes, viz., oxygen acids, chlorine acids, 
 bromine acids, iodine acids, Jiuorine acids, cyaiiogen acids, sul- 
 phur acids, selenium acids, and tellurium acids. 
 
 Tiie oxygen acids are more numerous and better understood 
 
CHEMICAL COMPOUNDS. 97 
 
 in general than the other classes ; they may be subdivided into 
 two kinds ; those with a single base; and those with a compound 
 base. The acids with a single base amount to between thirty and 
 forty, and include most of the best known and most important of 
 those used in chemical processes and in the arts ; such as carbonic 
 acid, sulphuric acid, phosphoric acid, nitric acid. Sic. The 
 oxygen acids with a compound base are chiefly derived from the 
 vegetable or animal kingdoms ; they are still more numerous than 
 those with a single base, the number at present known amounting 
 to upwards of sixty ; as instances may be mentioned the tartaric 
 acid, the citric acid, the malic acid, the lithic acid, &c. 
 
 The chlorine acids are perhaps as numerous as those contain- 
 ing oxygen, but they have been much less studied, and are, con- 
 sequently, much less understood. One of the most familiarly 
 known belonging to this class is the muriatic or hydrochloric acid, 
 which is composed of chlorine, united with hydrogen : and here 
 may be noticed a remarkable circumstance, that not only chlorine, 
 but all the other allied principles, when they combine with hy- 
 drogen, form powerful acids ; while the compound of oxygen with 
 hydrogen, as we have formerly noticed, is ivater, a substance al- 
 together dissimilar. Such is the wonderful and inexplicable na- 
 ture of chemical combinations ! 
 
 The acids containing bromine, iodine, and fluorine, are still 
 less satisfactorily known than those containing chlorine. As just 
 observed, the acids formed by these different principles with hy- 
 drogen, viz. the hydrobromic, the hydriodic and the hydrofluoric 
 acids, possess the most decided properties and are best understood. 
 
 The cyanogen acids are numerous and important, as most of 
 them are poisonous ; thus the compound of cyanogen and hydro- 
 gen (analogous to those above mentioned) is the hydrocyanic, or 
 prussic acid, one of the most virulent poisons in nature, and in- 
 stantly fatal to organic life in every form. 
 
 Of the remaining acids, the sulphur acids, the selenium acids, 
 and the tellurium acids, we know very little. Those with which 
 we are at present best acquainted are analogous to the preceding 
 acids, and are formed by the union of the different principles with 
 hydrogen. These acids were formerly knov\^n under the names 
 of sulphuretted, seleniated, and telluretted hydrogen; but some 
 chemists have now given them new names conformably to the 
 above nomenclature. 
 
 Of alkalies and bases. Bodies of this class, are, like the acids, 
 composed of different elementary principles, and particularly of 
 certain metals, combined with oxygen, chlorine, &c., but usually 
 in less proportions than in the acids. Hence the alkaline bases 
 are as numerous as the acids, and may be divided in a simi- 
 lar manner into oxygen alkalies, chlorine alkalies, &c. Of 
 
 9 
 
98 cHE:\nsTRY. 
 
 these the oxygen alkalies are by far the best known and most im- 
 portant, and they may, like the oxygen acids, be subdivided into 
 uvo kinds, viz. those with a single base, and those with a com- 
 pound base. The alkalies with a single base include all the well 
 known common alkaline bodies, potash, soda, lime, baryta, Sic. ; 
 while the alkalies with a compound base are chiefly from the ve- 
 getable kingdom, and comprehend the newly discovered alkaline 
 matters, so successfully introduced into medicine ; such as quinine, 
 from hd.Yk, morphine, from opium, &;c., the composition of which 
 at present is not well understood. »,^mmonia or the volatile alkali, 
 may perhaps be referred to this class of alkalies ; though its com- 
 position as consisting of hydrogen and azote only, without oxygen, 
 may be considered as constituting an exception or anomaly. 
 
 The other alkaline bodies into which chlorine, iodine, &c., 
 enter, are very little known, and some perhaps may be even in- 
 clined to doubt their existence. 
 
 Of neutral compounds. These are arranged by Dr. Thomson, 
 under seven heads, the mere naming of which will probably be 
 all that is required, to convey to the general reader a sufficient 
 notion of their nature. They are water, spirits or alcohol, ether, 
 ethcd, (a peculiar oily substance obtained from spermaceti) vola- 
 tile oils, Jixed oils, and bitumens. 
 
 Such is a summary of the primary cojipounds and of the prin- 
 ciples upon which they have been most recently arranged. We 
 come now to consider briefly 
 
 The SECONDARY COMPOUNDS, or those formed by the union of 
 the primary compounds. As the neutral primary compounds (if 
 we except water) enter into few combinations, it is obvious that 
 the SECONDARY COMPOUNDS must cousist chiefly of substances 
 formed by the union of the other two general classes of bodies, 
 namely, of acids and alkalies. These secondary compounds 
 are usually denominated salts ; they constitute a very numerous 
 and most important class of bodies ; and as resulting from the 
 mutual union and saturation of all the diflerent principles capable 
 of combining with each other, they of course are more abundant 
 than any other bodies ; indeed, the surface of our globe, may in 
 a great measure, be considered as made up of them. The term 
 salt was originally confined to common salt ; but by a singular 
 fate, this body, as being composed of chlorine and sodium only, 
 is now excluded from the class of salts: saks being, as we have 
 just said, considered by chemists, to be formed by the union of 
 acids and alkalies only. As there are nine classes of acids, of 
 course there must be as many classes of salts ; of these, the 
 oxygen acid salts are by far the best known and the most im- 
 portant; and, indeed, this class includes the greater number of 
 those salts employed by chemists or in the arts. If these salts 
 
RECAPITULATION. 99 
 
 be arranged according to their bases, which perhaps upon the 
 whole, in the present state of our knowledge, is the best mode 
 of arranging them, they will be found to constitute upwards of 
 fifty genera; and if we consider that each of these genera includes, 
 in most cases, a great number of species, we may form some idea 
 of the wonderful variety of bodies existing in nature, and with the 
 properties of which the chemist is required to be conversant. 
 Familiar instances of the oxygen acid salts are, nitre, common 
 chalk, gypsum ; various metallic salts, as the white, green, and 
 blue vitriols, &c. &:c. 
 
 Of the chlorine and the other classes of salts very little is 
 known, and tliis little is chiefly confined to the salts composed of 
 these principles and of hydrogen. The hydrochloric or muriatic 
 acid combines with ammonia, and forms the well-known compound 
 sal-ammoniac, a salt supposed to be a true hycho chlorate or mu- 
 riate. But this is the only instance known ; and in all other 
 analogous instances, the hydrogen of the hydrochloric acid and 
 the oxygen of the base, unite to form water, which is separated 
 or separable ; and thus the chlorine and the metallic base are left 
 in union by themselves in the state of a chloride. This is the 
 case, for instance, with common salt ^ which, as we before said, 
 is in reality a chloride of sodiitin, that is to say, a simple com- 
 pound of chlorine and the metal sodium. Similar remarks ap- 
 pear to be applicable to the other analogous compounds. It must 
 be confessed, however, that our knowledge with respect to all 
 these matters is at present in a very unsatisfactory state, and is 
 probably destined at no very distant time to undergo a complete 
 revolution. 
 
 Section IV. 
 
 Recapitulation. General Reflections on the Subjects treated of 
 
 in the preceding Chapiters. 
 
 The subjects considered in the present chapter may be viewed 
 as a continuation of what has engaged our attention in those that 
 have preceded ; and the principal circumstances detailed may be 
 thus recapitulated. 
 
 1. All perfecdy gaseous bodies combine with reference to 
 their volume ; that is to say, any volume or bulk of a gas always 
 combines with an equal volume or bulk of the same or of another 
 gas ; or with a volume having some simple relation to its own 
 volume, as half, or twice as much ; &c. and not with any inter- 
 vening fractional part of a volume. 
 
 2. The same volume of different gaseous bodies has very 
 
100 CHEMISTRY. 
 
 different ivcights : hence on the supposition formerly advanced, 
 that all perfectly gaseous bodies under tlie same pressure and 
 temperature contain an equal number of self-repulsive molecules, 
 tlie molecules of different gaseous bodies must also have different 
 weights ; Avliich weights will be as the specific gravities of the 
 gases, and may be represented by numbers proportional to these 
 specific gravities. 
 
 3. From the above relation between the volumes and the 
 weights of bodies in the gaseous state, it follows, that all bodies 
 must combine ivith reference to their weights ; that is to say, 
 that the same weight of the same body (or half or twice as much, 
 &c.) must always combine with the same weight (or half or twice 
 as much, &;c.) not only of the same, but of every other body. 
 
 4. The numbers representing the relations among the specific 
 gi'avilies of bodies in the gaseous state, are called the molecular 
 or atomic ivcights of the different bodies. 
 
 Such is the foundation of what is usually called the Atomic 
 Theory, the principles of which are generally admitted as regu- 
 lating chemical combinations. 
 
 AVe shall now conclude the present Treatise on chemistry- 
 with a {^\N remarks more especially relating to the object of these 
 volumes. And here it may be observed, once for all, that through- 
 out the preceding pages, as well as in what follows, we have 
 endeavoured to state each argument as distinctly as possible, 
 without encumbering it too much with details — in short, to illus- 
 trate principles rather than to enumerate particulars. When the 
 principles of a cumulative argument are understood, the details 
 are readily supplied by the reader. 
 
 First. On taking a general and collective review of the facts 
 brought forward in the preceding chapters, the circumstances 
 calculated to strike our attention in the first place, are the won- 
 derful coincidence between the priority of existence, and the uni- 
 versal prevalence of the primordial agents and elements of nature, 
 on the one hand ; and on the other, the beautiful adaptation of 
 the agents and elements of a later and more subordinate character 
 to these primordial principles ; so that when the whole are taken 
 together they constitute one harmonious and connected series, 
 in which all the various parts are mutually adapted and dependent. 
 In the following chapters we shall have occasion to notice many 
 of the more important of these subordinate arrangements ; at 
 present we shall chiefly confine ourselves to a general review of 
 what has been already stated. 
 
 We are told by the inspired historian that after matter had been 
 created and endowed with motion, the next Almighty fiat was 
 "let there be light;" and if we suppose this fiat, to have in- 
 cluded the other imponderable forms of matter, heat, &c., how 
 
GENERAL ARGUMENTS. 101 
 
 entirely do the whole phenomena of nature accord with the sacred 
 narrative ? Light, and probably its attendant heat, are the most 
 generally diffused and universal of all the subordinate agencies ; 
 so much so, that they are not confined to our globe or even sys- 
 tem, but extend throughout the universe. Their laws and influ- 
 ences, therefore, seem to be as general and as necessary to the 
 present order of things, as those of gravitation itself. The prior- 
 ity of existence also of light and of heat is self-evident ; for until 
 they existed, nothing else, as we are acquainted with things, 
 could have had existence. Now all subsequent creations have 
 been made with the most exact regard to the influences of these 
 prior agencies. The globe, for example, which we inhabit, is at 
 a certain distance from the sun, the great centre of our system 
 and of light and of heat ; and where of course, according to the 
 laws which light and heat obey, they must act with a certain in- 
 tensity. Hence it was necessary that the materials of this globe 
 should have a certain degree of fixity, otherwise they could not 
 exist. If indeed there had been no ulterior views, with respect 
 to the destination of this globe ; all that would have been requi* 
 site, would have been to have made it sufiiciently firm to move 
 through space ; and for this purpose the more homogeneous and 
 compact its composition had been the better. But what are the 
 facts ? Our globe, though stable, so far from being homogeneous, 
 is composed of a variety of substances all differing from each 
 other in their properties ; some being solid, some fluid, some 
 aeriform under the common circumstances in which they have 
 been placed, and all beautifully adapted, both by their physical 
 and chemical properties, to the purposes they fulfil in nature ; 
 and what is more, to the purposes they were designed to fulfil in 
 nature ; for on no other supposition would their properties be in- 
 telligible. 
 
 Thus water, ivithin very narroiv limits of temperature, is a 
 solid, or a liquid, or a gas ; and yet these very narrow limits of 
 temperature, neither more nor less, are precisely those which ex- 
 ist upon the surface of our globe ; where they are the natural and 
 necessary results of its situation in the universe, and of the general 
 laws which govern the distribution of light and heat. Had the 
 properties of this body been other than what they are, or had the 
 general temperature of our globe been different, water would have 
 existed altogether in the solid or in the gaseous state, and its most 
 important properties would have been unknown. Hence it seems 
 almost impossible to arrive at any other conclusion, than that the 
 temperature of the earth, and the properties of the water on its 
 surface, have been mutually adjusted to each other. And further, 
 since the temperature of the earth, as just stated, is the natural re- 
 sult of the general laws which govern the distribution of heat and 
 of light ; the inference must be, that the properties of the water, 
 
 9* 
 
102 CHEMISTRY. 
 
 as the subordinate and later principle, have, at an after period, been 
 adjusted to the prior temperature of the earth. 
 
 If we do not admit of this adjustment, we must suppose that 
 the whole has been the result of chance, or of some other unin- 
 telligent principle ; and if water had been the only principle in 
 which such adaptations were apparent, the supposition of chance 
 might, perhaps, be received ; at least it would have been difficult 
 to prove the contrary. But when we see similar happy adjust- 
 ments in every object around us, — in the different elements of the 
 air we breathe, the soil we tread upon, the rocks in all their va- 
 rieties, composing the solid crust of our globe, not one of which 
 could have been more happily contrived for the purposes they ful- 
 fil, nor indeed be scarcely conceived to exist otherwise than what 
 they are, without destruction to the whole of the present arrange- 
 ments — when we see all these things, and duly reflect upon them, 
 it becomes absolutely impossible to admit that so much happy 
 adjustment, so much apparent intelligence, so much, in short, of 
 what the veriest sceptic under other circumstances would have 
 allowed to have been evidences of design, can be evidences of any 
 thing else than design, or have resulted from any unintelligent cause 
 whatever. Hence we are driven irresistibly to the only rational 
 conclusions which the premises appear to admit of, viz., that all 
 these happy adjustments and adaptations which we see in nature, 
 are really and truly what they appear to be, — so many evidences 
 of design ; and, consequently, that the whole have sprung from 
 the will of an intelligent and omnipotent Creator. 
 
 The above inferences are deducible from the plain and obvious 
 arrangements of nature, which every one can readily understand : 
 but when speaking of elementary bodies we remarked, that in a 
 variety of instances, their object and use were unknown to us ; 
 and before we quit this part of the subject, it may not be out of 
 place to consider briefly these difficult points. 
 
 When we see adjustments so wonderful, and such wisdom dis- 
 played in those parts of creation which are intelligible to us, we 
 cannot imagine that the Being who made them all would act other- 
 wise than with wisdom. Hence what we do not understand, or 
 what may appear incongruous to us, we naturally and properly 
 refer to our own ignorance. The phenomena of chemistry are so 
 extraordinary and often so unexpected, that little in general can 
 be predicated of them, beyond what is actually known. The 
 most experienced chemist, therefore, as compared with the Great 
 Chemist of nature, is immeasurably deficient; and can only con- 
 template His wonderful operations with astonishment and awe, 
 and own them unapproacliable. Who then can tell what design 
 is latent under apparent incongruities ? What elaborate contri- 
 vances and adaptations may have been requisite to have produced 
 
GENERAL ARGUMENTS. 103 
 
 water or carbon, or any other essential principle, out of the mate- 
 rials and in conformity to the laws, by means of which the Great 
 Author of nature chose to operate ? Who can tell that the minor 
 evil may not have been essential to the existence of the greater 
 good ? That the poisonous metals, for instance, are not, as it 
 were, the refuse of the great chemical processes by which the more 
 important and essential principles of nature have been eliminated? 
 That these poisonous principles have not been left with such sub- 
 dued properties as scarcely to interfere with His great design, — 
 not because they could not have been prevented — not because they 
 could not have been removed — but on purpose and designedly to 
 display His power ? 
 
 Secondly. If we pursue the subject a step further, and inquire 
 into the means by which all the beautiful adaptations we have 
 been considering are effected, we shall find that they principally 
 depend upon a certain due adjustment to each other of the quali- 
 ties and quantities of the difTerent substances, and more especi- 
 ally of the different elementary principles, of which our globe is 
 composed. These adjustments are so universal and so varied in 
 their character, that to enumerate them all, would be litUe else 
 than to enumerate all the objects in nature; we shall therefore 
 content ourselves with a few of the most familiar of each kind. 
 
 In the first place, with respect to the adjustment of quality. 
 Let us consider for a moment and by way of illustration, what 
 would happen if the qualities of water or of air were to undergo 
 a change : were, for example, the important fluid water to become 
 sour or sweet, or heavier or lighter, or indeed anything but what 
 it is ; or were the air of the atmosphere to acquire odour or 
 colour, or to become opaque : by either of such changes, slight 
 as they appear, the whole of the present economy of nature would 
 be deranged. Again, if the qualities of the acid existing in the 
 common salt of the ocean were to become so modified as to quit 
 the alkali with which it is at present associated, and to combine 
 with the limestone composing our rocks ; while the carbonic acid, 
 thus set free, v/as diffused through the atmosphere : in such a 
 case a large part of the solid crust of our globe would rapidly 
 disappear and become dissolved in the waters of the ocean, which 
 would thus be totally unfitted for their present purposes ; while 
 the liberated carbonic acid would instantly prove fatal to animal 
 life. Such would be the consequences of these trifling changes 
 in the qualities of a few substances only ; nor is it possible scarcely 
 to conceive any other change that would not be attended with 
 similar results. 
 
 In the next place, the importance of the adjustments o{ quan- 
 tity is equally striking. Let us, for instance, conceive what 
 would happen from the simple inversion of the quantities of dry 
 
104 CHEMISTRY. 
 
 land and of sea as they now exist: in such a case there would 
 not be enough of water to preserve the surface of the land in a 
 moist state, and the greater part would be in the situation of the 
 deserts of Africa, and totally unfit for the habitation of organized 
 beings. When speaking of the elements of water, we alluded to 
 the happy adjustment of the quantities of oxygen and hydrogen 
 in the world ; and to the consequences that would have ensued 
 if hydrogen, instead of oxygen, had predominated. The same 
 remarks apply to almost every other element ; for example, had 
 the proportions of chlorine, and of the soda in common salt ; or 
 of the carbonic acid, and of the lime in our marbles, been anything 
 but what they are, the one or the other of the ingredients must 
 have been in excess, and the present order of things could never 
 have existed. Again, were gold suddenly to become as abundant 
 as iron, and iron as rare as gold; were the carbon existing in the 
 present useful form of fossil coals, to assume the crystallized form 
 and become diamonds ; the whole order of nature would be sub- 
 verted, and the whole of the present arrangements be involved in 
 ruin. Those who deny the argument of design, of course, con- 
 sider such suppositions as these absurd ; and if carried too far, 
 they doubtless, under any circumstances, lose much of their effect; 
 but admitting the argument of design, the judicious application of 
 such suppositions is well calculated to place the advantages and 
 effects of certain arrangements in a more striking point of view 
 than can be obtained by any other means. More especially, such 
 suppositions, by showing the wonderful adaptations of subsequent 
 creations to prior existences, are admirably calculated to illustrate 
 the fitness, and consequently the apparent design displayed in 
 the formation of these prior existences ; and thus to show that 
 they must have been created with reference to ulterior purposes. 
 
 The argument of prior arrangements and the subsequent adap- 
 tation to these arrangements of other creations is one of such in- 
 terest, and its consequences are so important, that perhaps it may 
 not be deemed irrelevant if, for further illustration, we recapitulate 
 the principal points in a condensed form. For this purpose we 
 shall select the obvious and familiar relation between water and 
 air, and plants and animals. 
 
 The prior existence of water and air as compared with that of 
 plants and animals, is established by the fact, that water and air 
 can exist without plants and animals, but that plants and animals 
 cannot exist without water and air. Hence as water and air 
 must have existed with all their present properties before plants 
 and animals were created, tlie question naturally arises, how 
 water and air came to be endowed with their present properties ? 
 We suppose that water and air were created with their present 
 properties, with reference to the future existence of plants and 
 
GENERAL ARGUMENTS. 105 
 
 animals ; and on this supposilion the whole becomes intelligible. 
 Further, that this is the true explanation, and that water and air 
 have not obtained their present properties by chance or accident 
 is rendered still more probable by the following considerations. 
 We have said that water and air can exist without plants and 
 animals ; now as far as we know, water and air might have ex- 
 istedybr ever without plants and animals ; at least the contrary 
 cannot be proved or even rendered probable. Moreover, plants 
 and animals, as involving new principles of a higher order (those 
 of life), never could by any law of nature, necessary or proba- 
 ble, have resulted from an inferior agency. Hence there is no 
 necessary relation of cause and effect between the prior ex- 
 istence of water and air, and the subsequent existence of plants 
 and animals ; as some seem to have supposed. Hence too it 
 follows irresistibly, that plants and animals have been created, 
 and their properties adapted to tiiose of water and of air at some 
 subsequent period, and by some external and superior agent. 
 But the agent that could thus create plants and animals, could 
 surely have created the water and air likewise ; nay, must have 
 done so ; for, as the prior and subsequent creations taken together, 
 evidently form but different parts of one and the same general 
 design, the whole design must have been the work of one and 
 the same intelligent Agent. 
 
 It yet remains to draw the attention of the reader to another 
 circumstance connected with these adjustments in quality and 
 quantity, viz. the double adjustment. Of the causes of the qualities 
 of bodies we know but little, and that little is founded solely on 
 experience. We see that these qualities are admirably fitted for 
 their apparent purposes, and hence (as they might have been dif- 
 ferent), we arrive at the probable conclusion that they have been 
 so fitted by design. The collocation of quantities and numbers, 
 exacdy where they have been required, adds much to the proba- 
 bility of this conclusion ; as such a collocation could hardly 
 have been other than the act of an intelligent Being. But the 
 double adjustment in qucdity and quantity of the same thing at 
 the same time, adds almost infinitely to the weight of evidence ; 
 and indeed furnishes a proof in favour of design and of its conse- 
 quences, which amounts to all but actual demonstration. 
 
 Thirdly. There is another point of view in which we may 
 consider what has been stated, and by which we shall at the same 
 time be brought a step nearer to the existing order of things. 
 Amidst all that endless diversity of property, and all the changes 
 constantly going on in the world around us, we cannot avoid being 
 struck with tiie general tendency of the whole to a state of repose 
 or equilibrium. Moreover, this tendency to equilibrium is not 
 confined to the ponderable elements, but prevails also in the same 
 
lOG CHEMISTRY. 
 
 Striking degree among the imponderable agencies, heat and hght; 
 which as we have seen, cannot be any where h^ng retained in a 
 state of excess, on account of their natural disposition to acquire 
 a certain state of equilibrium ; depending generally upon the place 
 of the earth in the solar system. Now, tlie formation of this state 
 of equilibrium, and its preservation, may be considered as the 
 results of those wonderful adjustments among the qualities and 
 quantities of bodies above alluded to — the qualities being such as 
 to neutralize each other's activity, while the quantities are so 
 apportioned as to leave one or two only predominant. 
 
 The preceding is a general view of the subject. But it is to 
 be observed, that the state of equilibrium here described is not 
 absoluteh^^^cef/; as such an unyielding condition would be not 
 less incompatible with the present order of things than a condi- 
 tion of unlimited change. The whole are so adjusted therefore, 
 that slight deviations, or oscillations about the neutral point of 
 rest or equilibrium, take place, and are even necessary, as the 
 world is at present constituted; though these changes are bound- 
 ed within very narrow limits, and greater deviations would in- 
 stantly prove fatal to the whole. If we inquire into the principles 
 upon which these slight deviations take place and are regulated, 
 we shall find still further reason to admire the wonderful arrange- 
 ments displayed. When speakino^ of the elements of water, we 
 observed how much the stability of nature depended upon the 
 proportions of the elements of this fluid; and that one of its ele- 
 ments, oxygen, existed in excess, and in a free state, in the air. 
 Now, it is to the agency of this oxygen in a free state, and to'. the 
 annual and diurnal motions of the earth, tliat most of the minor 
 operations going on around us are to be referred. The universal 
 presence and peculiar properties of oxygen are such as to inter- 
 fere more or less with everything; while the motions of the earth 
 keep everything in a constant state of activity and change. Yet, 
 the general tendency of the whole, as before observed, is towards 
 a state of equilibrium; and the principles upon which this ten- 
 dency operates, are very intelligible. Thus, all bodies below the 
 neutral point of rest, if we may be allowed the expression ; that 
 is to say, all bodies of a marked elementary character, have a ten- 
 dency to combine with each other sxjntheticalhj ; while beyond 
 the neutral point, bodies have very little tendency to combine 
 further ; and if by intention on the part of the operator, or from 
 any other cause, they be so made to combine, when left to their 
 own operations, they speedily revert or oscillate back to the point 
 of equilibrium. 
 
 Such are the means by which the state of equilibrium we are 
 considering has been produced, and by which it is still preserved; 
 nor is it possible to reflect upon the subject for a moment with* 
 
GENERAL ARGUMENTS. 107 
 
 out arriving at the conclusion, that this state of equilibrium pos- 
 sesses all the characters of a prior arrangement, to which organized 
 beings have been subsequently adapted. We are thus led, in the 
 next place, to make a few remarks upon the subsequent adaptation 
 of organized beings to the pre-estabhshed equilibrium of nature. 
 
 Tlie present races of organized beings in all instances are pro- 
 duced only by the process of generation; and jf they were anni- 
 hilated, there are no natural operations going on in the world, 
 which can lead us to believe, that by any law of Piature such 
 organized beings could be reproduced. That is to say, we cannot 
 conceive that hydrogen, carbon, oxygen, and azote, with heat and 
 light, (fcc. from what we know of their properties, would ever be 
 able, of their own accord, so to combine as to form a plant or an 
 animal. Hence, when plants and animals were first produced, it 
 is evident that there must have been a power or agent in operation, 
 which has long since discontinued so to operate ; and that this 
 power or agent not only created plants and animals ; but at the 
 same time imparted to them a capability of perpetuating their ex- 
 istence, for a period, at least, commensurate with that state of 
 equilibrium in which they have been placed. Now, whether we 
 consider the power or agent who accomplished all these things, 
 to have been the Deity himself operating immediately, which is 
 most probable ; or whether we consider with some, that He ope- 
 rated by delegated agencies and laws, the result is the same as far 
 as our argument is concerned ; the object of which argument is 
 to show, that the present races of organized beings are somehow 
 or other influenced by the same general laws which appear to 
 regulate inorganic matters. That is to say, organized beings at 
 the present time, are at least as fixed and permanent in their 
 nature, as the state of equilibrium in which they have been placed ; 
 and consequently, no new plants or new animals can, as the world 
 now exists, be imagined to be produced without a new and spe- 
 cific act of creation ; or at least, without an entire change in the 
 standard of equilibrium. 
 
 We have alluded to the commencement of the present order of 
 things, and to a possible state of change in the condition of equi- 
 librium : perhaps it may not be amiss to make a few further re- 
 marks upon these points. That the present order of things most 
 certainly has had a beginning ; and as certainly will come to an 
 end, we cannot doubt ; the questions are, when was this begin- 
 ning ; when will be this end ? Of the end of course we can know 
 nothing : the beginning is less obscure ; and there are indelible 
 impressions left upon the materials and structure of our globe, 
 which throw no ordinary light upon this question. The consi- 
 deration of the changes which our earth has undergone, however, 
 belongs to another department : we shall only observe that these 
 
108 CHEMISTRY. ^ 
 
 changes appear to be of two distinct orders, which have alternated 
 with one another in succession. The first of these orders of 
 changes seems to have been of a slow and gradual kind, and such 
 as might be supposed to take place during a state of things, more 
 or less like the present, and existing for a considerable period. 
 The changes of the second order, on the contrary, have evidently 
 been violent, sudden, and disruptive, of comparatively short dura- 
 tion, and differing exceedingly in degree and in extent. In general 
 they appear to have operated from within ; but whether altogether 
 from internal or from external influences, is unknown to us. Now, 
 it is remarkable that these successive alternations seem each time 
 to have changed the standard of equilibrium ; and that during the 
 state of comparative quietude, or the interval of equilibrium be- 
 tween the convulsions, organized beings have existed, adapted to 
 the exigencies of that particular state of equilibrium ; and which 
 beings must have been successively created : moreover, the later 
 creations gradually approach to those at present in existence. 
 Hence, the change in the standard of organization seems to have 
 been not only simultaneous with the change in the state of equi- 
 librium ; but doth appear to have been progressively raised after 
 each convulsion. Finally, tiie last general catastrophe of the dis- 
 ruptive order was evidently a deluge.* Such are the conclusions 
 which geologists have deduced from a careful survey of that part 
 of the crust of the earth to which they have access; and these 
 conclusions are of the most important kind. In particular, by 
 demonstrating the existence of successive adaptations to different 
 successive states of equilibrium, they place the argument of design 
 in a new light, and add in no small degree to its force. This 
 part of the subject, however, belongs to the geologist, to whom, 
 for the present, we shall leave it. 
 
 Fourthly. The argument of design as connected with the 
 subject of equilibrium above treated of, may be considered yet 
 in another point of view. In this state of equilibrium we have 
 observed that the properties of bodies, as they actually exist around 
 
 • If we juclg'e from what we see going on in nature around us, and from 
 the little tendency there appears to be in tiling's at present to combine 
 into new forms, we must be almost led to the conclusion that the deve- 
 lopement of new elements, as well as of new agents, is necessary to pro- 
 duce new and specific arrangements. May we not then infer that during 
 those periodic convulsions alluded to in tbe text, new elements have been 
 developed, or old ones decomposed into others of a higher and more ele- 
 mentary kind; and that in virtue of the general laws in operation, these 
 new elements have subsequently combined to form series of new arrange- 
 ments ? Of course this supposition is intended to apply only to the means 
 adopted by the Deity to ellect his purpose. The formation and selection 
 of these new elements must in all instances be supposed to result Immedi- 
 ately from his will and agency. 
 
GENERAL ARGUMENTS. 109 
 
 US, are all so subdued and passive in their character, that no one 
 predominates over, or excludes the other. Now, when we re- 
 flect that almost all these bodies are compounds, and when we 
 compare the properties of these compounds with the properties 
 of the elements composing them, it is impossible not to infer, that 
 the properties of the compounds rather than those of the elements, 
 were, at their origin, the objects contemplated. That is to say; 
 in order that the compounds might be perfect, the elements cal- 
 culated to produce them, were created essentially such as these 
 compounds might require, without reference to the secondary pro- 
 perties of the elements tiiemselves ; which were left to be deter- 
 mined as the more general laws of matter might decide. For in- 
 stance, the properties of hydrogen in water, and of chlorine and 
 sodium in common salt, not being required in the economy of 
 nature, the properties of these elements have not been made com- 
 patible with organic existence ; and the whole attention (if such 
 a terra may be applied to the operations of the Deity) has been 
 directed to the properties of the compounds, water and salt. Thus, 
 on the one hand, where required, we have the most striking adap- 
 tation of property; while on the other, where not required, this 
 adaptation of property has not been attended to : nor is this true 
 of water and salt only, but of almost every other compound in 
 nature. Nay, what is more, the incongruities of the whole sys- 
 tem have, with the most consummate skill, been thrown, as it 
 were, among those properties not required. Hence, the arrange- 
 ments of nature viewed in this light, not only exhibit novel evi- 
 dences, but some of the most slrikina: evidences of design that we 
 possess. 
 
 The subject of the mcongruous properties of bodies is one of 
 great interest. We have seen that many of the elementary prin- 
 ciples are poisonous ; and that almost all of them, if liberated from 
 their affinities, and sent abroad in the world, like so many demons 
 let loose, would instantly bring destruction upon the whole fabric. 
 Now, why should such incompatible properties be necessary to 
 the properties of the compounds? Why, tor instance, should the 
 incombustible fluid water contain one of the most combustible 
 principles in nature ? or the mild and innocuous common salt be 
 composed of two elements, which, in their separate state, would 
 instantly destroy life ? Why, do we repeat, are these deleterious 
 properties of the elements necessary to the wholesome condition 
 of tlie compound ? What part do they perform ; or what property 
 do they contribute to, or represent ? These are questions utterly 
 beyond our comprehension, and are likely always to remain so. 
 That these incompatible properties of the elements, however, do, 
 in some way, contribute to the perfection of the compounds, we 
 cannot doubt ; and the only grounds upon which such incompati- 
 
 10 
 
110 CHEMISTRY. 
 
 bilily seems to admit of explanation is, that it results necessarily 
 from those limitations which the Deity has thouirht proper to pre- 
 scribe to his power, and to which he always most rigidly adheres. 
 iMoreover, be the reason what it may, it is evident that these ar- 
 rangements, so immediately calculated to lead to practical difficul- 
 ties, have been the result of choice. For we cannot but believe 
 that an omnipotent Creator, if he had so willed, could have made 
 the elements innocuous, as well as the compounds ; nay, to our 
 limited understanding this would have been the easiest and most 
 natural mode of proceeding. Why then did he choose the appa- 
 rently more difficult course ? Why, to use the language of Paley, 
 but " that he might let in and thereby exhibit demonstrations of 
 his wisdom." Throuirhout nature, the exigencies and incongrui- 
 ties necessarily arising from the arrangements we have been con- 
 sideringf, have given occasion for the display of the most astonish- 
 ing wisdom and power. And instead of that jarring and clashing 
 which might have been expected froin so many conflicting ele- 
 ments, the qualities and quantities of these elements have, upon 
 the whole, been so wonderfully adjusted to each other, that they 
 neutralize and balance each other's evils ; and the general result 
 has been, that all have finally settled down together into that har- 
 monious state of equilibrium before alluded to, so admirably adapt- 
 ed for the existence of organic life. 
 
 Fiftlily. We have hitherto confined our attention to general 
 principles and arrangements ; but the commonest chemical pro- 
 cess may be made to furnish us with some striking proof of the 
 omnipotence of the great Creator. Let us for example consider 
 what happens in a simple and familiar instance of chemical de- 
 composition ; as when a solution of lunar caustic (nitrate of silver) 
 is added to a solution of common salt. In this case, the chlorine 
 of the salt combines with the silver, and produces a curdy pre- 
 cipitate which falls to the bottom ; while the nitric acid combines 
 with the soda, and forms a soluble salt which remains in solution. 
 Now, we showed in a former chapter that the minutest fragment 
 of matter appreciable by our senses, consists of innumerable mole- 
 cules. If therefore we suppose a small quantity, as an ounce, of 
 the lunar caustic, and a proportionate quantity of common salt, to 
 be mixed together ; what countless myriads of molecules, in a 
 portion of time literally inappreciable, must have sought out, and 
 combined each with its fellow, in this simple process ! The hu- 
 man mind absolutely recoils from the contemplation of objects so 
 completely beyond its powers ; for the utmost that we can imagine, 
 must fall almost infinitely short of the reality. Were we, for il- 
 lustration, to conceive every human being at present in existence, 
 to be collected tofrcther into one vast array, and to be all dressed 
 exactly alike, and to perform the same military manteuvre at the 
 
OBJECTIONS TO DESIGN. Ill 
 
 same moment ; we should be probably as far short of the actual 
 numbers of similar molecules, each manoeuvring exactly alike in 
 the above simple experiment, as a single company falls short of 
 our congregated army ! Again, to take another familiar illustration, 
 as the working of a common steam engine; we are assured that 
 in this simple operation, there are more self-repulsive molecules 
 of water always constantly engaged, and conspiring to the same 
 end, than there are of quadrupeds in existence upon the whole 
 surface of the globe ! The above are designed to illustrate the 
 principles of the argument only : the argument itself, like all the 
 preceding is strictly cumulative, and applies more or less to every 
 operation in nature. 
 
 Such is a summary sketch of the wonders developed by che- 
 mistry ; and what an idea do they convey to us of the wisdom 
 and of the power of Him who contrived and made the whole ! Of 
 the capacity of that eternal Mind, who while He directs the uni- 
 verse, at the same time takes cognizance and regulates the move- 
 ments of every individual atom in it ! To whom the inmost nature, 
 and end, and object of every part are familiar ; and of whose com- 
 prehensive designs the whole forms but a single link, the antece- 
 dent and the consequent to which are merged alike in infinity ! 
 
 In the preceding pages we have pointed out a few of those 
 wonderful arrangements, which to common understandings appear 
 to indicate design, and consequently to prove that such arrange- 
 ments are the works of an intelligent and omnipotent Creator. 
 There are however some minds so obtuse, or so strangely con- 
 stituted that they either cannot, or will not admit the force of these 
 arguments, and who consequently deny the evidences of design 
 altogether. The consideration of this part of the subject properly 
 belongs to another department, to which the reader is referred for 
 details ; we shall therefore confine our observations to a brief 
 recapitulation of the leading objections to design, and offer such 
 answers to them as are more immediately furnished by our own 
 subject. 
 
 The objectors to the argument of design may be divided into 
 two classes ; those who denying a First Cause, affect to believe 
 that all the beautiful adaptations and arrangements, we see around 
 us, are the result of what they call the " necessary and eternal 
 laws of nature," and who in fact are Atheists, or rather Pantheists, 
 " to whom the laws of nature are as gods ;" and those who, with- 
 out denying a First Cause, contend that design cannot be /^roi'ef/,* 
 that the arrangements of external nature, as they appear to us are 
 little more than mental delusions ; and that things appear congri^ 
 
112 CHEMISTRY. 
 
 ous and adapted to us, however incongruous they may be in 
 reality, simply because we have nothing else than our own intel- 
 lects with which to compare them. 
 
 To the first class of objectors, we may thus briefly reply. The 
 " laws of nature," or rather our knowledge of them, may be con- 
 sidered as of two kinds ; First, laws founded upon reason or ne- 
 cessity, the phenomena regulated by which laws we cannot con- 
 ceive to be otherwise than what they are ; and laws founded upon 
 eoq) erience on\y , among whose dependant and sequent phenomena 
 we can discover no necessary relation whatever. Now, few, if 
 any, of the " laws of natiiie" can he proved to belong to the first 
 kind ; we know for instance, no reason or necessity why hydro- 
 gen, carbon, oxygen, and azote must combine to form plants and 
 animals ; we only know that they do so combine, but why and 
 how we know not. Hence, as the Atheist cannot ^;?'oi'e his " laws 
 of nature" to have a necessary existence, he has no right to make 
 the assumption. On the other hand, he cannot prove these laws 
 to be eternal ; for experience,, the sole ground upon which his 
 knowledge of them is founded, is decidedly hostile to this supposi- 
 tion, as we have in the next place briefly to show. 
 
 In reasoning from cause to effect in matters of experience, two 
 conditions at least are requisite ; first the efl^ect must be possible, 
 that is to say, must not be opposed in any way to the cause, or to 
 the facts of the argument; and secondly, it must he probable, or 
 in other words, the effect must accord and harmonize generally 
 with the accompanying phenomena. But the atheistical doctrine 
 of the " eternal laws of nature" seems to us to violate one, if not 
 both these conditions. In the first place, as to the facts, or possi- 
 bility of the case. We have seen, that a very superficial obser- 
 vation of the world as it exists, and as it obviously has existed 
 within the limits that its history can be traced, is sufficient to 
 show, that its course at all times has been progressive. That is 
 to say, the world itself before arriving at its present condition, has 
 not only undergone a progressive series of different states ; but in 
 these different states, different "laws of nature" have prevailed. 
 In the second place, putting the previous history of the world out 
 of the question, and judging solely from what we see around us, 
 it appears improbable in the highest degree, that the present va- 
 riable ^x\(\ finite order of things, should constitute a term or link 
 of an uniform and infinite progression. The notion therefore that 
 the " laws of nature" have existed as they now exist from eternity, 
 if not actually impossible, is so exceedingly improbable, that it 
 cannot be admitted for a moment. Hence as these laws cannot 
 be proved to have a necessary existence, or to have existed from 
 eternity as they now are; it becomes more than probable that they 
 
OBJECTIONS TO DESIGN, ETC. 113 
 
 have had a beginning ; and thus the inference of a pre-existent 
 Law-maker, and all its consequences are at once inevitable. 
 
 We come now to consider the second class of objections to the 
 argument of design ; those namely, which are founded on the 
 grounds that design cannot be jji'oved ; and tliat what we call de- 
 sign is little more than mental delusion. We admit at once that 
 everything we know of external nature we know from experience 
 only ; and consequently we admit that what we call design in ex- 
 ternal nature is only very probably design ; that is to say, cannot 
 be proved to be design by any argument founded on reason or 
 necessity. But liaving made this admission, we assert upon the 
 self-same grounds, that our opponents cannot, by any argument 
 founded on reason or necessity, prove that what we call design, 
 is anything else than design ; that is to say, is not design. Now 
 until this be proved the force of their objection may be considered 
 as completely neutralized; while the objection itself becomes thus 
 reduced to the condition of a mere sophism, that leaves everything 
 precisely in the same state as it was at the beginning. 
 
 Having thus briefly disposed of these objections to the argu- 
 ment of design, we finally recur with pleasure to that common- 
 sense view of the subject which we have already contended for, 
 and which we still maintain, viz., that design is independent of 
 the designer ; in other words, that design is design, whether ex- 
 emplified in the works of man or in those of his Maker — a view 
 which has been adopted by the wise and good in all ages — which 
 has all the probabilities on iis side, and which alone, of all others, 
 points out to man his true and natural position among created be- 
 ings. When man, indeed, compares himself with the universe, 
 his own insignificance appears quite overwhelming ; but the ar- 
 gument of design assures him that, insignificant as he is, while 
 he investigates and approves of the order and harmony around him, 
 he is exerting faculties truly god-like — that his reason though li- 
 mited in degree, must be immortal in kind, and thus differ from 
 that of the great Architect of all, only in not being infinite. And 
 hence the proud relationship in which man justly considers him- 
 self to stand with respect to his Maker ! hence the grand source 
 of that longing after a future state, where his knowledge will be 
 consummated, and where he will no longer " see through a glass 
 darkly" — notions at once the result and reward of his reason, and 
 which raise him far above all other animals. 
 
 10* 
 
114 
 
 BOOK II. 
 
 OF METEOROLOGY : COMPREHENDING A GENERAL SKETCH OF THE CONSTI- 
 TUTION OF THE GLOBE ; AND OF THE DISTRIBUTION AND MUTUAL INFLU- 
 ENCE OF THE AGENTS AND ELEMENTS OF CHEMISTRY IN THE ECONOMY 
 OF NATURE. 
 
 In the foregoing chapters, we have endeavoured to convey some 
 idea of the "limits which the Deity has been pleased to prescribe 
 to his own power ;" or in other words, of the properties of the 
 different subordinate agents and elements of our globe, and of 
 their mode of operation. We come now to consider a little more 
 closely the general distribution of these agents and elements ; and 
 the principles upon which this distribution is regulated, so as to 
 produce all the wonderful results which we see constantly going 
 on around us in nature. 
 
 In the present state of the world, as we have already observed, 
 the general tendency of its constituent principles seems to be 
 towards a state of equilibrium or repose. But a very superficial 
 examination of those parts of the earth's crust to whicli we can 
 obtain access, is sufficient to convince us that this quietude has 
 not always existed ; and consequently that the present state of 
 things must have had a beginning. In short the phenomena of 
 geology appear to show, that our earth in its progress, has 
 undergone, alternately, periods of comparative quietude like that 
 in which we now live ; and periods of derangement and convul- 
 sion, in which the preceding stales of quietude and their conse- 
 quences have been more or less subverted, and a new order of 
 things has been induced. To enter furllier into details regarding 
 these changes, however, would be quite foreign to the object 
 of the present volume. It is the business of the Geologist to 
 point out the changes w^hich our earth has evidently undergone 
 before it arrived at its present condition ; to trace the earth as it 
 were from a stale of chaos through all its metamorphoses, whether 
 sudden and convulsive, or slow and gradual ; and to show that 
 all these changes have not resulted from chance, but from the 
 agency of an intelligent Being operating with some ulterior pur- 
 pose, and according to certain laws, to which he had chosen to 
 restrict himself — to demonstrate, in short, that to these very con- 
 vulsions and changes we owe all that boundless variety of sea 
 and of land, of mountain and plain, of hill and valley ; all that endless 
 admixture of rocks, of strata and of soils, so essential to the ex- 
 istence of the present order of things ; without which the world 
 would have been a mass of crystals, or one dreary monotonous 
 
RELATION OF SEA TO LAND. 115 
 
 void, totally unfitted for the present race of organized beings ; 
 and particularly as a residence for man — apparently one great 
 end and object of creation. Such is the business of the geolo- 
 gist ; and where his duties terminate, those of the Meteorologist 
 may be said to begin. To him it belongs more especially to 
 consider the globe in [is present condition of quietude or equili- 
 brium, and the means by which this state of equilibrium is 
 maintained : in particular, to point out the influences of heat 
 and of light, and of the energies allied to them ; to study 
 the laws of the distribution and change of these important agents in 
 the production of climate ; to trace, in short, the effects of these 
 wonderful principles upon the earth, the ocean, and the atmo- 
 sphere, and all the infinite variety of phenomena dependent upon 
 them. 
 
 In so wide and varied a field of inquiry it is not perhaps easy 
 to devise a plan that shall be perfectly unexceptionable. For, as 
 there is no one subject so entirely isolated, as not to be more or 
 less influenced by the rest, w^e scarcely know which to commence 
 with. After a good deal of reflection, we have adopted that ar- 
 rangement which seems to ofler the most natural viev/ of these 
 subjects : and at the same time appears best calculated to illus- 
 trate the design and wisdom of the Great Creator. 
 
 CHAPTER I. 
 
 OF THE GENERAL STRUCTURE OF THE EARTH : PARTICULARLY WITH RE- 
 FERENCE TO THE DISTRIBUTION OF ITS SURFACE INTO LAND AND WA- 
 TER ; AND WITH RESPECT TO ITS ATMOSPHERE. 
 
 Section I. 
 
 Of the General Relations of the Sea and the Land to each 
 
 other. 
 
 Our earth may be considered as made up of materials naturally 
 existing in the solid, the liquid, and the gaseous state, the abso- 
 lute proportions of whicji to each other we cannot even conjecture. 
 Of the mean density of the whole, however, we can form some 
 estimate ; and philosophers have shown that this density lies 
 between five and five and a half, that of Avater being one. We can 
 also form a tolerably precise notion of the relative proportions of the 
 surface occupied by the solid and the liquid materials ; and of the 
 pressure and height of the atmosphere surrounding the whole. 
 
 With the general geographical distribution of land and ocean, 
 
116 METEOROLOGY. 
 
 we take it for granted that all are more or less acquainted. We 
 shall, therefore, confine our remarks chiefly to their relative pro- 
 portions ; which are such, that nearly three-fourths of the earth's 
 surface may be said to be covered with water, while barely one- 
 fourth, of course, must be occupied by dry land. Of this dry 
 land, as is well known, by far the greater part is confined to the 
 northern hemisphere ; while in the southern hemisphere, the 
 Pacific ocean exhibits a nearly continuous surface of water, greater 
 than the whole dry land of the globe put together. According to 
 the estimate of Humboldt, the dry land in the two hemispheres 
 is in the ratio of three to one ; between the tropics in the two 
 hemispheres as five to four ; and without the tropics as thirteen 
 to one ; the preponderance being in the northern hemisphere. 
 
 The height of the dry land above the general level of the 
 ocean is very various ; but its utmost height, as compared with 
 the diameter of the earth, is quite trifling ; and it has been shown 
 that if the whole of the dry land existing were equally distributed 
 over the bottom of the sea, the quantity of water in the sea is 
 amply sufficient to cover it entirely. Hence "dry land can be 
 only considered as so much of the rough surface of our globe as 
 may happen for the time to be above the level of the waters ; 
 beneath which it may again disappear, as it has done at diflerent 
 previous periods."* 
 
 The solid portions of our earth are all made up of various 
 combinations of the elementary principles described in a former 
 chapter. The relative situations these principles occupy in the 
 earth's structure ; the endless proportions in which they exist ; 
 and all the infinite diversity of their properties, it is the business 
 of the geologist and of the mineralogist to inquire into and ex- 
 plain : the observations, therefore, which we have to make on 
 the present part of our subject, will be chiefly confined to the 
 waters of the ocean, and to the atmosphere. 
 
 Section H. 
 
 Of the Ocean. 
 
 The waters of the ocean are not pure, but contain, as is well- 
 known, a variety of saline matters in solution. Indeed, when we 
 reflect upon the immense relative extent and general circumstances 
 of the ocean, we may naturally suppose that its waters will con- 
 tain more or less of every existing soluble principle. By far the 
 most abundant principle, however, in sea-water is common salt ; 
 
 • De la Bcche's Geological Manual p. 2. 
 
OF THE OCEAN. 1 17 
 
 which may be said to constitute, in general, nearly two-thirds of 
 the whole saline matter present. The saline matter lluctuates 
 between three or four per cent ; and the specific gravity of the 
 water varies, according to the proportion of the saline ingredients, 
 from about 1026 to 1030; pure water being supposed to be 1000. 
 The late Dr. Marcet, some years ago, made some interesting 
 experiments on this subject, and the following are the general 
 conclusions which he drew from them : — 
 
 1. That the southern ocean contains more salt than the 
 northern ocean, in the ratio of 1.02919 to 1.02757. 
 
 2. That the mean specific gravity of sea-water, near the 
 equator, is 1.02777; or intermediate between that of the 
 northern and that of the southern hemispheres. 
 
 3. That there is no notable difference in sea-water under 
 different meridians. 
 
 4. That there is no satisfactory evidence that the sea at 
 great depths is more salt tlian at the surface. 
 
 5. That the sea, in general, contains more salt where it 
 is deepest and most remote from land ; and that its sahness 
 is always diminished in the vicinity of large masses of ice. 
 
 6. That small inland seas, though commmiicating with 
 the ocean, are much less salt than the ocean. 
 
 7. That the Mediterranean contains rather larger propor- 
 tions of salt than the ocean.* 
 
 The saltness of the sea, therefore, is considerably influenced, 
 at least at its surface, by the neighbourhood of large rivers, and 
 by permanent accumulations of ice ; and in this way the inferior 
 saltness of small inland seas, particularly in high latitudes, may 
 in general be explained, as most of these inland seas are supplied 
 with comparatively large quantities of fresh water from the rivers 
 flowing into them. On the other hand, the superior saltness of 
 the Mediterranean has been ascribed to the immense evaporation 
 from its surface ; the consequence principally of its being situated 
 in a warmer climate. 
 
 The saline contents of the ocean are of immense importance 
 in the economy of nature. Such indeed is their importance, that 
 it is doubtful whether the present order of things could be main- 
 tained without them. Tiie efl^ects of these saline matters will be 
 more particularly pointed out hereafter. In this place we shall 
 only remark, that by lowering the freezing point of water; and 
 by diminishing its tendency to give ofl* vapour, they perform the 
 most beneficial oflices. Another valuable purpose which they 
 serve may be alluded to here, viz. the greater power of buoyancy 
 which they communicate to water; by means of which the wa- 
 
 * Philos. Trans. 1819. 
 
118 3IETE0R0L0GY. 
 
 ters of the ocean are belter fitted for the purposes of navigation. 
 Nor are these the only uses of the saline matters ; for there is 
 reason to believe that they contribute in no small degree to the 
 stability of the water ; and that an ocean of fresh water would 
 speedily undergo changes that would probably render it incom- 
 patible with animal life ; such an ocean perhaps would even suffer 
 decomposition, that might seriously interfere with the other ar- 
 rangements of nature. 
 
 Lastly, who will venture to assert that the distribution of sea 
 and of land, as they now exist, though apparently so dispropor- 
 tionate, is not actually necessary as the world is at present con- 
 stituted ? What would be the result, for instance, if the Pacific 
 or the Atlantic oceans were to be converted into continents ? 
 Would not the climates of the existing continents, as formerly 
 observed, be completely changed by such an addition to the land, 
 and the whole of their fertile regions be reduced to arid deserts ? 
 Now, this distribution of sea and of land, so wonderfully adapted 
 as it appears to be to the present state of things, depends of 
 course in a great measure upon the absolute quantity of water 
 in the world. While on the other hand, the relative gravity of 
 water as compared with that of the earth, keeps the ocean within 
 its destined limits, notwithstaudino: its incessant motion. Thus 
 Laplace has shown that the world would have been constantly liable 
 to have been deluded from the slightest causes, had the mean den- 
 sity of the ocean exceeded that of the earth ! Hence the adjust- 
 ment of the quantity of water and of its density, as compared 
 with that of the earth, afford some of the most marked and beau- 
 tiful instances of design. 
 
 Section IIL 
 
 Of the Atmosphere. 
 
 That immense body of gaseous matters surrounding our 
 earth, and usually known under the name of the Atmosphere, 
 is essentially composed, as we formerly stated, of two princi- 
 ples, oxygen and azote, in the proportion nearly of one part of 
 oxygen and four parts of azote. 13esides these two gases, the 
 atmosphere also contains a small and perhaps a variable quantity 
 of carbonic acid gas, amounting upon an average to about one 
 part in a thousand of the whole ; and of water in a state of va- 
 pour, likewise a variable quantity, (as will be shown iiereafter,) 
 but usually fiuctuating between one, and one and a half per cent. 
 In addition to these, there are, probably also other matters con- 
 stantly present in the atmosphere ; for as the sea contains a little 
 
OF THE ATMOSPHERE. 119 
 
 of everything that is soluble in water, so the atmosphere may be 
 conceived to contain a little of everything that is capable of as- 
 suming the gaseous form. 
 
 The atmosphere exerts a pressure or weight upon all parts of 
 the earth's surface, on an average equal to about fifteen pounds 
 upon a square inch ; or in other words, equal in weight to a co- 
 lumn of mercury one inch square and thirty inclies high. The 
 well-known instrument the common Barometer ox JVealJicr-glass, 
 consists of nothing more than such a column of mercury, poised 
 or pressed upw-ards into a vacuum, by the weight of tlie atmo- 
 sphere. With the changes constantly taking place in the height 
 of such a column, every body is familiar, and we shall have oc- 
 casion to recur to tliem hereafter; at present it is only requisite 
 to observe, tliat these changes are much less remarkable in tropi- 
 cal than in temperate climates. Thus, between the tropics the 
 barometer usually varies only about one- third of an inch ; while 
 in temperate climates, the changes amount to upw^ards of one- 
 tenth of the whole heio^ht. 
 
 The pressure of the atmosphere decreases as we ascend above 
 the earth's surface ; and for equal ascents, this decrease of density 
 is in what is called geometrical progression. Thus, at three 
 miles in height, the density of the atmosphere is only one-half 
 of what it is at the surface of the earth, or equal to a column of 
 mercury fifteen inches in height ; at six miles, the barometer 
 would stand at one-fourth of its usual height, or seven and a half 
 inches ; at nine miles of elevation, at three inches and three 
 quarters ; and, at fifteen miles, nearly at one inch only. Hence 
 by far the greater portion of the atmosphere is always within fif- 
 teen or twenty miles of the earth's surface ; though tVom various 
 circumstances it lias been inferred to extend from forty to forty- 
 five miles in height. This height, however, must be different in 
 different latitudes ; for the rotation of the earth npon its axis, and 
 the greater and more direct influence of the solar heat npon the 
 earth's equatorial regions, will necessarily cause the atmosphere 
 to be higher there than in the polar regions ; at the poles, the at- 
 mosphere must be lower than over any other part of the earth's 
 surface. These are most important circumstances in the economy 
 of nature, as we shall see hereafter. 
 
 Much difference of opinion has existed among philosophers as 
 to the mode in which the various principles entering into the com- 
 position of atmospheric air are associated ; some maintaining that 
 these principles exist simply in a state of mixture : others consi- 
 dering them as chemically united. We formerly stated that all 
 gaseous bodies, when they combine witfi one another, combine 
 with reference to their volumes ; that is to say, that on3 volume 
 of one gas always combines with one, two, or more similar vol- 
 
120 METEOROLOGY. 
 
 umes of the same, or of another gas, and not with any inter- 
 mediate fractional part. Now, as atmospheric air is composed 
 essentially of one volume of oxygen and four volumes of azote, 
 it is evident, whether its elements be in actual union or not, that 
 it is at least constituted upon strictli/ chemical principles ; 
 whence it follows, that the composition of the atmosphere has 
 not been the result of accident. In this point of view, therefore, 
 atmospheric air may be considered to be as much a chemical com- 
 pound as water, or any other similar body ; and instead of viewing 
 the atmosphere, according to a prevalent notion, as a mere acci- 
 dental and heterogeneous appendage connected with the denser 
 matters by no apparent tie, we may fairly rank the atmosphere 
 among the constituent principles of our globe, and as forming a 
 symmetrical part of the great harmonious whole. 
 
 But although atmospheric air has been thus originally constituted 
 upon chemical principles, and probably owes to this circumstance, 
 in no small degree, its stability; yet the mode in which its con- 
 stituent elements are associated, is very different from that in which 
 the elements of compounds in general are associated. Indeed the 
 constituent elements of atmospheric air do not appear to be com- 
 bined at all ; but to be only mixed, or simply diffused through 
 each other, in the same manner that the minute portions of car- 
 bonic acid gas and of vapour are known to be difiused through 
 the whole atmosphere ; that is to say, according to the laws of the 
 Sfeneral diffusion of graseous bodies M'hich we endeavoured to 
 explain in a former chapter. To this explanation we must refer 
 the reader for details. We shall merely observe here, that the 
 fundamental principle of this explanation consists in the assump- 
 tion, that the molecules of all bodies in the gaseous slate are 
 self-repulsive (or repulsive of one another, in preference to others), 
 for the same reason that in the solid state they are self-attractive 
 (or attract one another, in preference to others). When diiTerent 
 gaseous bodies therefore, are mixed together, t!iey will not assume 
 a position according to their specific gravities, as they might other- 
 wise be expected to do ; but the molecules of each gas will be 
 equally diffused throughout the whole space occupied by the 
 mixture. Hence, one direct and most important effect of the 
 mixed constitution of the atmosphere, is its nearly uniform com- 
 position^ at least within the limits attainable by man — a fact that 
 has been confirmed by innumerable analyses of the air, made in 
 all parts of the world, both at its surface and at the greatest heights 
 hitherto reached. Moreover, this constitution of the atmosphere 
 not only originally produced such uniformity of composition, but 
 it is the cause constantly operating to preserve that uniformity 
 — the grand conservative principle, as it were, preventing any 
 unequal distribution of the constituent elements of the atmosphere, 
 which would speedily prove fatal to organic life ! Were the ga- 
 
OF THE ATMOSPHERE. 121 
 
 seoiis principles composing the atmosphere in ever so slight a 
 state of union, they could not readily difluse themselves through 
 each other; and partial accumulations of one or other of them 
 would be constantly taking place ; but as the atmosphere is at 
 present constituted, if a little more oxygen be consumed in one 
 spot than in another, instantly the deficiency is supplied from the 
 neighbourhood by diffusion, and the equilibrium is scarcely af- 
 fected in a sensible degree. Another curious result of tliis inde- 
 pendent condition of the gaseous principles of the atmosphere is, 
 that of the whole pressure exerted, each principle exerts its own 
 force according to its quantity. Thus, of the thirty inches of 
 mercury supported by the whole atmospheric pressure, the azote 
 sustains 23 j^/q- inches, and the oxygen 6 -^-^^ inches ; while the 
 aqueous vapour sustains only -^^^ inch, and the carbonic acid still 
 less, or only yfo- inch. Hence it is evident that the fluctuations 
 in the height of the barometer, amounting to nearly three inches 
 in our latitude, cannot depend altogether upon the quantity of 
 aqueous vapour in the atmosphere ; for if the whole of this vapour 
 were annihilated, it would scarcely produce a difference in height 
 of half an inch. Attention is now drawn to this fact for purposes 
 that will appear in a subsequent chapter. 
 
 Lastly, had the absolute quantity, or the relative gravity, of the 
 atmosphere been materially different from what they are, the 
 present order of things could not have existed. Hence, the same 
 striking evidences of wise adjustments are displayed in these ar- 
 rangements of the atmosphere, as in those formerly shown to 
 exist with respect to the quantity and gravity of the ocean. 
 
 Before we close the present chapter, let us reflect for a mo- 
 ment upon the great arrangements we have been considering. 
 
 Why has the surface of this earth been divided into land and 
 sea? Why have the land and sea been so adjusted to each other, 
 that their condition and properties hardly admit of change with- 
 out destruction to the whole fabric ? Why has their present 
 stability been so wonderfully secured ! Again, with respect to 
 the atmosphere ; why has there been any atmosphere thrown 
 around this globe ? and why sucli manifest provisions to secure 
 its ubiquity and unvarying constitution ? 
 
 Viewed alone and without reference to organized beings, all 
 these things appear without an object. This globe might have 
 revolved about the central luminary — might have occupied its 
 point in the universe without any " gathering together of the 
 waters," w^ithout any circumambient air. But the scheme of the 
 great Creator extended beyond the mere adaptation of inanimate 
 matter. " Before its foundations were laid," He had destined 
 this earth to teem with life, and throughout has displayed his 
 original design of rendering it a fit habitation for living beings. 
 
 11 
 
122 METEOROLOGY. 
 
 For this purpose and acting at tiie same time, in strict conformity 
 to those laws, by which He had chosen to Uaiit himself. He has, 
 by means of successive convulsions and changes, so contrived to 
 mix and blend the different elements, and finally so to arrange 
 the dry land apart from the sea ; that, taken as a whole, and with 
 reference to the present order of things, their relative proportions 
 will scarcely admit of material change. While, to crown his 
 works, and as it were, the more strongly to evince his design, 
 and his wisdom, He has surrounded the whole with an atmo- 
 sphere, to preserve the homogeneity of which, its principles have 
 been so associated, as to constitute an exception to his usual ope- 
 rations, and even to the general laws of nature ! 
 
 CHAPTER n. 
 
 OF HEAT AND LIGHT THE BIODES OF ESTIMATING THEIR DEGREE, AND 
 
 THE WAYS IN V»'HICH THEY ARE PROPAGATED. OF THE GENERAL 
 TEMPERATURE OF THE CELESTIAL REGIONS, AND OF THE EARTH INDE- 
 PENDENTLY OF THE SUN. 
 
 Section I. 
 Of Heat and Light, and the Modes of estimating their Degree. 
 
 Our sensations are a very imperfect and uncertain measure of 
 temperature, and when we wish to speak with precision on that 
 subject, it becomes necessary to have recourse to other means of 
 comparison. For the sake of the general reader, we shall, there- 
 fore, in the first phice, briefly describe the principles of the con- 
 struction of the Thermometer, the instrument for measuring heat. 
 
 All bodies, as we have shown in a former chapter, become 
 more or less expanded when they undergo an increase of temper- 
 ature. Hence the relative degrees of expansion of a body may 
 be employed as a sort of measure of the degree of heat ; and most 
 of the thermometers employed, act upon this principle. Thus 
 the common thermometer, as is Avell known, consists of a portion 
 of some fluid, generally of mercury, enclosed in a small glass ball 
 furnished with a hollow stem, the narrow bore of which commu- 
 nicates with the general cavity of the ball. We shall suppose 
 the quantity of the mercury, and the size of the ball, to be so ad- 
 justed to each other, that when the instrument is placed in ice on 
 the one hand, and in boiling water on the other, the whole ex- 
 pansion of the mercury between these two fixed points, shall fall 
 within the range of the stem or tube. The points at which the 
 
PROPAGATION OF HEAT AND LIGHT. 123 
 
 mercury stands in the tube, at the freezing and boiling tempera- 
 tures are to be accurately noted; and the intermediate space upon 
 the scale attached to tiie tube, is to be divided into 180 equal 
 parts or degrees ; the freezing point is to be marked 32°, and of 
 course, the boiling point 180° above, or 212°. Such is Fahren- 
 heiVs scale, the one employed in this country, and to which the 
 numbers hereafter mentioned refer. In other countries different 
 scales are made use of; and in France particularly, what is termed 
 the centigrade thermometer is generally adopted. In this ther- 
 mometer the freezing point is marked 0° and the boiling point 
 100. In other parts of the continent Beaimiur^s scale is much 
 used. In Reaumur's the freezing point, as in the Centigrade, is 
 0°, but the boiling point is only 80°. These different gradua- 
 tions are easily convertible, but it is much to be regretted that 
 they exist, as they cause considerable trouble and confusion. 
 
 The instrument employed for measuring the intensity of light 
 is termed a Photometer ; of such an instrument various forms have 
 been proposed, but at present they are all very imperfect. 
 
 Section II. 
 Of the Propagation of Heat and Light. 
 
 The modes in which heat and light are propagated from one 
 body to another, and through the same body, have been already 
 explained, and we need not again enter into details : a brief recital 
 here, however, of the modes in which heat and light are propa- 
 gated, may not be unacceptable to the general reader. 
 
 Heat passes from the sun to the earth by radiation ^ and again, 
 by the same process, it is freely sent off from the surface of the 
 earth into the atmosphere. Below the surface of the earth, heat 
 is propagated in all directions through the solid matter, by what 
 is called conduction. A third mode in which this important agent 
 is extensively propagated in nature, is by the means we have 
 termed convection, or the carrying, "process. Convection is con- 
 fined, of course, to fluids, as water and air. A portion of water 
 or of air being heated above, or cooled below the surrounding 
 portions, expands or contracts in magnitude, and thus becoming 
 specifically lighter or heavier, rises or sinks accordingly; carry- 
 ing with it, the newly acquired temperature, whatever that tem- 
 perature may be. 
 
 Light, at present, is only known to be propagated by radiation. 
 
 By bearing in mind these modes of the propagation of heat and 
 light, the general reader will find no difficulty in understanding 
 what follows. 
 
124 METEOROLOGY. 
 
 Section III. 
 
 Of the Temperature of the Celestial Regions. 
 
 From tlie close and intimate relations between heat and light, 
 and from their almost invariable association as they exist around 
 lis, it seems not very unreasonable to conclude that these agencies 
 are generally associated in nature ; and that wherever one is pre- 
 sent, there the other must be present also. If this be really the 
 case, the innumerable fixed stars, considered to be so many suns, 
 must be supposed capable of diffusing heat as well as light through- 
 out the celestial regions ; and consequently there must be a certain 
 degree of temperature common to the whole. For this reason, 
 and for others that might be mentioned, philosophers have not 
 only inferred the existence of such a common temperature exist- 
 ing throughout the celestial regions, independently of our sun ; 
 but have even attempted to determine its degree. Moreover, it is 
 singular that all the diflerent modes which have been employed to 
 estimate this temperature, concur in showing that it does not differ 
 much from — 58° of Fahrenheit's scale ; that is to say, about 90° 
 below the freezing point of water ; a degree of cold '* not greatly 
 inferior to that at which quicksilver becomes solid, and much su- 
 perior to some degrees of cold which have been produced artifici- 
 ally."* If such a common temperature really exists throughout 
 space, or at least in our planetary system, it must have no incon- 
 siderable influence upon the temperature of the planets generally ; 
 and with respect to our own globe in particular, such a common 
 temperature must operate by diminishing the intensity of the cold 
 around the poles. 
 
 Section IV. 
 
 Of the Temperature of the Interior of the Earth. 
 
 The attention of philosophers has, for some years past, been a 
 good deal directed to the internal temperature of the earth, at great 
 depths, beyond the influence of the sun or of any other external 
 cause. From the earliest times some vague notions of a central 
 heat seem to have existed among mankind ; doubtless, arising 
 from their attention being forcibly drawn to the phenomena of 
 
 • Discovirsc on the Study of Natural Philosophy ; p. 157. By Sir J. F. 
 W. Herschcll. 
 
HEAT OF THE INTERIOR OF THE EARTH. 125 
 
 volcanoes and hot springs ; but it is not till a comparatively late 
 period that the subject has been carefully investigated. It would 
 be quite foreign to our design to enter here into details upon this 
 point ; we shall therefore merely state, that the arguments in favour 
 of the probability of a central heat are — " first, the experiments 
 made in mines, which, notwithstanding their liability to error from 
 various sources, still seem to show, particularly those made in the 
 rock itself, an increase of temperature from the surface down- 
 wards ; — secondly, the existence of thermal springs, wliich are 
 not only abundant among active and extinct volcanoes, but also 
 among all varieties of rocks in various parts of the world ; — 
 thirdly, the existence of volcanoes themselves, wliich are distri- 
 buted over the globe, and present such a general resemblance to 
 each other that they may be considered as produced by a common 
 cause, and that cause, probably, deep-seated ; — and lastly, the ter- 
 restrial temperature at comparatively small depths, which does not 
 coincide with the mean temperature of the air above it."* 
 
 Such is an abstract of the principal arguments which have been 
 brought forward in support of the opinion, that within our earth, 
 even at the present time, there exists a central heat of great inten- 
 sity. As corroborative of the same views, may be mentioned the 
 evidence derived from the characters of the fossil remains both of 
 plants and of animals, found in the colder regions of the woilJ ; 
 which ciiaracters are such as to prove beyond a doubt, that these 
 plants and animals must have existed in a climate much hotter 
 than that in which their remains are found, and indeed, of equal, 
 if not of superior, heat to that of the tropical portions of our earth 
 at this time. Hence it has been inferred, that the temperature of 
 our earth, formerly much above M^iat it is now, has been giadu- 
 ally dissipated into the surrounding planetary regions, and tlius 
 helped to increase the general temperature, above stated, as sap- 
 posed to exist throughout space. Moreover, the same distinguished 
 philosopher,! to whom we are principally indebted for these ob- 
 servations, has attempted to show that the earth has nearly reached 
 its limit of cooling, particularly near the surface. Near the surface 
 the temperature would necessarily decrease much more rapidly 
 than in llie interior ; where, in a globe of the earth's magnitude, 
 the temperature might be supposed to remain nearly unchanged 
 for a very great length of time. He has also attempted to show 
 that the temperature of the surface is still liable to be influenced, 
 by the gradual escape of heat from the interior which even yet 
 seems to be constantly going on ; and that the temperature of the 
 surface is thus somewhat higher than it would be if such a central 
 
 * De la Beche's Geolog-'ical Manual, p. 24, new ed. 
 f Baron Foiu-ier. 
 
 II* 
 
126 METEOROLOGY. 
 
 heat did not exist ; or than if the temperature of the surface of the 
 earth depended only upon the action of the sun. And this brings 
 us to the point at which our subject may be said properly to be- 
 gin, viz. the consideration of the present state of the earth's tem- 
 perature, as liable to be influenced by the presence or absence of 
 the sun, the great source of heat and of life to our system. 
 
 Before proceeding, we may remark, that the details of the sub- 
 ject we have now concluded, fall entirely within the province of 
 the geologist. To him it belongs, as we have already said, not 
 only to trace the wonderful changes which our globe has under- 
 gone in arriving at its present condition, but to point out the beau- 
 tiful adaptations of organic life and structure to the existing cir- 
 cumstances of its various epochs. Considered in this point of 
 view, geology is a subject of the highest interest and importance; 
 and, to use "the words of an eminent Professor, with which we 
 shall finish this chapter, " lends a great and unexpected^aid to the 
 doctrine of final causes ; for it has not merely added to the cumu- 
 lative argument, by the supply of new and striking instances of 
 mechanical structure adjusted to a purpose, and that purpose ac- 
 complished ; but it has also proved that the same pervading active 
 principle manifesting its power in our times, has also manifested 
 its power in times long anterior to the records of our existence. 
 
 *' But, after all," continues our author, " some men, seeing no- 
 thing but uniformity and continuity in the works of nature, have 
 still contended (with, what I think, a mistaken zeal for the honour 
 of sacred truth) that the argument from final causes proves nothing 
 more than a quiescent intelligence. I feel not the force of this 
 objection. In geology, however, w^e can meet it by another di- 
 rect argument ; for we not only find in our formations organs me- 
 chanically constructed, but at diff'erent epochs in the history of 
 the earth we have great changes of external conditions, and cor- 
 responding changes of organic structure ; and all this without the 
 shadow of a proof that one system of things graduates into, or is 
 the necessary and efilcient cause, of the other. Yet in all these 
 instances of change, the organs, as far as we can comprehend their 
 use, are exactly those which were best suited to the functions of 
 the being. Hence, we not only show intelligence contriving means 
 adapted to an end, but at successive times and periods contriving 
 a change of mechanism adapted to a change in external conditions. 
 If this be not the operation of a prospective and active intelligence, 
 where are we to look for it?"* 
 
 * Address delivered to the Geolog-icul Society of London, by the late 
 President, Professor Sedg-wick, 1831. 
 
127 
 
 CHAPTER III. 
 
 OF THE TEMPERATURE OF THE EARTH AT ITS SURFACE, AS DEPENDENT OK 
 
 THE SUN. 
 
 The general temperature of the earth is doubtless regulated by 
 its situation in the universe, and more especially by its position 
 with respect to the sun. To this position, as formerly observed, 
 the properties of its constituent principles have, most obviously, 
 been all adapted with consummate wisdom ; so that, under the 
 circumstances in which they are placed, some are solid, some 
 liquid, others gaseous, according to the purposes they are intended 
 to fulfil in nature. 
 
 But the heat and light derived from the sun are very unequally 
 distributed over the surface of the earth ; and every one is familiar 
 with the fact, that as we recede from the equator towards the north 
 or south, the temperature of the earth's surface gradually dimi- 
 nishes till we arrive at the polar regions. 
 
 Such is the general fact. But the circumstances which conspire 
 to interfere with this gradual distribution of temperature are so nu- 
 merous and so influential, that the actual temperature of a place 
 can be learnt only by observation. Among the circumstances thus 
 more especially aflecting the distribution of temperature, may be 
 mentioned the nature of the surface, whether water or land, — and 
 the situation, whether at a greater or at a less height above the 
 level of the ocean. To these may be added the particular confi- 
 guration and geographical relations of places : such as their aspect 
 to the north or south ; their being sheltered or exposed ; the com- 
 position and nature of the soil, such as its colour and state of ag- 
 gregation, on which depend its powers of absorbing and of radiating 
 heat and light, and of retaining or of parting with humidity, &c. ; 
 also the proximity or absence of seas ; the predominancy of cer- 
 tain winds ; the frequency of clouds, fogs, &c. These, and in- 
 numerable other circumstances, many of which will be pointed 
 out in subsequent chapters, contribute to influence the tempera- 
 tures of particular places, and to render them, in fact, as varied 
 as the places themselves. 
 
 Nor is difference of place the only cause of vicissitude of tem- 
 perature ; every one knows that at the same place the temperature 
 is in a constant state of change. Hence before we can obtain cor- 
 rect notions of the actual temperature of any given place or period, 
 certain expedients are necessary which we have in the first place 
 to consider. 
 
128 METEOROLOGY. 
 
 Section I. 
 Of Mean TeniperafKre. 
 
 If, on any given day, we observe the temperature at the earth's 
 surface, at the commencement of every one of the twenty-four 
 hours, we shall find, as before observed, that at each hour the 
 temperature is different; and we naturally inquire which of all 
 these temperatures is to be chosen in preference, as the one 
 characteristic of the day and place ? The answer to this ques- 
 tion obviously is ; that temperature, ivhatever it may be, ichich 
 is equidistant from the extremes, or, as it is usually termed, the 
 mean temperature of the tvhole. Now this mean temperature 
 may be obtained, nearly, by adding all the results together, and 
 dividing the sum by the number of observations ; thus we arrive 
 at the mean temperature of the day, by adding together the tem- 
 peratures observed at different hours of the day, and dividing the 
 sum by the number of icmperatures. In the like manner by 
 adding together the mean temperatures of every day of a week, 
 or of a month, and dividing the sum by the number of days, we 
 obtain the mean temperature of tiie "week or month ; and so on, 
 by similarly treating the mean temperatures of the monllis, or of 
 any number of years, we obtain the mean temperature of the year, 
 at a given place : and it is to be observed that the greater tlie num- 
 ber of observations the more accurate will be the mean result. 
 
 Lastly, it remains to state that the temperature always under- 
 stood by the Meteorologist (except otherwise expressed) is that 
 of the air near the surface of the earth, as indicated by a thermo- 
 meter cfTectually protected from radiation and foreign influence of 
 every kind. The temperature as indicated by a thermometer fully 
 exposed to solar radiation, and which in its turn is allowed to ra- 
 diate freely in the sun's absence, is altogether a dilTerent thing; 
 and may be imagined to coincide very nearly with the actual tem- 
 perature of the earth's surface, when similarly exposed. The 
 fluctuations of temperature indicated under these circumstances 
 are much greater than those of the air above noticed, though it is 
 probai)Ie that the mean of the whole of such observations, if this 
 mean could be accurately obtained, would differ little from the 
 mean of those of the air. 
 
TEMPERATURE OF THE POLES. 129 
 
 Section II. 
 
 Of the actual Distribution of Temperature over the Globe. Of 
 Isothermal Lines, 4'c. Climate. 
 
 The reader is supposed to be acquainted with the principles of 
 the common division of the surface of the globe into five zones or 
 portions, usually denominated the torrid, the iwo frigid, and the 
 two intermediate temperate zones ; and that generally speaking 
 the poles and the equator present the extremes of temperature 
 upon the earth's surface. Now, in considering the general distri- 
 bution of temperature over the globe, the extreme temperatures 
 naturally claim our attention in an especial manner : we shall, 
 therefore, in the first place, proceed to consider the temperature 
 of the polar and of the equatorial regions. 
 
 Of the Tetnperature of the Poles and of the polar Regions. — 
 The probable mean temperature of the poles has always been an 
 interesting subject of meteorological inquiry. It must be confess- 
 ed, however, that after all that of late years has been done by 
 our enterprising countrymen, much is yet necessary to enable us 
 to arrive at satisfactory conclusions. Thus it has been shown 
 that in attempting to calculate the tem.perature of the North Pole, 
 we shall obtain very dilTerent results by employing the tempera- 
 ture occuring in the old world, and that observed in the new 
 world ; the temperature of the old world indicating the temperature 
 of the pole to be about 10°; while the temperature of the new 
 world indicates it to be considerably below Zero. Hence it has 
 been inferred, that there are two points or poles of greatest cold 
 situated in about the latitude of 80° north, and in longitudes 95° 
 east, and 100° west ; and consequently that the geographical pole 
 of the globe is not the coldest point of the iVrctic hemisphere. 
 Whether this deduction be well founded or not must be decided 
 by future observation. At present the actual temperature of the 
 Polar regions cannot be considered as determined. 
 
 Although we are thus unable to state with certainty the temper- 
 ature of the Polar regions, it may nevertheless be deemed an object 
 of curiosity to know the lowest temperatures that have been no- 
 ticed. Perhaps the lowest authentic observations of temperature 
 we possess are those by Captain Parry at Melville Island. Here 
 the thermometer in the ship was often observed as low as — 50° ; 
 and at a distance from the ship even as low as 55° under Zero. 
 We believe still lower temperatures than these are on record, 
 but probably they are not to be relied on. The greatest degree of 
 cold hitherto produced artificially has been 91° under Zero. 
 
130 METEOROLOGY. 
 
 Of the mean annual Temperature of the Equator. The mean 
 annual temperature of the equatorial, like that of the polar regions, 
 is a meteorological problem of considerable interest. Humboldt, 
 from a very extensive generalization, fixed the mean equatorial 
 temperature at 8 11° ; and the same temperature has been adopted 
 by others. Attempts, however, have been recently made to show 
 that this temperature is 3° or 4° below the truth ; but Humboldt 
 in reply still maintains his former opinion. Since at the equator, 
 only about one-sixth oftlie whole circumference of the globe is dry 
 land, the general equatorial temperature, as actually found to exist, 
 is perhaps lower than upon theoretical principles it ought to be ; 
 and cerlaiuly much below what it ought to be, as deduced from 
 observations made on the continent in the neighbourhood of the 
 equator. Thus the mean temperature of Pondicherry, in latitude 
 11° 55' north is at least 85° ; and if from this temperature that of 
 the equator were deduced according to the common principles, 
 the deduction v/ould of course be much above the truth. Tlie fact 
 is, as in the case of the Polar regions, we do not possess the re- 
 quisite data for determining the equatorial temperature in a per- 
 fectly satisfactory manner. 
 
 As in speaking of the Polar regions, we noticed the lowest 
 degree of temperature which had been observed, perhaps while 
 speaking of the equatorial regions it may not be deemed irrele- 
 vant to notice the highest temperature. Observations, however, 
 of this kind, being principally founded on the incidental notices of 
 travellers, are not, in general, much to be relied on; or are to be 
 considered only as approximations. Thus the thermometer has 
 been recorded at Benares to stand at 110°, 113°, and even 118°. 
 At Sierra Leone, it has been observed, when placed on the ground 
 to indicate a temperature of 138°. Humboldt also gives many 
 instances of the temperature of the surface of the earth, amount- 
 ing to 118°, 120°, and 129° ; and on one occasion he found the 
 temperature of a loose and coarse granitic sand to amount to up- 
 wards of 140°, the thermometer in the sun at the time only indi- 
 cating a temperature of about 97°. 
 
 Of the Temperature of the intermediate Regions of the Globe. 
 Of Isothermal Lines, S,'C. With respect to the temperatures of 
 those parts of the earth between the poles and the equator, it may 
 be remarked, that, except for reference only, the old division, be- 
 fore mentioned, of the earth's surface into zones is now almost 
 entirely superseded by the more precise and natural arrangement, 
 termed tlic Isothermal arrangement. According to this arrange- 
 ment, all the places upon the globe having the same annual mean 
 temperature are classed together ; and lines drawn upon a map 
 through such a series of places, have been termed Isothermal 
 
ISOTHERMAL LINES. 131 
 
 lines, or lines of equal temperature. As niig-lit be expected from 
 what has been ah'eady stated, the courses of these lines are by no 
 means regular. Thus, suppose two travellers set out, the one 
 from London and the other from Paris, and each visit all the 
 places in the northern hemisphere in which the mean annual tem- 
 peratures are the same as in these two cities. It will be found 
 that the lines of their routes, or the isothermal lines of these two 
 cities, will not only not follow the parallels of their latitude, but 
 that they will not be parallel to each other ; and the same may 
 be said to be the case with any other two places upon the globe. 
 Hence, as the isothermal lines are as numerous as the places, 
 and as diversified as numerous, geographers have grouped them 
 into bands or zones. Thus Humboldt (to whom we owe most 
 that has been done on this subject) has divided the northern he- 
 misphere into the following six isothermal bands or zones, viz.: 
 
 1. The zone of mean annual temperature ranging- from 32° to 41°. 
 
 2. - - - - from 41° to 50°. 
 
 3. - - - - from 50° to 59°. 
 
 4. - - - - from 59° to 68°. 
 
 5. - - - - from 68° to 77°. 
 
 6. - - - - from 77° upv/ards. 
 
 The tables given in the appendix contain a general view of Hum- 
 boldt's results. We shall content ourselves with briefly pointing 
 out the approximate course of the most interesting of these lines, 
 viz. the Isothermal line of 32°. 
 
 If we begin to trace this important line from the eastern parts 
 of Siberia in longitude 130° east, we shall find that in this meri- 
 dian it commences nearly in the latitude of 59° north ; whence 
 it makes a gradual bend northwards, and crosses the parallel of 
 60°, nearly in longitude 90°. From this point it still advances 
 to the northward, and crossing the arctic circle in longitude 45° 
 east, arrives at its most northern extremity in about latitude 67^°, 
 longitude 10° east. From this its most northerly limit our line 
 takes a gradual sweep towards the south, recrosses the arctic 
 circle in longitude 15° west, and passing through the north-west 
 of Iceland, divides the parallel of 60° in longitude 42° west. 
 From this spot it proceeds southwards to the latitude of 54°, a 
 little to the north of Table Bay, in Labrador ; gradually de- 
 clining in its course till it arrives at longitude 100° west, in the 
 central parts of the new continent. Hence the Isothermal line 
 of 32°, ranges through a space of 14° or 15° of latitude ; while 
 its western extremity, in the central parts of America, is 5° or 6° 
 nearer the equator than its eastern extremity in Siberia— a cir- 
 cumstance strikingly illustrative of the greater cold of the new 
 

 132 METEOROLOGY. 
 
 continent in the same parallel of latitude. The most remarkable 
 circumstance connected with them is, that as tlio_y approach the 
 equator they gradually become less convex towards the north, so 
 tiiat the Isothermal line of 77° differs but little from a straight line, 
 coincident with the tropic of cancer. 
 
 In the arrangement above described the mean temperatures of 
 the whole year are supposed to be classed together ; but it is ob- 
 vious that the same principle may be applied to any portion of 
 the year, as the extreme winter and summer temperatures. Such 
 classifications are often, as we shall presently see, of great im- 
 portance in enabling us to estimate the characters of a particular 
 country. Thus, lines drawn through places having the same 
 summer and the same winter temperatures, are denominated Iso- 
 theral and Isocheimcd lines; while lines drawn through places 
 having other common temperatures, receive other appropriate 
 names. 
 
 After these general remarks, we proceed to give a summary 
 sketch of the actual distribution of temperature over the northern 
 hemisphere^ which we shall subjoin in the words of Humboldt. 
 The whole of Europe," says this distinguished philosopher, 
 compared with the eastern parts of America and Asia has an 
 insular climate ; and upon the same Isothermal line the summers 
 become warmer, and the winters colder, as we advance from the 
 meridian of Mont Blanc towards the east or the west. Europe 
 may be considered as the western prolongation of the old conti- 
 nent; and the western parts of all continents are not only warmer 
 at equal latitudes than the eastern parts ; but even in the zones 
 of equal annual temperature, the winters are more rigorous, and 
 the summers hotter on the eastern coasts than on the western 
 coasts of the two continents. The northern part of China, like 
 the Atlantic region of the United States, exhibits seasons strongly 
 contrasted ; wliile the coasts of New California and the embou- 
 chure of the Columbia have winters and summers almost equally 
 temperate. The meteorological constitution of those countries in 
 the north-west resembles that of Europe as far as 50° or 52° of 
 latitude. In comparing the two systems of climates, the concave 
 and the convex summits of the same Isothermal lines, M^e find at 
 New York the summer of Rome and the winter of Copenhagen ; 
 at Quebec, the summer of Paris and the winter of St. Petersburgh. 
 At Pekin, also, where the mean temperature of the year is that 
 of the coasts of Brittany, the scorching heats of summer are 
 greater than at Cairo, and the winters are as rigorous as at Upsal. 
 So also the same summer temperature prevails at Moscow, in the 
 centre of Russia, as towards the mouths of tlie Loire, notwith- 
 standing a difference of 11° of latitude ; a fact that strikingly illus- 
 
TEMPERATURE OF THE N. AND S. HEMISPHERES. 133 
 
 Irates the effects of the earth's radiation on a vast continent 
 deprived of mountains. This analogy between the eastern coasts 
 of Asia and America sufliciently proves," continues Humboldt, 
 " that the inequalities of the seasons depend on tlie prolongation 
 and enlargement of continents towards the pole ; on the size of 
 seas in relation to their coasts ; and on the frequency of the 
 north-west winds, and not on the proximity of some plateau or 
 elevation of the adjacent lands. Tlie great table lands of Asia do 
 not stretch beyond 53° of latitude ; and in the interior of the new 
 continent, all the immense basin bounded by the Alleghany range, 
 and the rocky mountains, is not more than from 656 to 920 feet 
 above the level of the ocean." 
 
 The following remarks apply to the temperature of the south- 
 ern hemisphere. 
 
 The general temj)eratures of the northern and of the southern 
 hemispheres are understood to differ very considerably. This 
 difference, however, does not depend upon any material difference 
 in the proportion of heat and light derived from the sun, as will 
 be presently show^n ; but on the very unequal distribution of sea 
 and of kxnd in the two hemispheres. The small quantity of land 
 in the southern hemisphere contributes not only to equalize the 
 seasons, but also to diminish the annual temperature of that part 
 of the globe ; and hence the Polar ice in the southern hemisphere 
 advances more tow^ards the equator than in the northern hemi- 
 sphere, particularly where the Antarctic Ocean is free from land. 
 
 Humboldt has shown, that near the equator, and indeed so far 
 south as 40° or 50°, the correspondent Isothermal lines are in 
 both hemispheres almost equally distant from the poles; and 
 that, in considering only the transatlantic climates between 70° 
 and 80° of west longitude, the mean temperatures of the year, 
 under corresponding geographic parallels, are even greater in the 
 southern than in the northern hemisphere. It is the division of 
 heat, therefore, between the different seasons of the year, rather 
 than the absolute amount of heat during the whole year, that gives 
 a particular character to southern climates, and approximates them 
 generally to the character of insular climates. Thus, in the 
 southern hemisphere, and on the Isothermal lines 46.4° and 50° 
 we find summers which, in our hemisphere, belong only to the 
 Isothermal lines of 35.6° and 40°. The mean temperature is not 
 precisely known beyond 51° of south latitude; yet there is no 
 reason to infer that the Isothermal line of 32° is much further 
 from the south pole, than in the opposite hemisphere, the similar 
 line is from the north pole ; and some circumstances at first sight 
 appear to show that the Isothermal line of 32° is even nearer to 
 the south pole than it is to the north pole ; though these circum- 
 stances are probably deceptive. With respect to the temperature 
 
 12 
 
134 METEOROLOGY. 
 
 of the south pole itself, like that of the north pole, we have no 
 means of forming an accurate estimate. 
 
 Such is a summary account of the general distribution of tem- 
 perature over the northern and southern hemispheres. Now amidst 
 the infinite changes every where going on, there is nevertheless 
 at the same place a certain average state of things which talven to- 
 gether, constitute what is called the climate of the place. Of 
 climate, undoubtedly, temperature is the most important ingredi- 
 ent. But the circumstances, besides mere temperature, whicii 
 enter into the formation of climate, are so numerous and diversified, 
 and their operation, in consequence, is so complicated, that it 
 becomes exceedingly difficult to unravel and display them in a 
 satisfactory manner. The constituents of climate, however, ap- 
 pear to be most naturally divided into two great sections ; viz., 
 those of a primary kind depending vpon the globular Jigiire of 
 the earth ; upon its motion in its orbit, and upon its axis : and 
 those of a secondary, or subsidiary kind, more immediately 
 connected ivith the globe itself, and depending upon the nature 
 of its surface, as composed of Icmd or icater ; or, as connected 
 with its atmosphere. Under these two points of view, -we purpose 
 to consider the subject of Climate, in the following chapters. 
 
 CHAPTER IV. 
 
 OF THE PRIMARY CONSTITUENTS OF CLIMATE .* OR, OF THE TEMPERATURE 
 OF THE EARTH, AS DEPENDENT ON ITS GLOLULAR FORM ; AND ON ITS AN- 
 NUAL AND DIURNAL MOTIONS. 
 
 The distance of the earth from the sun is such, that the solar 
 rays may be supposed to arrive at the earth's surface in a state of 
 parallelism. Now, when parallel rays fall upon a globe, it is ob- 
 vious that any number of such rays falling perpendicularly, as at 
 the equator of our earth, will occupy a very different portion of 
 the surface of the globe, from what an equal number of the same 
 rays will occupy where they fall obliquely, as in our polar regions. 
 Hence, as we recede from the equator towards each pole, heat and 
 light are diflfused over gradually increasing portions of the earth's 
 surface, and thus the intensity of both decreases in a like propor- 
 tion. The exact law of such decrease is well known to mathema- 
 ticians, but need not be here repeated. For our present purpose 
 it is sufhcient to observe, that among the natural causes afiecting 
 the distribution of heat and light in different latitudes, the globular 
 figure of the earth is the principal. 
 
 The second great natural cause of the unequal distribution of 
 
PRIMARY CONSTITUENTS OF CLIMATE. 135 
 
 heat and light over the earth, is the obliquity of the earth's motion 
 in its orbit with respect to the phme ot ils etiualor. From this 
 obUquity it happens that, during the annual revolution of the earth 
 round the sun, every part of ils surface, between the latitudes of 
 23^° north and south from the equator, is in turn exposed to the 
 perpendicular influence of the sun. To this oblique motion of 
 the earth in its orbit we owe the endless variations and vicissitudes 
 of seasons in different latitudes. 
 
 There is also another circumstance connected with the earth's 
 motion in its orbit, which, as partaking of the character of a pri- 
 mary cause, may here be briefly noticed. The earth's orbit is 
 not a circle, but an ellipse, of which the sun occupies one of the 
 foci. Now, it has been so arranged, that in the middle of our 
 winter, the earth is in that part of its orbit which is nearest to the 
 sun. The earth, therefore, is at Christmas actually about three 
 millions of miles nearer to the sun than at Midsummer. Hence 
 it might be inferred that the temperature of the southern hemi- 
 sphere, which during our winter is direcQy exposed to the sun, 
 would be affected by this greater proximity. Such, however, is 
 not the case ; for this greater proximity to the sun is almost ex- 
 actly counterbalanced by the swifter motion of the earth along this 
 part of its orbit. The eccentricity of the earth's orbit, therefore, 
 has little or no influence on ils temperature as at first sight might 
 be supposed.* 
 
 The third o-reat natural cause affectino^ the distribution of heat 
 and light over the earth is the earth's revolution on its axis. To 
 this revolving motion we owe the innumerable minor vicissitudes 
 of temperature, and of light and shade, daily and hourly experi- 
 enced throughout the world. 
 
 Such are the three great natural causes which regulate the dis- 
 tribution of heat and light over our globe. They may be consi- 
 dered as the nece;fsary results of more general laws to which the 
 Great Author of nature has chosen to restrict himself, and to which, 
 
 * Or, perhaps, to quote the more precise explanation of Sir J. Herschel, 
 " The momentary supply of heat received by the earth from the sun varies 
 in the exact proportion of the angular velocity, that is of the momentary 
 increase of long-itude. Hence the greater proximity of the sun in the winter 
 is exactly compensated for by the earth's more rapid motion, and thus an 
 equilibrium of heat is, as it were, maintained. AVere it not for this, the 
 eccentricity of the orbit would materially influence the transition of the 
 seasons ; and the effect would be to exaggerate the difference of summer 
 and winter in the southern hemisphere, and to moderate it in the northern j 
 thus producing a more violent alternation of climate in the one hemisphere, 
 and an approach to perpetual spring in the other. As it is, however, one 
 such inequality subsists, but an equal and Impartial distribution of heat 
 and light is accorded to both." Treatise on Astronomy, p. 198, (Lardner's 
 Cyclopaedia). 
 
136 METEOROLOGY. 
 
 as usual, He most rifridly adheres. Why, among the numerous 
 possible moans by wliich heat and light might have been, and in 
 other instances, are distributed from a central sun over a distant 
 planet, these regulating causes have been selected for our earth, is 
 absolutely unknown to us. That this selection has been made 
 with some ulterior view we cannot hesitate to beheve ; and one 
 such view or purpose may have been to demonstrate to us His 
 wisdom and His power, by the methods cliosen for obviating the 
 difHculties necessarily resultinff from these primary arrano-ements. 
 In other planets, M-here other primary arrangements for the dis- 
 tribution of heat and light have been adopted, there are probably 
 other modes of obviating the difliculties arisinsf from them. Of 
 such arrangements we can form no conception ; but to the inhabi- 
 tants of these planets, they are doubtless an equal evidence of the 
 wisdom and the power of the Deity. 
 
 CHAPTER V. 
 
 OF THE SECONDARY OR SUBSIDIARY CONSTITUENTS OF CLIMATE : COMPRE- 
 HENDING A SKETCH OF THOSE CIRCUMSTANCES CAPABLE OF INFLUENCING 
 CLIMATE WHICH ARE MORE IMMEDIATELY CONNECTED WITH THE SUR- 
 FACE OF THE GLOBE, AS CONSISTING OF LAND OR WATER ; OR W^HICH ARE 
 CONNECTED WITH THE ATMOSPHERE. 
 
 In the preceding chapter we have alluded to the difhculties or 
 exigencies necessarily arising from tlie modes in which heat and 
 light are distributed over our globe ; and of these, before we pro- 
 ceed, it may be proper to specify some of the most striking. 
 
 Had the heat and liofht derived from the sun to the earth not 
 been in any way moditied, the equatorial and the polar regions 
 would have been alike inaccessible to organic life. The heat with- 
 in the tropics and the cold towards the poles, would both have been 
 destructive ; while the intermediate regions would have been ex- 
 posed to a constant succession of violent and sudden alternations 
 of temperature, that would have rendered the present state of things 
 no less an impossibility. In order, therefore, to render this earth 
 an appropriate dwelling-place for such beings as at present occupy 
 its surface, it was necessary that these extremes and sudden vicis- 
 situdes of temperature should be in some way diminished and al- 
 leviated. Accordingly these objects have been effected with the 
 most consummate wisdom. Indeed, some of the most splendid 
 instances of design in nature are offered by those subsidiary 
 arrangements, by which the difficulties necessarily arising from 
 the primary arrangements are obviated or mitigated; and by 
 which the greater portion of the earth's surface has been made ac- 
 
SECONDARY CONSTITUENTS OF CLIMATE. 137 
 
 cessible to organic beings of the same general character. These 
 subsidiary arrangements it will be our business to explain in the 
 present chapter. 
 
 The secondary or subsidiary constituents of climate naturally 
 divide themselves into two great sections; viz., those connected 
 with the surface of the globe, as composed of land or water ; 
 and those connected ivith the atmosphere. 
 
 In the following sketch of these constituents of climate we have 
 endeavoured as usual to elucidate principles rather than to enter 
 into details ; and, as far as is compatible with a general and popular 
 view, have attempted to point out the m.odes in which the laws of 
 light and heat, described in the first Book, operate, so as to pro- 
 duce the phenomena of climate. 
 
 Section I. 
 
 Of the secondary Constituents of Climate, immediately connected 
 with the Surface of the Globe ; and depending on the Nature 
 of that Surface as composed of Land or PFater. 
 
 In attempting to illustrate the operation of the laws of heat and 
 light in the formation of climate, we shall follow the order nearly 
 in which these laws were discussed in the previous chapters ; that 
 is to say, we shall first consider the influence of heat and light as 
 depending on their latent and decomposed forms ; and afterwards 
 their influence as depending on their radiation, conduction, and 
 convection. 
 
 In the prosecution of this difficult inquiry, the first circumstance 
 which naturally claims our attention, is the absolute quantity of 
 heat and light derived from the sun to the earth. 
 
 I. Of the Proportion of Solar Heat and Light that actually 
 arrives at the Surface of the Earth. Of the absolute quantity of 
 heat and light derived from the sun to our globe we have no means 
 of forming an exact estimate. M. Pouillethas attempted to show 
 that the amount of heat annually received by the earth from the 
 sun, is equal to that which w^ould be required to melt a stratum 
 of ice nearly forty-six feet thick, and covering its whole surface.* 
 This estimate, however, is to be viewed only as a rude approxi- 
 mation. The difficulty lies not only in the impracticability of form-" 
 ing precise notions of the heat and light, which actually arrive at 
 any given place in a given time ; but in the utter impossibility of 
 forming even a conjecture of those portions, which become latent 
 or are otherwise lost in the passage of the solar rays through the 
 
 * Elemens de Physique experimentale etde Meteorologie, torn. ii. p. 704, 
 
 13 * 
 
138 METEOROLOGY. 
 
 atmosphere. The following observations will give some idea of 
 the absolute quantity of liglit which reaches the earth; but it is 
 proper to apprize the reader, that the results stated are to be con- 
 sidered as liable to much uncertainty. Nor do we know whether 
 they are equally applicable to heat, which, though it obeys laws 
 somewhat analogous to those of light, may nevertheless have its 
 own peculiar laws. 
 
 A vertical ray of light, in its passage through the clearest air, has 
 been calculated to lose at least a fifth part of its intensity before it 
 reaches the earth's surface. From this cause, and from the actual 
 condition of the atmosphere, it has been estimated that under the 
 most favourable circumstances, of a thousand rays emanating from 
 the sun, only 378 on a medium, can penetrate to the surface of 
 the earth at the equator, 228 at the latitude of 45°, and 110 at the 
 poles ; while in cloudy weather these several proportions are a 
 great deal less.-^ 
 
 At present, our attention is solely directed to those portions of 
 heat and light which thus make their way to the earth's surface. 
 On those portions retained in the atmosphere we shall offer a few 
 remarks hereafter. 
 
 2. Of the Distribution of Heat and Light over the Earth''s 
 Surface in the latent and decomposed Forms. The distribution 
 of heat and light in the latent state over the surface of the globe, 
 probably follows laws nearly similar to those of the distribution 
 of sensible heat and light formerly mentioned; that is to say, the 
 quantity latent, like the quantity sensible, diminishes from the 
 equator toward the poles. On tTiis subject, however, we want 
 the necessary data, even for forming an opinion, much less for de- 
 termining the amount and the exact law of distribution ; all of 
 which must be left for future inquirers. But of the infinite im- 
 portance of the latency of heat, in the economy of nature, the fol- 
 lowing brief remarks will serve to convey some notion. 
 
 Let us take the familiar instance of water, than by which im- 
 portant fluid, the influence of the latency of heat cannot perhaps 
 be more strikingly exemplified. We formerly showed that the 
 temperature of water in becoming solid on the one hand, and ga- 
 seous on the other, makes, as it were, a pause ; and that these 
 changes never take place abruptly. The consequence of this ar- 
 rangement is, that ice and vapour are formed slowly and gradu- 
 ally, and as slowly and gradually again become water ; while 
 sudden transitions from one state to the other are thus entirely pre- 
 vented. Were it not for this beautiful provision, we should be 
 constantly liable to inundations, and other inconveniences, that 
 would absolutely have rendered the world uninlrabitable. It is 
 
 • Article Climate in the Encyclopaedia Britannica. 
 
DISTRIBUTION OF ELECTRICITY AND MAGNETISM. 139 
 
 impossible, therefore, to reflect upon the arrangement itself, or 
 upon the means by which it has been effected, without being im- 
 pressed with the most profound admiration, not only of the wis- 
 dom of the Great Designer of the whole, but of his goodness and 
 benevolence. 
 
 The distribution of heat and light in the decoinposed forms, like 
 the other conditions of these great principles, decreases from the 
 equator towards the poles. We formerly alluded to the opinion 
 that heat, whatever it may consist of besides, appears occasionally 
 to be convertible into the electric and magnetic energies. This 
 conversion, under certain circumstances, may be true of sensible 
 heat ; but heat, in the latent or combined form, is perhaps most 
 liable to be so converted. Without pretending to offer any opi- 
 nion, one way or the other, on this view of the nature of heat, we 
 shall, nevertheless, adopt it for the sake of convenience, and shall, 
 therefore, next consider the subject. 
 
 Of the Cicnercd Distribution of Electricity and Magnetism 
 over the Earth. The recent discoveries on the connection of elec- 
 tricity and magnetism, formerly described, have thrown much light 
 on the distribution of these important agencies over the globe ; and 
 the present extent of our knowledge regarding them will be un- 
 derstood by the general reader from the following summary. 
 
 Every one is familiar with the ordinary phenomena of a mag- 
 netic needle freely suspended, and with its tendency to assume a 
 position more or less approaching to parallelism to the earth's 
 axis ; that is to say, that all over the world it points nearly north 
 and south. Most persons, probably, are also acquainted with the 
 phenomenon termed the dip or inclination of the magnetic needle : 
 thus, in the latitude of London, a needle exactly poised and freely 
 suspended, instead of assuming a horizontal position, will settle 
 at an angle of 70°, the north pole being downwards. If we carry 
 such a needle southwards, towards the equator, we observe that 
 the dip gradually diminishes ; till at a certain point, nearly coin- 
 ciding with the earth's equator, it has no dip at all, but assumes a 
 perfectly horizontal position. A.s we still proceed towards the 
 south, the dip again makes its appearance, but in an opposite di- 
 rection, the soutli pole being now next the earth's surface. To 
 understand the reason of this dip of the magnetic needle and of 
 its general direction, we have only to consider that the earth itself 
 is a magnet, the poles of which are situated beneath its surface. 
 The directive property of the needle is owing to these poles ; and 
 when the needle is on the north side of the equator, the north 
 pole of the earth having the greatest effect, the needle is attracted 
 downwards, towards the north pole ; hence, exactly over the pole 
 the needle would be vertical. Similar phenomena happen in the 
 southern hemisphere ; but here the south pole predominates, and. 
 
140 METEOROLOGY. 
 
 of course, depresses the corresponding pole of the needle ; while, 
 at the magnetic equator, from the equal action of both poles, the 
 needle will assume an exactly horizontal position. It may be re- 
 marked, that neither the magnetic poles nor the magnetic equator 
 coincide exactly with those of the earth; and that this non-coin- 
 cidence is owing to, or rather constitutes, wliat is termed the 
 variation of the needle ; which is not only different in different 
 parts of the world, but appears to be liable to periodical differences 
 in the same place, at present not well understood. Such are the 
 principal phenomena of the magnetic needle as demonstrative of 
 the earth's magnetism, and which we shall now attempt to illus- 
 trate a little further. 
 
 We have mentioned, that the earth may be considered as a 
 great magnet. Now, we have formerly shown that when a mag- 
 netic needle is in its natural position of north and south, there 
 exist electri^tal currents in planes at right angles to the needle, 
 descending on its east side, passing under it from east to west, 
 and ascending on its west side. Hence, we must suppose cur- 
 rents of electricity to circulate within the earth, more especially 
 near its surface, and to be constantly passing from east to west, 
 in planes parallel to the magnetic equator ; which electrical cur- 
 rents, if such can be demonstrated to exist, will in their turn com- 
 pletely account for the magnetic directive property of the earth. 
 The next question is, therefore, how far we are justified in as- 
 suminfif the existence of such electric currents within the earth ? 
 
 We have already alluded to the opinion that heat occasionally 
 passes into the electric and magnetic energies ; an opinion which 
 some consider to derive much probability from the phenomena of 
 what has been termed thermo-electricity ; that is to say, electri- 
 city (and magnetism) developed by the unequal distribution of 
 heat through bodies. Now, whether the phenomena of thermo- 
 electricity actually depend on the decomposition of heat, latent or 
 sensible, or upon any other cause, is of little importance; the 
 phenomena tliemselves are well established, and they seem to 
 account, in the most satisfactory manner, for the general distri- 
 bution of electricity and magnetism over the earth. The explana- 
 tion is this : the earth during its diurnal motion on its axis from 
 west to east, has its surface successively exposed to the solar rays 
 in an opposite direction, or from east to west. The surface of the 
 earth, therefore, particularly between the tropics, will be heated 
 and cooled in succession, from east to west, and currents of elec- 
 tricity, on thermo-electric principles, will at the same time be 
 established in the same direction : now these currents once esta- 
 blished from east to west, will, of course, give occasion to the 
 magnetism of the earth from north to south. Hence the magnetic 
 directive power of the earth, in a direction nearly parallel with its 
 axis, is derived from the thermo-electric currents, induced in its 
 
DISTRIBUTION OF COLOURS. 141 
 
 equatorial regions by the unequal distribution of heat there pre- 
 sent, and depending principally on its diurnal motion. 
 
 These recent and beautiful discoveries show, in the most 
 striking manner, that the operations of nature are more extraor- 
 dinary, and indicate more of simplicity and wisdom of design in 
 proportion as they are better understood. By what simple expe- 
 dients, when known, are those wonderful phenomena of the 
 earth's electricity and magnetism produced, which formerly ap- 
 peared so anomalous and perplexing ! And what encouragement 
 do these discoveries hold out to us, with respect to future disco- 
 veries, that may throw still further light upon the operations of 
 the Great Architect of the universe. 
 
 Of the Distribution of Light in the decomposed Form over 
 the Globe. Every one is familiar with the general fact, that the 
 most splendid exhibitions of colours of every description are dis- 
 played in the warmer climates ; and that the tints of natural objects, 
 generally speaking, become more sad and faded as we approach the 
 colder regions, till they merge into the white of the polar snows. 
 Most persons, also, are aware of the well known circumstances 
 attending the total abstraction of light from plants and animals, 
 and that they thus become more or less white or etiolated. 
 Hence, we need scarcely do more than remind the reader, of 
 what must be already familiar to him, viz., that the decided 
 colours of tropical productions of every kind, whether we con- 
 sider the gaudy plmnage of the birds, of the variegated adornment 
 of the fishes and insects, &;c., are so striking, as to be quite cha- 
 racteristic of these productions. In the higher latitudes, also, 
 where the contrast between the summer and winter seasons is 
 very great, the colours of some animals vary with the seasons ; 
 being in the summer generally of some dark hue, but in the 
 winter nearly white ; while still further, in the polar regions 
 all is more or less white, and the natural covering of the earth, 
 the snow, is the whitest body in nature. Putting out of sight 
 the great importance of the colours of objects, which will fall 
 more naturally to be spoken of hereafter ; it may be remarked 
 here, that colours have usually been considered as offering to 
 us one of the most striking instances of the benevolence of the 
 Deity. Colours are universally agreeable to mankind ; and 
 the most incurious and ignorant are attracted by, and delighted 
 with, sliowy exhibitions of them. Now, all this pleasure is 
 the gratuitous git't of the Creator, and places his benevolence in 
 the strongest possible point of view. There was no reason why 
 man should have distinguished colours at all, much less have 
 been delighted witli them : but what is the fact? not only are we 
 gifted with organs exquisitely sensible to the beauty of colours ; 
 but, as if solely to gratify this feeling, the whole of nature, from 
 
142 METEOROLOGY. 
 
 the liighest to the lowest of her productions, forms one gorgeously- 
 coloured picture, in which every possible tint is contrasted or as- 
 sociated in every possible manner. Is there a iiuman being who 
 can witness the splendid colouring of the atmosphere above him by 
 the setting sun ; who can witness the beauty and endless variety 
 of tint displayed by every object of the landscape around him, 
 down to the minutest insect or flower or pebble at his feet ; who 
 is conscious of the pleasure he derives from these objects, and 
 who reflects that this pleasure was not necessary to his existence, 
 and might have been withheld ? Is there we ask, a hum.an being 
 who duly considers all these things, and who \v\\\ dare to assert 
 that the Beins: who made them all is not benevolent? 
 
 3. Of the Laws of Absorption^ Radiation, and Reflection of 
 Heat and Light. — These laws as applied to the earth generally, 
 are at present but very imperfectly understood. The following 
 remarks will serve to convey some idea of the little we know on 
 the subject. 
 
 The reader will bear in mind what was formerly stated, that 
 the absorbing power of bodies with respect to heat (and per- 
 haps light also) is directly as their radiating power, and inversely 
 as their reflecting power. Such is the general opinion ; and, as 
 far as solar heat and light are concerned, this opinion appears to 
 be well founded ; but we shall see presently that there are strong 
 reasons for suspecting that the radiating power does not always 
 follow the same law as the absorbing power. In the mean time, 
 however, we shall proceed to state what has been advanced on 
 these points. 
 
 Mr. Daniell has attempted to show that the absorption and ra- 
 diation of solar heat increase as we proceed from the equator to- 
 ward the poles. Thus, in a tropical climate, and under a vertical 
 sun, the greatest extent of the difference between two thermome- 
 ters, the one covered with black wool, and exposed to the direct 
 rays of the sun, in order that it may absorb to the utmost the in- 
 cident heat, and the other, uncovered in the shade, is no more 
 than about 47° ; while two thermometers, similarly circumstanced, 
 in the middle of summer, in London, give a difference of G5° ; 
 and in the Arctic regions the diflerence often amounts to 90° at 
 least: so that in the Arctic regions there is twice as much heat 
 and \\^\\i absorbed under similar circumstances, as there is in the 
 tropical regions. The same gentleman has also attempted to 
 show (what might have been inferred indeed from the assumed 
 relation between the absorption and radiation of heat and light 
 above mentioned), that that the radiation of iieat from the errlh's 
 surface obeys similar laws ; that is to say, that the quantity radi- 
 ated from the earth increases from the equator toward the poles. 
 Laws somewhat analogous, and which, when they^ are better un- 
 
ABSORPTION, ETC. OF HEAT AND LIGHT. 143 
 
 ilerstood, will probably throw much information upon these phe- 
 nomena, seem to hold with respect to light. Thus we formerly 
 menticned tliat when a ray of light falls upon fluids, transparent 
 bodies, or metals, the quantity reflected increases with the angle 
 of incidence reckoned from the perpendicular; while the quantity 
 absorbed of course decreases in the same proportion : but that on the 
 contrary when a ray falls upon ivhite opaque bodies, the quantity 
 reflected decreases as the angle of incidence increases ; while, of 
 course, the quantity absorbed, increases in the like proportion. 
 Hence if heat follows the same law, it is evident that the quantity 
 of heat absorbed by the earth from the solar rays, must increase 
 from the equator towards the poles; that is to say, as the angle 
 of their incidence increases, as Mr. Daniell has attempted to show. 
 It is proper, however, to observe that Mr. Daniell's views have 
 been called in question, and that some late observations made in 
 liiffh latitudes do not entirely corroborate them.* We have al- 
 luded to the subject merely with the view of drawing the atten- 
 tion of Meteorologists to it as one of great interest and curiosity, 
 and as one by no means at present understood. There is every 
 reason to believe that the absorption (and perhaps the radiation) 
 of heat and light, under some of its modifications, are much in- 
 fluenced by polarization, and consequently by certain angles of 
 incidence and reflection ; and that diese circumstances, in conse- 
 quence, have much to do with the distribution of heat and light, 
 particularly in the higher latitudes, where they may exert no 
 small influence upon organized beings. The above observations 
 seem to point to the existence of certain general laws, which no 
 doubt hereafter will be elucidated. 
 
 In noticing the influence of different colours on the absorption 
 and reflection of heat and light, we stated that black and dark 
 colours generally absorb most and reflect least ; and vice versa, 
 that white and li^ht colours, reflect most and absorb least ; and 
 we are now come to illustrate this interesting subject, and to con- 
 sider the following questions. — Why does whiteness prevail in 
 the Polar regions ? Why, for instance, is snovv white ? On the 
 contrary, why are all sorts of dark and decided colours met with 
 in the tropical climates, except whiteness, which is comparatively 
 rare? Might not snow have been black instead of white; which 
 
 * We allude here to the observations made in those regions, and given 
 in the appendix to Captain Franklin's Second Journey, by Dr. Richard- 
 son, Captain Back, and Lieutenant Kendal. In these observations Dr. R. 
 states that the radiation was much stronger in the spring months, ivhen 
 the ground was covered with snow, than in the summer months, when the 
 altitude of the sun was greatest. Dr. R. ascribes this greater radiation 
 to the greater clearness of the air at these seasons, but were there no 
 other reasons ? 
 
144 METEOROLOGY. 
 
 was just as likely if its colour had been the result of accident ? 
 or might not wliiieness have been predominant under the equator? 
 Perhaps the best mode of answering these questions, and of 
 placing the subject in a striking view, is to examine what would 
 have been the consequence, if whiteness had prevailed under the 
 equator, and blackness at the poles. 
 
 As heat and light are supposed to obey nearly the same laws, 
 as far as absorption, radiation, and reileclion arc concerned, it is 
 obvious that if white had prevailed in the tropical climates, almost 
 all the solar lieat and light, instead of being absorbed, would have 
 been reflected. The consequence of this refleclion would have 
 been, that the accumulation of heat and the glare of light in the 
 lower regions of the atmosphere, near the surface of the earth, 
 would have been intolerable, and would have rendered these re- 
 gions quite uninlia])itable, at least by the present race of beings. 
 The surface of the earth, also, though it would have been heated 
 slowly, would have been overlieated in time ; and at length would 
 probably have become so very hot, from its comparatively low radi- 
 ating powers, tliat the heat could not have been borne. As it is, the 
 heat and light of the sun are absorbed readily, and as freely given 
 off* again by radiation ; or perhaps the heat, like the light, is de- 
 composed ; and thus the whole is preserved in that comparatively 
 moderate and nicely balanced state, which renders even the hot- 
 test parts of the earth inhabitable. 
 
 On the other hand let us consider for a moment v/hat would 
 have been the consequences if snow had been black, or in other 
 words, if blackness had prevailed in the Polar regions. In this 
 case, all the little light and heat that reach tliem would have been 
 absorbed, and the effect would have been darkness, more or less 
 complete. From the rapid melting also of the snow on the least 
 exposure to heat and light, we should have been constantly liable 
 to inundations. Thus the whole of the Polar regions of the earth 
 would have been one dark and dreary void, inaccessible to organic 
 life. But by the present arrangement, all these consequences 
 are obviated. The white snow absorbs a certain portion of light 
 and of heat (by a beautiful provision more as the angle of inci- 
 dence increases ?) while so much light is reflected as is useful, 
 and no more.* Thus the adjustment of the colours of bodies to 
 
 * The reader will observe that, under ordinary circumstances, ivhite 
 reflects most and of course absoi-bs and radiates least solar heat and fig-ht ; 
 but if the above remarks on lig-lit be well-founded, the absorption of light 
 (and heat i*) by white bodies increases with the angle of inciclence. Now, 
 as nothing of this sort is known, or can be well conceived to happen, with 
 respect to radiation, the doubt expressed at the beginning of this section 
 arises, viz., whether under all circumstances, the radiating and absorbing 
 powers of bodies obey similar laws, even as far as the solar rays are con- 
 
PROPAGATION OF HEAT BY LAND. 145 
 
 tlie circumstances in which they are placed, constitutes an exam- 
 ple of tlie expedients hy which those minor inconj^ruities are ob- 
 viated, that are necessarily incidental to the modes in which heat 
 and light are distributed over the globe ; and presents altogether 
 one of the most obvious and beautiful instances of design connected 
 with the agency of heat and light. 
 
 Lastly, it may be worth while to draw the attention of the 
 reader to the strikingcontrast displayed between the ponderable and 
 imponderable forms of matter, as to the ease with which they are 
 decomposed, and the modes in which they exist in nature. 
 
 We have seen that to preserve the homogeneity and integrity 
 of ponderable bodies, as of water and air, elaborate arrangements 
 have been adopted, evincing the most extraordinary design and 
 wisdom ; because the decomposition or derangement of water and 
 air would at once prove destructive to organized beings. But, to 
 preserve the homogeneity of heat, and particularly of light, no 
 such care is shown, because no such care was particularly neces- 
 sary. The decompositions of these agencies, therefore, are per- 
 mitted to take their natural course; and by an admirable provi- 
 sion, so far are colours, magnetism, Sic. from being injurious to 
 us, that they constitute one of the chief sources of our knowledge 
 and happiness ! 
 
 4. Of the Conduction of Heat below the Earth'' s Surface on 
 Land, The soil, from a few inches to a foot or more below the sur- 
 face, participates very much in the fluctuations of the surface tem- 
 perature. In general, perhaps, it may be stated, that the temperature 
 of the surface of the eartli is a little above that of the incumbent at- 
 mosphere by day, and below it by night ; though much will de- 
 pend in this respect upon the nature of the soil, on its radiating 
 and conducting powers, and on a multiplicity of other conditions 
 that will readily occur to the reader. At a certain distance, how- 
 ever, below the surface, and varying with tiie latitude and other 
 circumstances, there must be a determinate stratum, where the 
 temperature is uniform, or nearly so, throughout the year. Ex- 
 periments on this subject are very limited ; but there is reason to 
 believe, that tlie temperature of this invariable stratum coincides 
 nearly, with the mean annual temperature of the place ; and that 
 its depth below the surface, in different latitudes, varies between 
 forty and eighty feet. The reader need scarcely be reminded, 
 that the well known uniformity of the temperature of cellars and 
 
 cerned. The absorption and radiation of heat of low intensity, and un- 
 accompanied by lig"lit, seem to depend more upon tiie nature of the sur- 
 face than upon colour. It must be admitted, however, that at present a 
 great deal of obscurity hang's over the whole of this subject. 
 
 13 
 
146 METEOROLOGY. 
 
 caves, depends chiefly upon the circumstances we are now con- 
 sidering. As an instance of the uniformity of temperature in 
 such places, it may he mentioned, that a thermometer placed in 
 the caves under the observatory in Paris, at a depth of about 
 eighty-five feet below the surface, has, during fifty years, scarcely 
 varied more than a quarter of a degree from 1 r82° of the centi- 
 grade scale ; equal very nearly to 53|° of Fahrenheit. 
 
 A few experiments have been made to determine the variation 
 of the temperature, throughout the year at different depths from 
 the surface, dov/n to the invariable stratum ; and the following is 
 a summary of the results, which, perhaps, may be considered as 
 generally applicable to the northern hemisphere. 
 
 In the month of August the temperature of the ear'h goes on 
 decreasing in nearly a uniform manner, from a little below the 
 surface to tlie stratum of invariable temperature. In the month 
 of September the temperature is nearly uniform to fifteen or 
 twenty feet below the surface ; beyond which depth the temper- 
 ature decreases a little and slowly to the stratum of invariable 
 temperature. During the months of October and November the 
 temperature increases from the surface to the depth of fifteen or 
 twenty feet ; and below this point it remains nearly uniform to 
 the invariable stratum. During December, January, and Feb- 
 ruary, the temperature, being at its minimum upon the surface, 
 increases in a manner nearly uniform, downwards to the invaria- 
 ble stratum. During March and April there is a rapid decrease 
 of temperature to the depth of one or two feet ; below this depth 
 the temperature decreases less rapidly ; and still lower, the tem- 
 perature increases a little. During the months of May, June, 
 and July, the temperature being at its maximum, at the surface, 
 decreases downwards, but less rapidly and to a greater depth ; it 
 then begins to increase a little till it attains the temperature of the 
 invariable stratum. The rapidity and degree, however, with 
 which these changes lake place, as well as the changes themselves, 
 appear to fluctuate very considerably not only in diflerent places 
 under the same Isothermal line, but in the same place in different 
 seasons. 
 
 Since heat is propagated through the soil by conduction, of 
 course it is propagated in all directions. Hence, it may be sup- 
 posed to move laterally as well as downwards ; and, generally 
 speaking, the temperatures of contiguous spots probably tend to 
 equalize each other. But upon the whole, the influence of the 
 lateral propagation of heat through the solid parts of the earth, 
 must be very limited. 
 
 5. Of Ike Propas^aflnn of Heat and Light beloio the Earth'' s 
 Surface ui Wafer. VV-jter is a very imperfect conductor of heat 
 in the usual acceptation of the term. Thus, almost any degree of 
 
PROPAGATION OF HEAT, ETC, BY WATER. 147 
 
 heat may be applied, for a considerable time, to the upper surface 
 of a mass of water, without materially influencing the tempera- 
 ture below ; so imperfectly and slowly is heat conducted through 
 this fluid. The process by which heat is communicated through 
 water, we have termed convection. When heat is applied to the 
 bottom of a vessel full of this fluid, the portion of the water first 
 heated expands in bulk, and thus becomes specifically lighter ; it 
 then rises to the top, carrying with it the newly acquired tem- 
 perature, while another cold portion, sinking to the bottom, is 
 heated in turn, and so on, till the whole mass becomes uniformly 
 heated. 
 
 With respect to the propagation of light through water, it has 
 been calculated that not a tenth part of the incident light can ad- 
 vance five fathoms dovv'nwards in the most translucent water ; that 
 even of vertical rays, one half is lost in the first seventeen feet, 
 and that they become reduced to one-fourth by traversing thirty- 
 four feet, which correspond to the mass of an atmosphere. It 
 thus follows, that only the hundred thousandth part of the verti- 
 cal rays can penetrate below forty-seven fathoms, which is 
 scarce!}' equal to the glimmer of twilight ; and that the depths of 
 the ocean must be always in perpetual darkness.-^ 
 
 Such are the general principles by which heat and light are 
 propagated in water. But in speaking of this fluid in a former 
 chapter, we alluded to one of the physical properties of water, of 
 the utmost importance in the economy of nature, and which, 
 perhaps, almost more than anything else, indicates design ; since, 
 like the composition of the atmosphere, this property of water 
 constitutes an exception, as it were, to a general law, expressly 
 directed to a particular object. We have mentioned that it is a 
 general law, that all bodies, in every state of aggregation, expand 
 by heat and contract by cold ; now water forms a marked excep- 
 tion to this law. Like other bodies, water continues to contract 
 on the removal of heat, till its temperature comes down to within 
 a certain distance (7° or 8°) from its freezing point. At this 
 distance, water begins again to expand, and the expansion con- 
 tinues till it becomes ice ; at which moment of freezing, a sudden 
 and considerable expansion takes place. Hence, the specific 
 gravity of ice is decidedly less than that of water, and the solid 
 necessarily swims on the surface of the fluid. The importance 
 of this anomalous property of water is so great, that it is doubt- 
 ful whether the present order of nature could have existed with- 
 out it, even although everything else in the world had remained 
 the same. For instance, were it not for the comparative lightness 
 of ice, this solid, instead of beginning to be formed at the surface 
 
 * Article Climate, in the Encyclopjedia Britannica. 
 
148 METEOROLOGY. 
 
 of water, would have begun to be formed at the bottom; as the 
 colder water from its greater specific gravity would naturally 
 have sunk: for similar reasons, also, the lowest stratum of ice 
 would have been the last to have melted. Now, let us reflect for 
 a moment upon the consequences of such an arrangement. In 
 the northern and indeed even in temperate climates, the bottoms 
 of all lakes and deep waters would have been a mass of ice, and 
 totally inaccessible, therefore, to organized beings. During the 
 summer a few feet of the upper part of the ice, would, perhaps, 
 have been melted ; but what little had thus become melted in 
 summer, would again have become solid during winter ; and as 
 the accumulations of ice would have been constant, all the seas, 
 even perhaps to the tropical climates, at least at their bottom, 
 would, long before this time, have been a mass of ice ! But 
 what in reality happens ? In consequence of the above anomalous 
 properties of water, this mischief is entirely prevented, and not a 
 particle of ice can be formed in a lake or other collection of water, 
 till the whole mass is cooled down to the temperature of 40°, at 
 which temperature the specific gravity of water is at its maxi- 
 mum. 
 
 These properties of water operate in the following manner. 
 On the application of cold to the surface of water, the cooled 
 portion sinks, and its descent forces up a portion of warmer water 
 to the surface, which after communicating some of its heat to the 
 superincumbent air, sinks in its turn ; and this process goes on 
 for a greater or less time according to the depth of the water. If 
 the depth be not very considerable, the whole body of water be- 
 comes cooled down to 40°; at which temperature the specific 
 gravity not increasing, the circulation ceases, and the surface of 
 the water, (not the bottoin) becomes at length so far cooled as to 
 be covered with ice. If the depth of the water be considerable, 
 the application of cold may be long continued without the result 
 of freezing ; hence, in this and in other countries, not intensely 
 cold, it often happens that deep lakes remain unfrozen during the 
 coldest winters. 
 
 The above anomalous properties of the expansion of water and 
 its consequences, have always struck us as presenting the most re- 
 markable instance of design in the whole order of nature — an in- 
 stance of something done expressly and almost (could we indeed 
 conceive such a thing of the Deity), at second thought, to accom- 
 plish a particular object. Further, if in conjunction with this 
 anomalous property of water, we take into account the still more 
 anomalous constitution of atmospheric air, and at the same time 
 consider the relations of water and air to organic existence, we 
 are unavoidably driven to the conclusion, that the Maker of water 
 and of air has designedly created these anomalies, to obviate dif- 
 
PROPAGATION OF liEAT BY WATER. 149 
 
 ficuliies which would have rendered organic existence a physical 
 impossibility. TJius, had means not been taken to secure the 
 fluidity of water under the varying circumstances of temperature 
 in which it is placed ; the greater portion of this fluid in the world 
 would long ago have been a solid mass of ice, and consequently 
 inaccessible to organic life. Had means not been taken to secure 
 the homogeneity of air at all times, and under all circumstances ; 
 this important medium would not only have been constantly 
 liable to local deteriorations ; but its properties, long ere now, 
 would have probably become deteriorated to such a degree, as to 
 have rendered the permanence of organic life not less physically 
 impossible. Nor do the suppositions which the sceptic will urge, 
 that these properties of water and air flow naturally from their 
 constitution, diminish the force of the argument. The force of 
 the argument lies, in the first place, in the fact that water and air 
 have been created with such anomalous properties ; and, in the 
 next and chief place, that these anomalous properties have been 
 brought into action precisely where they are required. Moreover, 
 the argument is greatly strengthened, by the fact that two ano- 
 rnalies, rather than that two ordinary circumstances, have been 
 thus expressly adjusted. 
 
 Having stated the general principles on which heat is distri- 
 buted through water, and its most remarkable consequence ; we are 
 now to enter into a few details with respect to some other conse- 
 quences of this distribution. Of these one of the most striking 
 is, that the temperature of the water at the bottoms of deep lakes 
 or inland seas, must remain nearly unilorm during the whole year. 
 Thus it has been found that the temperature of the water at the 
 bottoms of many of the lakes in Switzerland often varies no more 
 than 3° or 4°, while the temperature of the surface often varies 
 20° or 30"^. Hence in deep waters, in temperate climates, the 
 changes of temperature are chiefly confined to the upper strata of 
 the water ; nor can ice (except from some very sudden and pow' 
 erful accessions of frost) form on the surface of such a lake, till, 
 as before observed, tlie whole of the water in it is cooled down to 
 40°, at which temperature all circulation ceases. When a coat 
 of ice has been once formed, this ice, as we shall see presently, 
 has also a powerful tendency to prevent the further cooling of 
 the inferior strata. 
 
 With respect to ivaters in motion, as small streams, or rivers 
 of no great depth and magnitude, and containing fresh waters ; 
 though unfavourably circumstanced for freezing, they do never- 
 theless congeal. The process usually commences at the shores 
 where the water is shallowest, and its motion is least rapid ; 
 from whence the ice gradually advances towards the centre of the 
 stream. When the whole of the surface has once become fixed, 
 
 13* 
 
150 METEOROLOGY. 
 
 congelation goes on actively, particularly by night. As the 
 thickness of the ice increases, however, the quantity added daily, 
 even supposing the cold to remain the same, gradually diminishes, 
 on account of the bad conducting power of the ice. Hence in a 
 block of ice taken from a river or lake, we may often observe the 
 strata corresponding with the daily, or rather nightly additions, 
 presenting a gradually decreasing series from several inches down 
 to a few lines in thickness. 
 
 Of the Temperature of the Waters of the Ocean at great 
 Depths. — Between the Tropics, the temperatnre of the ocean di- 
 minishes with the depth ; in the Polar seas, on the contrary, the 
 temperature augments with the depth. In the temperate seas, 
 comprised between 30° and 70° of latitude, the temperature of 
 tlie water gradually decreases as the latitude increases, until 
 about the latitude of 70° ; when the temperature begins to rise as 
 before mentioned. Hence about the latitude of 70° there exists 
 a zone or band at which the mean temperature of the ocean is 
 very nearly constant at all depths. The temperatures of particu- 
 lar parts of the ocean, however, have been observed to be much 
 influenced by the depth and extent of the water, particularly in 
 hio-h latitudes. 
 
 We have already mentioned the influence of the saline matters 
 of the ocean upon the freezing point of sea-water^ and we have 
 now to point out the important consequence of this property in 
 the economy of nature. In its natural slate sea-water freezes at 
 about 28° or 29°, but when it has been concentrated by previous 
 freezing the congealing point is reduced to 15° or 16° ; while water 
 saturated with salt, it is said, does not freeze at a temperature 
 above 5°. Besides this property of lowering the freezing point 
 of sea-water, the saline matters also increase its specific gravity 
 and its point of maximum density. Hence from these circum- 
 stances, and from their immense depth and extent, the waters of 
 the ocean resist freezing still more efl^ectually tiian even running 
 fresh water, and are indeed rarely frozen, except in latitudes where 
 the most intense cold prevails. 
 
 Of the under Currents of the Ocean existing between the 
 Equatorial and Polar Regions. — That the diminished tempera- 
 ture of the waters of the ocean, at great depths near the equator, 
 could not have been acquired in the torrid zone, is evident ; nor, 
 on the other hand, could the comparatively liigh temperature of 
 the waters, at the bottom of the Polar seas, have been acquired 
 in the frigid zone ; at least this high temperature of the Polar seas 
 cannot be caused from without. Hence it has been supposed that 
 there is a constant interchange going on between the waters of 
 the Equatorial, and those of the Polar regions ; though there are 
 considerable difliculties at present as to the means by which this 
 
TEMPERATURE BY LAND AND WATER. 151 
 
 interchange is effected. These difficulties arise principally from 
 some uncertainty with respect to the point of maximum density 
 of sea-water, which does not appear lobe satisfactorily established. 
 Whether in the profound and comparatively quiescent abyss of 
 the ocean, the process of diffusion, or the central heat of the earth 
 formerly alluded to, exert any influence, we have no means of 
 determining. But if a central heat really do exist, its effects must 
 be considerable, particularly within the frigid zone. Whatever 
 be the cause of this approach to uniformity of temperature through- 
 out the waters of the ocean, at great depths all over the globe, its 
 use in the economy of nature, in lending to equalize the distri- 
 bution of temperature, cannot be questioned ; since it constitutes 
 one of those beautiful provisions by which the difficulties of the 
 distribution of temperature, necessarily incidental to the earth's 
 figure and moiions, are obviated ; whilst among the minor circum- 
 stances contributing to the same end, may be mentioned the tides 
 and the innumerable superficial currents produced by winds and 
 by other causes which are to be considered elsewhere. 
 
 W^e have alluded, in a former chapter, to the difference of tern- 
 perature as depending upon whether the surface be land or sea; 
 and perhaps it m:iy not be amiss, in this place, to make a few re- 
 marks upon the actual general amount of the differences of tem- 
 perature, as produced by land and water. 
 
 In the middle of oceans, and far from the influence of land, the 
 diurnal change of temperature of the air near the surface of the sea 
 is much less than upon land. Thus, in the equatorial regions the 
 greatest difference between the temperature of the day and that 
 of the night at sea is said to amount to 3^ or 4° only ; while upon 
 land the difference often amounts to 9° or 10°. In temperate re- 
 gions, and particularly in latitudes extending from 25° to 50°, the 
 difference between the maximum and the minimum diurnal range 
 of the thermometer at sea is slill very trifling, amounting only to 
 4° or 6° ; wliile upon the continents, as for example, at Paris, the 
 range often amounts to 20° or 30°. To these circumstances it is 
 owing that small insular situations, partaking of the character of 
 the surrounding ocean, are much less liable to great diurnal changes 
 than continents ; and hence, in general, they possess more equa- 
 ble climates. 
 
 Both by sea and land the minimum temperature takes place 
 about sunrise. The maximum temperature at sea occurs about 
 noon, or very soon after ; while upon land it takes place from two 
 to three hours after noon. Between the tropics the maximum 
 temperature of the air is said to exceed a little that of the surface 
 of the sea. But when the temperatures are observed at short in- 
 tervals, as for example, every four hours, and all the temperatures 
 are compared, the results are different; and ihey seem to show 
 
152 METEOROLOGY. 
 
 iliiit even between the tropics tlie temperature of the surface of the 
 sea is higher than that of the incumbent atmosphere. Between 
 the latitudes of 25° and 50° the air is rarely warmer than the sur- 
 face of the sea ; and in the Polar regions it is very unusual to find 
 the air as warm as the sea ; it is in fact almost always colder, and 
 generally very much colder. 
 
 As connected with this part of our subject, it may perhaps, be- 
 fore we close, be desirable to offer a few remarks upon the tem- 
 perature of natural springs, and their relation to the mean tem- 
 perature of the earth at the places where they make their appear- 
 ance. 
 
 Springs discharging large quantities of water, and thus indicating 
 that ihey come from considerable depths below the surface of the 
 earth, preserve nearly the same temperature during the v/hole 
 year. In our hemisphere, what little augmentation of temperature 
 springs undergo, is generally in the month of September, while 
 they are coldest in the month of March ; though the differences 
 seldom exceed two or three degrees. If w^e compare the temperature 
 of the springs of any place, with the mean annual temperature of 
 that place, we find that there is a near connection between the two, 
 all over the globe. In the torrid zone, however, the mean annual 
 temperature of the air is usually higher by three or four degrees 
 than that of the springs ; v/hile in the temperate zone, on the con- 
 trary, the springs are warmer than tlie air. The excess of tem- 
 perature of springs, as compared with the mean annual tempera- 
 ture, goes on increasing with the latitude ; so that, between 60° 
 and 70° of latitude, this excess amounts to from 5° to 7° ; a cir- 
 cumstance we sliall again have occasion to notice. Other things 
 being the same, the temperature of springs varies considerably ac- 
 cortiing to ilieir copiousness; as a large body of water will be less 
 liable to be influenced by the surrounding soil, than a smaller body 
 of water; and may even, in turn, influence the temperature of the 
 soil itself. 
 
 The subject of thermal springs, as intimately connected with 
 the history of volcanoes, belongs to the Geologist. 
 
 We have thus enumerated the principal circumstances connected 
 with the distribution of temperature upon the surface of the earth, 
 and at such parts below it as are within our reach. We now come 
 to the second great division of the subject of climates ; viz., that 
 connected with the atmosphere. 
 
DISTRIBUTION OF HEAT IN THE ATMOSPHERE. 153 
 
 Section II. 
 
 Of the Secondary Constituents of Climate immediately connected 
 
 with the Atmosphere. 
 
 The phenomena of the atmosphere originally constituted the 
 proper study of the Meteorologist, and even yet they claim the 
 largest share of his attention, 'i'he subject, in all its bearings, 
 is very extensive, and many of the details are imperfectly under- 
 stood. We shall endeavour to present a brief outline of t!ie prin- 
 cipal phenomena under the following heads. — Of the distribution 
 of heat and of light through the atmosphere, and of the conse- 
 quences; — of the distribution of water through the atmospherej 
 and of the phenomena dependent upon this distribution; and, 
 lastly, — of the occasional presence of foreign bodies in the at- 
 mosphere. 
 
 1. Of the Distribution of Heat and of Light through the At- 
 mosphere, and of the Consequences. — Every one is familiar with 
 the general fact of the diminished temperature of the higher 
 regions of our atmosphere ; and that in the hottest countries, by 
 ascending a lofiy mountain, we encounter, at diflerent heights, 
 every variety of temperature, even to that of perpetual snow, and 
 of the Polar regions. One of the first circumstances, therefore, 
 that claims the attention of the Meteorologist, is the law of tliQ 
 distribution of sensible heat, or of temperature, through the atmo- 
 sphere. 
 
 The law of the distribution of temperature through the atmo- 
 sphere is tolerably uniform, though it is occasionally liable to 
 variations and interruptions, depending upon local difTerences, 
 and perhaps upon other circumstances, not satisfactorily under- 
 stood. The mean results of a great number of observations made 
 in different parts of the world appear to show, that for every 100 
 yards of altitude, Fahrenheit's thermometer sinks one degree. 
 This statement, probably, does not, within moderate limits, differ 
 much from the truth ; though some late researches have rendered 
 it probable tliat while at different heights the rate of the decrease 
 of temperature is uniform, the rate of altitude increases constantly, 
 and according to laws very similar all over the world ; that is to 
 say, supposing the first 252 feet are equal to one degree, the 
 second degree will be equal to 255 feet, the third to 258, the 
 fourth to 261, &;c. 
 
 The causes upon which tins great cold of the higher regions 
 depends are chiefly the two following; first, the perfect permea- 
 bility of the atmosphere to the solar rays, on which account they 
 radiate through it almost without affecting its temperature, till 
 
154 METEOROLOGY. 
 
 reacliing t!ie earlli they exert their utmost force ; and secondly 
 the increased capacity for heat which air possesses in proportion 
 as it becomes more ran^. From the first of these causes it hap- 
 pens that the temperature of the lower regions of the atmosphere 
 is derived, not immediately from the sun, but from the earth. The 
 earth absorbing the solar heat, recommunicates it to that portion 
 of the atmosphere immediately incumbent on the surface, while 
 all the atmosphere above remains unaffected; for though, from 
 diminished specific gravitj^ heated air naturally ascends, yet as 
 its capacity for heat at the same time increases, ascending air 
 rapidly loses its sensible heat : as in the second place we have to 
 explain. 
 
 Dr. Dalton, and afterwards Sir Jolin Leslie more completely, 
 have attempted to show that the equilibrium of heat in the atmo- 
 sphere is obtained ivhen each of its molecules, or in other words, 
 when the same rveighl of air, in the same perpendicular column, 
 is possessed of the same quantify of heat. Now, since atmo- 
 spheric pressure diminishes with tiie height according to a certain 
 law, it is obvious that the same iveigkts of air at the surface of 
 the earth, and in the higher regions, ^w'\\\ occupy very different 
 spaces. But since the absolute quantity of heat is exactly the 
 same in both portions, it is likewise obvious that in the higher 
 regions of the atmosphere, from the increased capacity of the air 
 for heat, the quantity of latent heat is gradually augmented, while 
 the quantity remaining sensible, becomes less. Hence the tem- 
 peratuie of the air diminishes as we ascend, exactly in the pro- 
 portion that its latent heat, that is to say, its capacity for heat as 
 produced by rarefaction, increases. In consequence of this ar- 
 rangement, to use the words of Dr. Thomson, "if a quantity of 
 cold air were suddenly transported from an elevated region to the 
 surface of the sea, its density would be continually increasing 
 during its descent, while its latent heat would diminish in the 
 same proportion ; and when it reached the level of the sea its tem- 
 perature would be just as high as that of other portions of air in 
 the same latitude and elevation. Air, therefore, does not feel cold in 
 consequence of falling from an elevated situation, though this be 
 an opinion commonly entertained, but in consequenee of its being 
 suddenly transported from a more northerly to a more southerly 
 situation."^ Thus, to the above beautiful and simple law, we 
 owe the permanent state of equilibrium of temperature in the 
 atmosphere ; for, in spite of all the disturbances constantly pro- 
 duced by minor causes, this equilibrium, from the natural tendency 
 to right itself, is never very seriously afrected. 
 
 Of the Limits of Perpetual Snow. — Connected with the dimi- 
 
 * On heat and electricity, p, 129. 
 
LIMITS OF PERPETUAL SNOW ; GLACIERS. 155 
 
 nution of temperature in the liigher regions of the atmosphere are 
 the limits of perpetual snow m different latitudes. These limits, 
 of course, may be naturally supposed to follow the mean tempe- 
 rature of 32°, from the level of the sea in the Polar regions to 
 the highest point of their range under the equator. This infer- 
 ence is obvious, and, genenilly speaking, correct ; though it is 
 liable to certain modifications, and to some anomalies, of which 
 the following are the most remarkable. 
 
 Under the equator the limits of perpetual snow are the most 
 fixed and steady, and seem to exist generally at an altitude of be- 
 tween 15,000 aiid 16,000 feet. As we recede from the equator, 
 the oscillations for the most part become more striking, and all 
 the phenomena assume a more irregular form. Such, for example, 
 is the case in the Mexican Cordilleras ; but still more evidently 
 in the Himmala range, where there is a differeuce of no less 
 than 4000 feet between the limits of perpetual snow on the north- 
 ern and on the southern sides of the mountain, that on the north- 
 ern being the higliest. As we proceed towards the temperate 
 zones, we find, in mountainous countries, below the limits of 
 perpetual snow, immense bodies of ice, or glaciers^ as they are 
 termed. These glaciers are formed by the alternate melting and 
 congealing of the extensive beds of snow that lie above them. 
 The glaciers, accumulating in vall^s, are often by the enormous 
 and increasing weight of the snow and ice in the upper parts, 
 pressed downwards far beyond the limits of the snow itself. 
 Such are the glaciers of Switzerland, of Norway, and of other 
 countries in temperate climates. All these circumstances, with 
 others that might be mentioned, and many probably that are un- 
 known to us, combine to render the limits of perpetual snow ir- 
 regular. These irreffularities are so great, that Humboldt has 
 given as a mean of many observations, that at the equator the 
 limits of perpetual snow are nearly 3° above the freezing point, 
 while in the temperate zone they are nearly 5° below that point, 
 and in the frigid zone no less than 10° or 11° below freezing ; 
 which observations seem to pro\^e that the general temperature of 
 the air decreases in the equatorial, otherwise than in the colder 
 regions. From the peculiar distribution of the land in the southern 
 hemisphere, little is known of the Ihie of perpetual snow in that 
 part of the world ; but it will probably be found to be different 
 from that in the north, and generally lower. 
 
 The perpetual snow resting on the tops of mountains consti- 
 tutes a most important provision in the economy of nature, par- 
 ticularly in the warmer climates, where the accumulated snow 
 becomes the prolific source of innumerable rivers without which 
 those regions wonld be uninhabitable. 
 
 There is a striking difference between the elevated and the 
 
156 METEOROLOGY. 
 
 lower regions, which must have considerable influence upon or- 
 ganization, though this influence has not been studied so carefully 
 as it ought to be ; viz., the difference of atmospheric pressure. 
 At the surface of the earth, the atmospheric pressure is nearly the 
 same in all latitudes, but as we ascend above the surface, the 
 pressure rapidly diminishes. Everything else, therefore, being 
 supposed to be the same, the difference of pressure is probably 
 alone sutficient material!)' to influence organization, and to render 
 certain provisions and accommodations necessary, of which, at 
 present, we are ignorant ; but which might be doubtless much elu- 
 cidated by a careful study of Alpine plants and animals, as com- 
 pared with those that occupy the plains. 
 
 Of the Distribution of Heat and Light through the Atmo- 
 sphere in their latent and decomposed Forms. — In the preceding 
 paragraphs we have alluded to the quantity of heat existing /a/e?7^ in 
 the higher regions of the atmosphere. But besides this quantity, 
 which may be supposed to be common to the whole atmosphere, 
 the distribution of latent heat and light must in some degree follow 
 the same law as that of sensible heat and light ; that is, must de- 
 crease from the equator toward the poles. Thus there can be no 
 doubt, that the expanded air of the equatorial regions contains 
 much more heat and light in the latent state, than the comparatively 
 dense and dry atmospheric air of the Polar regions ; and it is pro- 
 bable that the rigours of each extreme are mitigated by this pro- 
 vision. The distribution of electricity through the atmosphere 
 seems also to be regulated by very similar laws. It may, how- 
 ever, be remarked that the effects of heat and light, in the latent 
 and decomposed forms, are much more striking as connected with 
 the water in the atmosphere, than with the constituents of the at- 
 mosphere itself. We shall, therefore, defer what we have to say 
 on those subjects till we speak of the water in the atmosphere. 
 
 Of the Propagation of Sensible Heat through the Atmo- 
 sphere. — x\s the difl^usion of gaseous bodies through each other is 
 so far a mechanical process that it is regulated solely by the rela- 
 tions of their specific gravities, it follows that under the same pres- 
 sure, different portions of the same gas, having different tempera- 
 tures, and consequently different specific gravities, will have a 
 similar tendency to dilfusion. Hence, independently of all other 
 circumstances, the warm and light air of the equatorial regions 
 has a natural tendency to diff'use itself toward the poles ; while 
 the colder and heavier air of the poles possesses a similar tendency 
 to dilfuse itself towards the equator, though in a greatly mitigated 
 degree. The exact amount of these tendencies we have no means 
 of estimating, but they, doubtless, exert considerable influence ; 
 and, as the diffusive power may happen to coincide with, or op- 
 pose the atmospheric currents, to be next considered, it may aug- 
 ment or diminish their effects. 
 
PROPAGATION OF HEAT IN THE ATMOSPHERE. 157 
 
 Though difTusion be thus largely concerned in the lateral pro- 
 pagation of temperature through the atmosphere, this propagation 
 is evidently affected to a much greater extent by the {)rocess termed 
 convection. Convection, like diffusion, of course, implies motion 
 or currents ; which currents as existing in the atmosphere, we 
 need scarcely observe, are denominated Winch. The winds, 
 therefore, are of the utmost importance in the economy of nature, 
 as tending to equalize the distribution of temperature over the 
 globe ; and the fohowing brief explanation will serve to give a ge- 
 neral knowledge of their nature. 
 
 Atmospheric currents may be considered under two heads : those 
 of a general kind, and which extend more or less over the whole 
 globe ; and those depending upon various transient derangements 
 of the distribution of temperature, tlie effects of which are limited 
 to particular localities. On each of these we shall make a few re- 
 marks. 
 
 The general currents of the atmosphere depend principally up- 
 on the two following circumstances, which, if borne in mind by 
 the reader, will furnisli him with a clue to tlie whole subject : 
 viz., the unequal temperature of the equator and of the poles ; and 
 the diurnal motion of the earth upon its axis. The conveclive 
 operation of the first of these general causes may be thus illustrated. 
 We have stated that the entire pressure of the atmosphere all over 
 the earth's surface is nearly the same, and equal to that of a 
 column of mercury about thirty inches in height. We have also 
 stated that the mean temperature of this atmosphere near the equa- 
 tor, and at the level of the sea is upwards of 80°, whde in the Po- 
 lar regions it is constantly below 32°, the freezing point of water. 
 Hence, as air expands by lieat, and becomes specifically lighter, 
 it is obvious that a given bulk of air at the level of the sea round 
 the poles, must be considerably heavier than a similar bulk of air 
 at the level of the sea under the equator. The air, therefore, round 
 the poles being colder and heavier, will have a tendency to flow 
 along the earth's surface from the poles towards the equator, and 
 to displace the lighter air under the equator; whiie the equatorial 
 air so displaced, will, owing to its lightness, ascend and flow back 
 a2[ain over llie colder air, north and south toward the poles, so as 
 to preserve the equilibrium. Moreover these currents will be per- 
 petual ; for the heat of the equator and the cold of the poles being 
 constant, the same tendency to change will always exist, and thus 
 the currents will be constant likewise. 
 
 These atmospheric currents constitute one primary element of 
 the winds, and are the grand means by which the equalization of 
 temperature over the globe is effected. If the earth were at rest, 
 and its surface free from irregularity, these currents or winds would, 
 of course, be in the northern hemisphere always due north, and 
 
 14 
 
158 METEOROLOGY. 
 
 in the southern hemisphere clue south ; while the velocity would 
 in each case gradually diminish from the poles towards the equa- 
 tor, where there would be a perpetual calm. 
 
 But the earth is in a constant state of motion upon its axis from 
 west to east, by which motion the currents are deflected from their 
 northern and southern course towards the east; and this eastern 
 deflection constitutes the other primary clement of the winds to 
 be next considered. 
 
 On the surface of a globe revolving like the earth on its axis, 
 the general reader will bear in mind that the motion of any given 
 point at the equator is t!ie greatest^ and at the poles the least pos- 
 sible. Thus while the poles are quiescent, the velocity of any 
 given place at the equator of our earth, is about 1000 miles an 
 hour ; from which extreme, the velocity gradually diminishes to- 
 ward the poles. Tiiis motion of the earth on its axis operates in 
 the production of an easterly current in the atmosphere as follows. 
 Supposing there were no atmospheric currents from the north and 
 south towards the equator, and that the earth revolved upon its 
 axis as at present, one of two things must happen. Either the 
 earth during its revolution would carry with it the incumbent at- 
 mosphere ; in which case there would be a perpetual calm over 
 its surface : or the earth would revolve within the atmosphere, 
 leaving, as it were, the atmosphere behinii it : in which case there 
 would be an apparent current or wind over the whole of the earth's 
 surface, in a direction opposite to that of the earth's motion, that 
 is from east to west; which wind, supposing the atmosphere did 
 not move with the earth, would, of course, be at its maximum at 
 the equator. Now both these causes are continually operating, 
 and give origin to all the variety of the eastern currents upon the 
 earth's surface, which, with the northern and southern currents, 
 before described, conspire to produce the well known currents 
 called the trade winds. Before we attempt to explain the trade 
 winds, their phenomena may be thus briefly described. 
 
 The trade winds in the AUantic ocean extend to about 28° on 
 each side of the equator. At their extreme northern and southern 
 boundaries these winds generally blow from the east ; but as they 
 proceed towards the equator from the north and from the south, 
 they gradually pass from the east through all the intermediate 
 points of the compass, till near the equator they become in the 
 northern hemisphere, due north, and in the southern hemisphere 
 due south. The trade winds are subject to some slight variations 
 chiefly arising from the position of the earth with respect to the 
 sun. On these variations we do not think it necessary to enlarge. 
 The general phenomena are as we have stated them, and they, 
 upon the principles advanced, appear to admit of the following 
 explanation : 
 
CURRENTS IN THE ATMOSPHERE. 159 
 
 In the temperate regions of the earth tlie winds seem to obey 
 no certain laws ; at least laws so determinate as those of the 
 trade winds. But about the tropics, both in tlie northern and in 
 the southern hemispheres, the operation of the double currents 
 and motions before described, becomes distinctly perceptible. 
 Thus about the tropics, the surface of the earth begins to move 
 faster than the incumbent atmosphere ; and hence in these regions, 
 the prevailing currents are from the east. Indeed near the tro- 
 pics the currents are nearly due east, principally on account of 
 the great and sotnewhat sudden change of temperature produced 
 by the vertical sun of the tropical regions ; which may be sup- 
 posed to interfere \v\[h, and perhaps to check momentarily, the 
 regular progress of the great northern and southern currents. As we 
 proceed, however, towards the equator, in both hemispheres, the 
 atmosphere gradually acquires the velocity of the earth, while the 
 intensity of the eastern current diminishes in the same proportion, 
 and at length entirely disappears. At the same time the currents 
 from the north and the south continuing, slowly deflect the cur- 
 rents, from the east towards the north in the northern hemisphere, 
 and from the east towards the south in the southern hemisphere, 
 till left alone by themselves the polar currents proceed onward to 
 the equator, as if the motion of the eaith had no existence. 
 
 The first clear and satisfactory theory of the great atmospheric 
 currents or winds w^as given, we believe, by Mr. Daniell. The 
 tlieory of the winds was subsequently illustrated by Captain Basil 
 Hall, in his interesting essay on the trade winds, to which for 
 details we must refer the reader.* Before we quit this subject 
 we may remark that Mr. Daniell traces to these great currents 
 the fluctuations of the barometer, and all the innumerable modifi- 
 cations peculiar to different localities of sea and land, of mountain 
 and plain. For, as he justly observes, in the nicely balanced state of 
 the forces producing these currents, slight irregularities of tempera- 
 ture are capable of causing great disturbances; and expansions and 
 contractions acting unequally upon the antagonist currents, ope- 
 rate by deranging the adjustment of their several velocities. Hence 
 accumulations in some parts, and corresponding deficiencies in 
 others, necessarily arise ; and occasion fluctuations in the baro- 
 meter, far surpassing what would be occasioned by the whole 
 vapour, supposing it were at once added or annihilated. At the 
 same time these irregular distributions, in seeking to regain the 
 proper level, and in struggling to restore the equilibrium, produce 
 temporary and variable winds, which modify the regular currents 
 and often reverse their courses, particularly in the temperate 
 
 • See Meteorolog''ical Essays and Observations, by J. F. Daniell, Esq., 
 Professor of Chemistry in King-'s College, &c., page 465, second edition; 
 
160 METEOROLOGY. 
 
 regions; where, as formerly mentioned, the alternations of tempe- 
 rature, and the fluctuations of the barometer, are the most re- 
 markable. 
 
 Such are the elements of the general currents pervading our 
 atmosphere, and such the modes in M'hich these currents obviate 
 extreme temperatures and their consequences. The same causes 
 are constantly operating in different forms and degrees, so as to 
 produce all the infinite variety among the winds, which we ob- 
 serve in nature. These are so numerous and diversified, as actu- 
 ally to bafiie all attempts at explanation or arrangement; we shall 
 therefore content ourselves with one instance only, by way of 
 illustration, viz., the sea and land breezes. 
 
 The explanation of what are denominated the sea and land 
 breezes is very obvious, and is not less applicable to many similar 
 phenomena. During the day, the surface of the land acquiring 
 heat, imparts its temperature to the incumbent air. This air ex- 
 panding in bulk becomes specifically lighter, and rises in conse- 
 quence ; while the cooler air from the surrounding sea rushes in 
 to supply its place, and thus produces the current called the sea 
 breeze. During the night, on the contrarj'-, the waters of the 
 ocean part with their heat much more slowly than the land, and 
 the reverse action, or the land, breeze takes place. In hot cli- 
 mates near the sea-shore, and in insular situations, these alterna- 
 tions constitute a most agreeable variet3^ 
 
 2. Of the Presence of JVater in the Atmosphere. — In tlie fore- 
 going section we have endeavoured to give an outline of the beau- 
 tiful provisions that have been adopted to prevent, by means of 
 the air of the atmosphere, the consequences necessarily arising 
 from the unequal distribution of heat and light over the globe. 
 We now come to another subject of not less importance, viz., 
 the phenomena depending upon the existence of water in the 
 atmosphere, and which, taken together, principally constitute what 
 we emphatically denominate the TV^eatlier. 
 
 Of the Relations of the fVafer in the Atmosphere to Tempera- 
 ture. — We have before stated the fact, that water has a tendency 
 to assume the elastic form at all temperatures. From the tendency 
 of water, thus to rise " above the Firmament," not only the ocean, 
 but ice and snow, are unceasingly contributing their supply of 
 moisture to the air ; and this important fluid, so indispensable to 
 vegetable and animal existence, is distributed over the surface of 
 the whole earth. In considering, therefore the relations of the 
 water of the atmosphere to temperature, the phenomena which 
 first claim our attention, are the processes by which water is taken 
 up and again separated from the atmosphere ; that is to say, the 
 processes of Evaporation and Condensation. 
 
 In treating of the nature of Evaporation., the questions to be 
 
EVAPORATION AND CONDENSATION. 161 
 
 answered at the outset are, — Why is moisture present in the at- 
 mosphere ? By what force is its presence determined, and its 
 quantity limited ? The reply to these questions depends upon 
 the properties of matter in general, and of vapour in particular, as 
 formerly described ; which, if the reader bears in mind, will en- 
 able him readily to understand what follows. 
 
 When water is exposed to the air in an open vessel, the mole- 
 cules of its uppermost or superficial stratum, being released from 
 the influence of those below them, have a natural tendency to as- 
 sume that degree of polarity which is appropriate to their tempe- 
 rature. Hence, after acquiring the latent heat necessary to pro- 
 duce this polarity, either at the expense of a portion of their own 
 sensible heat, or that of the atmosphere, the superficial molecules 
 of water become self-repulsive, and fly off" into space in the form 
 of vapour. If the space over the v/ater be circumscribed and be 
 a vacuum, the molecules fly off* with such rapidity as instantane- 
 ously to fill it. But, if the space be occupied by air, or be of in- 
 definite magnitude, the molecules fly oft' more slowly, so as gra- 
 dually to difTuse themselves through the whole space ; quite on 
 the same principle, and in the same manner, that one gaseous 
 body is diff'used through another. 
 
 Such, in few words, may be deemed a simple statement of 
 what evaporation is. We shall next proceed to inquire into the 
 nature and operation of the means by which evaporation not only 
 takes place, but is limited within certain boundaries. 
 
 In a former chapter, we remarked, thnt the elastic force exerted 
 by all bodies in the gaseous state bears a certain relation to their 
 temperature, but that the degree of this elastic force varies accord- 
 ing to other circumstances ; particularly according to whether the 
 gaseous body, at the given temperature, be capable of existing in 
 the fluid or in the solid states, as well as in the gaseous state. 
 Thus, atmospheric air, at the temperature of 32° (and indeed at 
 all known temperatures), is a gaseous body, and, under ordinary 
 circumstances, exerts an ehistic force equal to the weight of a col- 
 umn of mercury 30 inches high ; whereas, at the same temperature 
 of 32°, water is a solid, and the force of the elasticity of its va- 
 pour is not more than equal to about l-5ih of an inch of mercurv. 
 But at, and above 212°, its boiling point, water, under ordinary 
 circumstances, can exist only as a gas ; and in this gaseous form, 
 and at the temperature of 212°, water obeys precisely the same 
 laws, and exerts the same elastic force as atmospheric air would 
 do under similar circumstances. Hence it will be readily under- 
 stood, that the law of the elastic force of vapour below 212°, is 
 very different from the law of that force above 212° ; as by ex^ 
 periment is found to be the fact. 
 
 From the preceding remarks it will appear that, all other things 
 
 14* 
 
162 METEOROLOGY. 
 
 being the same, the tendency of water to assume the form of va- 
 pour, or the rate of its evaporation, as well as the actual quantity 
 of water in the state of vapour in the atmosphere, will increase as 
 the temperature increases. The exact law of this increase, in all 
 its details, we need not state. It is suflicient for our purpose to 
 observe, that at all temperatures below the boiling point of water, 
 that is to say, at all common atmospheric temperatures, while the 
 late of the increase of temperature is slow and uniform, or in an 
 arithmetical progression, the corresponding rate of the elastic force 
 of vapour, by which the quantity of water as vapour is determined, 
 increases much more rapidly, or nearly in a geometrical progres- 
 sion. This important fact is connected with several most inte- 
 resting circumstances. 
 
 The phenomena of the Condensation of vapour from the at- 
 mosphere, are next to be explained. As the quantity of water in 
 solution in the atmosphere can never be greater, though it may 
 be less, than the quantity proper to the temperature ; Avhen vapour 
 (or what is the same thing, when a portion of air saturated with 
 vapour), at any given temperature, is cooled below the point of 
 saturation ; a portion of the vapour is separated in the form of fluid 
 water, while the remainder assumes the elastic condition proper 
 to the newly acquired and diminished temperature. The forms 
 assumed by the water so separated are various, and depend very 
 much upon the quantity separated, and on the separation taking 
 place in atmospheric air. When the quantity of water separated 
 is small, the minute detached particles diffused through a large 
 space, are suspended in ib.e attnosphere by its buoyancy, and as- 
 sume the form of what, for the sake of distinction, we shall call 
 Visible Vapour, viz. mists, clouds, &;c. When the quantity se- 
 parated is greater, the particles collect into drops too large to be 
 upheld by atmospheric buoyancy, and they fall to the earth in the 
 shape of rain, hail, &;c. 
 
 Of the two great processes of evaj)oration and condensation, it 
 may be further remarked, that by a beautiful provision, they have 
 a constant tendency to limit each its own operations ; evaporation 
 is increased by heat and produces cold ; condensation is produced 
 by cold and liberates heat. Moreover, in virtue of another won- 
 derful arrangement, by evaporation, water is separated entirely 
 from all forei'ni bodies, and is thus condensed in a state of abso- 
 lute purity. 
 
 We now come more particularly to consider the subject of the 
 vapour of the atmo8})iiore. To facilitate the understanding of this, 
 we ^hall, m the first place, suppose the air to be absent, and shall 
 inquire what would be the covA\'nions of an atmosphere of vapour, 
 under the pressure and temperature existing at the surface of the 
 earth, and at different heights above the eartli's surface. 
 
 As the clastic force of vapour increases faster than the tempe- 
 
ATMOSPHERE OY VAPOUR. 163 
 
 ratiire of the vapour ; and as tlie mean temperalure at the Equator 
 is, at least, 80"", and that at the Poles below 32° ; it follows, that 
 in an atmosphere of vapour, heated similarly to that of our earth, 
 the specific gravity of the vapour at the Equator, would greatly 
 exceed the specific gravity of the vapour at the Poles. Vapour 
 thus exhibits a condition directly opposite to that of air, under the 
 same circumstances. Hence the tendencies of the currents, and of 
 diffusion, in an atmosphere of vapour, at the surface of the earth, 
 would be precisely the reverse of those in an atmosphere of air ; 
 the tendency of the currents would be from the Equator toward 
 the Poles, while the tendency of diffusion would be from the Poles 
 toward the Equator.* 
 
 We have elsewhere stated the law of the decrease of the tem- 
 peralure of the atmosphere, observed in ascending from tlie surface 
 of the earth ; the atmospheric air being supposed to be free from 
 moisture. A similar law would regulate the decrease of tempera- 
 ture in an atmosphere of vapour; but the rate of decrease would 
 be much more slow than in an atmosphere of perfectly dry air. 
 Thus under the Equator, where, at tlie level of the sea, the mean 
 temperature is at least 80, the temperature of an atmosphere of 
 perfectly dry air would sink to the freezing point at a height of 
 15,000 feet; while tlie temperature of an atmosphere of vapour 
 would, at the same height, sink only to 70°. At all the parallels 
 of lower mean temperalure, onv/ard to the lowest round the Poles, 
 at any height above the level of the sea, similar differences would 
 exist between the temperature of an atmosphere of perfectly dry 
 air and the temperature of an atmosphere of vapour; these differ- 
 ences, of course, varying with the mean surface temperature. At 
 the same time, throughout the whole range, from the Equator to 
 the Poles, the specific gravity of the vapour at the level of the sea 
 would always exceed its specific gravity at any height above. 
 Hence, in an atmosphere of vapour, there would be no vertical 
 currents; but there would be a strong tendency to diffusion from 
 above downwards ; while the tendency to lateral diffusion, would, 
 at all heights, be nearly tlie same as at the surface, or would be 
 quite contrary to what would hold in an atmosphere of perfectly 
 drv air. 
 
 * We may here observe, once for all, that our former remarks on the 
 diffusion of air of different temperatures, and om- remarks now on the si- 
 milar diffusion of \apour, are inferences only from the g'er.erai law of dif- 
 fusion ; and that the diffusion of such fluids has not, at least in so far as we 
 know, been yet the subject of experiment. We do not, tlierefore, think 
 it necessary to dwell on the precise law of this diffusion. Our remarks 
 have been chiefly made witii tiie view of drawing the attention of philo- 
 sopiicrs toward these interesting- phenomena. Tl.e diffusion of gases and 
 of vapour, taken in conjunction with the diffusion or radiation of impon- 
 derable matters, would form a noble field to those competent for such 
 physical inquiry. 
 
164 METEOROLOGY. 
 
 Having thus stated the leading properties of an atmosphere of 
 air and of an atmosphere of vapour separately, we come to the 
 proper subject of our inquiry ; viz., //^e condition of an atmosphere 
 resulting from a mixture of air and vapour — of such an atmo- 
 sphere, indeed, as that in which we actually live. 
 
 The reader will have no difficulty in understanding the nature 
 of a mixed atmosphere, provided he has clearly apprehended what 
 has been above stated, regarding the simple atmospheres which 
 are its components, and will advert to two other circumstances 
 that are now to be noticed. These two circumstances are inti- 
 mately connected with the principles previously stated, and with 
 each other ; and an exposition of them is absolutely necessary for 
 obtaining a true knowledge of the relations of an atmosphere of 
 vapour with an atmosphere of air. These circumstances have 
 not been mentioned sooner, the consideration of them having been 
 intentionally delayed, in order that their influence might be seen, 
 where their application is more immediately requisite. They are 
 as follow. 
 
 When vapour and air are mixed together, the resulting volume 
 of the mixture depends on the amount of the elastic forces of the 
 vapour and of the air ; not on any relation between their volumes. 
 Thus when a cubic foot of air at the temperature of 32^, and ex- 
 erting an elastic force equal to 30 inches of mercury, is mixed 
 with a cubic foot of vapour, having the same temperature, and ex- 
 erting an elastic force equal to only l-5th of an inch of mercury; 
 the volume of the mixture resulting is not two cubic feet, but only 
 1-0066 foot. Hence, as the addition of vapour to air adds com- 
 paratively little to the bulk of the air, and consequently diminishes 
 only in a trifling degree its specific gravity; the great aerial cur- 
 rents formerly described as pervading the atmosphere, are scarcely 
 affected by the vapour they contain. 
 
 When two portions of vapour, having different temperatures, 
 are mingled together; or when a portion of vapour is brought into 
 a state of mixture or contact, with a portion of water, or with any 
 other body colder than the vapour ; the resulting mean tempera- 
 ture, whatever that may be, is, in both cases, the temperature which 
 regulates the elastic force of the mixture. Now, since the elastic 
 force of vapour increases most rapidly from the temperature of 32° 
 to 212°, the increase being in a geometrical progression, while 
 the increase of the temperature is in an arithmetical progression; 
 it follows, that v/hen two portions of vapour of e([ual bulk but of 
 difl'erent temperatures, are mixed together ; or when a portion of 
 vapour is brought into contact with any solid colder body ; the 
 resulting mean temperature is always below that requisite to pre- 
 serve the water in a state of vapour. Hence, such mixture or 
 contact is always followed by a portion of the vapour being con- 
 densed into water. In a future part of this section, it will be 
 
MIXED ATMOSPHERE OF VAPOUR AND AIR. 165 
 
 necessary to illustrate further this important fact, but a familiar 
 instance may be noticed here. Let us suppose that a pound of 
 water at tlie temperature of 212°, which being in a state of steam, 
 would occupy a space of about 27 cubic feet, were suddenly 
 brought into mixture with a pound of water at the temperature of 
 32°: the effect would be an instantaneous condensation of the 
 greater part of tiie steam into water. For the resuhing mean tem- 
 perature would obviously be far short of 212°, below which tem- 
 perature the elastic force of vapour most rapidly diminishes. On 
 this property of vapour depends the working of the common 
 steam-engine. 
 
 The reader is thus at length prepared to enter on the compli- 
 cated subject of a mixed atmosphere of vapour and of air. 
 
 We have shown that the rate of decrease of the temperature 
 of an atmosphere of vapour, in ascending from the earth's surface, 
 M^ould be very much slower than that of an atmosphere of air. 
 Now since, at all temperatures, the existence of atmospheric air 
 is permanent ; while the very existence of vapour is dependent 
 on temperature ; it follows, that in a mixed atmosphere of vapour 
 and of air, the quantity of vapour contained in the mixture is 
 regulated solely by the temperature of the air : that is to say, the 
 quantity of vapour present in an aerial atmosphere, can never ex- 
 ceed, though it may be less than, the quantity which is proper to 
 the temperature of the air. If the quantity of vapour in such a mixed 
 atnjosphere, be precisely the quantity that is proper to the tem- 
 perature of the air, such an atmosphere is said to be saturated 
 with vapour. 
 
 But, neither at the earth's surface, nor at any height above if, 
 can the degree of saturation of a mixed atmosphere of air and 
 vapour, be quite equal to that which is proper to the temperature 
 of the air ; and the difference between these two degrees of sa- 
 turation, augments from above downwards. The cause of this 
 dilference may be thus explained. The rate of increase of the 
 temperature of air, from above downward, being in arithmetical 
 progression, and the air being, in a mixed atmospliere, that ingredi- 
 ent M^iich controls the whole mixture; the rate of increase of the 
 tension of the vapour, instead of following the geometrical rate 
 which belongs to it as vapoin-, is obliged to conform to the arith- 
 metical rate of increase of the temperature of the air. The result 
 of this controlment necessarily is, that the quantity of vapour 
 present in a mixed atmosphere will, at any successive diminution 
 of the height above the surface of the earth, become successively 
 less and less than tliat which would be required to saturate the 
 air. An example will make this result evident. 
 
 At the Equator, as we have said, the temperature of the air, at 
 the height of about 15,000 feet, above the level of the sea, is 
 nearly 32°. Now, for the sake of illustration, let us suppose 
 
166 METEOROLOGY. 
 
 this air to be saturated with vapour. From Dr. Dalton's table of 
 the tension or elastic forces of vapour at different temperatures, 
 it appears that the tension of vapour at 32° is equal to the weight 
 of .200 inch of mercury ; and that the difference between the 
 tension of vapour at 32° and the tension of vapour at 33°, that is 
 to say, the value of the first term or unit, in our assumed arithme- 
 tical series is .007 inch of mercury. Now, the difTerence between 
 32° and 80° the mean temperature at the level of the sea under 
 the Equator, is 48° ; and supposing each of these 48 degrees to 
 increase in an arithmetical progression, .007 for each degree, the 
 tension for the whole 48 degrees will amount to .336, which 
 added to .200, the tension at 32° gives the tension of .536 inch, 
 as that corresponding to the vapour at 80°, the temperature of the 
 earth's surface under the Equator. But, by Dr. Dalton's same 
 table of tensions, we find that .536 does not represent the proper 
 tension of vapour at 80°, but of vapour at about 61° only. Ac- 
 cording to this estimate it follows, that at the Equator, while the 
 temperature of the air over the earth's surface is 80°, the point 
 of saturation with vapour is 19° below that temperature. Hence, 
 at the Equator, the air immediately incumbent on the earth's sur- 
 face niust be comparatively very dry. Moreover the cause which 
 has been thus shown to produce the dryness of the Equatorial 
 air, at the earth's surface, must all over the globe exert different 
 degrees of the same influence. The air, everywhere incumbent 
 on the earth'' s surface, must, therefore, always be under the point 
 of saturation ; — the relative degree of dryness being highest un- 
 der the Equator, and gradually diminishing as we recede north or 
 south towards the Poles.*' 
 
 In such a mixed atmosphere as we have supposed, and as in reality 
 surrounds our globe, if its equilibrium be undisturbed, and if it be at 
 rest ; the vapour it contains will have nearly the same tendencies 
 to motion and to dilTusion that would exist in such an atmosphere 
 of pure vapour, as we have formerly described. But from the 
 more equal distribution of vapour, when mingled with air, the con- 
 trasts between the specific gravities of different portions of vapour, in 
 different parts of the atmosphere, will be much less striking than 
 if the atmosphere consisted of vapour alone. Consequently, the 
 rates of motion and of diffusion, wliich depend upon such diff'er- 
 ences of specific gravity, will be less remarkable in a mixed atmo- 
 sphere, even though saturated with vapour, than they would be 
 in a purely aqueous atmosphere ; while in an unsaturated atmo- 
 
 • The mathematical reader will observe, that the quantities g-lven in the 
 text are not rigidly accurate, but are intended only for flimiliar illustration I 
 of the principles reg-ulating' moisture. The truth is, as has been noticed 
 hi the tvxt, in no part of a vertical column of a mixed atmos])here, in a 
 condition of equilibrium and at rest, can the air be in a state of saturation. 
 It has been remarked, that the deg'ree of saturation often continues nearly 
 uniform up to a certain point, and then suddenly decreases. 
 
MIXED ATMOSPHERE OF VAPOUR AND AIR. 167 
 
 Sphere the motions of the vapour must be still more liable to be 
 influenced by the motions of the air, than they would be in an 
 atmosphere of air, at its utmost point of saturation. 
 
 Before we close this part of our subject let us reflect for a mo- 
 ment upon the consequences of such a stale of comparative dry- 
 ness of the lower atmosphere next the earth. Over the greater 
 portion of the earth, the air which, during the day at least, is 
 warmed by contact with the earth's surface, and thus becomes 
 lighter, has, as we have observed, a constant tendency to rise 
 into the higher atmosphere. Novv, if tliis air were saturated witli 
 vapour, of course, whenever the air by rising became mixed with 
 colder air, its vapour would be more or less condensed, and a 
 cloud would be formed. Hence, if we lived in such an atmo- 
 sphere, we should be always enveloped in a mist, through which 
 the sun would not be visible. Rut, by the benevolent arrange- 
 ment we enjoy, this consequence is so entirely prevented, that, 
 unless under peculiar circumstances, and always for beneficial 
 purposes, the air at the earth's surface is hardly ever saturated 
 with moisture. The air that has been warmed by contact with 
 the earth can, therefore, rise from the surface, without any con- 
 densation of its nature within the limits of its point of saturation. 
 Thus, at the Equator, before the air reaches the temperature of 
 61°, the presumed point of its saturation, it must ascend to the 
 height of 6000 or 7000 feet. At this height its vapour will be 
 condensed, and a cloud will be formed ; which may either be 
 precipitated on the spot from which its constituent vapour had 
 risen, or may be transported by the currents of the atmosphere, 
 similarly to refresh a distant country, or may be again dissolved 
 in the air ; while under all these contingencies the whole of the 
 lower part of the atmosphere is exempt from mist, and continues 
 perfectly transparent. These operations are unceasingly carried 
 on in our atmosphere, over the whole surface of the earth. More- 
 over, the very clouds, by giving out their latent heat, and shield- 
 ing the earth's surface from the direct influence of the sun, pro- 
 duce a still further eff'ect, and have a constant tendency to modify 
 their own formation and existence. 
 
 The general result of all the complicated and beautiful ma- 
 chinery connected with the movement of vapour is, that water is 
 incessantly raised into the higher parts of the atmospliere, where 
 it is again condensed in the form of rain, &;c. over the whole 
 earth. We have, therefore, in the next place to examine a little 
 more in detail the relations of these two great processes of evapo- 
 ration and condensation, as they are exhibited in nature. 
 
 Of the general Bclafions of Evaporation and condensation. — 
 The first point in the inquiry that naturally claims our attention, 
 are the rnechanical motions by which the relations between eva- 
 poration and condensation are maintained. 
 
168 METEOROLOGY. 
 
 The motions of vapour, in a mixed atmosphere of vapour and 
 air, may be considered as of three kinds : those motions arising from 
 convection, in which the vapour is carried along by the air ; those 
 motions arising from the tendency of the vapour to recover its 
 dynamical (and thermal) equilibrium, when that equilibrium has 
 been disturbed, and which motions we shall, for distinction, term 
 ihe propei' motions of the vapour ; and those motions of vapour 
 which are caused by diffusion. 
 
 In a mixed atmosphere of vapour and air, the motions of the va- 
 pour, on the large scale of the operations of nature, are influenced, 
 no doubt, in a very great degree, by the motions of the air. For 
 example, large masses, more or less saturated with vapour, in pro- 
 portion to tiieir respective temperatures, and having either verti- 
 cal or lateral motion, must carry with them the vapour they con- 
 tain, whether t.here be much or litUe vapour so contained. On 
 the other hand, motions of the air, on a smaller scale, as we shall 
 presendy see, may be even caused — may certainly be accelerated 
 or retarded, according as the proper motion of the vapour, to be 
 next considered, may agree with, or may be opposed to, these 
 motions of the air. When once, however, the vapour in the at- 
 mosphere has been separated, and has assumed the form of visi- 
 ble vapour, its own proper powers of motion cease, and it be- 
 comes entirely subject to those of convection. Visible vapours, 
 therefore, of all kinds, from their being liable to be wafted by 
 every breeze, are in a constant state of motion, and are thus fre- 
 quently carried where vapour, in virtue of its own tendency to 
 motion, would never reach. 
 
 In an atmosphere of vapour, when the temperature, and conse- 
 quently the elasticity, of any portion is reduced ; the surrounding 
 vapour, by virtue of its greater elastic force, continues to advance 
 towards the cooler locality and to be there condensed until the 
 thermal equilibrium is restored. 'i"he motion thus arising, which 
 depends upon its dynamical properties, constitutes what we have 
 denominated \\ic proper motion of vapour. In an atmosphere of 
 vapour this restoration of the dynamical equilibrium, upon which 
 the tliermal equilibrium also depends, would take place with so 
 great rapidity, as to be almost instantaneous. But in a mixed 
 atmosphere, the case is dilTerent. In such an atmosphere, the 
 presence of the heavier and more abundant air modifies, in a re- 
 markable degree, the rapid motion of t!ie lighter and less abun- 
 dant vapour. Hence, instead of a rush of vapour and a momen- 
 tary deluge, the motions of the vapour take place slowly ; and 
 sudden evaporation and condensation, with their consequences, are 
 efTectuully prevented. 
 
 These tendencies to motion, in vapour of difierent tempera- 
 tures, have, no doubt, great influence on the contiguous surfaces 
 of large masses of air dilTerenily saturated ; and, in particular, 
 
MIXED ATMOSPHERE OP VAPOUR AND AIR. 169 
 
 are liable to affect smaller masses of air differently saturated, 
 when they are in the immediate neighbourhood of each other. 
 Thus, as we have already noticed, the disturbance of the equili- 
 brium of the vapour may be to such an extent, in some portion of the 
 mixed atmosphere ; that the surrounding vapour, urged to move 
 by its tendency to restore the equilibrium, may occasionally be 
 supposed to drag with it the air and the clouds, and thus produce 
 local currents. For instance, let us imagine a mass of warm and 
 almost perfectly dry air to be brought into the neighbourhood of 
 another mass of air of precisely the same temperature, but satu- 
 rated with vapour. The two masses of air, from being of the 
 same temperature, would, as air, have no tendency to intermingle. 
 But as being portions of a mixed atmosphere of vapour and air, 
 the dryer air would be, as it were, a vacuum, towards which the 
 vapour from tlie moist air would have a tendency to flow till both 
 masses of air became equally moist. In such a case, the motion 
 of the vapour might be supposed to cause more or less of motion 
 in the air, while a momentary cloud would probably be formed ; 
 which cloud would be dissipated when the equilibrium was re- 
 stored. In this way, it is likely that many of the minor motions 
 of the atmosphere are produced."^ 
 
 The motions of vapour arising from its diffunive powers are 
 quite distinct from those motions of vapour which are controlled 
 by the motions of the air, or by die dynamical tendencies of the 
 vapour itself to recover its condition of thermal equilibrium. 
 These diffusive motions of vapour, as formerly observed, depend 
 on differences between the specific gravities (the absolute quanti- 
 ties of matter) of contiguous and communicating gases, under the 
 same circumstances of pressure and temperature. Though the 
 motions of vapour depending on diffusion may retard, or be re- 
 tarded by, the other motions to which vapour is liable ; in gene- 
 ral, there is reason to believe that the motions of vapour by 
 diffusion, in their most decided form, surpass, or take place in- 
 dependently of, all the other motions of vapour, and in this free- 
 dom from control, resemble the radiation of imponderable bodies. 
 The laws which diffusion obey have been already stated, and 
 need not be again repeated. These laws may be applied to the 
 consideration of the diffusion of vapour in the following manner. 
 
 The diffusive tendencies of an atmosphere of perfectly dry air, 
 and of an atmosphere of vapour, would, as we have seen, at the 
 earth's surface be in opposite directions ; the diffusive tendency 
 in the aerial atmosphere, being from the Equator toward the 
 Poles, and that in the aqueous atmosphere being from the Poles 
 
 * In all the cases given in the text, the effect of electricity is, for the 
 sake of distinctness, kept out of view. 
 
 15 
 
170 METEOROLOGY. 
 
 towards the Equator. The vertical tendencies also of the two atmo- 
 spheres would be very different. An atmosphere of perfectly dry 
 air, in astate of thermal and dynamical equilibrium, would have no 
 tendency to diffusion ; for the colder air in descending, and the 
 warmer air in ascending, by change of bulk, acquire the temperature 
 appropriate to the height. The effect of this change of bulk and 
 acquisition of temperature is, as we have elsewhere stated, such, 
 that if air from any height in the atmosphere were brought to the 
 surface of the earth, it would have precisely the same tempera- 
 ture as the air already incumbent on the surface. But the case is 
 different with vapour, even in the comparatively rare state in 
 which it exists in a mixed atmosphere. We have seen that in 
 an atmosphere of vapour, if the temperature at the surface of the 
 earth were 80°, the temperature at the height of 15,000 feet 
 would be only 70° ; while in an atmosphere of perfectly dry air, 
 having a similar surface temperature of 80°, the temperature, at 
 the same height of 15,000 from the surface, would be 32°. Now, 
 as in a mixed atmosphere of vapour and air, the temperature of 
 the air determines that of the vapour ; if in such a mixed atmo- 
 sphere, vapour having the temperature of 32°, were brought from 
 the height of 15,000 feet to the surface, where the temperature 
 is 80° ; the temperature of the vapour would, by increased pres- 
 sure and the consequent evolution of more latent heat, be in- 
 creased only to about 42° ; while, as we have seen, where the 
 temperature of the surface is 80°, the point of saturation of the 
 air with vapour is at least 61°. Hence the specific gravity of 
 vapour from the height of 15,000 feet, when reduced to the same 
 degree of pressure as that at the surface, is found to be much be- 
 low the specific gravity of that vapour which actually exists at 
 the surface. Consequently, throughout a mixed atmosphere of 
 vapour and air, tliere is a tendency to vertical diffusion, the pre- 
 dominant tendency being from above downwards. From the 
 extreme tenuity of vapour in the higher regions of the atmo- 
 sphere, and the great tendency therefore, which that vapour has 
 to diffusion, it is probable that the diffusive motion of the vapour 
 may occasionally have a velocity approaching, as we have said, 
 to that of radiant matter, itself. In this way the rare and cold 
 molecules of water may be supposed to dart, or radiate, as it 
 were, far into the warmer atmosphere before their velocity is ar- 
 rested. Nay, in the Polar latitudes, the molecules of water, from 
 the higher parts of the atmosphere, may even reach the earth's 
 surface, by shooting, like rays of heat and light, directly through 
 the air, without materially affecting its temperature. 
 
 After these general remarks on the motions of vapour, we shall 
 now take a rapid view of the mutual relations of the two great pro- 
 cesses of evaporation and condensation. 
 
EVAPORATION AND CONDENSATION, MUTTJAL. 171 
 
 We have already described the general phenomena of evapora- 
 tion and condensation, and have slated llie laws on which these 
 phenomena depend. It will, tlierefore, in this place, be sufficient 
 to remind the reader that the degree, and the rate, of evaporation 
 though they increase with the temperature, are regulated chiefly 
 by the existing degree of saturation of the air. That is to say, 
 under all temperatures evaporation decreases, as the air that re- 
 ceives the vapour, approaches its point of saturation. Hence it 
 follows, that in an atmosphere perfectly saturated with moisture, 
 and in a state of thermal and dynamical equilibrium, there can be 
 neither evaporation nor condensation. The processes of evapo- 
 ration and condensation, therefore, always indicate a disturbance 
 of the thermal equilibrium in some part of the atmosphere : con- 
 densation denoting a depression of tlie temperature below the mean, 
 or point of thermal equilibrium: evaporation, on the contrary, de- 
 noting that the temperature in some part of the atmosphere has 
 been raised above the mean ; or at least that the temperature having 
 been depressed below the mean, is again undergoing an elevation 
 to the mean point. Evaporation and condensation may be thus 
 considered as mutually dependent ; so that one process cannot 
 take place without the other. For this reason, in the great expanse 
 of nature, these two processes oscillate or fluctuate about the point 
 of equilibrium, within certain limits which are never passed ; and 
 which limits, though subject to countless anomalies, in general, 
 decrease from the Equator toward the Poles. 
 
 With respect to the temperature which constitutes the point of 
 equilibrium ; in an atmosphere of vapour, that point would, of 
 course, be the maximum point of saturation. But in a mixed at- 
 mosphere of vapour and air like that of our globe, the point of 
 equilibrium cannot be the point of utmost saturation, but must be 
 that inferior point of saturation formerly described, as being de- 
 termined by the temperature of the predominant air. Thus at 
 the Equator, where the mean temperature at the level of the sea 
 is about 80°, the mean point of saturation will, according to our 
 former estimate, be 61° ; while in London, where the mean annual 
 temperature is about 49^°, the mean point of saturation, (or the 
 deiv pointy as it is termed,) has been fixed by Mr. Daniell at 445°. 
 In temperate climates, the mean point of saturation at any particu- 
 lar place, varies with the seasons from day to day, being higher 
 in summer than in winter. During any shorter period, as that of 
 a day and night, the mean point of saturation, as might be ex- 
 pected, generally bears a certain relation to the lowest degree to 
 which the ten^iperature has fallen during the period ; since the 
 Hygrometer^ shows that the degree of saturation, at any hour, is 
 
 * The Hygrometer is an instrument for measuring' the degree of m-ois* 
 
172 METEOROLOGY. 
 
 seldom below the point of saturation corresponding to tlie lowest 
 temperature of the twenty-four hours ; at which point it continues 
 nearly uniform, so that the point of saturation during the warmer 
 parts of the day generally varies only a few degrees. The ele- 
 vation and depression of the dew point in temperate climates is 
 thus another, and unceasing cause of change, and produces a va- 
 riety in evaporation and condensation so great as to baffle any at- 
 tempt at accurate inquiry. 
 
 From what has been said, it will appear that in a mixed atmo- 
 sphere, the rate of evaporation and of condensation, other things 
 being equal, will depend, not on the ditlerence of the tempera- 
 ture of the air from the maximum point of saturation, but on the 
 difference of the temperature of the air from that of the mean dew 
 point ; that is to say, will increase or diminish as this difference 
 increases. 
 
 The accidental circumstances which principally operate to af- 
 fect the rate of evaporation, are the greater or less extent of the 
 evaporating surface, and the velocity and degree of saturation of 
 the current of air over that surface. But besides these causes of 
 variation, there are other circumstances wliich probably have great 
 influence on evaporation ; some of which are to us of the utmost 
 interest, as being brought more immediately in contact, as it were, 
 with our existence. The chief of these additional circumstances 
 affecting evaporation which we shall notice, are. Diffusion; — 
 Circumstances incidental to the IVater which undergoes evapo- 
 ration ; and Circimistances incidentcd to the Air into which the 
 water is evaporated. 
 
 By the general arrangement which we formerly considered, it 
 appears that evaporation and condensation diminish from the Equa- 
 tor, onward to the Poles. But since increased temperature, which 
 is the cause of evaporation, predominates at the Equator; while 
 diminished temperature, which is tire cause of condensation, pre- 
 dominates at the Poles ; it may perhaps be inferred, that generally 
 speaking, evaporation will be relatively greater at the Equator; and, 
 on the other hand, that condensation will be relatively greater at 
 the Poles. In an atmosphere of vapour such unequal effects could 
 not indeed take place ; from the rapid nature of the motions which 
 would arise throughout the whole of such an atmosphere, so as 
 instantaneously to restore the equilibrium. But in a mixed atmo- 
 sphere of vapour and air, the result would be different. If there 
 were an excess of condensation at the Poles ; before the corre- 
 
 ture of the atmosphere. That of Mr. Daniel! is here alluded to, which is 
 the only one that acts upon scientific principles. Danicll's hygrometer 
 shows the degree of temperature at which water is deposited from the at- 
 mosphere, and consequently its state of saturation. 
 
EVAPORATION AND CONDENSATION, MUTUAL. 173 
 
 sponding evaporation could take place at the Equator, innumerable 
 changes would be produced in the atmospliere over all the other 
 parts of the globe intervening between the Equator and the Poles. 
 Further, we shall see presently that much more water is at all 
 times condensed on the land, than is ever evaporated from the land. 
 The excess that is condensed flows off in rivers in warm and tem- 
 perate climates, and thus accumulation is prevented ; but in the 
 Polar regions this outlet is cut off, and the superfluous water would 
 be locked up in the shape of ice. From these circumstances, 
 therefore, and from others that might be noticed, it is not unreason- 
 able to suppose, that in the colder climates, other things being 
 alike, and the arrangements which regulate vapour being alone 
 considered, condensation of water would proceed much more ra- 
 pidly than its evaporation ; and hence that around the Poles there, 
 would be a constant accumulation of water in the condition of ice. 
 But we know that there is not any such accumulation, in those 
 parts of the Polar regions which have been explored. It is mani- 
 fest, therefore, that in these regions the energy of evaporation 
 must be fully equal to that of condensation. It is indeed true, 
 that evaporation goes on very rapidly from snow and ice. Thus 
 Howard mentions an instance in the month of January, in a cer- 
 tain year, when the vapour, from a circular area of snow five inches 
 in diameter, amounted to 150 grains between sunset and sunrise; 
 and before the next evening, 50 grains more were added to the 
 amount, the gauge having been exposed to a smart breeze on the 
 housetop. Under like circumstances an acre of snow would, in 
 the course of twenty-four hours, evaporate the enormous quantity 
 of 64,000,000 grains of moisture ! Even by the evaporation du- 
 ring the night only, a thousand gallons of water would, in that 
 short time, be raised from an acre of snow. It may thus be easily 
 understood how a moderate fall of snow may entirely vanish du- 
 ring a succeeding northerly gale, without the slighest perceptible 
 liquefaction on the surface.* 
 
 We have given this statement to satisfy the general reader of 
 the fact, that evaporation is constantly going on from snow and 
 ice. But the quantity, great as it appears, does not surpass, or 
 even equal, what it might be supposed to be, on admitted princi- 
 ples. Whether, thereiore, evaporation really takes place in a re- 
 latively greater degree in the Polar regions, so as to compensate 
 for that portion of the condensed water which is there fixed as 
 ice, but which in warmer climates flows off to the sea, in the 
 form of rivers, remains to be proved ; though, to preserve the 
 equilibrium and to prevent accumulations, some such supposition 
 appears to be necessary. Can the difficulty be solved by the aid 
 
 • Article Meteorology in the Encyclopedia Metropolitana. 
 
 15* 
 
174 METEOROLOGY. 
 
 of the principles of diffusion ? Does not a portion of the attenu- 
 ated vapour of the Polar latitudes difl'use itself, and penetrate 
 from thence towards the Equator ; thus leaving the higher re- 
 gions of the atmosphere in the Polar latitudes comparatively dry, 
 and the lower portion of the atmosphere more apt for evaporation ? 
 And is not this diffusion of moisture from the Poles one of those 
 beautiful expedients, which compensate for the inequalities of 
 evaporation and condensation, and by which these inequalities 
 are obviated ? 
 
 The circumstances incidental to ivater, and affecting evapora- 
 tion and saturation, arise chiefly from its purity or impurity. 
 The presence of foreign bodies, as of saline matters, for instance, 
 is well known to raise considerably the boiling point of water ; 
 in other words, they lower its tendency to become vapour, and 
 thus diminish its evaporating and saturating powers. Hence the 
 air over the sea, though, of course, much nearer, in general, to 
 the point of saturation appropriate to the latitude and temperature, 
 than air over the land, is comparatively seldom in a state of per- 
 fect saturation ; and sea-water, so far from being capable of satu- 
 rating the air with moisture, up to the dew point, has even the 
 power of abstracting a portion of the moisture from an atmo- 
 sphere so saturated, and of thus, to a certain extent, drying the 
 air. 
 
 Evaporation on land is precisely similar to evaporation from 
 sea-water, since the various rocks and soils may be considered as 
 so many saline matters, diminishing, in their several degrees, the 
 tendency to become vapour possessed by the water united with 
 them. Hence, under like circumstances, some rocks and soils 
 are dry, while others are moist ; so that, in proportion to the 
 evaporating powers of the rocks and soil of a country, will that 
 country be liable to all the consequences of dryness or of damp- 
 ness of soil. Plants also seem to differ much in their capacity 
 for retaining water. The dryness of a country will, therefore, 
 be considerably affected by the nature of its vegetation ; and the 
 predominance of certain plants or trees in a district may thus in- 
 crease the dampness of its soil. 
 
 Regarding the effect that foreign matters in the atmosphere 
 have in influencing evaporation from the subjacent land or water, 
 we are unable to speak with as much confidence, as we have 
 spoken of the controlling power of the foreign matters in the water 
 iiself. Many years ago, particular circumstances led us to form 
 the opinion, that a combination of water and oxygen is a frequent, 
 if not a constant, ingredient in the atmosphere. This ingredient, 
 which we suppose to be a vapour, and analogous to (we do not 
 say identical with) the deutoxide of hydrogen, may be the cause 
 of numerous atmospheric phenomena, which at present are very 
 
EVAPORATION AND CONDENSATION, MUTUAL. 175 
 
 little understood. Among such phenomena are those of evapo- 
 ration we are now considering. 
 
 The dilhcullies attending an investigation of the atmosphere, 
 and more than all, the total want of opportunity, have rendered us 
 unable satisfactorily to verify the opinion we have advanced. 
 We have stated the opinion as conjectural only, and in order that 
 the attention of those more fortunately situated may be drawn to 
 so important an inquiry. 
 
 When treating of the composition of atmospheric air, we ob- 
 served that the best analyses almost invariably indicated a slight 
 excess of oxygen above the amount of 20 per cent,, which 
 there ought to be in the atmosphere, if its composition were, as 
 there can be little doubt that it is, determined by the laws of che- 
 mical proportions. Now this excess of oxygen in the atmosphere, 
 we have every reason to think, becomes periodically associated 
 in some way with the vapour that is also in the atmosphere ; and 
 thus not only modities the properties of the vapour, but at the 
 same time materially influences the rate of evaporation from the 
 earth's surface. This excess of oxygen may operate in the fol- 
 lowing manner. The vapour in union with oxygen (deutoxide 
 of hydrogen?) ceases, of course, to act as vapour; hence in air 
 saturated with vapour, and as moist as possible, if a portion of the 
 vapour were suddenly to combine with oxygen, the air would as 
 suddenly appear to become dry, though in reality it contained the 
 same quantity of water in solution as before. Moreover the rate of 
 evaporation would be increased by such a combination of vapour and 
 oxygen ; for its efiects, whatever these might be, would be super- 
 added to the ordinary eflects of evaporation, and would thus more 
 or less increase the quantity of water converted into vapour. 
 
 Oxygen in this state of combination with vapour seems to be 
 particularly grateful, if not necessary to animal life. The air in 
 which it abounds is dry, bracing, and exhilarating, while the pre- 
 dominance of moisture, from its occasional and sudden abstraction, 
 induces the opposite feeling of dulness and listlessness. It is 
 probable that some soils and situations are more favourable than 
 others to its existence, and that places are more or less healthy 
 according as it is present or absent. 
 
 The oxygen and vapour in this combination are so feebly as- 
 sociated that they appear to be separated by the slightest cause. 
 Hence the results of every common analysis and examination of 
 air are the same nearly as if such a state of combination did not 
 exist. We may mention, however, as corroborative of our opi- 
 nion, the bleaching qualities of dew and of the air itself, as also 
 the large proportion of oxygen sometimes contained in snow wa- 
 ter and in rain water ; attention being at the same time directed to 
 the well known bleaching qualities of the deutoxide of hydrogen. 
 
 Much more might be said on this curious subject, especially 
 
176 METEOROLOGY. 
 
 regarding its relation to the electricity of the atmosphere. But 
 as our observations must be in some measure speculative we shall 
 for the present desist. 
 
 Of the actual Quantity of Water that is evaporated and con- 
 densed over the Globe. — From the principles we have stated it 
 will appear that the quantity of water evaporated and condensed 
 over the globe may be supposed to vary with the mean temperature, 
 and consequently with the latitude. But, from local or other 
 causes, the quantity varies so much, even in the same place, in 
 different years, that the exceptions are more numerous than the 
 instances of the correctness of the rule. 
 
 The following table, however, shows the general truth of the 
 supposition, and that the average quantity of rain diminishes from 
 the Equator to the Poles. In fact, a much larger quantity of rain 
 must fall in the Equatorial than in the Polar regions, as is suffi- 
 ciently proved by the magnitude of the rivers within the Tropics ; 
 for the size of the rivers of course depends on the quantity of the 
 rain ; the rivers being the conduits along which a certain portion 
 of the precipitated water is borne to the sea. 
 
 TABLE. 
 
 Inches. 
 
 Uleaborg _..._.- 13.5 
 
 Petersburg - - - - - - 16, 17.5 
 
 Paris 19.9 
 
 London *20.7, 122.2, +25.2 
 
 Edinburgh 22., 24.5, §26.4 
 
 Mean of Carlsruhe, Manheim, Stuttg-ard, Wurtzburg", Augsburg, 
 
 and Ptegensburg, (Schow) .... - 25.1 
 
 Epping ... ... 27.0 
 
 Bristol 29.2 
 
 England (Dalton's mean) - - - - - 31.3 
 
 Liverpool -..----- 34.1 
 
 Manchester .....-- 36.1 
 
 Rome ... ..... 39.0 
 
 Lancaster - ..-.-- 39.7 
 
 Geneva ....--.- 42.6 
 
 Penzance .....-- 44.7 
 
 Kendal ....-.-- 53.9 
 
 Mean of twenty places in the lower valleys at the base of the Alps 58.5 
 
 Great St. Bernard ...... 63.1 
 
 Vera Cruz - . - - - - - - 63.8 
 
 Keswick ....... 67.5 
 
 Calcutta - - - - - - - - 81.0 
 
 Bombay ....... 82.0 
 
 Ceylon ....---- 84.3 
 
 Adam's Peak, ditto ..-.-- 100. 
 
 Coast of Malabar ------- 123.5 
 
 I.,cogane, St. Domingo . . - - - 150.[1 
 
 * Dalton. t Danicll. i Howard. § Adie. 
 
 H From the Encyclopaedia Metropolitana. Article Meteorology, p. 123, 
 
QUANTITY EVAPORATED AND CONDENSED. 177 
 
 In this table the names of the places to which it refers are 
 arranged progressively, according to the amount of rain that falls 
 in each place ; and though the progression exhibits great irregu- 
 larities, yet the table fully establishes the general decrease of rain 
 with the increase of distance from the Equator. 
 
 Sir John Leslie has shown that if all the aqueous vapour which 
 can at any time be held in solution by the whole atmosphere, 
 were at once precipitated on the earth in the form of rain, it would 
 not be more than about five inches in depth : now as in the course 
 of a year many times this quantity of rain falls from the atmo- 
 sphere, its replenishment of course must depend upon evapora- 
 tion; of which evaporation we may thus infer the general amount. 
 With respect to the quantity of rain that descends annually on 
 the entire surface of the earth, we want the means of forming an 
 estimate, though tjiere is no proof that this quantity is subject to 
 any material diflerence. The distribution indeed, as we have 
 seen, diminishes with the latitude, and varies according to nume- 
 rous local peculiarities, to some of which we shall hereafter allude. 
 Often also, no doubt for the wisest purposes, the same place is 
 liable to considerable fluctuations in the annual amount of rain, 
 or at least in the times of its precipitation ; yet all these variations 
 oscillate within certain limits, and scarcely afTect the mean quan- 
 tity proper to the place ; thus showing that the distribution of 
 rain obe3's the same laws that regulate the more general and fixed 
 operations of nature. 
 
 Of the whole water that is condensed upon the surface of the 
 earth, a certain portion, of course, enters into the soil. The 
 depth to which such water sinks is determined by the declivity 
 of the surface, by the nature of the inferior strata, and by other 
 circumstances ; but, after a greater or less period, and range of 
 circulation, it usually again makes its appearance in the open day, 
 in the form of Springs. The conjunction of springs and the oc- 
 casional addition of a portion of rain water, which is neither im- 
 mediately absorbed by the soil, nor evaporated, constitute brooks 
 and rivulets ; these again uniting in their progress from the higher 
 and interior parts of the countries where this water has been 
 deposited, form the larger rivers, which, after dispensing innu- 
 merable benefits to the inhabitants of the plains in their course, 
 finally discharge their superfluous waters into the ocean. As the 
 origin of the superfluous water which flows from the rivers to the 
 ocean is thus, unquestionably, derived from the vapour condensed 
 in the interior of the countries where the rivers originate, it fol- 
 lows, that in every country where there are rivers, condensation 
 must surpass evaporation. That is to say, a large proportion of 
 water condensed on the land, must have been evaporated not from 
 the land, but from the neighbouring ocean. 
 
178 METEOROLOGY. 
 
 The relative proportions of the water that is condensed, and of 
 the water that is evaporated vary exceedingly in different countries. 
 Such indeed is the amount and variety of the differences that it is 
 impossible to estimate them ; though it is probable that in the same 
 country the proportions are nearly constant ; or, at least, that there 
 is a mean proportion about which the differences oscillate within 
 trifling limits. In this country, Dr. Thomson has estimated that, 
 taking the whole of Great Britain together, the mean fall of rain 
 amounts in the course of a year to 3G inches, the dew being in- 
 cluded, (which is considered to amount to about four inches) ; and 
 that the quantity of water evaporated is about 32 inches. Conse- 
 quently, the excess of four inches must be supposed to go to sup- 
 ply the springs and rivers : and as these four inclies are thus not 
 taken up again by evaporation from the land, they must be drawn 
 from the seas that encircle our shores.* These estimates of the 
 water that is condensed and evaporated in Great Britain can only 
 be viewed as rude approximations ; and, even admitting them to 
 be correct, they could scarcely be applied with any advantage to 
 an inquiry into the actual condensation and evaporation in other 
 countries or climates, which in all instances must be determined 
 by observation and experiment. 
 
 Having spoken of the accidental circumstances which influence 
 evaporation, we are now, in the last place, to treat of those acci- 
 dental circumstances which injiuence condensation. 
 
 The condensation of vapour fi'om the atmosphere, as we have 
 already stated, differs in some degree, according to the origin of 
 that diminished temperature by which the condensation is pro- 
 duced. We shall, therefore, commence with the phenomena of 
 the precipitation of moisture depending on the radiation of heat 
 from the earth's surface ; the most remarkable of these phenomena 
 are Dew, Hoar Frost, and certain forms of Mist, 
 
 Of Dew. — The phenomena of dew were flrst satisfactorily ex- 
 plained by the late Dr. Wells, who showed by the most decisive 
 experiments that, apparently, they were all owing to the effects 
 of the radiation of heat from the earth's surface into space, during 
 the absence of the sun. The reader is referred to Dr. Well's " Es- 
 say on Dew'^ for details. It is suflficient for our present purpose 
 to'observe, that when the direct influence of the sun is removed 
 in the evening, and the surface of the earth thus no longer conti- 
 nues to acquire heat; at that instant, from the ceaseless activity 
 
 • On heat and electricity, p. 266. It Is proper to observe, that this es- 
 timate differs considerably h-ooi a previous estimate of Dr. Dalton, who 
 fixes the proportion of water as flowinj^ ofl'by the rivers, in Eng-land and 
 Wales, at thirteen inches. It is probable that the truth lies somewhere 
 between the two estimates. 
 
DEW. 179 
 
 of heat to maintain a state of equilibrium, tlie surface of the earth, 
 being the warmer body, radiates a portion of its superfluous tem- 
 perature into the surrounding space ; and thus the air immediately 
 in contact with the surface becomes cooled below the point of sa- 
 turation, and gives olT a portion of its water in the form of dew. 
 
 We formerly stated that the radiating powers of bodies differ 
 exceedingly according to their composition, the nature of their sur- 
 face, their colour, &c. These differences, of course, produce cor- 
 responding effects on the deposition of dew ; and, as beautifully 
 demonstrated by Dr. Wells, explain its greater or less deposition 
 under certain circumstances, or its entire absence under others. 
 Thus, what formerly appeared so extraordinary, viz. why in the 
 self-same state of the atmosphere, Sic. one portion of the earth's 
 surface, or one portion of herbage, should be covered with dew, 
 while another in the immediate neighbourhood should remain dry, 
 is no longer a mystery, but is perfectly explicable on the suppo- 
 sition of their different radiating powers. 
 
 The deposition of dew is always most abundant during calm 
 and cloudless nights, and in situations freely exposed to the atmo- 
 sphere. Whatever interferes in any way with the process of ra- 
 diation, as might be expected, has a great effect on the deposition 
 of dew. Hence the radiation of heat, and consequently the deposi- 
 tion of dew, is not only obviated by the slightest covering or shel- 
 ter, as by thin matting, or even muslin ; by the neighbourhood of 
 buildings, and innumerable other impediments, near the earth's 
 surface ; but matters interposed at a great distance from the earth's 
 surface have precisely the same effect. Thus clouds effectually 
 prevent the radiation of heat from the earth's surface ; so that 
 cloudy nights are always warmer than those which are clear, and, 
 in consequence, there is usually on such nights little or no depo- 
 sition of dew. 
 
 From dew there is an insensible transition to Hoar Frosty hoar 
 frost being in fact only frozen dew, and indicative of greater cold. 
 We observe, therefore, that frosty nights, like simply dewy nights, 
 are generally still and clear. 
 
 The influence of radiation in producing cold at the earth's sur- 
 face would scarcely be believed by inattentive observers. Often 
 on a calm night, the temperature of a grass plot is 10° or 15° less 
 than that of the air a few feet above it. Hence, as Mr. Daniell 
 has remarked, vegetables, in our climate, are during ten months 
 of the year liable to be exposed at night to a freezing temperature, 
 and even in July and August to a temperature only two or three 
 degrees warmer. Yet, notwithstanding these vicissitudes, in the 
 words of the same gentleman, — " To vegetables growing in cli- 
 mates for which they are originally designed by nature, there can 
 be no doubt that the action of radiation is particularly beneficial, 
 
180 METEOROLOGY. 
 
 from the deposition of moisture which it determines upon the fo- 
 liage ; and it is only to tender plants, artificially trained to resist 
 the rigours of an unnatural situation, tliat this extra degree of cold 
 proves injurious."-^ It may be observed also, that trees of lofty 
 growth frequently escape being injured by frost, when plants 
 nearer tlie ground are quite destroyed. 
 
 Such is the explanation of the phenomena of dew now univer- 
 sally admitted, of the general accuracy of which there cannot be 
 the least doubt. But, we may ask, are all the phenomena of dew 
 strictly referrible to radiation ? and does not a portion of the water 
 deposited as dew arrive at the earth's surface by diffusion from 
 the higher and colder regions of the atmosphere, as formerly sug- 
 gested ? 
 
 Of Mists and Fogs. — Mists are not necessarily connected with 
 the deposition of dew, because during the deposition of dew the 
 atmosphere often continues transparent, even to the earth's sur- 
 face. At other times, however, and for reasons which, in the 
 present state of our meteorological knowledge, cannot be satisfac- 
 torily explained, the deposition of dew is accompanied by a visi- 
 ble vapour or mist, more or less dense, and extending from the 
 surface of the earth to a greater or less height in the atmosphere. 
 When mists, from other causes, are general, and extend to consi- 
 derable heights above the earth's surface they acquire the name of 
 fogs. The optical properties and the buoyancy in the atmosphere 
 of mists and fogs, would seem to mdicate that they are not formed 
 of solid particles, but of minute hollow vesicles, having the quality 
 of mutual repulsion; the tendency to repel each other, preventing 
 the coherence of the vesicles into drops, at least under ordinary 
 circumstances. These vesicles have been occasionally observed 
 of considerable magnitude. Thus Saussure, in one of his Alpine 
 journeys, saw vesicles float slowly before him having greater di- 
 ameters than peas, and whose coating seemed inconceivably thin. 
 It is proper to mention, however, that there is diversity of opinion 
 respecting the actual constitution of visible vapour. 
 
 That the cause of the formation of mists and of fogs is, to a 
 certain extent, similar to that of the formation of dew, appears by 
 their prevalence over rivers and large masses of water, especially 
 durin<r the autumnal months. The radiation of heat from the 
 land and from the water is at tliese seasons very different ; the 
 difference being greatest when the temperature of the water ap- 
 proaches 40°, its point of maximum density. The water is then 
 of a temperature nearly uniform, both by day and by night, while 
 the temperature of the land is, during the day, much higher than 
 40° and during the night, often much under that temperature. 
 
 • Meteorological Essays and Observations, p. 511, second edition. 
 
MISTS AND FOGS. 131 
 
 The water in most cases occupying the lowest situations ; when- 
 ever, from the inequalities of the surface of the land, or from any 
 other cause, the colder air produced by radiation over the land, is 
 made to mix itself with the warmer air over the water, the mois- 
 ture in the warmer air is condensed so as to become mist. Hence 
 the formation of mist differs slightly from that of dew, inasmuch 
 as there is occasionally (not always) an intermixture of air of dif- 
 ferent temperatures. The reason is thus evident of the fogs and 
 mists so frequently seen over rivers and in valleys, or in other 
 situations where there is a collection of water. The occurrence 
 of these mists is usually on clear and cold nights, — oftener in 
 autumn, and seldom or never in cloudy weather ; the state of the 
 atmosphere having exactly ihe same influence on them, as on the 
 deposition of dew. 'J'here cannot be a doubt that these mists, like 
 clouds, produce a great eifect in impeding radiation, and in thus 
 mitigating the intensity of cold. Mists are therefore of much im- 
 portance in the economy of nature. Plants growing in low 
 grounds are by them shielded from the destroying influence of the 
 sudden cold, that would almost certainly be produced, not only by 
 the free radiation of heat in such situations, but by the descent of 
 cold air from the surrounding high grounds. 
 
 The fogs that hang over great towns admit of an explanation 
 similar to that of other aqueous fogs. The air of the town being 
 warmer than that of the surrounding country, and being at the 
 same time charged with moisture nearly to the point of satura- 
 tion, is, in cold weather, suddenly cooled, either by the radiation 
 of its own heat, or by the admixture of the neighbouring cold 
 air ; while the superfluous moisture is condensed as a fog. 
 
 The fogs of high latitudes, more especially the fogs of the 
 Polar seas, are in the same manner owino- to the radiation of 
 heat. The cooling of the warmer air over the immense masses 
 of floating ice, gives rise to an unequal distribution of temperature, 
 and thus at certain seasons, to uninterrupted fogs. In all these in- 
 stances the effect of fogs is probably beneficial in alleviating the 
 severity of cold by checking great and sudden alternations of 
 temperature, which would otherwise interfere much with the 
 operations of organic life. 
 
 Fogs have been sometimes observed of a strong odour, appa- 
 rently the result of an admixture of foreign bodies. In a subse- 
 quent paragraph these fogs will be fully considered. 
 
 Of Clouds. — From mists and fogs the transition to clouds is 
 easy and natural ; as clouds, in reality, are nothing more or less 
 than masses of visible vapour, precisely similar to that compos- 
 ing fogs, but existing at a distance above the earth's surface. 
 Clouds diflfer principally from mists and fogs in their mode of 
 formation. Thus mists, like dew, as we have seen, are the re- 
 
 16 
 
182 METEOROLOGY. 
 
 suits of the cooling of the lower strata of the atmosphere by ra- 
 diation. Fogs are so far the result of radiation that they usually 
 arise from the influence that air cooled by radiation, exerts on 
 warmer air. While clouds probably depend altogether on con- 
 vection, and result from the intermixture of strata of air of dif- 
 ferent temperatures, and in different states of saturation, in the 
 higher regions of the atmosphere. 
 
 Such is the general opinion of the formation of clouds ; but it 
 must be confessed that there are considerable difficulties about the 
 subject ; and that the mere assumption of strata of diff'erent tem- 
 peratures, more or less saturated with vapour, and having the 
 proper motions supposed to depend upon such different tempera- 
 tures and degrees of saturation, seems quite inadequate to account 
 for all the phenomena connected with the formation and appear- 
 ance of clouds. May not many of the phenomena of clouds de- 
 pend upon the diffusion of vapour from cold and distant regions ? 
 May not other phenomena result from the more or less sudden 
 decomposition (by electricity ?) of the deutoxide of hydrogen 
 which we conceive to exist in the atmosphere ? 
 
 From the principles formerly stated when we described the 
 phenomena and properties of a mixed atmosphere of air and va- 
 pour, it appears that clouds in general must be formed at that 
 elevation in the atmosphere in which the mean temperature of 
 the air becomes equal to, or falls below the point of saturation of 
 such air. This elevation which may be said to constitute the 
 region of clouds, must of course be highest under the Equator — 
 an inference supported by fact ; for it has been observed that 
 within the tropics, the clouds are most frequently higher than in 
 the temperate zones ; and in the temperate zones the clouds ap- 
 pear to be higher in summer than they are in winter. In the 
 temperate zones Gay Lussac thinks that clouds, in general, are 
 upheld at an average distance from the earth's surface of between 
 1500 and 2000 yards. Occasionally, however, clouds have a 
 much greater altitude ; and the Cirnis, a form of cloud to be 
 presently described, has been seen far above the greatest elevation 
 hitherto attained by man. 
 
 In some parts of the world clouds are rarely seen, M'hile in 
 other parts the sky is seldom cloudless. Such extremes are 
 usually confined to extreme climates, or depend upon local causes. 
 In the temperate zones, from the irregularity of tlie atmospheric 
 currents, and from the other innumerable circumstances calculated 
 to disturl) the equilibrium of the atmosphere, the general character 
 of clouds varies much even under the same parallel of latitude. 
 Hence all the infinite variety of sunshine, of cloud, and of shower, 
 which more especially distinguish the temperate zones, and our 
 
CLOUDS. 183 
 
 own variable sky in particular; where ihey exert such constant 
 and commanding influence upon our comfort and well-being, as to 
 become almost interwoven with our very existence. 
 
 Though clouds are of such endless diversity o^ figure and ap- 
 pearance, they have been classed by Howard under three primary 
 forms, and four modifications. The three primary forms are : 
 
 The Cirrus, composed of fibrous-like stripes, parallel, flexuous, 
 or diverging, and extensible in all directions. 
 
 The Cumulus, heaped together in convex, or in conical masses, 
 and increasing upwards from a horizontal base. 
 
 The Stratus, spreading horizontally in a continuous layer, and 
 increasing from below. 
 
 The first of these forms, the cirrus, is confined chiefly to the 
 higher regions of the atmosphere. The second form, the cu- 
 mulus occupies a lower but still an elevated station ; while the 
 third form, the stratus, usually rests on the surface of the earth, 
 constituting the mist already described in this chapter. 
 
 Of the four modified forms of clouds, two are intermediate, and 
 two are composite. 
 
 The first of the intermediate forms is the Cirro-CumuIus, 
 consisting of small roundish, and well-defined masses in close 
 horizontal arrangement. 
 
 The masses that compose the second intermediate form of 
 clouds, the Cirro- Stratus, are likewise small and rounded, and 
 are attenuated towards a part or towards the whole of their cir- 
 cumference. They are sometimes separate ; when in groups, 
 their arrangement is either horizontal, or slightly inclined, and 
 the masses are either bent downwards, or are undulated. 
 
 Of the two composite forms of clouds, the first is the Cumulo- 
 Stratus, made up of the Cirro-Stratus blended with the Cumulus ; 
 the Cirro-Stratus being either intermingled with the larger masses 
 of the Cumulus, or widely enlarging the cumulous base. 
 
 The second composite form, and the last of the four modifica- 
 tions, of clouds, is the Cumulo-Cirro- Stratus, or JVhnbus, the 
 raiii- cloud ; being that cloud or system of clouds from which 
 rain is falling. The nimbus is a horizontal layer of aqueous va- 
 pour, over which, clouds of the cirrous form are spread, while 
 other clouds of the cumulous form enter it laterally and from be- 
 neath. 
 
 A little attention will enable any one to discriminate these va- 
 rieties of clouds, at least when their forms are well defined. Yet, 
 it must be acknowledged that clouds often assume forms to which 
 it is difficult to give a name. 
 
 With respect to the motion of clouds, it may be remarked that 
 there is not perhaps a more frequent subject of optical delusion, 
 nor anything regarding which, we are more liable to be mistaken, 
 
184 METEOROLOGY. 
 
 Into such inquiry it would be quite inconsistent with the design 
 of this treatise were we to enter minutely ; but we offer the fol- 
 lowing brief illustration. Let us suppose a cloud moving from 
 the distant horizon towards the place where we stand. Let us 
 also suppose that the cloud during its motion retains the same size 
 and figure, and that it proceeds along its course in a uniform 
 horizontal line. A cloud so moving, when first seen, will appear 
 to be in contact with the distant horizon ; and will thus necessa- 
 rily, from its remote position appear to be much smaller than in 
 reality it is. During its advance towards us, the cloud will seem 
 to rise into the sky, and to become gradually larger, till it is al- 
 most directly overhead. Continuing its progress it will then 
 seem again to descend from the zenith, and to lessen in size as 
 gradually as it had before increased, till at last it vanishes in the 
 distance, opposite to where it commenced its movement. Thus 
 the same cloud, without deviating from its motion in a straight 
 line, and retaining throughout the same size and figure, will, by 
 optical delusion, seem continually to vary in magnitude. The 
 line of its motion also, instead of being straight, will appear to be 
 a curve having its vertex directly above us, and its extremes 
 boundless in opposite points of the horizon. We have given the 
 most simple case that can be supposed. But clouds, as they ex- 
 ist in nature are unceasingly varying in shape, in magnitude, in 
 direction, and in velocity; so that to form a just estimate of their 
 figure and direction, or to unravel their motions, becomes abso- 
 lutely impossible. 
 
 After what has been stated, it will be superfluous to dwell upon 
 the uses of clouds in the economy of nature ; we shall therefore 
 briefly remind the reader of a few only of the most obvious be- 
 nefits derived from clouds. The first of these that claims our at- 
 tention is, that upon the large scale at least, clouds constitute a 
 sort of intermediate state of existence between vapour and water, 
 by which sudden depositions of water and their consequences are 
 entirely prevented. If all the water separated from the atmo- 
 sphere fell at once to tlie earth, in the slate of water, we should 
 be constanUy liable to deluges and other inconveniences, the 
 whole of which are obviated by the present beautiful arrangement. 
 Again clouds are one great means by which water is transported 
 from seas and oceans to be deposited far inland, where water 
 otherwise would never reach. Clouds also greatly mitigate the 
 extremes of temperature. By day they shield vegetation from 
 the scorching influence of the solar heat, and produce all the 
 agi'ecable vicissitudes of shade and sunshine : by night, the earth, 
 wrapt in its mantle of clouds, is enabled to retain that heat 
 which would otherwise radiate into space, and is thus protected 
 from the opposite influence of the nocturnal cold. These bene- 
 
SNOW. 185 
 
 fits arising from clouds are most felt in countries without the Tro- 
 pics, which are most liable to extremes of temperature, Indeed, 
 clouds constitute one great means by which, in temperate climates, 
 the extremes of heat and cold are regulated. Lastly, whether we 
 contemplate them with respect to their form, their colour, their 
 numerous modifications, or, more than all, their incessant state 
 of change, clouds prove a source of never-failing interest, and may 
 be classed among the most beautiful objects in nature. 
 
 Having finished the consideration of the various states of visi- 
 ble vapour, we are now to examine the phenomena of the preci- 
 pitation of water from the atmosphere in the form of Snow, Sleet, 
 Rain^ and Hail. We shall first speak. 
 
 Of Snow. — We commence with snow because it offers the 
 most simple case of the precipitation of water from the atmo- 
 sphere ; snow being nothing more than the frozen visible vapour 
 composing clouds. Hence a flake of snow examined with a 
 high magnifier exhibits a beautiful display of minute crystals, 
 often possessing the greatest variety of form. 
 
 W^hen the temperature of the atmosphere, down to the enrth's 
 surface, is constantly below the freezing point, it is obvious that 
 any moisture separated from the atmosphere must assume the 
 solid form. If the quantity separated be small, the frozen parti- 
 cles of water remaining detached, float in the atmosphere in the 
 form of crystallized spiculae, and thus give origin to what is called 
 ihe frost-smoke, a phenomena not unfrequently witnessed in polar 
 latitudes. Even in temperate climates, the same thing has been 
 supposed occasionally to take place in the higher regions of the 
 atmosphere, and thus to produce certain optical phenomena to 
 which we shall hereafter refer. 
 
 The above are comparatively rare phenomena. Most generally 
 the quantity of water separated is so large that the crystallized 
 particles are agglutinated together into masses or flakes, and thus 
 fall to the earth in the form of snow. When the quantity depo- 
 sited is very great, as is often the case, there can be no doubt that 
 the causes operating to produce such large deposition, are pre- 
 cisely similar to those which produce rain in warmer climates, 
 and which will be considered in a subsequent paragraph. 
 
 Such, in few words, are the principles upon which snow is 
 formed, and from these the reason is at once apparent, why during 
 the winter in temperate climates, and throughout the whole year 
 in the polar climates, most of the water that falls to the earth as=. 
 sumes the form of snow. 
 
 We formerly mentioned how nwich we owe to the lohiteness 
 of snow ; and we may now remark that we owe still more to its 
 low co^nducting properties, and to its lightness. Thus by its 
 low conducting properties snow shields vegetation from the rigo=^ 
 
 16* 
 
:^ 
 
 186 METEOROLOGY. 
 
 roiis cold of the higher latitudes, where everything herbaceous would 
 be destroyed during the winter, were it not for the protecting in- 
 fluence of snow. Again if the water which now descends to the 
 earth as snow, were to be precipitated in the form of solid masses 
 of ice, vegetation would be destroyed, and the whole of the colder 
 parts of the earth would be uninhabitable ! 
 
 It has been remarked, in temperate climates more especially, 
 that the air is usually warmer during a fall of snow, than before 
 or after. This increase of temperature probably arises from the 
 extrication of heat in the sensible form durino; the transition of the 
 vapour from a fluid to a solid state. Snow^-water has also been 
 said to contain much oxygen, and thus to be particularly favoura- 
 ble to vegetation. 
 
 Sleet is snow in a half melted condition, and constitutes the 
 intermediate state between snow and rain, to be next considered. 
 
 Of Rain. — When the temperature of the air is above 32°, the 
 freezing point of water, the water separated from the air falls to 
 the earth in the state of rain. Such is a general expression of 
 the fact ; but after all the attention that has been bestowed on the 
 phenomena of rain, many difficulties attend the investigation, that 
 have not yet been surmounted. 
 
 It cannot be doubted that rain is in some way connected with 
 change of temperature ; the perplexity attending the subject, 
 arises, pardy from the impossibility in many instances of account- 
 ing for the supposed change of temperature ; but much more from 
 the difficulty of understanding how this change of temperature 
 operates. According to the usual opinion, the precipitation of 
 water from the atmosphere is the effect of the mingling together 
 of currents of warm and of cold air, which are supposed to ope- 
 rate on each other in the following manner. 
 
 From the law of the tension of vapour, already described, it 
 follows, that when two currents of air having dilferent tempera- 
 tures, but both alike saturated with vapour, are mixed togetlier ; 
 though the resulting temperature of the mixture will be the mean 
 of the two, the resuhing tension of the vapour will not be likewise 
 the mean. The resulting tension of the vapour will always ex- 
 ceed the tension belonging to the resulting mean temperature ; 
 consequently there will be an excess of vapour which will be 
 precipitated in the form of water. Thus let us suppose two cur- 
 rents of air, both saturated with vapour, the one having a tempe- 
 rature of 40°, and the other a temperature of 60° and that these 
 two currents of air are mingled together ; 
 
 Inches of Mercury. 
 The tension or ekistic force of vapour at 40° is eqnul to - .263 
 of vapour at 60° is - - - - .524 
 
RAIN. 187 
 
 Whence it appears that the mean temperature of the two volumes 
 of air is 50°, and the mean of the elasticities of their vapour .393 
 inches. But the actual tension or elastic force of vapour at 50° 
 is not .393 inches, but only .375 inches ; after the intermixture, 
 therefore, of the two currents, a quantity of vapour will remain, 
 proportionate to the tension of 0.18 inches ; and as this superflu- 
 ity of vapour cannot be held in solution by air of the mean tem- 
 perature of 50°, it will be separated in the form of clouds, or of 
 rain, according to circumstances. 
 
 Such, in few words, are the opinions respecting rain first ad- 
 vanced by Dr. Hutton ; and notwithstanding some difficulties 
 about these opinions, there can be little doubt of their general 
 accuracy. The subject of condensation, in general, may perhaps 
 receive some additional elucidation from the principles regulating 
 a mixed atmosphere of vapour and air formerly described ; and 
 which may be thus applied. When two currents of atmospheric 
 air of diff'erent temperatures, and each charged with vapour up to 
 the point of saturation, are brought into contact ; they will begin 
 to intermingle in virtue of the proper motions of the air and va- 
 pour, and the immediate result will be the formation of visible 
 vapoKT, that is to say, of a cloud. If the currents are continuous 
 and uniform, the clouds soon spread in all directions, so as to oc- 
 cupy the whole horizon ; while ihe additional moisture incessantly 
 brought by the warmer current, or the occasional difl'usion of 
 vapour from a distant and colder region, keeps up a constant 
 supply for condensation, and produces a great and continued de- 
 position of moisture in the form of rain. By degrees the currents 
 completely intermingle, and acquire a uniform temperature ; con- 
 densation then ceases, the clouds are redissolved, and the whole 
 face of nature, after being cooled and refreshed by the necessary 
 rain, is again enlivened by the sunshine, thus rendered slill more 
 agreeable by its contrast with the previous gloom. 
 
 In this manner the principles formerly detailed may be applied 
 to the explanation of the phenomena of rain ; and as far as the 
 explanation goes it is perhaps quite satisfactory. It must, how- 
 ever, be allowed, as we have before stated, that the utmost infor- 
 mation which we can at present bring to bear upon the subject of 
 the general condensation of moisture from the atmosphere, and of 
 rain in particular, leaves it involved in considerable obscurity. 
 
 The following additional particulars regarding the ej/'ects of dif- 
 ferent localities, and of different circinnslances in the same lo- 
 cality which appear to influence the fall of rain, may interest the 
 general reader. 
 
 It has been remarked that in the greater nnmber of instances 
 more rain falls in tlie neighbourhood of the sea than in the sea; 
 a fact easily understood from the principles that have been stated. 
 
188 METEOROLOGY. 
 
 Among mountains also more rain falls than on plains; the excess 
 is indeed striking. Thus in our own country, at Kendal and at 
 Keswick, both inclosed by mountains, the annual fall of rain 
 amounts to 67i and 54 inches respectively, while in many inland 
 places the quantity of rain that falls in the course of a year hardly 
 exceeds 25 inches. So at Paris, the annual fall of rain is only 
 about 20 inches, but at Geneva 42| inches ; and on the Great St. 
 Bernard, the highest meteorological station in Europe, upwards 
 of 63 inches of rain fall during the twelve months. 
 
 Although more rain falls in mountainous districts than in plains, 
 it has been completely established, that more rain falls at the foot 
 of a mountain, than on its top. In general, too, a larger propor- 
 tion of rain is separated from the air, near the eartNs surface, 
 than at any height above it ; a discrepancy of which the present 
 extent of our knowledge does not enable us to give a satisfactory 
 explanation. 
 
 In most Tropical countries rain falls only at particular seasons 
 of the year, there being scarcely any rain during the other seasons. 
 Thus, at Bombay, the rainy months are June. July, August, 
 September, and October, while the other months are almost with- 
 out rain ; but on the opposite side of India, along the Coromandel 
 coast, the time of the occurrence of the rainy season is reversed; 
 a fact strikingly illustrative of the effect of the intervention of the 
 high table land that separates the two coasts, and which probably, 
 by influencing the atmospheric currents, give rise to this singular 
 alternation of weather. 
 
 In temperate climates, though the total quantity of rain that 
 falls be much less than within the Tropics, there is no protracted 
 dry season ; and the rainy days in the year are more numerous 
 the nearer we go to the Poles. Still in general, more rain seems 
 to fall in temperate climates during the last six, than during the 
 first six months of tiie year. 
 
 Among tiie circumstances which influence the quantity of rain 
 in the same locality, the most remarkable are diminution of 
 temperature^ and the unusual prevalence of certain ivinds. 
 
 With respect to diminution of temperature it has been observed 
 that almost all wet seasons, or at least wet summers, in temperate 
 climates, are unusually cold. Now from the principles formerly 
 advanced it will be easily understood, how a depression of the 
 temperature below the general standard in any locality, may give 
 rise to a greater precipitation of moisture in that locality. The 
 locality that has become colder than those around it, acts as a 
 refrigeratory, and not only condenses and thus deprives of their 
 elastic force, all the vapours that are in contact with it; but the 
 neighbouring vapours rush towards the colder locality as towards 
 a vacuum, either in the form of visible vapour or clouds, in 
 
HAIL. 189 
 
 which case they are carried by the winds ; or as invisible vapour, 
 in which form, their movement may be determined by diffusion. 
 
 The effect of the tmusual prevalence of certain winds in pro- 
 ducing an increase of rain, or tlie reverse, is well known, and is 
 quite intelligible on the principles we have explained. Thus in 
 tropical climates, during the steady prevalence of the trade winds, 
 the currents intermingle but little, the atmosphere is perfectly 
 cloudless, and no condensation takes place. But when these 
 great currents, following the course of the sun, begin at certain 
 seasons of the year to shift their direction ; their uniform course 
 suffers derangement, they become intermixed, and condensations 
 of moisture commensurate with the high temperature, are pro- 
 duced to an extent quite unknown in temperate climates. These 
 condensations form the violent periodical rains of hot climates. 
 So also in temperate climates, as for instance in our own country, 
 winds coming from the south and from the west, are from a 
 warmer climate, and hold much vapour in solution ; while winds 
 from the opposite points are colder, and therefore relatively drier. 
 Hence winds from the south and from the west, are more fre- 
 quently accompanied by rain, than winds from the north and from 
 the east : though as we might expect, the precipitation of rain is 
 most decided during the conflicts between these opposite currents, 
 which sometimes extend over a large tract of country. The long 
 prevalence of certain winds may thus cause the seasons to be wet 
 in one part of the world, and dry in another; the water being as 
 it were, distilled off from the one, in order that it may be precipi- 
 tated on the other. Yet the whole amount of the rain in the two 
 countries may perhaps differ very little from the usual average, 
 while the two countries have the benefit of variety in the general 
 amount of their rain ; which variety may be salutary at particular 
 periods, and may even be necessary to their well-being. 
 
 Before we end the examination of the phenomena of rain, it may 
 be proper to advert to the generally admitted influence of the Moon 
 on the weather, and especially on the fall of rain. This influence, 
 however, can hardly in the present state of our knowledge be 
 brought to elucidate the phenomena of rain ; so great are the dis- 
 turbing effects of local and other peculiarities. 
 
 Of Hail. — The last form in which we have to consider the pre- 
 cipitation of water from the atmosphere, is hail. Hail may be re- 
 garded as consisting of drops of rain more or less suddenly frozen 
 by exposure to a temperature below 32°. If the degree of cold 
 has been very sudden and intense, which is often the case, the 
 icy nucleus, from its being of a temperature far below the freezing 
 point, acquires magnitude as it descends, by condensing on its 
 surface the vapour of the lower regions of the atmosphere. Hence, 
 even under ordinary circumstances, hail stones often become of 
 
190 METEOROLOGY. 
 
 considerable size, are nearly always more or less rounded, and 
 when broken are seen to be composed of concentric layers. 
 
 From what has been stated it will be readily inferred that hail 
 is not a product of extreme climates ; indeed hail may be said to 
 be peculiar to temperate climates, as it rarely ever occurs beyond 
 the latitude of 60°. Hail is most frequent in spring and in sum- 
 mer, when it is often accompanied by thunder. It seldom hails 
 in winter, and hail during the night is very uncommon. In tro- 
 pical countries there is little hail in any place that is not more 
 than 2000 feet above the level of the sea: in temperate climates, 
 on the contrary, mountain tops are almost free from hail. Certain 
 countries, especially some parts of France, are very liable to hail 
 storms ; and such is at times the fury of these storms that they 
 lay waste whole districts. There are on record many instances 
 of these calamitous visitations, which are usually accompanied 
 by whirlwinds and by the most appalling electrical phenomena. 
 During storms of such degree of severity, hail stones have some- 
 times fallen of enormous magnitude, and often of an irregular 
 shape, as if they were the fragments of a thick sheet of ice suddenly 
 broken : a supposition which alone will explain the formation of 
 angular masses, many inches in size, and many pounds in weight. 
 The production in the middle of summer of the intense cold that 
 is thus indicated is a puzzle which philosophers have been unable 
 to solve. 
 
 Of the Distribution of Heat and Light in their latent and de- 
 composed Forms through the Vapour of the Atmosphere ; and 
 of the Effects of that Distribution. — The general distribution of 
 heat and light in their latent forms through the vapour of the at- 
 mosphere, seems to follow the same laws as the distribution of 
 sensible heat formerly explained. That is to say, the distribution 
 of these forms of heat and light decreases from the Equator toward 
 the Poles. The most remarkable effects of the distribution of la- 
 tent heat have already been incidentally mentioned, and need not 
 be here repeated. We shall therefore proceed to consider the par- 
 ticular distribution of the decomposed forms of heat and light in 
 the vapour of the atmosphere, and the efiects of this distribution. 
 
 Of the Relations of Electricity to the Vapour of the Atmo- 
 sphere. — Atmospheric air, when perfectly dry and pure, is one 
 of the most complete non-conductors of electricity that are known. 
 Whether water in the state of vapour possesses similar non-con- 
 ducting properties does not appear to be satisfactorily established. 
 But the non-conducting powers of aqueous vapour must be very 
 considerable, otherwise, since the atmosphere is never entirely 
 free from vapour, electrical insulation could not takd place. On 
 the other hand, the moment that vapour assumes the form of water, 
 it acquires the property of being a conductor of electricity. Hence 
 
RELATION OF ELECTRICITY TO VAPOUR. 191 
 
 a mass of visible vapour or cloud, when floating in a mixed atmo- 
 sphere of air and vapour, is perfectly insulated, and is thus capa- 
 ble of electrical accumulation. Now the phenomena arising from 
 the equalization of such derangements of electrical distribution, 
 are lightning and thunder. Lightning and thunder therefore are 
 nothing, either more or less, than the phenomena of electricity on 
 a large scale ; that is to say, a cloud and the earth, or two clouds, 
 become surcharged with the two opposite forms of electricity, and 
 thus represent the interior and the exterior coatings of an electrical 
 jar similarly surcharged ; the intervening and non-conducting air 
 are represented by the interposed and non-conducting glass ; 
 while the lightning and the thunder are the spark and the explo- 
 sion caused by the union of the two electricities. If the reader 
 bear in mind this analogy, it will enable him to understand the 
 whole electrical phenomena of the atmosphere. 
 
 The distribution of electricity, like that of heat and light, de- 
 creases from the Equator toward the Poles. Thus, in intertropi- 
 cal countries alone, are the effects of this energetic agent displayed 
 in all their power ; there, thunder storms are quite terrific, and far 
 surpass anything of which those, who have not witnessed them, 
 can form a conception. In temperate climates the effects of at^ 
 mospheric electricity are usually most severe in the summer; and 
 their severity is greater in mountainous districts than in plains. 
 Yet, even under these circumstances, they are much subdued, as 
 compared "with what takes place between the Tropics ; while in 
 the Polar regions electrical phenomena are still less striking. 
 
 Notwithstanding, however, that the general distribution of elec- 
 tricity in the atmosphere, evidently follows the general distribu- 
 tion of sensible heat, it is a remarkable fact, that whenever elec- 
 trical phenomena are more than ordinarily vehement, they are ac- 
 companied by some unusual appearance of cold. Thus the alarm- 
 ing descents of hail formerly noticed, which occur most generally 
 in temperate climates, have, in nearly every instance, been attend- 
 ants of violent thunder storms. Snow also is almost always highly 
 electric. These, and manv other circumstances connected with 
 the great and sudden production of cold in the higher regions of 
 the atmosphere, during the display of electrical agency, cannot, 
 in the present state of our knowledge, be explained. For example, 
 whence, in the middle of summer, arises that instantaneous deve- 
 lopement of extreme cold, which occasionally produces the terrific 
 hail storms above alluded to ? At present the answer does not ap- 
 pear. Whether the principles advanced in the present volume 
 be capable of solving the difficulty, time must determine. 
 
 With respect to the sources of the electricity of the atmosphere 
 there have been many opinions. It seems now to be admitted 
 that electrical excitement does not arise from the mere evapora- 
 
192 METEOROLOGY. 
 
 tion and condensation of water ; but that in order to produce such 
 excitement, there must always be some chemical combination or 
 separation.* Thus electrical excitement is the result of the che- 
 mical changes which often accompany the evaporation of water. 
 During combustion also there is an ample evolution of electricity ; 
 the burning body giving out negative, the oxygen positive electri- 
 city. In like manner, the carbonic acid sent forth during vegeta- 
 tion is charged with negative electricity, and at the same time the 
 oxygen, as is most likely, is charged with positive electricity. 
 Derivation from these sources has been deemed quite sufficient to 
 explain the very large quantities of electricity that are so often ac- 
 cumulated in the clouds. It is however probable that there are 
 yet other causes, or at least one other cause, on which, in nume- 
 rous instances, this accumulation may still more immediately de- 
 pend. AVe allude to the combination of oxygen with the vapour 
 of the atmosphere formerly mentioned. For reasons which we 
 cannot here detail, our opinion is, that this combination of aque- 
 ous vapour with oxygen, more than any other cause whatever, is 
 in some way concerned with the piienomena of atmospheric elec- 
 tricity. 
 
 The Jlurora horeaUs is a phenomenon supposed to have some 
 connection with electricity, though its precise nature is involved 
 in considerable obscurity. The phenomenon evidently indicates 
 currents of some kind ; and if the light be electrical, we can only 
 suppose such electrical currents to take place in an imperfectly 
 conducting medium. That is to say, if the phenomenon, as some 
 contend, exist in the lower regions of the atmosphere, luminous 
 electrical currents can be produced only by water in the liquid 
 state ; if the phenomenon exist in the higher regions of the atmo- 
 sphere, as at present is supposed, such currents may depend upon 
 the extreme tenuity of the atmosphere in these higher regions. 
 Our own opinion is, that at different times, the aurora borealis 
 exists at different heights in the atmosphere, and consequendy 
 may depend upon both these causes. Has the diffusion of vapour 
 from the Polar towards the Equatorial regions of the globe any 
 connexion with the phenomenon ? 
 
 The phenomenon depending upon the decomposition, refrac- 
 tion, and rejlection of light by the vapour of the 'atmosphere 
 are not less striking and important than tliose produced by electri- 
 city. To such effects upon light by the atmospheric vapour we 
 owe not only the cacrulean tint of the sky, and all the splendid 
 colouring of the clouds, but tlie beneficial morning and even- 
 ing twilight, nay even the light of day itself. " Were it not," 
 
 • Pouillct, Elemensde Physique experimentale etde Moteorolog-ie, torn, 
 ii. p. 823. 
 
MIRAGE. FATA MORGANA. HALOS, ETC. 193 
 
 says Sir J. Herschel, " for the reflecting and scattering power of 
 tlie atmosphere, no objects would be visible to us out of direct 
 sunshine, every shadow of a passing cloud would be pitchy dark- 
 ness ; the stars would be visible all day, and every apartment 
 into which the sun had not direct admission would be involved in 
 nocturnal obscurity." Again to use the words of the same author, 
 in speaking of twilight, — " After the sun and moon are set, the 
 influence of the atmosphere still continues to send us a portion of 
 their light ; not indeed by direct transmission, but by reflection 
 upon the vapours and minute solid particles which float in it, and 
 perhaps the actual material atoms of the air itself."* Such are 
 the beautiful phenomena and the important results of the action 
 of the vapour of the atmosphere upon light. It remains to men- 
 tion a few others, of a similar character, produced by the same 
 causes, but of less frequent occurrence and of less importance in 
 the economy of nature. 
 
 The first of these minor phenomena which we shall notice is 
 the Mirage, a phenomenon depending partly on the vapour of 
 the atmosphere, and pardy on the intermixture of strata of air of 
 difierent temperatures and densities. The mirage is not unfre- 
 quent in level countries, when their surface is strongly heated by 
 the sun's rays, and evaporadon results from the continuance of 
 the heat. The mirage assumes the appearance of a sheet of water, 
 often exhibiting the reflected or inverted images of distant ob- 
 jects. In Egypt and in the neighbouring sandy plains, where 
 the mirage is very common, the illusion is at times so perfect, 
 that travellers can hardly be convinced of the non-existence of 
 what they imagine they see.t The phenomena are quite expli- 
 cable on well known optical principles.;}: 
 
 Nearly allied to the mirage is the appearance termed Fata 
 Morgana,, which is occasionally witnessed in the Straits of Mes- 
 sina. There are many similar phenomena, all of them owing to 
 the refraction of light by media of various densities. 
 
 The next class of phenomena to be noticed are those produced 
 upon light by crystals of ice floating in the atmosphere, or by 
 visible vapour. The angular forms of the crystals of ice, by de- 
 termining the rays of light in different directions, give origin to 
 various eccentric halos ; which, by their united intensities, par- 
 ticularly where they cross one another, occasionally produce con- 
 spicuous masses of light, denominated parhelia and paraselenes, 
 or mock suns and mock moons. Visible vapours, consisting of 
 water in the fluid state, likewise sometimes form halos ; but 
 
 • Treatise on Astronomy, p. 33. 
 
 f See Clarke's Travels. 
 
 ^ See WoUaston, Philosophical Transactions, 1800, p. 239. 
 
 17 
 
194 METEOROLOGY. 
 
 these halos (when more than one exists) are always concentric, 
 the sun or moon being in the centre. These two phenomena not 
 unfrequenlly take place at the same time. 
 
 The last and most frequent phenomenon of the general kind 
 ■which we shall notice is produced by the action o^ fluid drops of 
 water upon light, viz. the well known phenomenon termed the 
 Rainbow. The concomitants of the rainbow are familiar to every 
 one : there must be rain along with sunshine. Under these cir- 
 cumstances if the spectator turns his back to the sun, he sees the 
 coloured bow project on the opposite cloud, and displaying all 
 the tints of the prismatic spectrum. 
 
 We are informed in the sacred narrative, that this beautiful phe- 
 nomenon was chosen as a symbol to mankind of their exemption 
 from future deluge. The sceptic may be challenged to state 
 what pledge could have been more felicitous or more satisfactory. 
 In order that the rainbow may appear, the clouds must he partial. 
 Hence the existence of the rainbow is absolutely incompatible 
 with universal deluge from above. So long, therefore, as " He 
 doth set his bow in the clouds" so long have we full assurance 
 that these clouds must continue to shower down good and not 
 evil upon the earth. 
 
 3. Of the Occasional Presence of Foreign Bodies in the at- 
 mosphere and of their Effects. — The foreign bodies that occa- 
 sionally exist in the atmosphere may be considered as of two 
 kinds ; viz. those which are merely suspended in the atmosphere 
 in a state of mixture ; and those which pervade the atmosphere 
 in a state of solution. 
 
 Both in ancient and in modern times, and in various parts of 
 the world, rain and snow have been observed to be coloured by 
 an admixture of extraneous matters. The nature of these colouring 
 matters has been found to be very different in different instances ; 
 some have proved to be of vegetable origin, consisting of minute 
 lichens and other cryptogamous plants^ brought from a distance 
 by the agency of the winds, and diffused in myriads through the 
 atmosphere. Such vegetable matters have been sometimes more 
 or less red: whence those imagined showers of blood we read of 
 as producing so much popular excitation. In other'instances the 
 colour has been given by earthy and metallic matters in a state of 
 very fine powder, and in this case tlieir descent has been usually 
 accompanied by violent electrical phenomena, simihir to those 
 which almost always attend the descent of Meteoric stones or 
 Aerolites, to which perhaps they are nearly allied. 
 
 Of the falling of stones from the atmosphere, there can now be 
 no doubt ; though the origin and the nature of these stones are 
 very obscure, and indeed cannot, in the present state of our 
 knowledge, be explained. Tliere have been various opinions on 
 
FOREIGN BODIES IN THE ATMOSPHERE. 195 
 
 the subject. Some, considering aerolites to be the productions of 
 our own planet, have viewed them as masses projected from 
 volcanoes to a great height and distance in the atmosphere ; or as 
 formed by the agglutination of the earthy and metallic powders 
 from volcanoes, as before mentioned. Others ascribing to aerolites 
 quite a different origin, have viewed them as fragments scattered 
 through space, which happening to come within the sphere of our 
 earth's attraction, have been determined to its surface, (fee. 
 
 Although we are thus uncertain regarding the origin of aerolites, 
 or their use in the economy of nature ; it now seems by innume- 
 rable observations to be completely established, that aerolites, 
 while in the higher regions of the atmosphere, are often in a 
 state of intense ignition. They there assume the form of bril- 
 liant meteors, which as they approach the earth, burst with a 
 loud explosion, followed by a shower of stones. These stones 
 generally exhibit evident marks of fusion : and many of them 
 have been picked up while still warm, so as to leave no doubt of 
 their being real aerolites, it is singular too, that the composition 
 of aerolites is in some degree peculiar. They invariably con- 
 tain, either iron, or cobalt, or nickel, or all these three metals, in 
 union with various earthy substances. Aerolites have been 
 found of every size, from that of a kw grains to the weight of 
 several hundreds of pounds ; for of this weight are some of those 
 isolated masses of iron seen in different parts of the world, and 
 which are generally allowed to be of meteoric origin. 
 
 Intermediate, as it were, between substances suspended, and 
 substances dissolved, in the atmosphere, are those matters, what- 
 ever their nature may be, which have Ibeen known to spread as 
 a haze over large districts, and have been termed " Dry Fogs.'''' 
 
 In the year 1782, and still more in the year following, a re- 
 markable haze of this kind extended over the whole of Europe. 
 Seen in mass this haze was of a pale blue colour. It was thickest 
 at noon, when the sun appeared through it of a red colour. Rain 
 did not in the least degree affect it. This haze is said to have 
 possessed drying properties, and to have occasionally yielded a 
 strong and peculiar odour. It is also said to have deposited in 
 some places a viscid liquid, of an acrid taste, and of an unplea- 
 sant smell. About the same time, there were, in Calabria and in 
 Iceland, terrible eardiquakes, accompanied by volcanic eruptions. 
 These earthquakes and eruptions were supposed to have been 
 connected with the haze. Indeed it has been generally remarked, 
 that such a condition of the atmosphere has been usually pre- 
 ceded by an Ccirthquake, either in the same or in some adjoining 
 countty. The dispersion of this haze in the summer of 1783 
 was attended by severe thunder storms. As might be expected, 
 the general stale of health has, for the most part, been deranged 
 
196 METEOROLOGY. 
 
 during the continuance of these phenomena. Simultaneously 
 there have been epidemic diseases of various kinds. Thus, in 
 the above mentioned years, 1782 and 1783, an epidemic catarrh, 
 or influenza, prevailed throughout Europe ; affecting not only 
 mankind but likewise other animals,* 
 
 The nature of the matter thus difi'used through the atmosphere 
 is quite unknown. It may be as various at ditlerent times as the 
 character of the epidemics to which it gives origin. As an ex- 
 ample of the extraordinary effects which foreign bodies, when 
 diffused through the atmosphere, are capable of producing, we 
 may mention those produced by Selenium when, in combination 
 with hydrogen, it is diffused as a gas through the air, even in 
 the most minute quantity. The effects of this gaseous combina- 
 tion of selenium with hydrogen are thus described by the cele- 
 brated chemist, Berzelius, its discoverer. " In the first experi- 
 ment which I made on the inhalation of this gas, I conceive that 1 
 let up into my nostrils a bubble of gas, about the size of a small 
 pea. It deprived me so completely of the sense of smell, that I 
 could apply a bottle of concentrated ammonia to my nose without 
 perceiving any odour. After five or six hours, I began to recover 
 the sense of smell, but a severe catarrh remained for about fifteen 
 days. On another occasion, while preparing this gas, I became 
 sensible of a slight hepatic odour, because the vessel was not 
 quite close ; but the aperture was very small, and when I covered 
 it with a drop of water, small bubbles were seen to issue, about 
 the size of a pin's head. To avoid being incommoded with the 
 gas, I put the apparatus under the chimney of the laboratory. I 
 felt at first a sharp sensation in my nose ; my eyes then became 
 red, and other symptoms of catarrh began to appear, but only to 
 a trifling extent. In half an hour I was seized with a dry and 
 painful cough, which continued for a long time, and which was 
 at last accompanied by an expectoration, having a taste entirely 
 like that of the vapour from a boiling solution of corrosive subli- 
 mate. These symptoms were removed by the application of a 
 blister to my chest. The quantity of Seleniuretted Hydrogen 
 Gas which on each of these occasions entered into my organs of 
 respiration ivas much smaller than would have been required 
 of anv other inorganic substance whatever, to produce similar ef- 
 fects f't' 
 
 As we have already stated, selenium is for the most part found 
 in association with mineral sulplu'h'. Selenium is also, like sul- 
 phur, a volcanic product. Now, though we can hardly imagine 
 the possibility of the diffusion of selenium through the atmo- 
 
 * See article Influenza, in the Encyclopaedia of Practical Medicine, 
 f Annals of Philosophy, Old Series, vol. xiv. p. 101. 
 
EFFECTS OF FOREIGN BODIES IN THE AIR. 197 
 
 sphere in combination with hydrogen ; selenium may be so dif- 
 fused in some other form of combination, which may produce 
 eilects analagous to those of seleniuretted hydrogen. We do not 
 mean to assert that the diffusion of any such substance really 
 takes place. Our intention is merely to show that a small quan- 
 tity of an active ingredient, like selenium, is sufficient to con- 
 taminate the atmosphere over a wide extent of country. Such a 
 substance being ejected from the crater of a volcano during an 
 eruption, or through a crevice in the earth during an earthquake, 
 may thus produce an epidemic disease. Nor is it improbable 
 that many epidemics, particularly those of a catarrhal kind, have 
 so originated. 
 
 The matters occasionally diifused through the atmosphere, 
 which appear to be in a state of solution., are not often percepti- 
 ble by our senses, unless in some cases, perhaps, by the sense 
 of smell. 
 
 As an instance of the presence of such bodies in the atmo- 
 sphere we may mention a very remarkable observation which oc- 
 curred to the writer of this treatise during the late prevalence of 
 epidemic cholera. He had for some years been occupied in in- 
 vestigations regarding the atmosphere ; and for more than six 
 weeks previously to the appearance of cholera in London, had 
 almost every day been engaged in endeavouring to determine, 
 with the utmost possible accuracy, the weight of a given quantity 
 of air, under precisely the same circumstances of temperature and 
 of pressure. On a particular day, the 9th of February, 1832, 
 the weight of the air suddenly appeared to rise above the usual 
 standard. As the rise was at the time supposed to be the result 
 of some accidental error, or of some derangement in the appa- 
 ratus employed ; in order to discover its cause, the succeeding 
 observations were made with the most rigid scrutiny. But no 
 error or derangement whatever could be detected. On the days 
 immediately following, the weight of the air still continued above 
 the standard ; though not quite so high as on the 9th of February, 
 when the change was first noticed. -The air retained its aug- 
 mented weight during the whole time these experiments were 
 carried on, namely, about six weeks longer. The increase of the 
 weight of the air observed in these experiments was small ; but 
 still decided, and real. The method of conducting the experi- 
 rnents was such as not to allow of an error, at least to an amount 
 so great as the additional weight, without the cause of that error 
 having become apparent. There seems, therefore, to be only one 
 mode of rationally explaining this increased weight of the air at 
 London in February, 1832 ; which is, by admitting the diffusion 
 of some gaseous body through the air of this city, considerably 
 heavier than the air it displaced. About the 9th of February the 
 
 17* 
 
198 METEOROLOGY. 
 
 wind in London, which had previously been west, veered round 
 to the east, and remained pretty steadily in that quarter till the 
 end of the month. Now, precisely on the change of the wind 
 the first cases of epidemic cholera were reported in London ; and 
 from that time the disease continued to spread. That the epi- 
 demic cholera was the effect of the peculiar condition of the at- 
 mosphere, is more perhaps than can be safely maintained ; but 
 reasons, which have been advanced elsewhere, lead the writer of 
 this treatise to believe that tlie virulent disease, termed cholera, 
 was owing to the same matter that produced the additional weight 
 of the air. The statement of these reasons here would be quite 
 out of place : it is enough to say, that they are principally founded 
 on remarkable changes in certain secretions of the human body, 
 which, during the prevalence of the epidemic, were observed to 
 be almost universal ; and that analogous changes have been ob- 
 served in tlje same secretions of those, M^ho have been much ex- 
 posed to what has been termed JMalaria. The foreign body, 
 therefore, that was diffused through the atmosphere of London, 
 in February, 1832, was probably a variety of malaria, a subject 
 which we now proceed to consider. 
 
 \\\ districts partially covered with water, and having a luxuriant 
 vegetation, such as marshes and fens, particularly in warm coun- 
 tries ; or in colder countries, at seasons of the year when the 
 sun is most powerful ; noxious exhalations arise, whose nature 
 differs perhaps in some degree according to the locality. Such 
 exhalations have received the general name of Malaria, and are 
 well known to be the fertile source of various diseases, more or 
 less, of the intermittent febrile type. In cold and in temperate 
 climates, those diseases for the most part assume the character of 
 regular ague, or of rheumatism : but on approaching to, and with- 
 in tlie Tropics, they appear as tlie more formidable remittent and 
 continued fevers, tlie well-known scourges of hot climates. 
 
 With respect to the nature of these exhalations our knowledge 
 is very imperfect. Evidently, they are in some way connected 
 with vegetation ; not however with vegetation living and in a 
 state of growth, but with vegetation in a state of decay. It has 
 therefore been thought likely that these exhalations contain some 
 gaseous body, composed chiefly of hydrogen and carbon. Their 
 effect may arise from a gaseous compound of this description, 
 though no such compound is at present known; and the pro- 
 bability is, t-jiat malaria occasionally owes its properties to other 
 elements, besides the hydrogen and carbon disengaged from de- 
 caying vegetables. 
 
 We have thus endeavoured to oive a concise statement of that 
 wonderful assemblage of Laws, of Adaptations, and of Arrange- 
 ments, which viewed together constitute what we term Climate; 
 and which, as affecting the welfare of the denizens of this globe. 
 
GENERAL DESIGN EVINCED BY CLIMATE. 199 
 
 undoubtedly, are not surpassed in interest or importance by any 
 others throughout the whole of nature. Of the innumerable suns 
 and planets that m.ay occupy the boundless expanse of the uni- 
 verse we feel not the influence ; even their existence scarcely 
 obtrudes itself upon our notice. But in the light and the heat of our 
 own sun, and in the wind and the rain of our own atmosphere, every 
 organized being on this earth, from Man, the Lord of its creation, 
 down to the humblest plant that drinks the dew, is alike most 
 intimately concerned. The subject of Meteorology, therefore, in 
 all ages and countries, has attracted the especial attention of man- 
 kind. In ruder states of society empirical prognostics, founded 
 on the aspects of the clouds, on the movements of animals, and 
 on other incidental occurrences, formed the study of those who 
 pretended to a foreknowledge of tlie weather; while electrical 
 phenomena were to them objects of superstitious awe. In 
 modern times much of this wonder and uncertainty has been 
 removed. The gloom or the clearness of the air, the mists and 
 the halos of a stormy sky, the restlessness and clamour of ani- 
 mals, &c., are now referred simply to that overcharge of moisture, 
 and to that unequal distribution of electricity which precede a 
 fall of rain. Nay, the very thunderbolt has been arrested in its 
 course, and from being no longer an object of amazement, has 
 been divested of half its terrors. 
 
 But is this advance in knowledge calculated to lessen our 
 veneration for the great Author of nature, or to derogate from his 
 wisdom and his power ? On the contrary, our estimate of both 
 must be greatly increased. Of the Deity, infinite as he is, and 
 dwelling in infinity, we finite beings can form no conception. 
 What little, therefore, we can know of Him, we know nearly 
 altogether from His works. Consequently he who has the most 
 studied His works, will be the best qualified — nay, will be alone 
 qualified, to form an adequate conception of Him. Thus to 
 measure, to weigh, to estimate, to deduce, may be considered as 
 the noblest privileges enjoyed by man ; for only by these opera- 
 tions is he enabled to follow the footsteps of his Maker and to 
 trace His great designs. Instructed by these, he sees and appre- 
 ciates the wisdom and the power, the justice and the benevolence 
 that reign throughout creation: he no longer gazes on the sky 
 with stupid wonder ; nor dreads the thunderbolt as manifesting 
 the wrath of a vengeful Deiiy. 
 
 The constituents of climate, even imperfectly as they can be 
 understood by us, are seen to be adjusted and arranged in a man- 
 ner so surprising, that to those who admit the existence of design, 
 they require only to be stated and apprehended, in order to their 
 being received as additional proofs of that great argument. Where 
 all are great, and splendid, and good, selection is precluded; but 
 
200 METEOROLOGY, 
 
 the circumstances accompanying the distribution of Water oyer 
 this globe, more perhaps than any other, arrest our notice as in- 
 dicative of design. Leaving out of view the other properties of 
 water ; on what other supposition, besides that of design, can 
 we account for all these astonishing properties on which de- 
 pend its evaporation and diflusion through the atmosphere — its 
 subsequent condensation, not at once in tlie form of water or of 
 ice, but in the intermediate state of clouds — its colour and light- 
 ness when in the state of snow — its power of refracting light and 
 of conducting electricity — in short, all the numerous, minute, and 
 happily contrived qualities displayed by this highly elaborated 
 fluid ? These together form such a union of adaptations and ar- 
 rangements, each most successfully accomplishing a particular 
 purpose, and apparently directed to, and designed for, that pur- 
 pose, that to doubt the agency of .design would seem impossible. 
 Yet there are some men's minds so warped that they either can- 
 not or will not be persuaded of the existence of design ; but 
 asserting the omnipotence of the laws of nature, they forget Him 
 who framed these laws, and are reluctant to give credence to His 
 being or to His power. To such persons Meteorology offers one 
 or two exclusive arguments, which, at the risk of being accused 
 of tediousness, and unnecessary repetition, we shall urge briefly 
 in tliis place. 
 
 The great Author of Nature, as we have before said, has 
 chosen to act agreeably to certain established laws, by which he 
 is invariably guided. Some of these laws we are able more or less 
 to comprehend, and we can refer them to more general principles. 
 Others are beyond our comprehension : we see only their etlects ; 
 and even these eflects are most imperfectly revealed to us. As 
 instances of tlie laws of nature which it is in our power to refer 
 to general principles, may be mentioned the currents in the ocean 
 and in the atmosphere, by which the equilibrium of temperature 
 over tlie globe is maintained. These currents, we know, are 
 strictly referrible to hydrostatic and pneumatic principles. The 
 argument of design, which is deduciblc from these principles, rests, 
 therefore, not so much on the principles themselves, as on their 
 application precisely where they are requisite. On the other 
 hand, as we stated at ilie commencement of this book, the laws 
 of chemistry are founded solely on experience ; so that our ac- 
 quaintance with them is very defective ; for in very few instances 
 are they referrible to the laws of quantity, and even when they 
 can be so referred, it is only in a manner very imperfect. But 
 though we do not comprehend the laws of chemistry, we see 
 that many of them, perhaps all, in so far as they are intelligible 
 to us, are entirely consilient with each other ; and are as uniform 
 in their operation as those which obviously depend on mechanical 
 
GENERAL DESIGN EVINCED BY CLIMATE. 201 
 
 principles, or on the laws of gravity. Thus the laws, that all 
 bodies are expanded by heat and are contracted by cold — that 
 chemical substances do not mix, but always combine in certain 
 proportions, and in no others, — are general laws, to which there 
 are so few exceptions, that they are calculated on almost with as 
 much certainty, in the operations of nature, and in the common 
 intercourse of mankind ; as the invariable and necessary results, 
 that a heavy body will fall to the earth, or that two and two 
 make four. We have selected these laws of chemistry partly 
 from their general and indisputable character, and partly that the 
 force of the argument which follows may be more conspicuous: 
 
 tdll bodies are expanded by heat and contracted by cold. If 
 water had not constituted an exception to this law, though all its 
 other properties had been the same as they now are, long before 
 this time, as we have seen, half tlie water on the globe would 
 have been converted into ice ; and the existence of organized 
 beings would have been physically impossible. 
 
 *^ll chemical substances combine in certain proj^ortions, and 
 in no others. If air had been formed according to this law, every- 
 thing else being the same as at present, long before this time, 
 half of the air in the atmosphere would have been contaminated 
 and rendered unfit for the support of animal life. In order, there- 
 fore, that ivater might not be frozen ; and that air might not 
 become irrespirable ^ laws inns t be infringed — and they are 
 INFRINGED ; infringed too, precisely where their infringement, 
 both in kind and degree, is indispensably necessary to organic 
 existence. Now, we appeal to the most inflexible sceptic re- 
 garding the argument of design, and ask him, on what other prin- 
 ciple, unless that of express adaptation and design, can two such 
 general laws have been infringed exactly in those instances in 
 which their infringement is wanted, and nowhere else ? Of the 
 sophistry by which the evasion of this plain question may be at- 
 tempted, we are quite ignorant. But we cannot resist the con- 
 viction, that one purpose of the arrangement has been that of 
 confounding the presumptuous sceptic ; who is thus perpetually 
 reminded of the infringement of his boasted ""laws of nature," 
 by the very water he drinks, and by the very air he breathes. 
 
 With respect to foreign bodies in the atmosphere, which have 
 been treated of in the last section, it remains to observe, that 
 though of very opposite characters, they have yet this resem- 
 blance ; that they all apparently exist less on their own account, 
 than as being the inevitable results of general laws established 
 for a higher purpose. Such results of general laws may be con- 
 sidered as analogous to the coldness and darkness, which neces- 
 sarily prevail around the poles, from the earth's position in rela- 
 tion to the sun ; and they have been alike permitted, not because 
 
202 METEOROLOGY. 
 
 tliev could not have been avoided or removed, but in the language 
 of Paley, before quoted, " because the Deity has been pleased 
 to prescribe limits to his own power, and to work his ends with- 
 in these limits." 
 
 Man, forgetting how insignificant he is, and how limited his 
 utmost knowledge, is too apt to measure Omnipotence by the 
 standard of his own narrow intellect, and to be guided by his own 
 selfish feclincfs, in judo-inff of the extent of Divine benevolence. 
 That this earth, a minute fraction, as it is, of a great and wonderiul 
 system, should be amenable to the general laws by which the 
 whole system is governed, is, at the least, exceedingly proba- 
 ble. Of such general laws, of their changes, of their aberra- 
 tions, or of their influences, we, situated in this extremity of the 
 universe, cannot see the object. What, therefore, appears to us 
 anomalous or defective, may in reality be parts of some great 
 cycle or series, too vast to be comprehended by the human mind, 
 and only known to beings of a higher order, or to the Creator 
 himself. So again, amidst the desolation of the hurricane, or of 
 the thunder storm ; in the settled ailliction of malaria, and in the 
 march of the pestilence ; the goodness of the Deity is impugned, 
 his power even, is regarded doubtfully. But whai, in truth, are 
 all these visitations but so many examples of the " unsearchable 
 ways" of the Almighty ; " He sits on the whirlwind, and di- 
 rects the storm :" a hamlet is laid waste ; a few individuals may 
 perish ; but the general result is good : the atmosphere is puri- 
 fied ; and pestilence with all its train of evils disappear. Nay, 
 however inscrutable the object of the deadly malaria itself, do we 
 not see one end which it serves, namely, to stimulate the reason- 
 ing powers, and the industry of man? By his reasonf man has 
 been guided to an antidote beneficently adapted for his use, which 
 has stript malaria of half its terrors. By his industry, the marsh 
 has been converted into fertile land, and disease has given place 
 to salubrity. 
 
 Wjien, therefore, we duly consider all these things ; when we 
 reflect also on the number, the properties, the various conditions 
 of the matters composing our globe ; the wonder surely is, not 
 that a few of these matters occasionally exist as foreign bodies 
 in the atmosphere, but that others of these matters are not at all 
 times (liflTused throuirh it, and in such quantity as to be imcompa- 
 tible with organic life. Thus, the original constitution of the at- 
 mosphere, and the preservation of its purity against all these 
 contaminating influences, may be viewed as the strongest argu- 
 ments we i^ossess, in demonstration of the benevolence, the 
 wisdom, and the omnipotence of the Deity : benevolence in ha- 
 ving willed such a positive good ; wisdom in having contrived it ; 
 and omnipotence in having created it, and in still upholding its 
 existence. 
 
203 
 
 CHAPTER VI. 
 
 OF THE ADAPTATION OF ORGANIZED BEINGS TO CLIMATE ; COMPREHEND- 
 ING A GENERAL SKETCH OF THE DISTRIBUTION OF PLANTS AND ANIMALS 
 OVER THE GLOBE j AND OF THE PRESENT POSITION AND FUTURE PROS- 
 PECTS OF MAN. 
 
 In the general survey of climate, and of its reference to organ- 
 ization, given in the preceding chapter, we have seen, on the one 
 hand, that, by a series of wonderful expedients, the climate or 
 temperature of the greater portion of the earth's surface has been 
 so equalized as to be brouglit within the range of organic exist- 
 ence. On the otlier hand, we sliall find that, by a series of ex- 
 pedients, no less wonderful, organic existence has been so diver- 
 sified and extended, as to include all the possible varieties of soil 
 and climate. Hence, the arrangement, taken altogether, presents 
 us with such extraordinary instances of mutual adaptation of its 
 various constituents to each other, as to admit of explanation 
 only upon the supposition of the whole being different parts of 
 the same magnificent Design ; while the infinite variety, where 
 all might have been otherwise, must be considered as equally in- 
 dicative of the Benevolence, and the Power of the Designer. 
 
 Next to Climate, the circumstances in which organized beings 
 are more immediately concerned is Soil ; a subject already al- 
 luded to, but which it will be necessary to illustrate a little fur- 
 ther before we proceed. 
 
 The soil is that collection of matters, more or less in a state 
 of comminution, which immediately covering the general surface 
 of the earth, fills up its minor inequalities, and rounds off its 
 asperities. On this layer of comminuted mineral substances and 
 organic remains, all vegetables and animals, at least all land ani- 
 mals, depend for their existence ; and, if there ever was a time 
 when the materials composing this globe were collected into 
 solid masses, it is evident that such a condition must have ex- 
 cluded organic life ; even if everything else had existed the 
 same as at present. 
 
 The formation of the soil has apparently been a work of time, 
 and the result of the gradual attrition of the solid materials com- 
 posing the crust of this globe. Hence the formation of soil has 
 probably been al\va3'S progressive, and is still going on. Besides 
 this gradual attrition, the harder materials of our globe seem to 
 have suffered much disintegration during those periodic convul- 
 sions formerly mentioned. By the same convulsions, also, the 
 different comminuted materials have evidently been mixed and 
 
204 METEOROLOGY. 
 
 scattered, and finally deposited over the surface of the whole 
 earth, so as to give occasion to that infinite variety which every- 
 where prevails. 
 
 The foregoing remarks naturally lead to the conclusion that the 
 characters of the soil will generally agree with those of the rocks 
 composing the crust of tlie earth ; and this inference is correct. 
 The more common ingredients in rocks are silex, alumina, lime, 
 magnesia, and iron ; and these mineral matters actuall}^ constitute 
 the greater bulk of every soil. The remaining matters consist of 
 more or less of various other earthy and saline principles, and 
 of vegetable and animal remains. 
 
 After these general observations upon soils, we come to the 
 proper subject of this chapter, which we shall consider under the 
 three following sections : — Of the Distribution of Plants over 
 the globes — Of the Distribution of Animals over the globe ; 
 and, — Of the present Condition and future Prospects of Man, 
 
 Section I. 
 Of the Distribution of Plants over the Globe, 
 
 From what has been stated, it will be readily understood that 
 Soil and Climate are the two great and immediate causes by which 
 vegetable and animal existence are likely to be affected. We shall, 
 therefore, in the first place, take a view, 
 
 1. Of the differences of Vegetation, as liable to be influenced 
 by Soil, and by other minor Loccd Circumstances, in the same 
 Climate. The most incurious observer, in travelling through a 
 country, must be struck with the different vegetation that prevails 
 in different parts of the country ; and with the effect which this 
 difference produces on the manners and on the health of the in- 
 habitants. Thus, in some parts of England, the Apple and the 
 Pear are seen growing spontaneously in every hedge-row; while, 
 in other parts, apple and pear trees will not flourish, even with 
 the utmost care. Some situations are favourable to the Oak, others 
 to the Beech, others to the Elm. Accordingly, these well-known 
 and beautiful trees predominate in some districts, almost to the 
 exclusion of every other, and thus constitute the leading feature 
 in the landscape. 
 
 These are familiar examples of partial changes among the larger 
 vegetables of a country; while the general vegetation is supposed 
 to remain nearly the same. Between such partial change, and 
 the complete cstal)lishment of a peculiar vegetation, there exists 
 among dilVerent localities, every possible shade of diversity. Many 
 of these diflerences in vegetation are obviously connected with 
 
DISTRIBUTION OF PLANTS. 205 
 
 difterences in soil and in situation. Thus, some plants will thrive 
 only on a calcareous soil ; as a few of the Orchis tribe in our own 
 country, and the Teucrium montcmum in Switzerland. Others, 
 like the Salsolas and the Salicornias, will only grow in salt 
 marshes. Some plants flourish in sea water, some in fresh; while 
 to others again, water, at least in excess, is so prejudicial, that 
 they can exist nowhere, unless on bare rocks, or in arid deserts. 
 Mountainous situations are most favourable to the increase of some 
 plants, while others abound in plains. The larger number of 
 plants prefer sunshine, but some are most vigorous in the shade ; 
 and others are so impatient of light, that they are found only where 
 there is absolute darkness. There are, besides, parasitic plants, 
 like the Mistletoe, whose nourishment is derived from the plants 
 to which they are attached. In short, the varieties in the nature 
 of plants are countless, nor is the enumeration of them requisite. 
 What has been stated is more than enough to show the wonder- 
 ful arrangements that have been made, to ensure the clothing of 
 every part of the earth's surface with vegetable organization. There 
 is not a soil, however barren, nor a rock, however flinty, that has 
 not its appropriate plant; which plant has no less wonderfully 
 found its way to the spot adapted for it, nay, will perish if removed 
 elsewhere. Saline plants, for instance, will grow only where sa- 
 line matters are abundant; plants of the marsh, and of the bog, 
 flourish only in marshy and boggy ground ; those of the parched 
 desert and of the cloudy mountain, each in its fitting locality. 
 Thus the soil and its occupant seem to have been made for each 
 other ; and hence one source of that astonishing variety exhibited 
 in nature. 
 
 There are still more remarkable deviations among the plants 
 of different countries remote from one another; even where the 
 circumstances of climate and of soil are in every respect alike. 
 The plants of the Cape of Good Hope, for instance, diff'er exceed- 
 ingly from those of the south of Europe, though the climate and 
 much of the soil be not dissimilar. Often, on the same continent, 
 nay, on the same ridge of mountains, the plants on the opposite 
 sides have no resemblance. " Thus, in North America, on the 
 east side of the rocky mountains, Azaleas, Rhododendrons, Mag- 
 nolias, Vacciniums, Aciseas, and Oaks, form the principal features 
 of the landscape; while on the western side of the dividing ridge, 
 these genera almost entirely disappear, and no longer constitute a 
 striking characteristic of the vegetation."* 
 
 In general, the plants of America are diflerent from those of 
 the old world, except towards the north, where, as it might be 
 expected from the near approximation of the two continents, many 
 individuals are common to both. The plants of islands, and those 
 
 * Lindley's Introduction to Botany, page 489. 
 
 18 
 
206 METEOROLOGY. 
 
 growing in isolated situations are often quite peculiar. Tlius the 
 plants of New Holland, with comparatively few exceptions, differ 
 froin those of all the rest of the world ; and, "of sixty-one native 
 species, in the little island of Saint Helena, only two or three are 
 to be found in any other part of the globe."* These facts are quite 
 inexplicable upon any known principles ; and are calculated to 
 excite a more than ordinary degree of attention, as being solely re- 
 ferrible to the will of the Great Creator; who has chosen to pro- 
 vide infinite diversity where all might have been uniform and 
 monotonous ; and has thus rendered more conspicuous his wisdom, 
 his power, and his goodness. 
 
 2. Of the Influence of Climate on Vegetation. — The climate 
 of a place, as has been before shown, independently of minor lo- 
 cal causes, is influenced chiefly by the two following circum- 
 stances: — the Latitude of the place ; in other words, the general 
 portion of heat and light which it receives from the sun ; — and its 
 height above the surface of the sea ; by which circumstance of 
 elevation, the heat at least received from the sun, is liable to be 
 varied as much as by latitude ; but the variation is according to 
 other laws than those which depend on mere latitude, indeed, ac- 
 cording to laws which vary in diflerent latitudes. 
 
 Every one is acquainted with the general fact of the difference 
 between the plants of warm and those of cold countries ; between 
 the plants that grow on plains, and those that grow on mountains. 
 Thus, " in the countries lying near the Equator, the vegetation 
 consists of dense forests of leafy evergreen trees, Palms, apd ar- 
 borescent Ferris, among which are intermingled epiphytal herbs, 
 and rii^id Grasses. There are no verdant meadows, such as form 
 the chief beauty of our northern climate, and the lower orders of 
 vegetation, such as Mosses, Fungi and Confervfe are very rare. 
 As we recede from tiiC Equator, the plants above mentioned gra- 
 dually give way to trees with deciduous leaves ; rich meadows 
 appear, aboundmg with tender herbs; the epiphytal Orchideie are 
 no longer met with, and are replaced by terrestrial fleshy-rooted 
 species ; Mosses clothe the lrun!;s of aged trees ; decayed vegeta- 
 bles are covered with parasitical Fungi ; and the waters abound 
 with Corfervx. Approaching the Poles, trees wholly disappear; 
 dicotyledonous plants of all kinds become comparatively rare ; 
 and Grasses and cryptogamic plants constitute the chief features 
 of the vegetation."! 
 
 (Changes not very dissimilar are observed in the vegetation at 
 diflcrent heights on the mountains of warm climates- Thus, at 
 
 • See Principles of Geolog-y, by C. Lyall, vol. ii. where this interesting" 
 subject is considered in detuil. 
 
 ■j- Lindley's introduction to Botany, pug^e 484. 
 
DISTRIBUTION OF PLANTS. 207 
 
 the base of the celebrated Peak of Teneriffe, the plants have all 
 the disliniruishinof characters of those of Africa. Tfiere flourish 
 the succulent Euphorbia, the Mesemhryanthenia, Draccvna^ &;c. : 
 also the Dale pahn, the Plantain, the SuQ;ar-cane, and the 
 Indian-Jig. A little higher, grow the Olive tree^ the fruit trees 
 of Europe, the Vine, and Wheat. Then succeeds the woody 
 region of the mountain ; where from the numerous springs the 
 ground is always verdant. In that region is seen a profusion of 
 beautiful evergreens : such as various species of Laurel, one of 
 Oak, two species of Iron tree, an Arbutus, and several others. 
 Next above is the region of pines, characterized by a vast forest 
 of trees resembling the Scottish fir, intermixed with Jumper. 
 Then follows a tract remarkable for the abundance of a species of 
 broom. At last the scenery is terminated by Scrqfularia, Violas 
 a few Grasses, and cryptogamic plants.* 
 
 The proportions which different groups of plants bear to each 
 other, vary exceedingly in different latitudes. An interesting table 
 given in the Appendix, slightly altered from Humboldt, exhibits 
 the proportional amount of some natural groups of plants to the 
 whole mass of vegetation in the zones mentioned ; and will enable 
 the reader to understand the relation of vegetable forms to the 
 greater or less distance of their place of growth from the Equator. 
 The arrangement is so obvious as scarcely to require explanation. 
 Thus in the equatorial zone, between 10° north and 10° south 
 latitude, the first group, including Ferns, Lichens, Mosses, and 
 Fungi, constitutes on the plains only 1-1 5th, but on the moun- 
 tains l-5th of the whole number of plants that exist in that zone. 
 While in the temperate zone the proportion of the tirst group of 
 plants is at least one-half of the whole number, and in the frigid 
 zone, the entire vegetation consists of plants of that group. The 
 distribution of the other groups is equally remarkable. 
 
 From this table we learn many interesting particulars in addi- 
 tion to what has been already stated regarding the distribution of 
 plants over the surface of the globe. We may notice especially 
 the striking difference between the Flora of the Old and that of 
 the New World, in corresponding parallels of latitude. These 
 differences, in a great many instances, are undoubtedly referrible 
 to the unknown causes to which we have before alluded. But 
 in other instances, they are obviously connected with the differ- 
 ence of temperature that prevails in the two continents under the 
 same parallel. Before we proceed, let us dwell a little longer on 
 the consideration of these beautiful arrangements. 
 
 In Tropical countries alone, beneath a vertical sun, do we see 
 vegetation in all its glory and magnitude. There, the form, the 
 
 * Humboldt. 
 
208 METEOROLOGY. 
 
 colour, and the odour of plants are developed to the utmost; and 
 wliere else could they be so developed ? where else could the 
 majestic palm rear its towering stem, and send forth its gigantic 
 leaves ? where else could we expect to find groves ever verdant, 
 blooming and productive ? Amidst eternal summer, all this is in 
 character ; forests denuded of their leaves, and for half the year 
 assuming the appearance of deatli, would in such a climate be 
 perfectly incongruous. But in countries remote from the Equa- 
 tor, and in which, during many months, the temperature is more 
 or less depressed, a vegetation tlius incessantly active could not 
 exist nor would it be appropriate. Accordingly, the palm tribe, 
 and many of the more distinguishing productions of the Tropics 
 become gradually fewer irj number as we recede from the 
 Equator, and at last give way entirely to deciduous plants ; 
 that is, to plants endued with the power of hybernating, or 
 sleeping, as it were, in the colder season ; and which vegetate 
 only during the warmer portion of the year. And here we have 
 displayed another of those admirable provisions, which at once 
 strike us irresistibly as being the effect of design ! In Tropical 
 countries, where the seasons are uniform, and where there is no 
 cold to injure, the leaf buds of plants are without covering or 
 protection, and are freely and confidently exposed to the atmo- 
 sphere. But in climates where the seasons change, and where 
 vegetation is liable to be suspended by the cold, the leaf buds 
 exhibit a structure remarkably different. Developed in the latter 
 end of summer, or autumn, they are almost invariably provided 
 with tegmenta or coverings ; within which, during their period 
 of torpor they are cradled, safe from cold and from accident ! 
 
 As we advance still further to the north or to the south, where 
 the winter becomes more severe and of longer continuance, decidu- 
 ous plants in their turn diminish both in number and in magnitude ; 
 and after having shown themselves under a variety of stunted 
 forms, are at length almost entirely superseded by a few coarse 
 grasses and lichens. Yet even here design is apparent. These 
 hardy natives of the poles are, from the simplicity of their struc- 
 ture, wonderfidly adapted to tlie climate of the region they occupy ; 
 in which alone they will flourish, and for which alone, therefore, 
 ihey have been expressly created. 
 
 Though it be generally true that plants will grow only in the 
 soil and climate adapted for them ; yet, as if intentionally to 
 evince His power, the Great Author of nature has created some 
 manifci^t exceptions to this rule. All organized beings have been 
 nunc, or less endowed with the faculty of accommodating them- 
 selves to circumstances. In the larger number of plants this 
 faculty scarcely exists; but in some it is much stronger; and in 
 others, constituting the exceptions to which we allude, the extent 
 
DISTRIBUTION OF PLANTS. 209 
 
 of the accommodating faculty is almost incredible. In general, 
 plants that are the natives of peculiar soils, and of extreme cli- 
 mates, are the most impatient of change ; while the natives of 
 ordinary soils, and of temperate climates, have a wider range of 
 growth. The exceptions to the rule of adaptation are ciiiefly 
 among plants that are natives of such soils and climates. Thus 
 ** the Sa7nolu8 Valerandi is found all over the world, from the 
 frozen north to the burning south ; associated here with Birches^ 
 and similar northern forms, and there mixed with Pahns and the 
 genuine denizens of the tropics. The number of plants, how- 
 ever, which can thus accommodate themselves to all circumstances 
 and climates is limited ; while those which readily naturalize 
 themselves in climates similar to their own, are, on the other 
 hand, numerous. Of the latter, indeed, examples present them- 
 selves at every step. All the hardy plants, for instance, of our 
 gardens may in some sort be considered of this nature ; for 
 although they do not grow spontaneously in the fields, they 
 flourish almost without care in our gardens. The Pine apple has 
 gradually extended itself eastward from America, through Africa, 
 into the Indian Archipelago, where it is now as common as if it 
 were a plant indigenous to the soil ; and in like manner the 
 Spices of the Indies have become naturalized on the coast of 
 Africa and the West India islands." To this property of natural- 
 izing themselves, no doubt, is to be referred, in a variety of in- 
 stances, the presence of the same plants in different countries. 
 For though, as we have just stated, the Flora of different countries 
 is generally different, yet in almost all instances, some plants 
 exist which are found in other countries. Thus, "above 350 
 species are said to be common to Europe and North America; 
 and even among the peculiar features of the Flora of New Hol- 
 land, Mr. Brown recognized 166 European species. The 
 presence of many such strangers may undoubtedly be referred to 
 the agency of man and other animals ; to currents in the ocean, 
 to winds, and a variety of natural causes." While " the pre- 
 sence of others, seems inexplicable on any other supposition than 
 that they have been created in the places where they now 
 exist."* 
 
 Hitherto we have considered plants only in relation to the soil 
 and to the climate in which they grow ; and have not entered into 
 details respecting all the beautiful arrangements, by which their 
 growth has been accomplished. The consideration of these 
 arrangements belongs to the Physiologist, the Botanist, and the 
 Geologist, wdth whose duties we wish as little as possible, to in- 
 terfere. There is, however, yet one point of view in which our 
 
 * Lindley, Introduction to Botany, p. 501. 
 18* 
 
210 » METEOROLOGY. 
 
 argument nalurally leads us to consider vegetation ; namely, as 
 forming the link, by which animals are connected with the earth ; 
 in other words, as furnishing to animals the means of subsist- 
 ence. 
 
 One circumstance, which, perhaps more than any other is cal- 
 culated to arrest our attention with respect to vegetable produc- 
 tions in general, is their vast profusion in every sense of the 
 term ; whether we contemplate their variety, their magnitude, or 
 their number. Tlius the numerous and varied plants growing in 
 tropical climates are equally remarkable from their size, the luxu- 
 riant foliage, and the exuberance of their roots and seeds. Let us 
 take, for instance, the palm tribe. It has been estimated that 
 there are a thousand species of palms ; and though the number 
 actually known to exist is by no means so large, yet late disco- 
 veries seem to render the estimate not improbable. In many of 
 the palm tribe the developement of the form, and the quantity of 
 flowers and fruit is altogether extraordinary. Among others, the 
 species which yields the well known Cocoa nuts grows to the 
 height of eighty feet ; each plant flourishes for a century, and, 
 during the greater part of that lime, continues to produce an- 
 nually at least a hundred of these large nuts. Yet the cocoa nut 
 species may be considered as one of the least productive of the 
 palm tribe : for every bunch of another species, the Seje palm 
 of the Oronoko, bears as many as 8000 fruit ; while a single 
 spatha of the Date palm contains 12,000 flowers ; and in a third 
 species, the .'ilfonsia Ainyis;daHna, there is the enormous num- 
 ber of 207,000 flowers on each spatha ; or 000,000 on a single 
 individual plant ! 
 
 In superlative exuberance, however, the Palm tribe must yield 
 to the Jianana, or Plantain, another inhabitant of tropical coun- 
 tries, 'i'he fruit of this plant is often a foot in circumference, and 
 seven or eight inches long: it is producetl in bundles, containing 
 usually from 160 to 180 fruit; and each bunch weighs from 06 
 to 88 pounds avoirdupois. As Humboldt has remarked ; the 
 small space, therefore, of 1000 square feet, on which from thirty 
 to forty Banana plants may grow, will, on a very moderate com- 
 putation afford, in the course of a year, 4000 pounds weight of 
 fruit ; a produce 133 times greater than could be obtained from the 
 same space, if covered with wheat; and 44 times greater than if 
 occupied by potatoes. 'J'lie Orange tree may be mentioned as 
 another instance of extraordinary fecundity ; thus a single tree at 
 St. Michael's has been known to bear in a season 20,000 oranges 
 lit for parking, exclusively of those damaged and wasted, amount- 
 ing to at least one-third more. An example to the same eflect, 
 but of a diflerent kind, is the Sugar cane, which furnishes an 
 unlimited supply of saccharine matter in its purest form ; while 
 
DISTRIBUTION OF PLANTS. 211 
 
 various roots, as those of the Cycas Jatropa, and many others 
 abound equally in farinaceous matters. 
 
 As we withdraw from the Equator into the regions of hyber- 
 nating plants, vegetation is seen on a much less magniiicent 
 scale ; though in the temperate climates, and even where we 
 might expect to find utter sterility, mimber, in some degree, com- 
 pensates for magnitude. Thus, instead of the single stupendous 
 tuft of the palm, we have the numerous congregated buds of our 
 deciduous trees ; instead of the gigantic and solitary grasses of the 
 torrid zone, we have the smaller and gregarious varieties. Some 
 of these varieties, as the Cerealla, or Corn tribe, with their 
 myriads of seeds, give us an inexhaustible supply of farinaceous 
 aliment ; while others, as the Grasses properly so called, clothe 
 our meadows with verdure, even to extreme latitudes ; and are 
 equally productive of matter purely herbaceous. In the warmer 
 parts of the temperate zone, the Olive and the Vine afford the 
 oleaginous and the saccharine principles under a form, different, 
 but not less useful than the oil and the sugar of the tropics ; 
 while in the colder parts, various seeds, and hardy fruits, produce 
 an ample store of the same valuable articles, though in a condi- 
 tion still further modified. 
 
 In the preceding sketch we have intentionally kept out of view 
 the existence of animals, that we might here ask the question, 
 Of what use is all this amazing exuberance of superfluous matter 
 throughout the globe ? The adaptation of plants to the climates 
 in which they flourish is evidently the work of an intelligent 
 Creator. But is this apparent waste of materials and of labour to 
 be reconciled with the same wise agency ? Surely, the mere ex- 
 istence of vegetation did not require such prodigality. Seeds, for 
 instance, need not have been enveloped in bulky fruits ; nor need 
 they have been produced by myriads : and all that foliage, all 
 those flowers, and roots, in such amazing profusion, of what use 
 are they ; why where they so created? Regarding vegetation as 
 a thing simply adapted to climate, and existing for its own sake 
 alone, the question scarcely admits of a rational answer. But, 
 considering at the same time the existence of animals, and view- 
 ing these superfluities as the means by which animal existence 
 is principally upheld, every difficulty vanishes, and the splendid 
 design of the whole wonderful scheme becomes at once apparent. 
 We are thus brought to the consideration of animal existence. 
 
•^l2 METEOROLOGY. 
 
 Section II. 
 Of the Distribution of ^^nimals over the Globe. 
 
 Animals have been so conslituled that food is to them indis- 
 pensable : they can, therefore, exist only where their food has 
 been supplied by nature. On land, at least in the warm and tem- 
 perate climates, by far the greater proportion of animals derive 
 their subsistence, either directly or indirectly, from the vegetable 
 kingrdom. For those animals that are themselves carnivorous, 
 prey on vegetable feeders much ofiener than otherwise ; and are 
 thus remotely dependent on vegetables. Of the habits of animals 
 livincr ill the sea, and thus concealed from our view, we know 
 still less ; but in general they appear to prey on each other, the 
 stronger, as is usual, devouring the weaker. 
 
 We have seen the wonderful diversities that prevail among 
 vegetables, in different situations and climates ; and it may be 
 truly said that tlie diversities among animals are not less nume- 
 rous, and are even more extraordinary. Thus, in every climate 
 and soil, almost every herb has its appropriate inhabitant ; some 
 little being, that comes into existence, passes its ephemeral life, 
 and dies on that plant ; to which, therefore, that plant constitutes 
 the world. Nay, in general, even different parts of the same 
 plant have each its separate occupants, one feeding on its fruit, 
 another on its flowers, a third on its leaves, perhaps a fourth on its 
 very woody core. This almost infinite diversity, and infinity of 
 number, are principally confined to the smaller animals, or insects. 
 As animals increase in size, the number of species as well as of in- 
 dividuals constantly diminishes. Thus, while there are hundreds of 
 species of the Beetle tribe, and the individuals are counUess, there 
 may be considered to be only one Elejdiant; and while Shrimps are 
 in numbers like the sand on the sea-shore, the Whale is as much 
 a solitary species. This striking dilierence with reffard to num- 
 bers has been considered to arise necessarily from a law of nature, 
 and in one respect such an explanation is very obvious ; but in 
 another point of view, we may contemplate an admirable evidence 
 of design. It is clear that millions of elephants could not exist, 
 if for no other reason, from want of food ; but why should ruil- 
 lions of beetles exist ? why should these little creatures, — whose 
 life is so transitory, that it consists of little more than of being 
 born, and of dying, whose structure is so frail as to be liable to 
 be annihilated by the slightest accident, who are everywhere sur- 
 rounded by all sorts of enemies, to many of which they constitute 
 a natural prey, — why, we ask, in spite of all these obstacles and 
 dangers, should these insignificant animals contrive to exist in 
 
DISTRIBUTION OF ANIMALS. 213 
 
 the numbers we see them ? No natural law, surely, will explain 
 tiie appearance of such multitudes. The difficulty requires another 
 solution ; and the only solution that can be offered is design — 
 that it was so designed by the Great Author of nature. And how 
 has He effected His purpose of multiplying to such an extent 
 these little animals ? The answer is, simply, by increasing their 
 fecundity. Had beetles, like elephants, brought forth only one 
 young at a time, long ere now, their race would have been ex- 
 terminated ; but being produced by thousands, some of the 
 numerous offspring chance to escape, and thus the race is per- 
 petuated. 
 
 We shall not dilate further on the arrangements that have been 
 made for the existence and preservation of animals, but shall pro- 
 ceed to consider their distribution. 
 
 The distribution of animals over the globe may be conveniently 
 treated of under the same heads as the distribution of vegetables ; 
 and, first: — 
 
 1. Of the Differences existing among Jinimals that live in 
 similar Situations in different Parts of the World. — The dwell- 
 ing of animals in the waters is, perhaps, the most remarkable as 
 regards their localities. Now, since, from circumstances formerly 
 staled, the distribution of temperature is very different in the sea 
 from what it is on land ; and since most aquatic animals prey on 
 each other, and consequently in some degree are independent of 
 climate ; the distribution of such animals over the globe follows 
 laws materially different from those wliich regulate the distribu- 
 tion of land animals. This distribution of temperature more 
 especially affects the distribution of animals in high latitudes ; and 
 must be taken into account at the very outset of this part of our 
 inquiry. We shall, therefore, state concisely the distribution of 
 land animals, and of sea animals, apart from each other. 
 
 The distribution of land animals resembles to a certain extent 
 that of vegetables ; for though animals differ from plants, in being 
 endowed with the power of locomotion, yet, as the larger number 
 of animals are dependent on vegetables for their subsistence, they 
 are necessarily confined to those places where their peculiar food 
 may be obtained. This limitation of range is most observable in 
 the case of the smaller animals. The existence of many kinds 
 of insects, especially, is intimately connected with that of certain 
 plants. In every tribe of animals, however, there are species 
 that occupy very different localities. Thus, in the same tribe, 
 some species dwell on the mountains, others on the plains; some 
 are most numerous on the sea-coast, others live on trees, while 
 there are others that burrow beneath the surface of the ground. 
 All these diversities, in regard to residence, are probably influ- 
 enced, like many others, by the greater or less degree in which 
 
214 METEOROLOGY. 
 
 the locality affords the means of obtaining subsistence. But, in 
 many animals, there is also a wonderful adaptation of structure to 
 the place ihey inlrabit ; proving, beyond a doubt, that the distri- 
 bution of animals has been arranged by design ; and that they 
 form but a part of the great symmetrical whole of creation. 
 
 In animals that dwell in the water, the same peculiarities of 
 habitude are observable, as in those that dwell on the land. Thus, 
 it is perfectly known that many animals can live only in salt wa- 
 ter ; others only in fresh. Some prefer the deep and open sea, 
 others are met with only in shallow water, or at the mouths of 
 rivers. Of those that flock to the coast, some shun turbid water, 
 others burrow in the mud. In short, though the habits and 
 adaptations of aquatic animals can be less satisfactorily ascer- 
 tained ; there is every reason to believe that they are at least as 
 wonderful, as those of the occupants of the land. 
 
 There is an equally striking diversity in the animals, as in the 
 plants, of similar localities and climates in different parts of the 
 world. Thus, in the old world, in the analogous climates 
 on the north, and on the south of the equator, though many ge- 
 nera exist in common, yet the species are totally different. For 
 instance, the northern hemisphere possesses the Horse, and the 
 Jiss ; while, in the south, these species are represented by the 
 Zebra and the Quags:a. In the southern hemisphere, there also 
 exist many species which are qiiite peculiar; as the GlraJ/e, the 
 Cape Buffalo, and a variety of animals having the Jintelope form. 
 So, likewise, the animals of the old and those of the new world 
 are, in general, quite distinct ; unless, perhaps, towards the north, 
 where the two continents approximate; and where, in conse- 
 quence, there are some species common to both. Thus the Eh- 
 phant, the Rhinoceros, the Hippopotamus, the Giraffe, the Camel, 
 the /Jromcdurif, the Horse and the ^^ss ; also the Lion and the 
 Tif^er, and various species o{ Apes, Baboons, and other animals, 
 with which we are familiar in the old world, were not found in 
 America. On the other hand, the American species, the Lama, 
 and the Feccari ; and among carnivorous animals, the Jaguar, 
 or American tiger; also the Jlgouti, tlie Paca, the Coati, the 
 Sloth, and others, were equally unknown in the old world. 
 Again, the animals of New Holland differ, like its vegetation, not 
 only from all those of our continent, but from those of all the 
 world besides. In New Holland, there are more than forty spe- 
 cies of marsupial or pouched animals, of which the Kangaroo is 
 that with which we liave become best acquainted ; while every- 
 where else, there is hardly a known instance of a pouched animal. 
 Nor are these diff«*rences confined to the more perfect animals. 
 They are even more striking as we descend in the zoological 
 scale, 'i'hus among birds ; the individual species of the Parrot 
 
DISTRIBUTION OF ANIMALS. 215 
 
 tribe, that are found in America, differ altogether from those of 
 Africa ; and those of Asia differ from both. The minute and 
 beautiful family o( Hutmnhig birds is peculiar to America. While 
 the species of the common Grouse of this country is met with 
 in no other part of the known world. 
 
 From the class of reptiles, may be mentioned the Great Saurian, 
 or Lizard tribe. Thus the Crocodile of the Nile is entirely dif- 
 ferent from the Cayman of America; and even from the Gavial 
 of the Ganges. In the division of snakes, too, the Boa of India 
 differs from the nearly allied Python of America; and of the 
 poisonous varieties, the Rattlesnake is peculiar to America, the 
 Cerastes to Africa, the Hooded snake to Asia. As we have al- 
 ready slated ; the diversities among insects are still more nume- 
 rous and remarkable than among the larger animals. To enter 
 into details would be endless ; we shall therefore mention only 
 one of the best known and widest extended of all the insect tribe, 
 viz. our common Bee. This insect did not exist in America, or 
 in New Holland; though it is found in all parts of the old world ; 
 the wax and honey of Europe, Asia, and Africa being obtained 
 from species having a close resemblance to each other. 
 
 Nor are these differences confined to land animals ; the inha- 
 bitants of the waters are equally diversified. Thus the Whales of 
 the northern ocean are quite unlike those of the south ; as are the 
 Seals, and other analogous animals in the polar regions. The 
 fishes of different seas, also, not only when far apart ; but even of 
 some which freely communicate, have fish exceedingly dissimilar. 
 Thus the fishes of the Arabian Gulf are said to differ entirely 
 from those of the Mediterranean ; notwithstanding the proximity 
 of these seas. Nor do these remarks apply only to the larger 
 fish in these seas, but hold equally with respect to their testace- 
 ous and molluscous species. 
 
 Such are a few of the more striking facts with regard to the 
 distribution of animals in similar climates and localities through- 
 out the world. We shall now briefly speak, 
 
 2. Of the Effects of Diversity of Climate on the Distribu- 
 tion of Jjnimah. In tropical climates, the qualities of animals, 
 as well as those of vj^ct.-^ tables, are developed to the utmost ; 
 whence arises that harmonious adaptation of all the works of 
 nature, conspicuous, indeed, in all climates, but in Tropical cli- 
 mates more especially. For, where else than amidst the profuse 
 exuberance of the vegetation within the tropics, could the Ele- 
 phant^ the Rhinoceros, the Giraffe, and other large quadrupeds 
 find subsistence 1 Where else could we expect to see such birds 
 as the Ostrich and the Cassowary ? Such reptiles as the Croco- 
 dile? such serpents as the Boa? To what other part of the 
 world could the magnificent butterflies, the enormous beetles and 
 
216 METEOROLOGY. 
 
 spiders be so appropriate. Even among the marine animals of 
 Tropical climates, some display the same wonderful enlargement 
 of size. Thus certain species of the Crab and Lobster^ and va- 
 rious shell-fish, often attain an enormous magnitude. INor is 
 there a developement of size only, but of every other property in 
 an equal degree. Countries within the tropics exhibit the most 
 beautiful forms — the most splendid colours in nature. There, in 
 short, is the most astonishing display of all those things which 
 seem to be entirely ornamental : as, for example, the singular 
 plumage of the Birds of Paradise — the gaudy liveries of many 
 of the Parrot tribe — the extraordinary and diversified forms and 
 colours of many insects and shells. 
 
 Not only is there in Tropical climates an assemblage of all 
 the concomitants of productiveness, and utility, and embellish- 
 ment of every kind ; in these climates, there is another and not 
 less marked demonstration of the power and the wisdom of the 
 great Creator. Within the Tropics death, the last, the inevita- 
 ble scene, assumes a character as new and diversified as that of 
 the life it terminates. There, rages the implacable ferocity of 
 the Tiger, and of the larger beasts of prey ; there, are the fangs 
 of the serpent charged with the most malignant venom ; there, 
 even the insects are as formidable as they are numerous. Nor 
 is this intensity of the destroying power incongruous or without 
 an object ; but obviously is in perfect harmony \vith the rest of 
 creation, and with the design of the Creator. The wonderful 
 productiveness of animals in Tropical countries renders unavoid- 
 able some checks against their excessive increase : and in devi- 
 sing these, the great Author of Nature has displayed the same 
 attributes that are manifest in all his other works. No one who 
 seriously refiects can doubt either the wisdom or the benevolence 
 of the provision. For why are Tigers and Serpents confined to 
 those parts of the world where their existence is not only accor- 
 dant, but where, for one great purpose at least, they are even 
 necessary. Surely such limitation could have happened only 
 from design ; and the argument is strengthened a hundred fold ; 
 when we contemplate the striking display of wisdom and of 
 power exemplified in the singular adaptation of structure in these 
 animals, to tlieir peculiar habits. Thus how wonderfully appro- 
 priate is that of the Tiger ; and how extraordinary as well as 
 wonderful that of Serpents ! Who (unless he had witnessed the 
 fact) could have believed that the animal frame was capable of 
 separating from its juices, and of retaining with impunity, a poi- 
 son instantly fatal, not only to other animals, but to the animal 
 itself; if again mingled with the juices from which it had been 
 separated ! 
 
 Nor in all these things is the benevolence of the Deitv less 
 
DiaTRIBUTION OF ANIMALS. 217 
 
 conspicuous than his wisdom. All must die ; and death from 
 rapacious or venemous animals is probably not in any degree 
 more pnintul than many other modes of death, wliich we con- 
 stantly witness. There is, in truth, to our own narrow and sel- 
 fish feelings something exceedingly painful in the idea of being 
 torn to pieces b)'^ a Tiger, or stung to death by a Rattlesnake ; 
 but how many thousands of little mice are destroyed by cats ? 
 and how many myriads of unfortunate flies are poisoned by spi- 
 ders, every day we live ? and yet we hardly commiserate them. 
 The question, therefore, is simply a question of degree ; and 
 viewing the existence and the destruction of animals, as they 
 ought to be viewed, on the great scale, we find that the whole is 
 perfectly in unison. While in temperate climates we have cats 
 and spiders, designed as checks on over-productiveness ; amidst 
 the grandeur and the luxurious developement of the Tropics, the 
 same wise purpose is executed by the Tiger and by the Rattle- 
 snake. 
 
 As wc advance from the Equator into the temperate climates, 
 the size of animals in general, like that of vegetables, becomes 
 gradually smaller. Like the vegetables, too, the animals of tem- 
 perate climates are more gregarious than within the Tropics, 
 Hence number^ as among vegetables, compensates in some de- 
 gree for diminished magnitude. The two kingdoms of nature 
 therefore are beautifully analogous ; for the gregarious grasses, 
 which, as we before observed, form so marked a feature in the 
 vegetation of temperate climates, constitute in one shape or other 
 the principal food of the gregarious tribes of animals. Thus 
 the whole cattle tribe — The Ox, the Sheep, the Goat ; the dif- 
 ferent varieties of Deer ; the Babbit and Hare: also the Horse 
 and the Ass : with a multitude of other well-known animals, of 
 a similar character, are natives chiefly of temperate climates, and 
 obtain their nourishment almost entirely from the grasses. 
 Among birds, the numerous species of the Gallinaceous, or Fowl 
 tribe, may be said to derive their food from the same source. 
 Therefore, as regards the existence of animals, the gramineous 
 tribe of plants is more important than perhaps any other ; and 
 could not be annihilated, without the destruction of the present 
 order of living beings. 
 
 As further examples of animal species indigenous to temperate 
 climates, may be mentioned the Canine species and those allied 
 to it, most of which are more or less carnivorous ; also the Hogy 
 and a variety of other animals that need not be here enume- 
 rated. The Hog tribe, as is well known, are omniverous ; but in 
 their natural state, they feed principally on the seeds and roots of 
 plants. Among birds peculiar to temperate climates are various 
 tribes of Water-foud that subsist on fish and on insects. Of the 
 ^ 19 
 
218 METEOROLOGY. 
 
 smaller land birds, the various So7igsfe)'S offer a remarkable con- 
 trast to those of similar form within the Tropics; not only from 
 their more melodious notes, but from the simple colouring of 
 their feathers. In temperate countries the Insects are still exceed- 
 ingly multiplied ; though, in general, like the other animals, they 
 are much smaller in size than those within the Tropics ; their 
 forms, their colours, and other peculiarities also are much less 
 remarkable. 
 
 As we advance toward the Poles, the animals of temperate 
 climates are observed gradually to decline in number. The ve- 
 getable feeders bec(mie reduced to a few hardy species ; and 
 at length in the remote north and south scarcely any vegetable 
 feeders remain. So far as shrubby plants continue to grow in 
 these inhospitable regions, individuals of the Squirrel tribe find 
 subsistence on their seeds and roots. But the most remarkable 
 herbivorous animal is i\\e Reindeer ; whose principal food is 
 afforded by nature in a species of moss peculiar to very cold cli- 
 mates. Those that exist beyond, are either carniverous or pisci- 
 vorous. The Arctic Fox and the Bear are familiar instances, 
 as terminating the Zoological series, viewed in connection with 
 the influence of climate. 
 
 We have, in the last place, to notice what is most remarkable 
 in the distribution of Marine animals. 
 
 For the reasons before stated, the general temperature of the 
 ocean ditfers considerably from that of the land. Owing to this 
 difference of temperature, and to the peculiar mode of subsistence 
 of marine animals, which find their prey chiefly in the waters they 
 inhabit; the distribution of these animals varies much, as compared 
 with the distribution of animals that are entirely terrestrial ; parti- 
 cularly within the frigid zone. It is true, indeed, that in all cli- 
 mates, the denizens of peculiar localities, as fresh water species 
 and those that resort to the shallows on the coast, are influenced 
 by the climate nearly as much as land animals: and within the 
 Tropics, this influence extends in some degree even to the species 
 that dwell on the wide ocean. But far to the north, and to the 
 south, such species are influenced in a manner altogether differ- 
 ent. Thus the largest of known animals, the Whale, and of course 
 those other animals that become its prey, roam through the ut- 
 most Polar seas ; where on land the intensity of the cold would 
 prevent the existence of any animal whatever. In that climate 
 t!ie whale is enabled to live, solely on accountof the greater warmth 
 of the Polar ocean, as has been formerly explained. Among the 
 larger inhabitants of the ocean in Tropical climates, may be men- 
 tioned the Shark tribe ; which in respect of ferocity and voraci- 
 ousness, may be clashed with the tiger, or any kindred species on 
 land. 'J'he influence of climate on marine animals is further shown. 
 
DISTRIBUTION OF ANIMALS. 219 
 
 as we have said, by the enormous size of many of the Tropical 
 shell-fish and mollusca. The colouring of these and also of other 
 productions of the Equatorial seas, often exliibits so much lustre 
 and beauty, as to rival the most splendid of the feathered race. In 
 temperate climates, and from the equal temperature of the sea, 
 even within the frigid zone; it is remarkable that fish, like terres- 
 trial animals, are much disposed to be gregarious. The shoals of 
 Herring, MackareU and other well known visitants of our coast, 
 are familiar examples of the gregarious tendency. The Salmon 
 and the Sturgeon may be adduced as instances of fish inhabiting 
 chiefly the rivers of the temperate and colder countries. While 
 in the same climates, instead of the magnificent Pearl oyster of 
 the Tropics, there appears our common Oyster, so diminutive and 
 unsightly, yet so profitable to man. 
 
 We have thus seen that animals, like plants, have in general 
 been adapted to particular climates. The numerous cold-blooded 
 animals of the Tropics — even the warm-blooded Tiger itself, amid 
 the Polar snows would instantly perish. The Arctic bear would 
 be not less unable to live, under the scorching rays of a vertical 
 sun. Yet though adaptation to one climate be the general law 
 regarding animals as well as plants ; some species of animals have 
 as remarkably as some species of plants, the faculty of accommo- 
 dating themselves to all climates. These species, like the plants 
 similarly endowed, are for the most part natives of temperate cli- 
 mates ; the transition from such climates to either extreme, being 
 much less violent than from one extreme to the other. Thus our 
 domestic animals, that have been successively introduced into the 
 New World at various periods since its discovery, are now, in in- 
 credible numbers, spread over the whole of that vast continent, 
 from Canada to Paraguay. The greatest increase has been of the 
 Horse, the Ox, the Sheep, the Goat, the Dog, the Cat, and the 
 Hog. The Rat, too, though an unwelcome intruder, has been not 
 the least prolific. The different varieties of domestic Poultry have 
 multiplied to an equal extent. Even insects have been introduced, 
 and spread in like manner, as is well known to horticulturists. 
 
 Like plants, most animals also are readily domesticated, and 
 thrive in climates similar to those of which they are natives. The 
 most striking instance is the Rein-deer ; so lately as in the year 
 1773 introduced into Iceland, and now exceedingly numerous in 
 the interior of that country. From these powers of accommodation 
 to climate, from the agency of man, and from accidental causes ; 
 the distribution of the larger animals over the globe has, in com- 
 paratively recent times, been very much modified. Nor is there 
 any reason to believe that the distribution of these animals is yet 
 stationary; but, on the contrary, that their distribution will under- 
 go still further changes. 
 
220 METEOROLOGY. 
 
 Amonir the more remarkable habits of animals, may be noticed 
 the migratory propensities of certain species. The migration of 
 land animals is, of course, always much limited, and may be en- 
 tirely prevented by natural obstacles — the asperities of the earth's 
 surface — sands — deep rivers — or other large accumulations of 
 water. But many birds and even insects, possessing powerful 
 locomotion, and whose course is through the air, may literally be 
 said to follow the sun in their migratory progress. It is hardly 
 necessary to state, as examples, the birds of passage, so well 
 known as the Swallo\v and the Cuckoo. These birds during the 
 summer months visit our northern climate, and feed on insects, 
 whose multiplication would otherwise be boundless. Having ful- 
 filled their office here ; on the declination of the sun, they again 
 retire to the south ; and are succeeded by different birds from coun- 
 tries still further north. Such are the Woodcock and others, which 
 escape to our shores from the rigorous cold of a Polar winter. 
 Nor is migration confined to the higher classes of animals. The 
 wonderful powers of flight possessed by many insects, enable 
 them to travel over an immense extent of country. The Locust 
 and the Ant tribe are familiar examples. These insects occasion- 
 ally migrate in coundess swarms from the lands to which they 
 are indigenous, and lay waste others far remote. 
 
 Equally remarkable is that habit of animals termed Hybernation. 
 Like the plants of temperate climates, some animals have the fa- 
 culty of passing the colder season of the year in a state of sleep. 
 The Hedgehog and the Dormouse may be mentioned as examples 
 of quadrupeds possessing this faculty. Additional instances might 
 be given in all the classes of animals. Nearly allied to Hyberna- 
 tion, is that remarkable instinct which guides many of the inferior 
 animals to deposit their eggs in the earth, or in some other place 
 of safety ; that they may be preserved during the season of dimi- 
 nished temperature. This instinct is particularly observable in 
 insects whose lives are ephemeral, or are, at the utmost, prolonged 
 for a summer. 
 
 There is yet another circumstance that remains to be noticed, 
 as being connected with the adaptation of animals to the climates 
 in which they live ; namely, the Clothing or covering with which 
 tliey have been supplied by nature. Every one is acquainted with 
 the general fact, that wool, fur, eider-down, and similar articles, 
 are obtained for the most part, not from the copious source of 
 every superfluous production, the countries within the tropics, but 
 from the cold, and comparatively unprolific regions of the tempe- 
 rate and of the frozen zones ; where they have constituted the 
 appropriate vesture of different animals. Perhaps, in the whole 
 range of creation there is not anything more calculated to excite 
 our admiration. However we may view these means of guard- 
 
DISTRIBUTION OF ANIMALS. 221 
 
 ing animals from being injured by the cold ; whether as a part 
 of that conservative faculty with which animals have been en- 
 dowed, and by wliich their existence is maintained ; or as an im- 
 mediate act of Providence; still the adaptations are so striking and 
 obvious, as to render it impossible to doubt for a moment, that 
 they have all been contrived for the purpose which is accom- 
 plished ; and that they are the results of foreknowledge and of 
 design. 
 
 We have thus given a rapid sketch of the distribution of ani- 
 mals over the globe. In this sketch we have endeavoured to point 
 out the wonderful adaptations of the several classes of animals to 
 the circumstances in which they are placed ; together with the 
 beautiful symmetry and equilibrium exhibited in zoology, not less 
 than in the arrancrements of inanimate matter. Throuf^hout we 
 have intentionally, and as far as was possible, avoided those de- 
 tails, the consideration of which belongs to other departments. 
 But it has been our aim to state such prominent facts, as appeared 
 best calculated for the elucidation of our argument. In particular, 
 it has been our desire to show — how number amonff the weak is 
 made to compensate for magnitude among the strong; how exube- 
 rance in one species is made to contribute to the existence of an- 
 other ; how ornament and boundless profusion characterize the 
 countries within the tropics, while the temperate climates are not 
 less distinguished by utility and capacity for change ; how, even 
 in the rigorous and barren neighbourhood of the Poles, where life 
 becomes a struggle for existence, animals have been expressly 
 furnished with clothing appropriate to these regions ; — in short, 
 we have endeavoured to demonstrate, how every animal, in every 
 climate, has its day ; and by some peculiar contrivance, has been 
 enabled to maintain its rank in creation, and to assist in preserving 
 the general equilibrium. 
 
 Hitherto we have considered the works of nature without 
 reference to Man. For aught we can see to the contrary, they 
 might all have existed, and every arrangement and operation 
 might have been very nearly, if not exactly, the same as at pre- 
 sent; though man had never been called into being. Butstill, for 
 a moment longer, keeping man's existence out of view ; let us, as 
 under a former division of this Treatise, inquire, vv'hat would 
 have been the r^se of all this elaborate design, without an ulterior 
 object. Would an intelligent Creator have made such a world, 
 and have left it thus incomplete ? It is evident that the other 
 beings inhabiting this earth, live and die, without in the slightest 
 degree comprehending the vast system of which they constitute a 
 part. Hence they are merely unconscious agents, from which 
 their Maker, while he has furnished them with the instincts ne- 
 cessary to their existence, and has awarded equal justice to all, 
 
 19 - 
 
 I 
 
222 METEOROLOGY. 
 
 has yet chosen to withhold the privilege of reason. That a Crea- 
 tor, evidently as benevolent as he is wise, might, for his own 
 gratification, have made such a world, and without any other 
 inhabitants, is indeed possible. But, even admitting that possi- 
 bility, the probability surely is, that he would not there have 
 finally "rested from his labour." His benevolence would have 
 prompted him to communicate to other beings a portion of the 
 gratification, which he himself is supposed to derive from the 
 contemplation of his works. In the beautiful world which he 
 had created, he would have wished to see one being at least, capa- 
 ble of appreciating to a certain extent his design and his objects. 
 Such is a plain inlerence deducible from the manifest attributes of 
 the Creator ; and what is the fact? Is not man such a being as 
 we have supposed ? Throughout the world, though perfectly 
 independent of him,;^is there not a clear foretoken of his existence ? 
 Has he not been placed at the head of that world, so obviously 
 prepared for him, and thus constituted " the Minister and Inter- 
 preter of nature ?" Surely no one will be inclined to doubt that 
 such is the situation of man in the world. Equally undeniable, 
 is the striking accordance of these deductions from the view of 
 external objects, with what is written of the origin of man by the 
 sacred historian : " and God said, that it (the world which he had 
 prepared) was good. And God said, Let us make man in our own 
 image, after our own likeness, (that is to say, endowed with 
 reason and with the power of reflection). And let him have 
 dominion over the fish of the sea, and over the fowl of the air, 
 and over the cattle, and over every creeping thing, that creepeth 
 on the earth." 
 
 We thus arrive at another, and to us the final step in the great 
 design of the Omnipotent: the creation and the faculties of Man. 
 
 Section III. 
 Of the present Position and future Prospects of Man, 
 
 The consideration of the faculties of man, and of his position 
 in the world he inhabits, belongs, in all its details, to another 
 department. We advert to these subjects here, with the view 
 only of completing our sketch of the physical relations of animated 
 beings. 'J'lic observations we have to ofler will be comprised 
 under two heads: — as to the means, by which man has acquired 
 and maintains the ascendency .,he enjoys : — as to the conclusions 
 to be drawn, from man's elevated position, and from his superior 
 intellectual character. 
 
 With regard to the means by which man has acquired and 
 
POSITION AND PROSPECTS OF MAN. 223 
 
 maintains his ascendency, it may be observed, that these means 
 are quite peculiar ; and iar from being such, as at first, perhaps, 
 we might deem conducive to such an object : though when once 
 known and understood, the beautiful design and harmony they 
 evince, immediately become apparent. 
 
 The supremacy of man has notheen the result of his own per- 
 sonal strength, nor is it so upheld. On the contrary, many ani- 
 mals are larger and more powerful than he is ; while few of his 
 size, are naturally so incapable of self-defence ; or during so long 
 a period suffer from the dependent helplessness of infancy and of 
 old age. Neither is his frame superior in external adaptation to 
 climate : for while nature has furnished other animals with 
 clothing appropriate to the temperature in which they live, man 
 has been brought into being absolutely naked ; and moreover re- 
 mains so, in every climate he inhabits, from the Equator to the 
 Poles. Lastly, the pre-eminence of man has not been owing to his 
 more extensive range of diet; or to his greater ability for assimi- 
 lation : for though man be omnivorous in one sense of the term, 
 he is not omnivorous according to the application of the term to 
 other animals; that is to say, man does not eat indiscriminately 
 of every kind of aliment, in the state in which it is afforded by 
 nature ; for even in his rudest condition, he adopts some process 
 of cookery. How then has man gained the high station which 
 he occupies ? The answer is simply — by his Reason. Man 
 has been created a reasonable being; and this endowment amply 
 compensates to him for the want of the animal requisites of 
 strength — for deficiency of natural covering — and for his restrict- 
 ed ability in assimilating his food. By his reason he is enabled to 
 command the strength of the elephant ; to choose from every 
 production of nature whatever is adapted for his clothing, and 
 thus to array himself according to his pleasure, or the exigencies 
 of the climate in which he resides ; to extract wholesome nou- 
 rishment from the most unpromising, even from the most delete- 
 rious articles. There was no necessity, therefore, why man 
 should himself be as unwieldy as an elephant; or be encumbered 
 with any vesture that in some situations might be oppressive ; or 
 be able to digest, without culinary preparation, any coarse and 
 intractable substances. Thus, mere animal endowments not 
 being requisite, the Creator's wisdom has been displayed in an- 
 other manner, and with a wider scope. In furtherance of his 
 design. He has limited the bulk of the human species to that 
 happy medium, combining strength with convenience; and to an 
 organization delicate and sensitive in the highest degree, but 
 nevertheless accommodating. He has superadded a form at once 
 peculiar, appropriate, and beautiful ! 
 
 When speaking of temperate climates, we remarked, that they 
 
224 METEOROLOGY. 
 
 seemed to be characterized by the utility of their productions ; 
 and that the plants and animals of these climates, generally pos- 
 sessed oreater powers of accommodation than those of either of 
 the extreme climates. Now Man, by an express arrangement of 
 his Maker, has apparently been constituted a native of temperate 
 qlimates; and only in these climates can his powers be said to be 
 completely deveh)ped. Within the tropics, indeed, human ex- 
 istence is nourishing; for there the immediate bounty of Provi- 
 dence affords to man a copious and admirably adapted nutriment. 
 Yet in the midst of that profusion, and without any adequate 
 motive to call forth exertion, his reason too often languishes ; while 
 his animal tendencies predominate ; and his life is spent in apathy 
 and in sensual gratifications. On the other hand, under the 
 cheerless sky of the frigid zone, imperfectly nourished by scanty 
 and unsuitable food, the powers of his mind, like those of his 
 body, are stunted ; or are engaged solely in combating the ri- 
 gours of his situation. But in the temperate climates the evil 
 consequences of both these extremes are avoided, while the bene- 
 ficial influences of climate remain. Urged by the stimulus of 
 necessity, and at the same time having at his command the 
 astonishing capability of nature, man is, in temperate climates, 
 surrounded by motives of every kind, and his faculties thus attain 
 their utmost developement. As familiar examples of the effect 
 of this expansion of the human reason, let us view man under 
 the three aspects to which we have before alluded ; namely, with 
 reference to his strength, his food, and Wis clothing, inclusive of 
 his habitation. 
 
 In the first place, with regard to his strength. The strength 
 of man is not only that which is his own, almost infinitely mag- 
 nified by ingenious mechanical devices of every kind, and of 
 every degree, up to the stupendous agency of steam ; man has, 
 moreover, subdued to his service many of the larger animals, 
 "while those whi(^li he cannot so appropriate, he destroys. As 
 weapons, he wields every instrument offensive and defensive, 
 from the rude but effective club or arrow, to the warlike engines 
 to which he has applied the discovery of gunpowder. Whatever 
 his wants require, he obtains by tools ; from the humble spade, 
 to that perfection of machinery, which almost rivals the opera- 
 tions of intelligence itself. In the next place, view man with 
 reference to his food : what wonders has not his reason enabled 
 him to achieve among the fellow inhabitants of his own tempe- 
 rate climate. In the vegetable kingdom, let us consider the as- 
 tonishing mutations and increase of the cerea/ia, or corn tribes ; 
 tlie transfornuUion of the sour and forbidding Crab into the rich 
 and fragrant Aj)ple; of the harsh and astringent Sloe ijito the de- 
 licious Plum ; of the coarse and bitter sea-side Brassica into the 
 
POSITION AND PROSPECTS OF MAN. 225 
 
 nutritious and grateful Cauliflower: all which changes, and nu- 
 merous others of a like kind, have been efl^ectcd by man. Nor 
 have the transformations which he has produced among animals 
 been less wonderful than those among vegetables. All the nu- 
 merous varieties of cattle, of sheep, of horses, of dogs, of poultry, 
 and of all the other animals reared as food, or for any purpose 
 domesticated, have sprung from a few wild and unattractive spe- 
 cies ; and have been made what they are, in a great degree, by 
 his intervention. Moreover, the most useful of these varieties of 
 animals have been transported by man into every region of the 
 globe, to which he has himself been able to penetrate. Lastly, 
 in the clothing and habitations of man, the surpassing influence 
 of his reason is equally conspicuous. For covering his naked 
 body, a surface of considerable extent is necessary ; larger, in- 
 deed, than is presented by any natural texture, unless, perhaps, 
 by the skins of other animals, or by the leaves of some plants ; 
 which therefore, in the rudest states of society, usually consti- 
 tute his only dress. But by the art of weaving^ he has been 
 enabled to produce garments of any size, and from materials that 
 would seem the least fitted for such conversion. Thus man can 
 not only clothe himself in any manner, and according to the tem- 
 perature of the climate in which he lives ; but he can associate 
 with the articles of his dress every species of ornament which 
 his fancy may dictate. His choice of materials for the construc- 
 tion of dwellings is not less extensive than that of his clothing. 
 As climate and other circumstances may require, he abides in the 
 humble cabin, or in the splendid palace ; in the temporary hut, 
 or in the enduring castle, formed to withstand alike the tempest 
 of war, and of the elements. 
 
 Such is man, and such are a few of tliose great changes in this 
 world, which, under the guidance of his reason, he has had the 
 power to accomplish. And what a splendid evidence of design 
 and of preconcerted arrangement on the part of the great Creator 
 is thus exhibited, by viewing the inherent properties of matter, 
 and its various conditions, witii reference to the works of man. 
 Had water, for instance, not been constituted as it is, man could 
 never have formed the steam engine. Had not the productions 
 of the temperate climates been formed Nvith that capability for 
 change, by which they are so much distinguished, man could 
 never have so moulded them to his uses, by altering their cha- 
 racter. There was no reason why such properties should have 
 been communicated ; there was even no reason why the objects 
 in w^hich these properties exist, should have been created. But 
 they have been so created ; and what are we to infer? No one 
 surely will contend that they have been the result of chance, or 
 
226 METEOROLOGY. 
 
 have been created without an object. They must therefore have 
 been created with design ; and if with design — most obviously 
 with design having reference to the being man, not yet in ex- 
 istence. 
 
 Thus far we have considered the state at which the earth has 
 arrived, and man, an animal endowed with reason, placed as its 
 chief inhabitant. But we may yet extend our view to the pros- 
 pects in futurili/. 
 
 We have seen that this earth has not suddenly emerged from 
 chaos to its present condition ; but that by a succession of violent 
 and disruptive changes, it has been progressively brought into 
 different conditions, and progressively tenanted by higher orders 
 of beings. We, the last of the series, in our owni creation and in 
 the faculties with which we have been endowed, behold the most 
 striking exemplification of the wisdom, and of the power of the 
 Deity. But does the great design abruptly terminate here? Has 
 this earth arrived at the ultimate stage of its existence ? Have 
 its inhabitants attained the utmost perfection of which they are 
 capable ? Are there not further convulsions, and still higher 
 orders of beings in contemplation ? Tlie answers to these ques- 
 tions are known only to the great Author of the universe, and 
 concern us not. There is one question, however, connected with 
 this siibject, in which we are deeply and personally interested — 
 What is to become of man? Is the being who, surveying na- 
 ture, recognizes to a certain extent, the great scheme of the uni- 
 verse ; but who sees infinitely more which he does 7iot compre- 
 hend, and which he ardently desires to know ; — is he to perish 
 like a mere brute — nil his knowledge useless ; all his most earn- 
 est wishes ungratified ? How are we to reconcile such a fate 
 with the wisdom — the goodness, — the impartiil justice — so 
 strikingly displayed throughout the world by its Creator? Is it 
 consistent with any one of these attributes, thus to raise hopes in 
 a dependent being, which are never to be realized ? thus to lift, 
 as it were, a corner of the veil — to show this being a glimpse of 
 the splendour beyond — and after all to annihilate him ? With 
 the character and attributes of the benevolent Author of the uni- 
 verse, as deduced from His works, such conceptions are abso- 
 lutely incompatible. The question then recurs — What is to be- 
 come of man ? That he is mortal, like his fellow creatures, sad 
 experience teaches him; but does he, like them, die entirely? 
 Is there no part of him, that, surviving the general wreck, is re- 
 served for a higher destiny ? Can that, within man, which rea- 
 sons like his immortal Creator — which sees and acknowledges 
 His wisdom, -.ind approves of His designs, be mortal like the 
 rest? Is it probable, nay, is it possible, that what can thus com- 
 
POSITION AND PROSPECTS OF MAN. 227 
 
 prebend the operations of an immortal Agent, Is not itself im- 
 mortal? 
 
 Thus has reasoned man in all ages ; and his desires and his 
 feelings, his hopes and his fears, have all conspired with his rea- 
 son, to strengthen the conviction, that there is something within 
 him which cannot die. That he is destined, in short, for a future 
 state of existence, where his nature will be exahed, and his know- 
 ledge perfected ; and where the great design of his Creator, 
 commenced and left imperfect here below, will be completed. 
 
BOOK III. 
 
 OF THE CHEMISTRY OF ORGANIZATION : PARTICULARLY OF THE CHEMICAL 
 PROCESS OF digestion; AND OF THE SUBSEQUENT PROCESS BY WHICH 
 VARIOUS ALnrENTARY SUBSTANCES ARE ASSIMILATED TO, AND BECOME 
 COMPONENT PARTS OF, A LIVING BODY. 
 
 Having in the foregoing- pages, given a summary view of the 
 Chemical properties of bodies not organized, and of the laws of 
 their union ; having also considered the general relations of ina- 
 nimate matter and of organized beings, on the great scale in which 
 they are offered to us by nature, together with the present posi- 
 tion and future prospects of man ; we now proceed, in the last 
 place, to inquire n)ore particularly into the means by which or- 
 ganization is accomplished ; or, in other words, to give a sum- 
 mary view of those chemical properties, and laws of union, by 
 whicii organized beings are distinguished from inorganic matters. 
 
 CHAPTER I. 
 
 OF THE NATURE AND COMPOSITION OF ORGANIZED BODIES IN GENERAL, AS 
 COMPARED WITH INORGANIC MATTERS. 
 
 ** A LIVING being considered as an object of chemical research, 
 is a laboratory, within which a number of chemical operations 
 are conducted ; of these operations, one chief object is to produce 
 all those phenomena, which taken collectively are denominated 
 />//e ; while another chief object is to devclope gradually the 
 corporeal machine or Laboratory itself, from its existence in the 
 condition of an atom, as it were, to its utmost state of perfection. 
 From this point of utmost perfection, the whole begins to decline 
 as gradually as it had been developed ; the operations are per- 
 formed in a manner less and less perfect, till at length the being 
 ceases to live ; and the elements of which it is composed, again 
 set free, obey the general laws of inorganic nature."* 
 
 Such is the history of organic existence ; nor, though the pe- 
 riods of developement and of decay be infinitely varied in dif- 
 ferent species, does a single individual remain for a moment sta- 
 tionary ; but all, sooner or later, transcend their prime, and finally 
 share the common lot of dissolution. 
 
 That peculiar principle or principles, which under some con- 
 dition or oilier, exists in all organized beings, and by wliich they 
 
 • rJerzclius, Traitc de Chimic, torn. v. p. 1. 
 
COMPOSITION OF ORGANIZED BODIES. 229 
 
 are distinguished from inanimate matter, has received various ap- 
 pellations. In the present inquiry these principles may be 
 viewed as agents : and to discriminate them from Heat, Electri- 
 city, and other agents or inorganic matters, they may be denomi- 
 nated organic agents. In conducting our investigations into the 
 nature of these principles or agents, our difficulty will be much 
 lessened, by endeavouring previously to have a clear understand- 
 ing of what these agents actually do. We shall, therefore, in 
 the first place, give a short sketch, 
 
 1. Of Organic Bodies considered as Chemical Compounds. 
 — In their well-marked forms no two things perhaps can be con- 
 ceived to offer a stronger contrast, than the two great divisions of 
 organic bodies — vegetables and animals. Yet these two kinds of 
 bodies so gradually approximate, and seem even to coalesce, thai it 
 is not possible to say where the one ends and the other begins. 
 The same remark applies to the chemical composition of vegeta- 
 bles and animals. Vegetable substances, in general, contain 
 essentially no more than three elements. Hydrogen, Carhon, and 
 Oxygen; while animal substances usually involve a fourth, Azote. 
 Yet there are many vegetable substances, of whose composition, 
 azote forms a considerable part; while certain animal substances 
 are entirely wanting in that principle. It is obvious, therefore, 
 that the mere chemical composition of a substance, at least its 
 essentially consisting of three or four of these elements, will not 
 enable us to determine whether it be vegetable or animal ; and 
 that, in many substances, when this point happens to be doubtful 
 or unknown, we must have other data before we can form a con- 
 clusion. Besides these four elements, of which all organic sub- 
 stances are essentially compounds ; other principles generally 
 enter into their composition. These other principles are in very 
 minute quantity, and are not so essential to the actual existence 
 of organic substances, as the four constituent elements above 
 named; yet, however minute the quantity, the influence of these 
 other principles seems to be most important ; they are. Sulphur, 
 Phosphorus, Chlorine, Fluorine, Iron, Potassium, Sodium, Cal- 
 cium, Magnesium, and probably more besides. These princi- 
 ples, have, by most chemists, been deemed extraneous, or foreign 
 to organized bodies ; but we shall presently show, that there 
 is good reason to believe, that the office of such additional prin- 
 ciples, though difl'erent from that of the constituent elements, 
 is nevertheless most remarkable. These four elements, along 
 with the additional principles, are, in the present state of our know- 
 ledge, alike denominated, The Ultimate Elements of organized 
 bodies ; but hydrogen, carbon, oxygen, and azote, may be termed, 
 for sake of distinction, the essential elements ; and sulphur, phos- 
 phorus, &c. the incidental elements of such bodies. The com- 
 
 20 
 
230 CHEMISTRY OF ORGANIZATION". 
 
 binations of these ultimate elements with one another, according 
 to certain laws, produce what are denominated the Immediate, or 
 Proximate Elements of organized bodies. Of these proximate 
 elements. Sugar, Oil, Albumen, &lq,. are familiar examples. 
 
 Perhaps it may be stated as a general law, that no substance, 
 entering into the composition of a living plant or animal, is so 
 pure as to be capable of assuming a reguhirly crystallized form. 
 Instead, therefore, of being defined by straight lines and angles, 
 almost all solid organized substances are more or less rounded, 
 and their intimate structure is anything but crystallized. The 
 composition of organized fluids is equally heterogeneous ; and 
 though the basis of nearly every one of such fluids be water, 
 many of them contain a variety of other matters. 
 
 Organized bodies may be ranged under two general classes ; 
 those which though they do not crystallize, while in the living 
 plant or animal, can yet, by various processes, be so far separated 
 from extraneous matters, as to be obtained in a state of purity, 
 and thus be made to assume the crystallized form ; and those 
 which cannot under any circumstances be made to crystallize. 
 The first substance of the crystallizable class which we shall 
 notice, is Sugar. 
 
 Sugar has been ascertained, and is now generally admitted, to 
 consist of three essential elementary principles — hydrogen, oxy- 
 gen, and carbon ; it is besides remarkable, that the hydrogen and 
 the oxygen in sugar are exactly in the proportion to each other, 
 in which they form water. It has been, therefore, with great 
 probability inferred, that these two elements are really so asso- 
 ciated in sugar; consequently, that sugar is a compound of water 
 and carbon ; or, in the language of Chemists, is a Hydrate of 
 Carbon. We cannot, however, produce artificially either sugar, 
 or any other organic compound, by directly combining their ele- 
 ments ; because we cannot bring the elements together, precisely 
 in the requisite stales and proportions. Still, there is no doubt, 
 that if the elements could be so brought together, the compound 
 thence resulting, would be the same as the natural compound. 
 For, as hereafter we shall endeavour to show, the organic agent 
 does not change the properties of the elements ; but simply com- 
 bines them in modes which we cannot imitate. 
 
 Vinegar is another well known proximate principle, which 
 not only forms crystallized compounds readily with many other 
 bodies ; but in its most concentrated state, is itself also crystal- 
 lized. Now, it is not less worthy of note than in the case of 
 sugar, that vinegar, altogether so diflerent from sugar in its pro- 
 pcrlies, is generally considered to be precisely analogous in its 
 composition ; that is to say, vinegar is a binary compound of 
 water and carbon ; but the proportions of water and carbon are 
 diflerent from those that form sugar. There is however, a cha- 
 
 1 
 
COMPOSITION OF ORGANIZED BODIES. 231 
 
 racleristic distinction between these two substances, inasmuch as 
 vinegar can be formed artificially ; not indeed, any more than 
 sugar, by directly associating its elements : but, by the process 
 of fermentation, and by other means, this acid may be formed 
 from sugar and from the allied substances to be presently men- 
 tioned. Yet we cannot work backwards, and by any artificial 
 process again form sugar from vinegar ; though the organic agent 
 seems to possess this power, as we shall have occasion to notice 
 more particularly hereafter. 
 
 We now proceed to consider the composition of a totally dif- 
 ferent class of substances, which under no circumstances, natural 
 or artificial, ever assume the crystallized form ; and the struc- 
 ture of which, in the common and strict snnse of the term, may 
 be said to be organized. Starch is a well knov/n instance of 
 these uncrystallizable or organized substances. 
 
 Tiie amylaceous or starchy principle is obtained in slightly 
 modified states, from a great variety of vegetables, but princi- 
 pally from the seeds of the Cerealia. Even by the unassisted 
 eye, starch is seen to be composed of minute particles ; and 
 when these particles are examined with a microscope, they 
 are found to be granules more or less rounded, and without the 
 least trace of crystallization. These granules are conceived to be 
 moulded in the cellules of the texture by which they are formed ; 
 for it would appear that their state when first secreted and de- 
 posited in the cpUnles is semifluid ; and that the excess of wat?y 
 is subsequently removed. Raspaii and Dumas have shown that 
 each of these little grains is covered with a smooth integument, not 
 afiected by water at the common temperatures ; within which in- 
 tegument is enclosed a substance rather more soluble. According 
 
 1 • • • 
 
 to some chemists, this interior substance has an analogy with 
 
 gum; but probably it is only a variety of amylaceous matter. 
 Berzelius affirms that starch when burnt, leaves about .23 per 
 cent of residuum, consisting entirely of the phosphates. But 
 when this residuum is abstracted and allowed for, the essential 
 composition of starch is found to coincide very nearly with that 
 of sugar; that is to say, starch is composed of water and carbon, 
 and the proportions of their combination are very nearly the same 
 as in sugar. Here a question arises : How does it happen that 
 substances which appear to resemble each other so closely in 
 their composition, should yet difier so widely in their sensible 
 properties ? This question we shall soon consider. But in the 
 mean time, we shall make a few remarks on another principle of 
 organized bodies, still very different, in its sensible properties, 
 from the three of which we have spoken, but apparently of a 
 similar constitution. This fourth principle is the ivoody fibre, or 
 Lignin, as it is termed by chemists. 
 
232 
 
 CHEMISTRY OF ORGANIZATION. 
 
 The woody fibre, though assuming a great variety of appear- 
 ances in different plants, and including very different incidental 
 matters ; has nevertheless, in all those plants in which it has yet 
 been examined, been found to possess very nearly the same es- 
 sential composition ; or to consist of equal weights of water and 
 of carbon. Such, at least, is the composition of woods, so very 
 different as the Box and the Willow, the Oak and the Beech ; 
 and these are the chief, if not the whole, of the woods which, we 
 believe, have yet been analyzed. Hence, it is perhaps not un- 
 reasonable to suppose that every variety of Lignin has a similar 
 composition. All woods, when burnt, leave a greater or less 
 quantity of incidental mineral residuum, in the shape of ashes ; 
 the nature of which, as above observed, differs exceedingly in 
 different sorts of wood. 
 
 The following Table presents a summary view of the compo- 
 sition of tlie four organic principles which we have considered in 
 the preceding paragraphs. It is offered, not only as an example 
 of the boundless subject of the Chemistry of Organization, but 
 as an instance of the mode by which we conceive, that depart- 
 ment of Chemistry may be best elucidated. 
 
 Substances Crystallizable. 
 
 Substances not Crystallizable. 
 
 Sugar, from 
 
 Carbon. 
 
 Water. 
 
 t 
 Starch, Arrow- 
 
 Carbon. 
 
 Water. 
 
 
 
 
 
 Starch - - 
 
 36.20 
 
 63.80 
 
 root in its 
 
 
 
 from Honey 
 
 3G.36 
 
 63.63 
 
 ordinary 
 
 
 
 East India 
 
 
 
 state - - 
 
 36.4 
 
 63.6 
 
 Moist - . 
 
 40.88 
 
 59.12 
 
 from Wheat, 
 
 
 
 Beet root and 
 
 
 
 in its ordi- 
 
 
 
 IMaplc - - 
 
 42.10 
 
 57.90 
 
 nary state 
 
 37.5 
 
 62.5 
 
 Enjrlisli Re- 
 
 
 
 ditto, ditto, 
 
 
 
 fined - - - 
 
 41.5 to 42.5 
 
 58.5 to 57.5 
 
 dried at 
 
 
 
 Pure Suj^ar 
 
 
 
 212° - - 
 
 42.8 
 
 57.2 
 
 Candy - - 
 
 42.85 
 
 57.15 
 
 
 
 
 Acetic Acid - 
 
 47.05 
 
 52.95 
 
 Lignin, in its or- 
 dinary stale 
 
 
 
 
 
 
 of dryness 
 
 42.7 
 
 57.3 
 
 
 
 
 from Willow, 
 
 
 
 
 
 
 dried at 
 
 
 
 
 
 
 212°. 
 
 49.8 
 
 50.2 
 
 
 
 
 from Box, do 
 
 50 
 
 50 
 
 A cursory inspection of the foregoing Table will evince to the 
 
C0I»1P0SITI0N OF ORGANIZED BODIES. 233 
 
 reader, how nearly the general composition of sugar and of starch 
 agree together ; and that the agreement extends even to their 
 several varieties. Vinegar, or acetic acid, has not, at present, 
 any known representative, among other organic principles ; 
 though it is not improbable that several substances exist of con- 
 formable proportions. The composition of vinegar, or acetic 
 acid, is intermediate to that of sugar and of Lignin ; while among 
 crystallizable organic substances, there is no known compound 
 analogous to Lignin. It may, at the same time, be remarked, 
 that both starch and wood can, by difi'erent artificial processes, 
 be converted either into sugar or into vinegar. We can also con- 
 vert wood into a sort of starch, as we may convert sugar into 
 vinegar ; but we are unable to reverse the process, and convert 
 vinegar into sugar, or starch into wood ; though these and innu- 
 merable changes of a similar kind are easily affected by organic 
 agency. 
 
 We proceed now to consider briefly the question we have 
 already stated, 
 
 2. How does it happen that substances, so nearly allied in 
 their composition, exhibit sensible properties so entirely differ- 
 ent? — This question, in all its bearings, is probably beyond our 
 powers of investigation : at least the extent of the requisite know-- 
 ledge we have yet attained, must be allowed to be exceedingly 
 inadequate. The few observations which we have to offer re- 
 garding this question may be comprised under the two following 
 heads : — The peculiarity of the composition of organic sub- 
 stances ; and the nature of the agents by which these substances 
 are produced. 
 
 The composition of organized bodies may be viewed as of two 
 general kinds, viz. their composition, as depending simply upon 
 differences among the proportions of their essential elements ; 
 and their composition as depending upon differences among their 
 incidental elements, the proportions of the essential elements being 
 the same.* As instances of the first kind of composition, we 
 may mention sugar and vinegar. Thus, sugar is composed of 
 42.85 per cent of carbon, and the rest water ; while the same in- 
 gredient, carbon, in the larger proportion of 47.05 per cent, with 
 the residue water, constitutes vinegar, a powerful acid. Why, 
 with such similarity of composition, the sensible properties of 
 these two substances should be so unlike, we know not ; any 
 
 * Of course there is a third, and perhaps the most extensive class of 
 bodies, hi which both the essential and the incidental elements may be 
 supposed to vary ; but partly from want of data, and partly to avoid too 
 much complication, we shall not enter upon the consideration of this class 
 at present. 
 
 30* 
 
234 CHEMISTRY OF ORGANIZATION. 
 
 more than we know why oxygen and hydrogen, when combined, 
 form water, or than we know any ultimate chemical fact. How- 
 ever wonderful, therefore the results of these slight differences of 
 composition may, at the first view, appear ; a little reflection 
 will convince us, that in reality, they are not more wonderful 
 than any other chemical phenomenon; and that they only form 
 a particular variety of such phenomena. The same remarks are 
 applicable, in part at least, to the striking dilTerences exhibited 
 by Sugar and Starch ; the essential composition of which two 
 substances, as we have before observed, is nearly the same ; but 
 the starch contains incidental bodies, from which the sugar is 
 free. On the operation of these incidental bodies we shall ofl'er 
 a few conjectural remarks. 
 
 At the commencement of this chapter, we stated that the inci- 
 dental substances existing in organized bodies have hitherto been 
 considered as foreign ; but that we could not subscribe to that 
 notion. We may now observe, that they seem to us, to contri- 
 bute chiefly towards the production of those striking differences, 
 observed among bodies having the same essential composition ; 
 and which diversity, at first sight, appears so mysterious. How 
 these minute quantities operate we do not precisely understand ; 
 but we can imagine them to be interposed among the constituent 
 molecules : further, that the molecules of these incidental matters 
 are in a state of strong self-repulsion. Such being the case, it is 
 not unreasonable to expect that they may have the power of 
 modifying the arrangement of the constituent molecules ; and thus 
 of altering the sensible properties of the substance produced by 
 their combination. 
 
 We have stated our opinion that the molecules of incidental 
 matters in organic substances are in a state of self-repulsion. 
 This opinion is founded principally, on the equal diffusion of 
 these im'idenlal molecules throughout the organic substances in 
 which they exist ; and on their consequent great distance from 
 eacli other, which, perhaps, can hardly be otherwise explained. 
 If these incidental matters were detached, or merely in a state of 
 mixture with the constituent elements, as is implied in the notion 
 of their being foreign, they would probably retain tlieir self-at- 
 tractive powers ; and instead of being equally diffused among 
 the constituent elements, they would be collected together into a 
 mass or crystal ; an arrangement never observed. For, though 
 crystallized bodies are found, not unfrequently, within organized 
 substances; yet these bodies are always extraneous, and do not 
 form any part of llic living structure ; of which, the molecules un- 
 der our consideration do actually appear to be integrants. In further 
 corroboration of this opinion, may be adduced the beautiful ex- 
 periments of Sir John llerschel, who has shown, that an enor- 
 
COMPOSITION OF ORGANIZED BODIES. 235 
 
 mous power, not less than 50,000 times the power of gravity, is 
 instantaneously generated by the simple agency of common mat- 
 ters submitted to galvanic influence ; as, for example, by the 
 agency of mercury alloyed with a millionth part of its weight of 
 sodium. These facts, while they place beyond all doubt, the 
 efficacy of minute quantities of matter, in producing the most 
 extraordinary change of the polarities of larger quantities ; at the 
 same time appear to throw great light on many natural opera- 
 tions. Tims the subtle matters of contagion and miasmata ; va- 
 rious medicinal substances, whose effects are most astonishing 
 even in the smallest doses ; the still more refined and recondite 
 mr*»ers of heat and of light, with many others, all probably act 
 on .'imilar principles. At least, the results of the operation of 
 th^ fie matters cannot be explained by iheir mere quantity ; which 
 ir'^the ordinary chemical acceptation of the term, is altogether in- 
 commensurate with the evident and striking changes, constantly 
 arising in the processes of nature, from such agency. 
 
 The observations that have now been offered, are intended to 
 apply to all those elementary substances, entering into the com- 
 position of a living organized being. For, no one element, when 
 thus assimilated, appears to be in its natural state ; or to be ca- 
 pable of exerting precisely those powers which it is known to 
 exert, when acting in virtue of its original inorganic properties. 
 In sbort, we may thus recapitulate what has been said : besides 
 the essential molecules constituting the ground-work of a living 
 organized being, and which probably exert on each other, to a 
 certain extent, the ordinary chemical influences of matter ; it 
 -would seem that there are, at the same time, diffused throughout 
 the whole living mass, in exceedingly minute proportion, va- 
 rious other matters, the molecules of which appear to be in a 
 high state of self-repulsion. By these incidental matters, it 
 would further seem, that the ordinary chemical properties of the 
 essential elements of the organized living structure are variously 
 modified ; in particular, that, the essential elements are hindered 
 from assuming a regularly crystallized form. Moreover, these 
 incidental matters entering into the composition of a living body, 
 apparently furnish to the organic agent new powers utterly beyond 
 our comprehension ; which powers the organic agent has been 
 endowed with the ability to control, and direct, in any manner 
 that, from the exigencies of the living organized being, may be- 
 come requisite.* 
 
 The intimate nature of the organic agent or agents^ or by 
 
 * In addition to what is stated in the text, we may remind the reader 
 of what we have elsewhere alluded to, viz . : that the organic agents have 
 
236 CHEMISTRY OF ORGANIZATION. 
 
 whatever other name we may choose to designate the peculiar 
 enero^ies which exist in plants and in animals, and by which they 
 are distinguished from inanimate matter, is now, and probably 
 will ever remain, altogether unknown to us. But though we be 
 thus ignorant of what these agents are i we can not only com- 
 prehend with tolerable certainty, what they are not ; but we can 
 also in some degree ascertain, what they are capable or incapa- 
 ble of eflecling. As it is of the utmost consequence to obtain 
 just views on these points, we shall consider them somewhat in 
 detail. 
 
 When we were treating of inorganic elements and agencies, and 
 of the laws which they appear mutually to obey, we found, that 
 though their nature be obscure, and the investigation of them very 
 difficult ; we were nevertheless enabled to adduce some, not al- 
 together unplausible, conjectures on the modes, in which the ele- 
 ments combine, to form regular crystals and the other conditions 
 of inanimate matter. Now with this insight into the nature of 
 inorganic operations, and with all the additional knowledge of 
 every kind that we can command, let us attentively survey the 
 most simple plant or animal ; let us observe the actions, the 
 changes, the modifications of form and properties it continually 
 exhibits ; and then let us seriously ask ourselves, whether every- 
 thing that we know, will enable us to make, even an approach, 
 toward an explanation of what we see. It is indeed true, that 
 the plant or animal we examine is composed of charcoal and 
 water, and of other ingredients with which we are equally fami- 
 liar ; that it is liable to be afiected by Heat, Light, Electricity, 
 and by other inorganic agents. But it is perfectly ascertained 
 that these elements and agents, out of an organized body, and 
 left enlirelij to themselves^ never would or could unite, either in 
 virtue of their own properties, or from accident, so as to form any 
 j)lant or ajiimal however insignificant. Are we not then compell- 
 ed to infer, that within a plant or animal, there exists a principle 
 or agent superior to those whose operations we witness in the 
 inorganic world; and which agent moreover possesses, under cer- 
 tain restraints, the power of controlling and directing the opera- 
 tions of these inferior agents? That this is a natural and a just 
 inference, no one who calmly views all the circumstances will 
 ever deny ; and if the existence of one such agent be admitted, 
 the admission of the existence of others can scarcely be withheld ; 
 for the existence of one only, is quite inadequate to explain the 
 
 probably tlie power, within certain limits, of separating the molecules of 
 bodies, considered at present as elementary, into more refined forms of 
 matter (submolcculcs •'). 
 
COMPOSITION OF ORGAMZED BODIES. 237 
 
 infinite diversity among plants and animals. Thus, in the words 
 of tlie excellent Paley, " there may be many such agents', and 
 many ranks of them:" in other words, there may be an ascend- 
 ing gradation of these agents, from that of the comparatively 
 simple plant, onward to that of the most complicated animal. 
 
 Such being the suggestions concerning organic agency that 
 arise from a general survey of organic operations ; let us, with 
 reference to the further bearing and tendency of these sugges- 
 tions, inquire a little more minutely into the powers and modes 
 of operation of organic agents. 
 
 3. Of the modes of Operation of Organic Agents. — In the 
 first place, with regard to what cannot be effected by organic 
 agency, we may observe, that no organic agent has the power 
 either of creating material elements, or of cJianging one such 
 element into anotiier. By element, it maybe right to premise, is 
 here meant, a principle that is not made up of others ; and which, 
 consequently, possesses an absolute and independent existence. 
 Whether one, or more, such elements exist, it is not now our ob- 
 ject to inquire. The astonishing discoveries of modern chemis- 
 try have shown, that many of those substances, formerly consi- 
 dered as elements, are, in fact, compounds ; and as the science 
 of chemistry is still progressive, it is probable that, with the 
 enlargement of its boundaries, there will be a still further di- 
 minution of the number of those substances which are, as yet, 
 held to be simple. Admitting, however, for the sake of argu- 
 ment, that elementary principles do exist, of such immutable 
 character as has been supposed ; from the nature of organic 
 beings, at least of all animals, it is impossible to conceive that 
 they possess the power either of creating or of altering these ele- 
 mentary principles. For no organized being has an independent 
 existence, but all animals derive their support from previous or- 
 ganization, which might be otherwise, did they possess a creating 
 power ; nor can they be nourished by ail substances indiscrimi- 
 nately, as they ought to be, were they possessed of a transmuting 
 power. Yet, while it is thus denied that organized beings 
 possess the power, either, to create or to change, in the strict ac- 
 ceptation of these terms ; it has been admitted to be exceedingly 
 probable, that the organic agent is, within certain limits, qualified 
 to compose and decompose many substances which are now 
 viewed as elements ; and that the organic agent does thus ap- 
 parently form and transmute these imagined elements. But to 
 enter further, in this place, on the elucidation of these obscurities 
 would be foreign to our present purpose. 
 
 The organic agent has not the power of combining elements 
 in such a manner, that the properties of the resulting compound 
 shall differ from those of a compound, formed from the same 
 
238 CHEMISTRY OF ORGAMZATION. 
 
 elemeiiis similarly combined by any other agent. The Deity has 
 cliosen to prescribe limits to his power, and to establish certain 
 laws, to which He at all times rigidly adheres ; and, again adopt- 
 ing the language of Paley, " when a particular purpose is to be 
 effected, it is not by making a new law, nor by the suspension 
 of the old ones, nor by making them wind, and bend, and yield 
 to the occasion ; but it is by the interposition of an apparatus 
 corresponding with those laws, and suited to the exigency which 
 results from them, that the purpose is at length attained." In the 
 instance before us, the attainment of the particular purpose of 
 organic life is effected, not by any departure from the great 
 scheme, but by new and different combinations. To suppose, 
 therefore, that the organic agent can, for example, combine oxy- 
 gen and hydrogen, in exactly tlie same proportion, and in the 
 same manner, in which they are combined, when they exist as 
 Avater ; and, from these elements so combined, can yet produce 
 something different from water, is contrary to all reason, and 
 wo jld be, in truth, to accuse the Deity of subverting, and of act- 
 ing in opposition to, his own laws. We have dwelt the more 
 strongly on these points, because among physiologists a vague 
 notion seems to have prevailed, that organic agents have the 
 power, not only of changing the inherent and peculiar properties 
 of bodies ; but likewise, of causing the results of their combina- 
 tion to be altogether different from those that are produced, under 
 exactly similar circumstances, by inorganic agency. If however 
 the arguments we have advanced be well founded, this notion 
 must be erroneous ; and its erroneous character will be rendered 
 still more evident, by the observations, we shall, in the second 
 place, offer, regarding the principles on which the operations 
 within living organized bodies are really conducted. 
 
 Tiie means by which organic agents accomplish the purpose 
 for which they are designed, may be naturally divided into two 
 kinds ; those which are dependent on peculiarity of composition 
 and of structure ; and those by which tJiis peculiarity of com- 
 position and of structure is produced. 
 
 hupiiry into the first of these means of action has already 
 been in great degree anticipated. A brief recital, therefore, is all 
 that is here necessar3^ We have seen that organized substances 
 are composed of the same elements, which exist abundantly 
 throughout the world in the inorganized state ; moreover that 
 these elements are subject to all the influences and agencies of 
 inorganic nature. We have seen that organic agents are enabled 
 to form certain proximate principles, by variously combining their 
 elements ; whicii proximate principles, even when in the con- 
 dition of crystals, it is not possible to imitate artificially. We 
 have, at the same time, seen that these proximate principles, 
 
COMPOSITION or ORGANIZED BODIES. 239 
 
 though they may have a riatural tendency to crystallize, are, as 
 they usually exist in living bodies, prevented from undergoing 
 that process, by the diffusion of minute quantities of other ele- 
 ments throughout their mass : the molecules of which are in some 
 unknown state of activity ; such perhaps as cannot naturally 
 exist in the universe, except when conjoined with organization. 
 Finally, we have inferred, that the differences and peculiarities 
 of these minute additional matters, are probably adequate for 
 explaining the differences and peculiarities, of the sensible and 
 chemical properties of the substances that are formed by organi- 
 zation. Having thus pointed out the general differences of com- 
 position existing among organized bodies; it remains to state, that 
 such differences of composition almost invariably indicate dif- 
 ferences of structure. For though similarity of composition does 
 not necessarily imply similarity of structure ; yet similarity of 
 structure perhaps, without exception, indicates similarity, or, 
 at least, analoi^y of com.position ; and, consequently, similarity 
 of action. Thus the woody fibre of plants is always formed of 
 the principle termed Lignin, and never of resin, or of albumen. 
 The relation of structure to chemical composition is not less 
 striking in tb.e muscular fibres of animals, and indeed in all or- 
 ganic compounds of a definite character ; the essential composi- 
 tion* of such substances, though exhibiting endless minor diver- 
 sities, being nevertheless, in all instances, precisely the same. 
 
 The means by which that peculiarity of cotnposition and of 
 structure is produced, which is so remarkable in all organic sub- 
 stances, like the results themselves, are quite peculiar ; and bear 
 little or no resemblance to any artificial process of chemistry. 
 For example, we have not, in artificial chemistry, any control 
 over individual molecules ; but are obliged to direct our opera- 
 tions on a mass, formed of a large collection of molecules. 
 The organic agent, on the contrary, having an apparatus of ex- 
 treme minuteness, is enabled to operate on each individual mole- 
 cule separately ; and thus, according to the object designed, to 
 exclude some molecules, and to bring others into contact. In 
 these processes, it may be conceived, that the molecules thus 
 •appropriately brought together, and, at the same time, guarded 
 from extraneous influence, by the organic agent, are in virtue of 
 their own proper aihnities, sufficiently disposed to unite, without 
 requiring that any new properties should be communicated to 
 them. Hence the organic agent, in its simplest state, may be 
 viewed as a power which so controls certain inorganic matters, 
 as to form them into an apparatus, by which it arranges and or- 
 ganizes other matters, and thus effects its ulterior purposes. Where 
 the operations of this simple organic agent terminate, those of 
 another and more effective organic agent may be supposed to 
 
240 CHEMISTRY OF ORGANIZATION. 
 
 beo-in ; which, by carrying the general process of organization a 
 step further, adapts the organized material for the operations of a 
 third and yet higher agent. Thus, each new agent may be sup- 
 posed to possess more or less control over all those below itself, 
 and to have the power of appropriating their services ; till at 
 length, at the top of the scale, we reach the perfection of organized 
 existence. The excellent Paley sanctions this view of organic 
 operations, and continues in the following words : " We do not 
 advance this as a doctrine either of philosophy or of religion ; but 
 we say that the subject may safely be represented under this 
 view ; because the Deity, acting himself by general laws, will 
 have the same consequences upon our reasoning, as if he had 
 prescribed these laws to another." . 
 
 This view of the successive creation of organic agents, which 
 harmonizes not only with the phenomena of Geology, but with 
 the differences which are observable among plants and animals, 
 and with the developement of the more perfect species ; is directly 
 opposed to the notion of spontaneous developement maintained 
 by some distinguished French philosophers ; as well as to the 
 opinion that life is the result of organization. Thus we consider 
 it impossible that by any accidental concurrence of circumstances, 
 a dog can, in the progress of time, be gradually converted into an 
 ape, or an ape into a man ; and moreover, we not only think such 
 an hypothesis directly at variance with the whole tenor of the laws 
 of nature, but quite absurd. The laws of nature, as we have shown, 
 are in all cases most rigidly adhered to by the Deity. These 
 laws, therefore, are unalterably stable, within the limits that have 
 been assigned to them. Now, from what we know of the laws 
 of nature, or of the properties of the elements of matter, or of the 
 agents by which they are moved, it is, as we have already stated, 
 impossible to conceive that carbon, water, and electricity, of their 
 own accord, and from any inherent influence, can so unite as to 
 form the humblest plant or animal; much less, so as to secure its 
 perpetual existence by reproduction. For similar reasons it is 
 equally impossible to conceive, that there can ever be such a spon- 
 taneous arrangement or combination of inferior organic agents, 
 as to foim a superior agent. Whenever, therefore, a new and 
 specific agent is required, a new and specific act of creation must 
 be performed by the Great Architect of the universe. Nearly si- 
 milar remarks apply to the opinion that the living principle is the 
 result of organization. The living principle is not the result of 
 organization, but the cause of organization. In accounting for the 
 phenomena of life, it is absolutely necessary to assume the exist- 
 ence of some agency different from, and superior to, that which 
 operates among inorganic matters. Now since, as we have seen, 
 no inferior agencies can be supposed so to combine as to form a 
 
COMPOSITION OF ORGANIZED BODIES. 241 
 
 superior agency; does it not accord better with our reason, as well 
 as with our experience, to assume at once a new creation of the 
 higlier principle ? 
 
 The first circumstance that arrests our attention, with reference 
 to the preceding remarks, is the wonderful adaptation of the ele- 
 ments and the agents of organic nature to each other. For exam- 
 ple, had not carbon, and azote, and water, been formed with the 
 properties which they now possess, organic agents, as we know 
 them, would have existed in vain ; and without organic agents, 
 the properties of these elements would equally have been useless. 
 And how truly wonderful, and utterly beyond our comprehension, 
 are the properties and adaptations displayed in the processes of 
 organization ! To enable ourselves to form some conception of 
 these processes, by bringing to a level with our understanding, 
 those things which they accomplish ; let us propose to ourselves 
 the question, — What ought to be the inherent properties and the 
 constitution of an elementary principle, which should not only be 
 capable of being formed into the hardest and the softest bodies in 
 nature; but which should also be capable of entering as an essen- 
 tial ingredient into substances so very unlike, as sugar, vinegar, 
 wood, oil, albumen, and many others, in all their countless forms 
 and varieties? Do we not feel all our fancied knowledge annihi- 
 lated by such a question ? Nay what is more, even when the 
 question is answered fur us ; and when, with the utmost care, and 
 to the furthest extent of our ability, we have studied all the che- 
 mical properties of Carbon — the substance by which the condi- 
 tions of the question are fulfilled ; how totally unable are we to ex- 
 plain these properties, or even to trace them through their simplest 
 modifications ? Why, for instance, is the diamond capable of as- 
 suming the form of charcoal ; or why is charcoal capable of as- 
 suming the form of the diamond? And how are these properties 
 modified, and altered, in all the numerous states of combination 
 into which we know carbon enters ? On what property or quality, 
 not possessed by other elements, do all those astonishing capabi- 
 lities of change depend, which are inherent in this element carbon? 
 And why has carbon been chosen for forming organized beings, 
 in preference to silex, or iron, or any other element?* To us all 
 
 * Since- there is nothing peculiar in the elements of which organized 
 beings are composed, and no reason can be assigned why carbon and other 
 elements have been cliosen for their formation, we are compelled to as- 
 cribe the choice of these materials to the will of the Great Creator. But 
 as He never acts without a purpose, we cannot doubt that these elements 
 have been selected for some specific design ; which design has probably 
 been, that the fabric of the beings dwelling on this earth, might be adapt- 
 ed to its general position in the Solar system. When we consider that 
 the same heat, and the same light diffused by the same central sun ; that 
 
 21 
 
242 CHEMISTRY OF ORGANIZATION. 
 
 these things are absolutely unknown; but what a conception do 
 they give, of that inscrutable agency by which the elements are 
 governed ; of the powers of that Almighty Mind who is conversant 
 with them all — by whom they were first desigtied, and by whom 
 they have all been created ! How infinitely must His knowledge 
 surpass whatever we can imagine : how far is His power beyond 
 our utmost calculation ! 
 
 On the other hand, if the properties of the elements of matter 
 be wonderful, yet more wonderful are those agents within orga- 
 nized bodies, by which they are directed. With the intimate na- 
 ture indeed of these agents we have not the remotest acquaintance, 
 nor, probably, ever shall have. But, as has been already stated, 
 we can trace, to a certain extent, the laws of action which these 
 agents obey ; we observe their unvarying adaptation to the pro- 
 perties of carbon, azote, and water, on which they chiefly act; 
 their power, within certain limits, of guiding and controlling inor- 
 ganic agents ; and more than all, that mysterious periodic deve- 
 lopement and decay, which every organized being undergoes. 
 These facts which continually present themselves to our notice, 
 are totally inexplicable according to those laws bv which inorganic 
 bodies are governed ; and are referrible only, to an order of laws, 
 which the Great Author of Nature has not chosen to reveal. 
 
 Lastly, we cannot close this chapter, without pointing out to 
 the reader a very remarkable contrast, in the two classes of objects 
 which have engaged our attention. The number and diversity of 
 organic agents appear to be endless ; in the creation, therefore, 
 of these agents, the Great Author of Nature has chosen to mani- 
 fest his attribute of infinity. But in the creation of the material 
 elements which compose the frame of organized beings, He has 
 adopted a plan directly opposite. Instead of different principles; 
 the same carbon, the same azote, the same water, enter into every 
 living being, from the lowest plant upward to man. Amidst the 
 wonders of creation, it is perhaps difficult to say what is most 
 wonderful ; but we have often thought, that the Deity has displayed 
 a greater stretch of power, in accommodating to such an extraor- 
 dinary variety of changes, a material so unpromising and so refrac- 
 
 the wliole system obeys the same laws ; and that the diflTcrent planets hi- 
 fluencc, and are influenced by each other; we are warranted in believing 
 that tlie phinets are essentially composed of the same elementary princi- 
 ples. But admittinfj that the heat and lii^ht of the sun are distributtd ac- 
 cording- to the hiws which they seem universally to obey ; the heat in Mer- 
 cuiy, close to tlie sun, and tiie cold in Saturn, at the other extreme, must 
 be Hlikcso intense, that org-anized being-s, such as inhabit this earth, could 
 not exist for :i moment. In the different planets, therefoi-e, may not the 
 living principle be attached to different elements, more or less fixed or 
 volatile, a3 tlie distance of the planet from the sun may require ? 
 
MODES OF NUTRITION. 243 
 
 tory as charcoal, and in finally uniting it with the human mind ; 
 llian was requisite for ifie creation of the human mind itself. To 
 Hin>, however, all things are alike easy of accomplishment ; and 
 He, doubtless, has willed these and other proofs of His omnipo- 
 tence, in order to convince us of this truth, — that the Creator of 
 the mind, could alone have created the matter with which the mind 
 is associated ! 
 
 CHAPTER H. 
 
 OF THE MODES OF NUTRITION ; COMPREHENDING A SKETCH OF THE ALI- 
 MENTARY APPARATUS ; AND OF ALIMENTARY SUBSTANCES IN PLANTS, 
 AND IN ANIMALS. 
 
 The subsistence of all organized beino;s is derived from sources 
 external to themselves. Their means of subsistence, however, 
 as well as the modes in which the aliments are applied, exhibit 
 an almost endless variety. As might be expected, the widest 
 differences, both in the nature of the alimentary substances, and 
 in the manner of their introduction, are between plants and ani- 
 mals. We shall, therefore, consider the subject of nutrition under 
 these two heads. 
 
 Section I. 
 
 Of the Modes of the Nutrition of Plants ; and of the Nature 
 of those Matters by which their Nutrition is effected, 
 
 A MINUTE investigation of the anatomy and the physiology of 
 plants would be quite foreign to the object of this treatise. At 
 the same time, it is necessary that the reader should have some 
 insight into these departments of knowledge, in order that he may 
 be enabled to understand the collateral researches which it is our 
 duty to illustrate. 
 
 " If we reflect upon the phenomena of vegetation," says Pro- 
 fessor Lindley, "our minds can scarcely fail to be deeply im- 
 pressed with admiration at the perfect simplicity, and, at the 
 same time, faultless skill, with which all the machinery is con- 
 trived, upon which vegetable life depends. A few forms of tissue 
 interwoven horizontally and perpendicularly constitute a stem; 
 the developement, by the first shoot that the seed produces, of 
 buds which grow upon the same plan as the first shoot itself, 
 and a constant succession of the same phenomenon, causes an 
 
244 CHEMISTRY OF ORGANIZATION. 
 
 increase in t?ie length and breadth of the plant ; an expansion of 
 the bark into a leaf, within which ramify veins proceeiHng from 
 the seat of nutritive matter in the new shoot, the provision of air 
 passages in its substance, and of evaj)oraling pores on its surface, 
 enables the crude fluid sent from the roots to be elaborated and 
 digested until it becomes the peculiar secretion of the species : 
 the contraction of the branch and its leaves forms a fiower ; the 
 disinteorration of tlie internal tissue of a petal forms an . anther ; 
 the folding inwards of a leaf is sufficient to constitute apistillum ; 
 and finally, the gorging of the pistillum with fluid which it can- 
 not part with, causes the production oC afridt.''^* 
 
 The "crude fluid sent up from the roots" of plants, or their 
 sap, as it is termed, is found to consist of water, mucilage, and 
 sugar, with some minute portions of other matters, generally 
 saline. Though, under certain circumstances, moisture be ab- 
 sorbed by the leaves of all plants, yet there is no doubt that a 
 great part of their nourishment enters by their roots ; not, how- 
 ever, by the whole root indiscriminately : the nourishment of 
 plants is taken up chiefly by the minute fibrous parts termed 
 spongioles. Hence, these minute fibrous parts are of the utmost 
 importance in the vegetable economy, and ought to be carefully 
 preserved in transplantation, otherwise the plant will certainly 
 perish. In some instances, roots appear to be intended to act as 
 reservoirs of nourishment for the support of the plants of the 
 succeeding year, on their first developement. There are such 
 roots in liie Orchis and Dahlia tribes, and in others. Of late it 
 seems to have been satisHictorily establisheil, that the roots of all 
 plants, besides imbibing nourishment, perform also an excretory 
 office ; and that in the soil in which plants grow, there are de- 
 posited by the roots, certain matters of an excrcmentitious nature, 
 injurious to the plants from which they have been separated ; and 
 which therefore, cannot be absorbed again, till they have under- 
 gone decomposition. Such excreted matters have been adduced 
 as the reason, why a soil becomes so much deteriorated by any 
 one species of plant having long grown in it, that it will not sup- 
 port other individuals of the same species : whence the necessity 
 of a rotation of crops. 
 
 The principal ingredient in the sap of plants, as already ob- 
 served, is water. 'JMie quantity of sap in some plants, is almost in- 
 credible ; and not less so, is the force with which, on the ap- 
 proach of warm weather in our climates, and at the commence- 
 ment of the rainy season within the tropics, that sap is determined 
 upwards. The general composition of the sap varies considerably 
 in diflerent parts of the same plant. For instance, sap taken from 
 
 • Introduction to Botany, p. 216. 
 
NUTRITION OF PLANTS. 245 
 
 the roots is little more than water ; while the quantity of saccha- 
 rine and oiher matters contained in the sap, increases in its pro- 
 gress 'dUmg the stem to the higher parts of the plant. When the sap 
 begins to rise, the leaves at the same time begin to be developed. 
 From the leaves principally the watery portions of the sap 
 are evaporated ; and the evaporation is copious and un<;easing. 
 The more solid matters thus remain dissolved iu a less proportion 
 of water ; and after undergoing further changes, as is supposed, 
 in the leaves chiefly, these matters are returned, along with the 
 remaining water, to be deposited in other parts of the plant, for 
 its future uses. It seems now to be generally admitted, that one 
 part of the food of plants is the matter extracted from the soil ; 
 and that this matter is taken up with the watery portion of the sap 
 above mentioned. It seems also to be admitted, that carbonic 
 acid gas is in some way indispensable to vegetation ; " for it has 
 been ascertained, that feed plants as you will, they will neither 
 grow nor live, whether you offer them oxygen, hydrogen, azote, 
 or any other gaseous or fluid principle, unless carbonic acid is 
 present." Like the other nutritious matters, this carbonic acid 
 is partly taken up by the roots ; but under certain circumstances, 
 it is also separated from the air, and absorbed by the leaves. The 
 circumstances under which this absorption, or rather decomposi- 
 tion, of carbonic acid, by the leaves takes place, are most curious 
 and important. They are understood to be as follows : 
 
 During the day, and particularly during sunshine, the leaves of 
 plants have the power of abstracting the carbonic acid from the 
 atmosphere. The carbon of the acid, and perhaps also a little of 
 its oxygen combine with the plant ; while the greater part of the 
 oxygen remains, and is diffused through the atmosphere in a 
 gaseous state. During the night, on the contrary, or in the shade, 
 plants, in general, convert a portion of the oxygen of the atmo- 
 sphere into carbonic acid ; but the quantity thus converted, is less 
 than that separated from the carbonic acid which they decompose, 
 under the influence of the solar light. At the same time with 
 this formation of carbonic acid by plants during the night, they 
 are said also to absorb from the atmosphere a certain portion of 
 oxygen ; to replace that which had been given off, during expo- 
 sure to sunshine, on the preceding day. Plants absorb carbon as 
 long as they are exposed to the light ; during the season, there- 
 fore, when the day is long and the night is short, plants give off 
 much less carbon than they absorb. This excess of the absorp- 
 tion of carbon, is probably one reason why in the Polar latitudes, 
 the progress of vegetation is so rapid. By a beautiful provision 
 of nature, in the course of the short summer of a few weeks, but 
 of unvarying light, plants, in these latitudes, go through all the 
 changes which in hotter climates require many months. 
 
 21 * 
 
246 CHEMISTRY OF ORGANIZATION. 
 
 These phenomena of gaseous absorption and secretion in the 
 leaves of phirits, seem to be produced by a portion of the leaf pe- 
 culiarly organized, and situated immediately under its external 
 covering or epidermis. Professor Burnet has lately explained 
 these phenomena, by referring them to the respiration and diges- 
 tion of plants. The process of respiration in plants, is supposed 
 to be continual ; and to be accompanied, as in animals, by the 
 formation and emission of carbonic acid gas. While digestion, 
 whicli consists in the decomposition of carbonic acid gas, takes 
 place only during the exposure of plants to the influence of the 
 light — the carbon of the carbonic acid being separated from the 
 oxygen, and absorbed. Hence a plant exposed to sunshine puri- 
 fies the air, by digesting the carbonic acid, the carbon of which 
 it appropriates ; while it sets the oxygen free. In the dark, on 
 the contrary, digestion ceases, but respiration continues ; and 
 carbonic acid gas is thus accumulated in the surrounding atmo- 
 sphere. 
 
 With respect to the " peculiar principles of plants," these are 
 as numerous as the individual plants themselves ; so that to at- 
 tempt any detailed account of them here, would be quite imprac- 
 ticable. Generally speaking, the peculiar principles found in 
 plants may be divided into three great classes : — those vegetable 
 principles in which hydrogen and oxygen are combined in the 
 proportions that form water; as in the division of 5acc/?r/rme 
 bodies, described in a former chapter : — those principles in which 
 hydrogen, or rather carbon and hydrogen, predominate ; which 
 gfucrally have more or less of an oily character ; — and those 
 principles in which oxygen predominates ; which have usually 
 an acid character. Besides these three great classes of vegetable 
 principles, there are some that contain azote, and perhaps other 
 elements ; many of which principles also exhibit weak alkaline 
 powers : such are the peculiar principles of Opium and other 
 Narcotics ; also of Cinchona ; and a variety of others, chiefly 
 eni ployed as Medicinal agents. 
 
 Section II. 
 
 Of the Modes of Nutrition in Animals ; and of the Alimentary 
 iSitO stances by which they are nourished. 
 
 To beings, like animals, endowed with locomotive powers, the 
 absorption of their nourishment from without, would have been 
 exceedingly inconvenient. Animals have, therefore, been fur- 
 nished willi an additional receptacle and apparatus subservient to 
 nutrition, into which, as inclination or circumstances may prompt 
 
ORGANS OF DIGESTION IN ANIMALS. 247 
 
 them, their food is conveyed at intervals ; and from which, after 
 havinof undergone certain chano^es, the food is absorbed and dis- 
 tribnted over their system, as the exigencies of that system may 
 require. Hence the distinction between plants and animals ; — 
 plants absorb their nourishment by external, animals by internal, 
 roots or spongioles. We need scarcely remark, that the stomach 
 and alimentary canal, with their appendages, are the internal ap- 
 paratus to which we ;illude ; and that this internal apparatus con- 
 stitutes a marked difference between plants and animals. 
 
 1. Of the Organs of Digestion in Animals. — Among the dif- 
 ferent tribes of animals, there is an almost endless diversity ia 
 the formation of the alimentary organs ; and as these organs vary, 
 not only in their own formation, but also with respect to the 
 auxiliary apparatus, and appendages of every kind, connected with 
 them ; any detailed account of the alimentary system would at 
 present be quite uncalled for. In general, the alimentary canal 
 of the higher classes of animals, consists of a tube of greater or 
 less elongation ; expanded in some parts of its length ; terminated 
 at one extremity by a mouth, into which the food is received ; 
 and at the other, by a provision for the removal of excrementi- 
 tious matters. In some of the less perfect animals, the alimentary 
 canal has only one aperture ; in these animals, of course, instead 
 of a canal, there is a kind of sac. In a very few other animals, 
 the alimentary cavity has numerous apertures. In all instances, 
 however, and whatever may be the nature of the alimentary mat- 
 ters, these matters, after having been retained for some time in 
 the organs appropriated to nutrition, are reduced, more or less, to 
 a fluid state — are dtgested, in the common sense of the term, 
 and are converted into what is denominated chyme. The more 
 nutritious parts of the fluid chyme, or the chyle as they are 
 termed, are then absorbed, and distributed through the system for 
 the reparation of the animal; while the insoluble and other mat- 
 ters, are separated as excrementitious. 
 
 We have already alluded to the endless diversity observable in 
 the form and arrangements of the alimentary canal in the different 
 kinds of animals. A few of the most remarkable of these diver- 
 sities among the more perfect animals will be noticed, in the out- 
 line we are now to give of the alimentary canal as existing in the 
 human body. 
 
 Of the Mouth and its Appendages. — " In no apparatus put 
 together by art," says Paley, " do I know such multifarious uses 
 so aptly contrived as in the natural organization of the human 
 mouth." " In this small cavity we have teeth of different shape, 
 — first for cutting, secondly for grinding ; muscles most artificially 
 disposed for carrying on the compound motion of the lower jaw, 
 half lateral and half vertical, by which the mill is worked ; foun- 
 
248 CHEMISTRY OF ORGANIZATION. 
 
 tains of saliva sprinjrin^ np in different parts of the cavity for the 
 nioi?:tening of the food, while the mastication is going on ; glands 
 to Iced the fountains ; a muscular construction of a very peculiar 
 kind in the back part of the cavity, for the guiding of the pre- 
 pared aliment into its passage towaids the stomach, and in many 
 cases for carrying it along that passage." "In the meantime, 
 and within the same cavity, is going on another business altoge- 
 ther different from what is here described — that of respiration 
 and of speech. In addition, therefore, to all that has been men- 
 tioned, we have a passage opened from this cavity to the lungs, 
 for the admission of air, exclusively of every other substance ; we 
 have muscles, some in the larynx, and without number in the 
 tongue, for the purpose of modulating that air in its passage, with 
 a variety, a compass, and a precision of which no other musical 
 instrument is capable. And lastly, we have a specific contrivance 
 for dividing the pneumatic part from the mechanical, and for pre- 
 veniitig: one set of actions inlerferino^ with the other." "The 
 niouih, with all these intentions to serve, is a single cavity ; is 
 one machine, with its parts neither crowded nor confined, and 
 each unembarrassed by the rest."'^ Such is Paley's graphic de- 
 scription of the human mouth and its appendages: we have quoted 
 it at length, that it may serve as a text for illustr-ation. 
 
 Man has been observed to differ more from other animals in 
 the form of his lower jaw, than in the form of any other bone of 
 his body. Tiiis difference consists chiefly in the prominence of 
 the cliin ; that peculiar characteristic of the human countenance, 
 which distinguishes more or less every race of mankind, and is 
 found in no other animal whatever. There is likewise a striking 
 dilference, among the various tribes of animals, in the mode of 
 articulation of the lower jaw ; which in all cases is singularly 
 adajilcd to the nature of the food of the animal. Thus, in the 
 carnivor'ous tribes, the artrcidalion is so arranged that the jaw can 
 move only up and down ; and is almost entirely incapable of that 
 lateral movement, which is essential to genuine mastication. 
 Hence such animals cut and tear their food, and swallow it in 
 large pieces. But those animals that live on vegetables, in addi- 
 tion to the vertical motion of their lower jaw, have the power of 
 moving it backwards forwards, or to either side, so as to produce 
 a grinding effect, admirably fitted for triturating the vegetable 
 matters on which they subsist. 
 
 -The feefh next claim our attention, as being not less suited to 
 the hattits of the animal, than in the form of the jaw in which 
 they arc set. Teeth arc divided by naturalists into three orders : 
 — The hiciaorca, or culling teelh, placed in the front part of the 
 mouth; the Cuspiduti^ canine, or corner teeth, usually placed 
 
 • Natuiul Theology', chap. ix. 
 
ORGANS OF DIGESTION IN ANIMALS. 249 
 
 near the angles of the jaw ; the Molares, grinding, or lateral teeth, 
 which always occupy the sides and back part of the jaw. In 
 man, and in those animals which most nearly resemble him in 
 their structure, teeth exist of all the above varieties of form. But 
 many species want one or other of these varieties; while the teeth 
 they possess, are of a form and size very unlike the same teeth 
 in man. I'hus, in animals which live chiefly on the harder ve- 
 getable substances, and which, from their peculiar mode of feed- 
 ing, have been termed gnawing animals, the. incisor teeth are 
 the most remarkably developed ; as these teeth are the best 
 adapted, and indeed are the most necessary, to their habits. 
 In carnivorous animals, on the other hand, the canine teeth are 
 of chief importance ; as enabling these animals to seize and hold 
 their prey: in such animals, accordingly, the canine teeth are the 
 most perfectly formed. LasUy, in the animals that feed on grass, 
 and other herbaceous substances, and whose aliments require long 
 and complete mastication, the Molares, or grinding teeth, attain 
 the greatest enlargement; and in many of these animals the inci- 
 sor and the canine teeth are entirely wanting. Besides the adapta- 
 tion of the form, the enamel or harder cutting portion of the teeth, 
 is distributed over and throughout their texture, according to 
 their intended uses, in a manner that is truly extraordinary. The 
 description however of the arrangement of the enamel, as well 
 indeed as a minute account of the teeth themselves, belongr to the 
 physiologist, on whose province we shall not further intrude. 
 But it is impossible to take even the most superficial view of the 
 teeth of animals, without being struck with the admirable design 
 and fitness they display, throughout their whole fabrication. 
 
 The next auxiliary appendages of the mouth are the glands 
 that secrete the saliva; in which we observe the same beautiful 
 arrangement as in the form and structure of the teeth. In man, 
 though the apparatus for the secretion of ih.e saliva, is by no means 
 of large size, yet the quantity of fluid whicii the salivary glands 
 are capabla of secreting, and do secrete during mastication, is 
 very considerable ; often amounting, it is said, to half a pint or 
 more. This fluid, in its perfectly healthy state, is neither acid 
 nor alkaline, or alkaline only in a slight degree ; but occasionally 
 it assumes an acid character. Besides the great utility of the 
 saliva in moistening the food, we cannot doubt that it assists, and 
 is even necessary to the full completion of the succeeding di- 
 gestive process. By a beautiful arrangement, those animals 
 that do not masticate their food, as the carnivorous tribes, have 
 very small salivary glands ; while in animals whose food requires 
 long mastication, as in ruminating animals — the cow and the 
 sheep, for example, the salivary glands are very large. 
 
 The passage by which the masticated food is conveyed from 
 the mouth to the stomach is termed the oesophagus. Like the 
 
250 CHEMISTRY OF ORGANIZATION. 
 
 wliole frame, the CEsopbagus is admirably adapted for its office ; 
 and in (btfcrent animals, varies in size and structure, according 
 to their habits. These differences, however, scarcely concern us at 
 present, and we pass on to that important organ — the Stomach. 
 
 The human stomach is a membranous bag, of a shape rather 
 difficult to be de.-cribed, so as to convey a clear notion of it to the 
 reader. If we imagine two cones united at their bases, and the 
 figure thus produced to be bent into a semicircular form, some 
 idea may be obtained of ihe outline of the stomach in the human 
 species. In respect to its size, the human stomach varies : but 
 in the adult, its capacity is usually such as to contain about two 
 or three pints. The stomach is situated immediately under the 
 diaphragm; but the precise place of the organ differs somewhat 
 with its state of repletion. The general position of the stomach 
 is transverse, or horizontal, supposing the body to be upright ; 
 the left orifice, or cardla, which communicates with the oeso- 
 phajjus, being somcwh;!t higher than the right orifice, ihe pylorus y 
 through which the food is transmitted to the further portion of 
 the alimentary canal. The upper space between the two ori- 
 fices is usually termed the small curvature ; the lower space, the 
 great curvature, of the stomach. Numerous glands occupy the 
 internal surface of the stomaf^h, particularly near its pyloric ori- 
 fice. By these glands a fluid is secreted of the highest import- 
 ance in the diofesiive functions, on the nature of which we shall 
 eidargpi hereafter. 
 
 Such is the stomach of man ; but the form and the magnitude 
 of this organ vary almost infinitely in different animals, according 
 to the nature of their food, and other circumstances. We can, 
 at present, notice only two or three of the most remarkable di- 
 versities. In most carnivorous animals, the stomach bears a re- 
 semblance to that of man. There is also a resemblance, at least 
 externally, in certain herbivorous animals ; as in the horse, the 
 rabbii, and others. The internal arrangements, however, are 
 diHerenl ; thus, in the animals al)0ve mentioned, the left or cardiac 
 half of the stomach is lined with cuticle; while the other half, 
 towards the pylorus, has the usual villous and secreting surface. 
 Hence, these two portions of the stomach perform very different 
 offures, and generally contain food in very different states of re- 
 dutrtion. Tlie most complicated and artificial arrangement, how- 
 ev(!r, both with respect to the structure of the parts, and the lining 
 meuibrancs, h found in the well-known four stomachs of the ani- 
 mals that ruminate and have divided hoofs ; as the cow and the sheep. 
 We shall endeavour to give a general description of these four sto- 
 machs. The first stomarh is denominated the Paunch, and in 
 the adult animal is by far the laro-est. The second stomach fol- 
 lows, and may be regarded as a globular appendage to the paunch; 
 
ORGANS OF DIGESTION IN ANIMALS. 251 
 
 from which it is distinguished, principally, by the regular and 
 beautiful distribulion of its internal membrane into polygonal 
 cells. The third stomach is the smallest of the four, and is the 
 most remarkable in its structure : its capacity is much diminished 
 by numerous and broad duplicatures of its internal membrane, 
 which are placed lengthwise, and vary in breadth in a regular 
 order. The fourth stomach is next in size to the paunch, and is 
 lined with a villous membrane approaching to that of the human 
 stomach, which this fourth stomach may be supposed to repre- 
 sent ; the three preceding stomachs having been evidently intended 
 to prepare the refractory food of the animal for the true digestive 
 pro(:ess, which it undergoes in this last stomach. Every one is 
 acquainted with the fact that animals furnished with the gastric 
 arrangements above described, ruminate; that is to say, have 
 the faculty of masticating a second time, and at their leisure, that 
 food which had been hastily swallowed, and deposited in their 
 first stomach. The contrivance by which rumination is effected 
 is very beautiful ; and is connected vi^ith the peculiar arrangement 
 already mentioned of the four stomachs, with respect to the osso- 
 phagus : but, as it would not be easy in a few words, to give 
 more than a general outline ; we must refer the reader to anato- 
 mical works, for a more particular description of the stomachs of 
 ruminating asiimals. The only other modification of the stomach 
 which we shall notice, is that which exists in some birds ; as for 
 example, in the common fowl. The common domestic fowl, as 
 well as many similar birds, has a sort of preliminary stomach, 
 termed the crop, formed by an expansion of the oesophagus. In 
 the crop, the hard seeds, and other compact substances which 
 birds devour, are macerated and s(»ftened, and perhaps undergo 
 further changes, before they enter the proper stomach, to be next 
 considered. The proper stomach, or gizzard, of birds, is a hol- 
 low muscle of great strength, lined with a firm and thick epider- 
 mis, disposed in rugae, and admirably adapted for triturating the 
 hard matters that constitute their food. The small stones which 
 these birds constantly swallow seem also to promote this tritura- 
 tion. 
 
 We have given the above short sketch of the structure of the 
 stomachs of animals, not only that we might impart to the general 
 reader a faint conception of the extraordinary design manifested 
 in that structure ; but to enable us to show the object of diversity 
 of structure, when we come to speak of the function of digestion 
 a little more in detail. 
 
 Alter the stomach we proceed to the consideration of the 
 Intestinal Canal. In man, and in the more perfect animals, this 
 canal assumes two well marked forms, usually termed, from their 
 relative size, the small and the large intestines. In most animals 
 
252 CHEMISTRY OF ORGANIZATION. 
 
 resembling man, the small intestines are the longest, and their in- 
 ternal snr(\ioe is villous. The coats of the large intestines are 
 thicker, and the membrane with which they are lined is very rare- 
 ly villous. The first portion of the small intestines, from its 
 supposed length termed the duodenum, or twelve-inch intestine, 
 begins from the pyloric orifice of the stomach ; and, in many 
 animals has a course not easy to be described, so as to be intelli- 
 gible to the general reader. The duodenum terminates in the 
 second portion of the small intestines, called the jejunum, from 
 its being usually empty. The duodenum differs from the sto- 
 mach and other parts of the canal, in being secured in its position 
 by various attachments ; while the stomach and other parts of 
 the canal, are comparatively loose and floating. This fixedness 
 appears to serve many wise purposes, on which we cannot dwell 
 here; but one purpose probably is, to ensure the easy and regu- 
 lar passage of the bile and the pancreatic fluids into this part of 
 the canal. As the organs producing these important fluids are 
 fixed, the conducting tubes necessarily require also to be con- 
 nected with a fixed organ ; otherwise the passage of the fluids 
 from the secreting organs to the intestine, would be constantly 
 liable to interruption. The duodenum is very highly organized, 
 and its functions are probably not less important than even 
 those of the stomach. The remainder of the small intestines 
 is divided into the jejioiwn already mentioned, and the ilimn; 
 but the precise place where one ends, and the other begins, is 
 scarcely definable ; nor are the differences of structure between 
 the two so obvious, as to require to be noticed in this place. 
 
 The large intestines exceed the small intestines in diameter, 
 but are considerably shorter : their form and structure are also 
 different. The first division of this portion of the alimentary 
 canal is termed the crecum ; and, in man at lenst, may be con- 
 sidered as little more than the head or commencement of the next 
 division-of the large intestines, termed the colon. The colon is of 
 much greater diameter than any other part of the intestinal canal, 
 and constitutes almost the entire length of the large intestines. 
 The colon begins low down on the right side of the abdomen, 
 then ascending to the level of the stomach, passes across to the 
 left side, immediately below that organ. On the left side, the 
 colon descends again, and at the same time forms what is called 
 the sigmoid flexure. The colon and the alimentary canal at 
 length terminate in what is named the rectum. The texture of 
 the colon is much thicker than that of any other portion of the 
 canal. Its organization also is peculiar ; and, like the whole ar- 
 rangement, wonderfully adapted for the purposes which this por- 
 tion of the c;uial is sujiposed to serve in the animal economy. 
 
 Such is the short account of the alimentary canal in man. We 
 
ORGANS OF PIGESTION IN ANIMALS. 253 
 
 shall now state some of the more remarkable diversities that are 
 observed in the lower animals. 
 
 One of the most striking circumstances relative to the alimen- 
 tary canal in animals, is its various lengths in the different classes. 
 In man, and other omnivorous animals, the proportion is inter- 
 mediate between that of carnivorous animals on the one hand, 
 and herbivorous animals on the other. In man, the whole length 
 of the canal is about six or seven times that of the body ; while 
 in carnivorous animals it is only from about three to five times 
 that length ; and in graminivorous animals, as in the sheep, the 
 length of the canal is twenty-seven times that of the body. In 
 other herbivorous animals, the length of the canal varies from 
 twelve to sixteen times that of the body. In most birds the ali- 
 mentary canal is much shorter than in quadrupeds ; the length 
 in general, being between twice and five times that of their bodies : 
 while in many reptiles and fish, the length of the canal scarcely 
 exceeds that of the body : in some fish it is even less ; as for 
 example, in the shark. There are animals that feed on vege- 
 tables, the length of whose alimentary canal is not so great, as 
 in the instance above stated ; the deficiency in length being ap- 
 parently made up in breadth. Thus, in the horse, the stomach 
 is simple, and not much developed, when compared with the 
 size of the animal ; nor are the intestines very remarkable for 
 their length ; but the ccecum and the large intestines are enor- 
 mously expanded in diameter. The coecum of the horse seems 
 to perform many of the ofl[ices of a second stomach, and is of 
 fully equal capacity. There are in animals, many other beautiful 
 arrangements of the digestive organs, which we shall pass with- 
 out further notice ; as our desire is to inform the reader of the 
 general connection and adaptation, which exists between the 
 structure of animals, and the food on which they live. It re- 
 mains to conclude this outline of the digestive organs, with a few 
 remarks on those almost invariable accompaniments of the ali- 
 mentary canal, — the liver ^ the pancreas, and the spleen. 
 
 The liver is the largest glandular apparatus in the body, and 
 one of its important ofiices is to secrete the Bile; which secre- 
 tion, as before observed, enters the intestines, near the commence- 
 ment of the duodenum. The general situation of the human 
 liver, is in the upper part of the abdomen, under the ribs on the 
 right side; from whence it. extends more or less to the region of 
 the stomach, and in some instances, even to the left side. The 
 appearance and form of the liver, are too well known to require 
 description here ; while to those who are unacquainted with 
 these particulars, they cannot be adequately made known by 
 words. In man, and the greater number of animals, the bile is 
 collected in a small bag, termed from its office, the gall-bladder. 
 
 22 
 
254 CHEMISTRY OF ORGANIZATIOX. 
 
 The animals wanting a gall-bladder are chiefly vegetable feeders ; 
 as the horse and the goat among quadrupeds, the pigeon and the 
 parrot among birds. On the contrary, most amphibia have a gall- 
 bladder ; but it exists in few animals lower in the zoological 
 scale. The liver assumes a variety of forms in different animals. 
 In many, and particularly in carnivorous, animals, the liver is 
 more divided than in man : while in ruminating animals, ^also in 
 the horse, the hog, and others, its divisions are not more nume- 
 rous than in man. The liver of birds consists of two lobes of 
 equal size. 
 
 The pancreas, or sweetbread, is a large gland, which, in the 
 Iiuman body, lies across the upper and back part of the abdomen, 
 behind the stomach ; and between the liver and the spleen. The 
 pancreas is composed of numerous small glands, whose ducts 
 unite and form the pancreatic duct. In man the pancreatic duct 
 joins tlie gall duct, at its entrance into the duodenum, and thus 
 tlie peculiar secretion of the pancreas is poured into that intestine, 
 commingled with the bile. In animals the pancreas, like the 
 liver, is much varied in its form ; and its duct, instead of entering 
 with the biliary duct, often ,oins the intestinal canal separately ; 
 as in the hare and others. In fishes the pancreas is wanting ; 
 but what are termed tiie coscal appendages, are supposed to have 
 a similar office. The nature of the pancreatic fluid will be con- 
 sidered presently. 
 
 The spleen in man is situated in the upper and left side of 
 the abdomen. Its shape is oblong, and its colour a deep mul- 
 berry ; more nearly resembling that of the liver than of any other 
 organ. The spleen has no excretory duct, and its use is very 
 little understood. Among the less perfect animals, the spleen is 
 much smaller than in those whose structure resembles that of 
 man : and where there is more than one stomach, the spleen is 
 always attached to the first. The situation also of the spleen 
 varies in the less perfect animals ; thus in the frog, it is fixed in 
 the mesentery. 
 
 We proceed to notice, very briefly, the peculiar circulation of 
 the blood in the abdominal viscera ; together with the character 
 and agency of that portion of the nervous system, which is con 
 nected with the digestive and assimilating functions of animals. 
 
 In the general circulation of the blood through an animal body ; 
 a large tube or artery, communicating with the heart, is gradually 
 subdivided as it is prolonged from that organ, till its subdivisions 
 finally become imperceptible. While in this state of minute sub- 
 division, the arteries assume the character of veins. The change 
 the veins undergo in their progress, is the reverse of that of the 
 arteries. They unite gradually, and, at lengtii, form one or two 
 principal tubes, which proceed to the side of the heart opposite 
 
ORGANS OF DIGESTION IN ANIMALS. 255 
 
 to that from which the artery originated. Such is the circulation 
 of the blood through the body generally ; the circulation through 
 the lungs is merely a repetition of the same ariangement. 
 Throughout the body, therefore, the general motion of the blood 
 in arteries is from greater to smaller tubes ; while in the veins it 
 is from smaller to greater tubes. By a beautiful provision, the 
 veins are also furnished with valves, which most effectually pre- 
 vent the regurgitation of the blood : without such valves, the 
 blood could scarcely flow in a regular stream. We have intro- 
 duced these remarks, with the view of stating, that the circulation 
 of the blood through the organs of digestion, presents a remark- 
 able exception to the general circulation of the body. Tiie venous 
 blood, from these organs, undergoes a preliminary arterializing 
 process in the liver, before it is remingled with the venous blood 
 from the rest of the body. That is to say, the veins from the 
 organs of digestion, unite into one large vessel termed the vena 
 "portab ; which, entering the liver, is ihere again subdivided, in 
 the same manner as an artery. These ultimate subdivisions of 
 the vena portse, together with the similar subdivisions of the 
 proper artery of the liver, coalesce ; and from the blood tlius 
 mixed the bile is separated. The coalesced blood-vessels assum- 
 ing the character of veins, then gradually unite, and at length form 
 two or three large tubes, which empty themselves into the general 
 veins going to the heart ; while the hepatic ducts, uniting in like 
 manner, convey the bile to the gall-bladder. Such are the prin- 
 cipal facts connected with the circulation of the blood in the abdo- 
 minal viscera, and with the secretion of the bile. We shall soon 
 have occasion to bring them to the recollection of the reader. 
 
 When speaking of organic agents, we noticed the probability 
 of the opinion, that in living beings, there exists a series of agen- 
 cies gradually raised one above another ; each agency having 
 more or less control over all those below it. Now, in the diges- 
 tive and assimilating functions, we appear to have, as we might 
 expect, the lowest of tliese agencies. The agencies operating 
 in digestion, and in the first stages of assimilation are, in man, 
 perhaps the same that exist in all organized beings, vegetable 
 as well as animal; and are only a few degrees, as it were, 
 above the agencies of mere inorganic matter. This resem- 
 blance is inferred from the phenomena of assimilation ; not less 
 than from the peculiar character of the nerves, distributed over 
 the digestive organs ; the effects of which nerves, as we shall 
 presendy endeavour to show, approach more nearly to those of 
 common chemical agents, than to the effects of any agent belong- 
 ing to the animal economy. These nerves compose what, from 
 their peculiar structure, rre termed the ganglionic nerves. In 
 animals of the very lowest kind, the ganglionic nerves alone ap- 
 
256 CHEMISTRY OF ORGANIZATION. 
 
 pear to exist ; and though in the more perfect animals, these 
 nerves are connected with others of a higher character, they 
 always form, by themselves, a peculiar system ; the functions of 
 which seem to be of the subordinate character above noticed. 
 
 2. Of Jilimentary Substances. — It may be considered as a 
 general rule, that organized beings adopt, as aliments, substances 
 lower than themselves in the scale of organization ; or which, if 
 not originally lower, in some measure become so, by certain 
 spontaneous changes they undergo. There are, of course, innu- 
 merable exceptions to this rule ; but viewing the whole of ani- 
 mated beings, it seems to be a law of nature. Thus plants, and 
 perhaps the very lowest kinds of animals, have the power of assi- 
 milating carbonic acid gas : the powers of assimilation of plants, 
 and of such animals, may also extend to other inorganic com- 
 pounds of carbon — indeed they seem to derive their chief nou- 
 rishment from matters of that nature. Higher in the zoological 
 scale, we find that animals almost invariably prey on those that 
 are inferior to themselves, either in magnitude, in organization, 
 or in intelligence; till we arrive at man himself. He, as his 
 necessities, or as his fancies may dictate, appropriates every nou- 
 rishing substance, even carbonic acid gas ; which his stomach, 
 perhaps in common with that of all animals, seems to have the 
 power of assimilating. Of course a lion, or even a crab, can 
 feed on the body of a man, as well as on that of an ox or of an 
 insect. But no one, we presume, will assert, that man is the 
 natural prey or food of these animals ; and that alone is the de- 
 gree of immunity, for which we here contend : for in all the 
 operations of nature, we must try to discover and bear in mind, 
 not the exception, but the rule ; otherwise we shall be constantly 
 liable to error. 
 
 By this beautiful arrangement in the mode of their nutrition, 
 the more perfect animals are exonerated from the toil of the initial 
 assimilation of the materials composing their frame; as in their 
 food, the elements are already in tiie order which is adapted for 
 their purpose. Hence the assimilating organs do not require that 
 complication, which they otherwise would have needed ; and 
 much elaborate organization is saved. Striking illustrations of 
 this abridgement of organization, are afTordcd by the differences 
 before mentioned, between the assimilating apparatus of carnivo- 
 rous and of graminivorous animals. According to the scale 
 which this difference exhibits, we can form some conception of 
 the complication that would be requisite, if such an animal as 
 man were, like a plant, destined to feed on carbonic acid gas ; or 
 carburelted hydrogen; or on any other simple compound of 
 carbon. 
 
 Another great purpose is efTected by this arrangement, without 
 
FOOD OF ANI3IALS. 257 
 
 which, organization, at least as at present constituted, could 
 hardly exist. If organized beings did not prey on each other, 
 their remains would, in time, accumulate in such quantity, as to 
 he nearly incompatible with life ; certainly with animal life in its 
 most perfect condition, as it is at present known to us. But by 
 the arrangement that animals are food to each other, not only is 
 an opportunity afforded, for the existence of a greater number of 
 animals, and of a greater variety among them ; but the obtrusion 
 of the bodies of animals, in whom life has become extinct, is 
 entirely prevented : nor, is the removal of the dead animal matter 
 the only good accomplished, but many other important results are 
 obtained. To enter upon the consideration of these, would be fo- 
 reign to our present object: there is, however, one consequence of 
 this system of universal voracity, which more immediately con- 
 cerns us, since it is of a nature so comprehensive, as to suggest 
 a natural classification of alimentary substances ; we allude to 
 the similarity of composition among the staminal principles which 
 constitute the fabric of organized beings. 
 
 T • 
 
 In our introductory remarks on the chemistry of organization, 
 we showed that organized matters, however apparently dissimilar, 
 yet, chemically speaking, are often nearly related. Of this rela- 
 tion we gave as an example, the composition of the extensive 
 class of substances, denominated the saccharine group ; all of 
 which, notwithstanding the endless diversity of their appearance, 
 we showed to be essentially alike in their composition, and to 
 consist of carbon associated with water. Saccharine substances 
 are chiefly found in the vegetable kingdom, of which they form 
 the characteristic staminal principle. 
 
 Another well known class of bodies, existing both in vegetables 
 and in animals, are those whose character is oily. Oleaginous 
 bodies occur in an infinite variety of forms, some being solid, 
 others fluid ; yet, in every instance, their peculiar properties are 
 so strongly marked, that we seldom hesitate about their nature. 
 In this distinctness of outward appearance, oily bodies are strong- 
 ly contrasted with the saccharine group before mentioned ; many 
 of which have few apparent and sensible properties in common. 
 The composition of all the bodies of this oleaginous group, which 
 we have hitherto had an opportunity of examining in a satisfac- 
 tory manner, we have found to be essentially the same : they are 
 either composed of olefiant gas and water, or have a reference to 
 that composition. Such is also the composition of the well known 
 proximate principle termed spirit ofwine^ or alcohol ; into which, 
 most substances belonging to the saccharine group, under favour- 
 able circumstances, are readily convertible by the process termed 
 fermentation. 
 
 When almost any part of an animal body, (with the exception 
 
 22 * 
 
258 CHEMISTRY OF ORGANIZATION. 
 
 perhaps of those matters of a purely oleaginous character) is boiled 
 in water, it is separated into two portions, — one soluble in water, 
 and lorminiT with the water a tremulous jelly, or gelatine — the 
 other remaining insoluble, indeed becoming harder, the longer it 
 is boiled ; and which, from the identity of its properties to those 
 of the white of an egg^ is denominated albumen. These animal 
 principles exist in very different proportions in the difierent tex- 
 tures ; some of these textures, as the skin, being convertible al- 
 most entirely into gelatine ; while others yield comparatively little 
 gelatine, and consist principally of albumen. In no animal com- 
 pound does gelatine exist as a fluid ; hence, it has been supposed 
 to be produced by boiling; but the supposition does not appear to 
 be well founded. One of the most remarkable properties of gela- 
 tine, is, its ready convertibility into a sort of sugar, by a process 
 similar to that by which starch may be so converted. Gelatine 
 may be considered as the least perfect kind of albuminous matter 
 existing in animal bodies ; intermediate, as it were, betw^een the 
 saccharine principle of plants, and thoroughly developed albu- 
 men : indeed, gelatine in animals, may be said to be the counter- 
 part of the saccharine principle in vegetables. Albumen exists in 
 the fluid state as a component of the blood : small quantities of fluid 
 albumen are also contained in certain animal secretions : but there 
 is much more of the principle in a solid state ; forming what is 
 termed coagulated albumen. The blood likewise contains Fibrin, 
 another modification of the albuminous principle, in a fluid, or at 
 least in a suspended state: though the most frequent condition of 
 Fibrin, is that of a tough fibrous mass, in which condition, toge- 
 ther with all)umen, it forms the basis of the muscular or fleshy 
 parts of animals. The curd of milk is also a modification of the 
 albuminous principle. Another modification of the same princi- 
 ple is the substance called gluten ; this substance though most 
 abundant in vegetables, so far resembles the fleshy parts of ani- 
 mals, as to be, in like manner, capable of separation into two por- 
 tions, analogous to gelatine and albumen. Neither of these mo- 
 difications of albumen exhibits the quality possessed by gelatine, 
 of being artificially convertible into saccharine matter ; at least by 
 any known process ; but all of them, including gelatine, difier from 
 the oleaginous and the saccharine principles, in this respect; tliat 
 they contain a fourth elementary principle, namely, azote. The 
 exact composition of the albuminous group cannot at present be 
 stated. 
 
 Such are tlie three great staminal principles from which all 
 organized bodies are essentially constituted. Of these staminal 
 principles it has already been remarked, that, without changing 
 ilieir essential composition, they are capable of assuming an infi- 
 nite variety of modified forms ; many of which are so peculiar, 
 that it is very diflicult to recognize their identity, from their sen- 
 
FOOD OF ANIMALS. 259 
 
 sible properties. Moreover, these staminal principles, in all their 
 forms, are capable of readily passing into one another, and of com- 
 bining with each other; at least the organic agents, as \\e shall 
 see liereafter, have the power of effecting these changes. Further, 
 these staminal principles are all susceptible of transmutation into 
 new principles, according to certain laws: llius the saccliarine 
 principle is readily convertible into the acid, termed oxalic ; or, 
 under other circumstances, into the modification of the oleaginous 
 principle, alcohol. Though an endless variety, however, of these 
 modifications of the staminal principles exist in difierent organized 
 beings, accompanied by numerous foreign bodies, the proportion 
 they bear to the staminal principles is very limited ; and they are 
 either confined to glandular secretions, or are excrementitious, or 
 extravascular : that is to say, these modifications and combinations 
 form no part of the living animal, though they are attached to it ; 
 as in the case of the various products of secretion, the shells of 
 the molluscous tribes, and many others. 
 
 The consequence then, to which we before alluded is; that as 
 all the more perfect organized beings feed on other organized be- 
 ings, their food tnust necessarily consist of one or more of the 
 above three staminal principles. Hence, it not only follows, as be- 
 fore observed, that in the more perfect animals, all the antecedent 
 labour of preparing these compounds clc novo, is avoided ; but that 
 a diet to be complete, must contain more or less of all the three 
 staminal principles. Such, at least, must be the diet of the higher 
 classes of animals, and especially of man. It cannot indeed be 
 doubted that many animals have the power of forming a chyle, 
 and if expressly organized for the purpose, may even live for a 
 while on one of these classes of aliments ; but that they can be so 
 nourished for an unlimited time, is exceedingly improbable. Nay, 
 if we judge from what is known from universal observation, as well 
 as from experiments which have been actually made by physiolo- 
 gists regarding food, we are led to the directly opposite conclu- 
 sion ; namely, that the more perfect animals could not so exist ; 
 but that a mixture, of two at least, if not of all the three classes of 
 staminal principles, is necessary to form an alimentary compound 
 well-adapted to their use. 
 
 This view of the nature of aliments is singularly illustrated and 
 maintained by the familiar instance of the composition of Milk. 
 All other matters appropriated by animals as food, exist for them- 
 selves ; or for the use of the vegetable or animal of which they 
 form a constituent part. But milk is designed and prepared by 
 nature expressly as food ; and it is the only material throughout 
 the range of organization that is so prepared. In milk, therefore, 
 we should expect to find a model of what an elementary substance 
 ought to be — a kind of prototype, as it were, of nutritious mate- 
 rials in general. Now, every sort of milk that is known, is a mix- 
 
280 CHEMISTRY OF ORGANIZATION. 
 
 ture of the three staminal prinoiples we have described ; that is to 
 say, milk always coiilains a saccharine principle, a bulyraceous 
 or oil') principle, and a caseous, or strictly speaking, an albumi- 
 nous principle. Though, in the milk of ditlerent animals, these 
 three staminal principles exist in endlessly moditied forms, and in 
 very different proportions ; yet neither of the three is ai present 
 known to be entirely wanting in the milk of any animal. 
 
 Of all the evidences of design in the whole order of nature, 
 ]\lilk affords one of t!ie most unequivocal. No one can for a mo- 
 ment doubt the object for which this valuable fluid is prepared. 
 No one can doubt that the apparatus by which milk is secreted 
 has been formed especially for its secretion. No one will main- 
 tain that tlie apparatus for the secretion of milk arose from the 
 wishes or the wants of the animal possessing it, or from any fan- 
 cied plastic energy. On the contrary, the rudiments of the appa- 
 ratus for the secretion of milk must h ive actually existed in the 
 body of the animal, ready for developement, before it could have 
 felt either wants or desires. In short, it is manifest that the ap- 
 paratus and its uses, were designed and made what they are, by 
 the great Creator of the universe ; and on no other supposition, 
 can their existence be explained. 
 
 The composition of the substances, by which animals are 
 usually nourished, favours the mixture of the primary staminal 
 alimentary principles ; since most of these substances are com- 
 pounds, of at least two, of the staminal principles. Thus, most 
 of the gramineous and herbaceous matters contain the saccharine 
 and the glutinous principles ; while every part of an animal con- 
 tains at least albumen and oil. Perhaps, therefore, it is impossi- 
 ble to name a substance constituting the food of the more perfect 
 animals, which is not essentially a natural compound of at least 
 two, if not of all the three great principles of aliment. But it is 
 in the artificial food of man that we see this great principle of 
 mixture most strongly exempliiied. He, dissatisfied with the 
 spontaneous productions of nature, culls from every source ; and 
 by the force of his reason, or rather of his instinct, forms in every 
 possible manner, and under every disguise, the same great ali- 
 mentary compound. This after all his cooking and his art, how 
 much soever he may be disinclined to believe it, is the sole ob- 
 ject of his labour ; and the more nearly his results approach to 
 this object, the more nearly do they approach perfection. Even 
 in the utmost refinements of his luxury, and in his choicest deli- 
 cacies, the same great [)rinciple is attended to ; and his sugar and 
 flour, his og(^s and butler, in all iheir various forms and combina- 
 tions, are nothing more or loss, than disiruised imitations of the 
 great alinuMitury prototype milk, as furnished to him by nature. 
 
261 
 
 CHAPTER III. 
 
 OF THE DIGESTIVE PROCESS ; AND OF THE GENERAL ACTION OF THE 
 
 STOMACH AND DUODENUM. 
 
 We proceed now to consider the most important function of 
 the stomach, by which the assimilation of the food is begun. 
 But before that function can be well understood, it is necessary to 
 make a (ew remarks on the influence of water, in modifying the 
 intimate constitution and the peculiar properties of alimentary 
 substances. We have intentionally delayed these remarks, in 
 order that in this place the chemical influence of water might be 
 more strikingly exemplitied. 
 
 Water enters into the composition of most organized bodies in 
 two separate forms ; which must be clearly distinguished, and 
 which it is requisite that the reader should always bear in mind. 
 Water may constitute an essential element of a substance, as of 
 sugar or of starch in their dryest states ; in which case, the water 
 cannot be disunited without destroying the compound : or water 
 may constitute an accidental ingredient of a substance, as of sugar 
 or of starch in their moist states ; in which case more or less of 
 the water may frequently be removed, without destroying the 
 essential properties of the compound. Now, a very large number 
 of organized bodies, (perhaps all those to which our present in- 
 quiry relates) contain water in both these forms ; both as an 
 essential element, and as an accidental ingredient ; and in most 
 instances, it is impossible to discriminate between the water that 
 is essential, and that which is accidental. The mode of union, 
 however, among the elements of bodies, in these two states of 
 their combination with water, must be altogether difl'erent. 
 Wherein the difference consists, is very imperfectly known ; but 
 perhaps the following remarks may throw some light on the sub- 
 ject; at least, they will serve to point out, the nature of these 
 two modes of union, to the reader. 
 
 In the first part of this volume, we stated that the molecular, 
 or combining, weights of carbon and of water are, by chemists, 
 usually considered to be represented by the numbers 6 and 9 ; 
 the weight of hydrogen being one. We also advanced the opinion, 
 that the molecules or atoms of carbon and of water, where more 
 than one exist, instead of remaining separate, as is now supposed, 
 are associated together into groups, or supermolecules ; and that 
 carbon, water, and similar bodies, always enter into combination, 
 not as single molecules, but as one supermolecule. To illustrate 
 our meaning, let us take as examples, the state of combination of 
 tlie molecules constituting the different varieties of sugar. 
 
262 CHEMISTRY OF ORGANIZATION. 
 
 Sugar from the cane, in its purest state, and when as free as 
 possible from accidental water, is, according to the present lan- 
 guage of chemists, composed of 9 atoms of carbon and 8 atoms of 
 water. Now, we suppose these 9 atoms of carbon, and 8 atoms of 
 water, to be associated into two supermolecules, weighing (9x6) 
 54, and (8x9) 72, respectively. So that, we conceive a molecule 
 of sugar from the cane to be a binary compound, of a supermole- 
 cule of carbon weighing 54, and a supermolecule of water weigh- 
 ing 72. Again, the sugar of honey, according to the present lan- 
 guage of chemists, is composed of 9 atonis of carbon, and 12 
 atoms of water ; or, according to our view of molecular arrange- 
 ment, the sugar of honev is composed of two supermolecules, one 
 of them, carbon, weigli-iig 54, as in the sugar of the cane — the 
 other, water, weighing;- no less than (12x9) 108. A similar state- 
 ment may be given of tlie composition of Lignin, another of the 
 saccharine class of bodies. This substance, which, in all its 
 various forms appears to consist essentially of equal weights of 
 carbon and water, may be said to be composed of 9 atoms of j:ar- 
 bon, and 6 atoms of water ; or, according to our views, of two 
 su pel molecules weighing (9x6) 54, and (6x9) 54, respectively. 
 Hence, the saccharine class of bodies may be represented in the 
 folio winir manner : — 
 
 LigTiln. 
 
 Cane Siig-ar ; Wheat Slurch. 
 
 Sugar of honey ; Arrowroot. 
 
 The molecular constitution of the saccharine bodies, above 
 stated, may be compared with that of Vinegar. According to the 
 present language of cliemists, vinegar, in its purest and most de- 
 tached form, is composed of 4 atoms of carbon, and 3 atoms of 
 water ; or, according to our views, of two supermolecules weigh- 
 ing (1x6) 21, and (3x9) 27, respectively. Thus, the molecular 
 consiiiuiion of tliese two did'erent states of vinegar may be repre- 
 sented as follows : — 
 
 Carl)on. AVater. 
 
 24 -f- 27 Absolute vineg-ar. 
 
 24 -|- 36 Crystallized or solid vinegar. 
 
 We have stated \hc composition of vinegar, in order to draw 
 the attention of the reader, to the ditlerence between the super- 
 molecule of the carbon in that acid, and the supermolecule of the 
 carbon in the saccharine class of bodies ; a diilerence to which 
 these two classes of bodies proliably owe the striking dillerences 
 in their sensible proj^erties. J3ut why the supermolecule of car- 
 bon should be 54 in bodies of the saccharine class, and why this 
 supermolecule shoidd in general exist in the sclfattraclive form, 
 
 Carbon. 
 
 
 Water, 
 
 54 
 
 + 
 
 54 
 
 54 
 
 
 72 
 
 54 
 
 + 
 
 108 
 
PROCESS OF DIGESTION IN ANIMALS. 263 
 
 and produce sweetness ; or why the supeimolecule of carbon in 
 vinegar should be 24, and wfiy this supermolecule should have 
 such a tendency, as it exhibits, to assume the self-repulsive form, 
 and to produce sourness ; we do not know, and probably shall 
 never be able fully to explain. Still, there can be little doubt 
 that a careful and philosophical examination of the phenomena, 
 would tro far to dispel the obscurity in which the subject is now 
 involved. 
 
 Such are the principles, which, we conceive to regulate the 
 chemical union of organic, and indeed of all other compounds ; 
 and if chemical union be so regulated, the inferences are most 
 curious and important. With these inferences in general, we 
 have at present no concern : but those more particularly relating 
 to alimentary compounds are the following: — 
 
 First. We would draw the attention of the reader to the con- 
 trast between the two snpermolecules of carbon, and of water, 
 constituting sugar ; the supermolecide of carbon being uniform 
 throughout the whole saccharine class, while the supermolecule 
 of water is that which is variable. Now, there is reason to be- 
 lieve that this contrast holds in other instances ; and that in dif- 
 ferent organized substances of the same kind, the supermolecule 
 of carbon, or of some of its compounds, remains the permanent 
 and characteristic element ; and that the different modifications 
 are produced by variations in the supermolecule of water ; which 
 may be called the modifying supermolecule. 
 
 Secondly. The manner of the operation of the modifying 
 agency may be thus illustrated. If to a portion of cane sugar, 
 we add that quantity of water, which, by an easy calculation, we 
 learn is necessary to be united with it, in order to its conversion 
 into sugar of honey ; we find that we cannot succeed in producing 
 such conversion; and that the excess of water which had been 
 added, flies ofl", and leaves the cane sugar in its original state. On 
 the other hand, if we apply heat to the sugar of honey ; though 
 we may indeed drive otl' part of the water essentially associated 
 with that sugar, we do not obtain sugar similar to that of the cane; 
 but we destroy, or altogether decompose the sugar of honey. 
 These facts, therefore, show that the excess of water, constituting 
 the difference of the sugar of honey from the sugar of the cane, 
 is really in some state of essential union, incapable of being imi- 
 tated ; while, in the cane sugar, the water may exist as an acci- 
 dental ingredient only. In fact, according to our views of mole- 
 cular arrangement ; every individual supermolecule of the weaker 
 sugar contains a portion of this excess of water, as an essen- 
 tied element of its composition. Hence such water cannot be 
 separated from any compound, without destroying the entire era- 
 sis, or constitution, of its molecular elements ; which, as in the 
 
264 CHEMISTRY OF ORGANIZATION. 
 
 case of the sugar of lioney, we find, by experiment, to be the re- 
 sult. On the other hand, we suppose the molecules of accidental 
 water to form no essential element of the molecules of sugar, or 
 of other bodies, but to be only loosely associated ivith them ; and 
 hence, the ease with which accidental water may be separated 
 without destroying such bodies. 
 
 Thirdly. It may be advanced as a general rule, that the larger 
 the number, representing the weight of the supermolecule of any 
 compound substance ; whether such number represent the cha- 
 racteristic, or the modifying supermolecule ; the more easily may 
 that compound substance be decomposed. Thus, the sugar of 
 honey is more easily decomposed — is much less permanent, than 
 the sugar of the cane ; and the purest sugar, is much less perma- 
 nent than Lignin. In like manner, when water is the modifying 
 element of any compound, as it is in most organic compounds, 
 the larger the number representing the supermolecule of the water, 
 the greater, for the most part, is the solubility of the compound. 
 
 Fourthly. There are, at present, no chemical terms corre- 
 sponding to those diflerences of composition, which we have 
 brought under the notice of the reader. Now, the terms strong 
 and weak, which in commerce, distinguish the ditTerent varieties 
 of sugar, are sufficiently expressive ; we have, therefore, made 
 choice of them, to denote the similar varieties of other organic 
 compounds. Thus, when we speak of a strong compound ; we 
 mean that its constituent supermolccules are, like those of strong 
 cane sugar, less complicated than the supermolccules of a weak 
 principle, like those of the sugar of honey. Again, there are no 
 terms expressive of the conversion of a strong substance into a 
 weak substance, or the contrary. T.o express such conversion 
 we have adopted the terms reduction, and completion. 
 
 In the above illustrations of the modifying influence of wa'er 
 in organic compounds, we have selected sugar as our example, 
 solely from its being the most familiar. But, as we have more 
 than once noticed, exactly the same laws appear to regulate the 
 composition of all organized bodies. Thus in the strong, fixed, 
 and solid, oils or fats, the ciiaracteristic supermolecule of which, 
 as we have already said, has some relation to olefiant gas ; the 
 modifying molecule of water is very small, perhaps, in some olea- 
 ginous bodies, is even a submolecule. Whereas, in alcohol, 
 which is the weakest condition of the oily principle, the weight 
 of the modifying supermolecule of water is more than half that 
 of the olctiant gas, and alcohol is perfectly soluble in water. 
 
 (i<3laiinous and albuminous substances, also, exhibit precisely 
 the game variations, 'j'lie strong tenacious glue, employed in tho 
 arts, is made from the firmer parts of the hides of old animals ; 
 wlule the gelatinous size, or weak glue, is made from the skins 
 
PROCESS OF DIGESTION IN ANIMALS. 265 
 
 of younger and more delicate animals. These two varieties of 
 glue diller from one another, in the weights of the modifying 
 supermolecules of water which enter into their composition. In 
 general, it may be observed, that the substances composing the 
 frame of old and of young animals, differ chiefly in the weights 
 of their modifying supermolecules of water ; and that the dissi- 
 milarity of their properties, is chiefly owing to this difference. 
 
 If the reader has clearly apprehended, and will bear in mind, 
 the principles that have now been stated, as regulating the che- 
 mical constitution of organized bodies, and the modes in which 
 they are influenced by their modifying constituent, water ; he 
 will be able to accompany us in the observations we are about to 
 offer ; and he will thus, more especially, be able to form a gene- 
 ral conception of the chemical operations of the stomach. The 
 operations of the stomach, viewed as a whole, may be stated as 
 follows : — 
 
 1. The stomach has the power of dissolving alimentary sub- 
 stances, or, at least of bringing them to a semifluid state. This 
 operation seems to be altogether chemical ; and is probably ef- 
 fected by reducing the properties of these alimentary substances. 
 
 2. The stomach has, within certain limits, the power of chang- 
 ing into one another, the simple alimentary principles, which 
 have been described in the last chapter. Unless the stomach 
 possessed such a power, that uniformity in the composition of 
 the chyle, which we may imagine to be indispensable to the ex- 
 istence of every animal, could not be preserved. This part of the 
 operations of the stomach, appears, like the reducing process, to 
 be chemical ; but not so easy of accomplishment ; it may be 
 termed the converting operation of the stomach. 
 
 3. The stomach must have, within certain limits, the power of 
 organizing and vitalizing the different alimentary substances ; 
 so as to render them fit for being brought into more intimate union 
 with a living body, than the crude aliments can be supposed to 
 be. It is impossible to imagine, that this organizing agency of 
 the stomach can be chemical. This agency is vital, and its nature 
 is completely unknown. 
 
 1. Of the Reducing Powers of the Stomach. — In order to 
 render more intelligible that function of the stomach, which it 
 owes to its reducing power, let us endeavour to trace the series 
 of phenomena, which appear to arise during the conversion of 
 simple albuminous matter into the albumen of the chyme ; with- 
 out taking into account any other change. 
 
 When a portion of fluid albumen, as of the white of an egg, or 
 of milk, is introduced into the stomach of an animal, as of a dog, 
 it instantly becomes solid ; or, in ordinary language, is coagulated. 
 This coagulation is probably a mere chemical change ; for the 
 
 23 
 
266 CHEMISTRY OF ORGANIZATION. 
 
 same change, would, under similar circumstances, take place out 
 of liie body. That is to say, if the white of an egg, or milk, 
 were mixed with a fluid more or less acid, like that which exists 
 in the stomachs of animals while the food is undergoing the pro- 
 cess of digestion ; it would be coagulated. There may be, how- 
 ever, and i)robably is, some object in the change produced by 
 coagulation ; since the stomachs of animals are fitted to operate 
 chiefiy on solid matters. Admitting the object of the change, we 
 can hardly consider it to be essential to the subsequent process ; 
 for gelatine, a staminal alimentary principle, nearly resembling 
 albumen in its composition, undergoes, under similar circum- 
 stances, no such solidifying cliange. The albumen thus solidified 
 by the stomach into a mass or curd, is soon altered further ; more 
 especially that part of the mass, with which the membrane of the 
 stomach is in contact. The curdy mass assumes a gelatinous 
 appearance ; then each portion is successively more and more 
 softened, till at length, the whole becomes nearly fluid, and after 
 some additional modifications, gradually passes into the state of 
 chyme. Through all these apparent changes, however, the al- 
 bumen has undergone no real change. What was introduced into 
 the stomacli as albumen, is still albumen in the chyme ; at least 
 chemists have pronounced it so to be. Yet it has assumed an 
 appearance altogether different. The albumen of the egg^ out of 
 the stomach, may be coagulated by heat, into a firm elastic solid. 
 The albumen of the chyme is indeed coagulable by heat, but its co- 
 agulation is so imperfect, and so wanting in tenacity, as to offer a 
 striking contrast with the coagulated albumen of the egg. What then, 
 in the stomach, has liappened to the albumen ? Viewing only its 
 susceptibility of coagulation, the albumen has merely become 
 chemically combined with a portion of water. The solid and te- 
 nacious albumen has, by this combination with water, been re- 
 duced to the weakest possible state — to the delicate state, as it 
 were, of infancy ; in short, to a state precisely analogous to that 
 of the weak sugars, and other organic compounds, as compared 
 with the strong and perfect varieties of the same substances, de- 
 scribed in the preceding chapter. 
 
 Such is, we believe, an accurate account of the merely solvent 
 or reducing powers of the stomach. We have next to show the 
 means by which this solution or reduction is efTected. 
 
 The process of combining diflerent substances MMth water, and 
 of thus reducing them from a stronger to a weaker condition, 
 may, in some instances, and to a certain degree, be effected arti- 
 ficially, lint in no instance do we appear to be able to invert 
 tlie process ; or to complete an organic compound, by again 
 separating the water. For example, we can, in some respects, 
 make a strong sugar weak, but we cannot change a weak into a 
 
PROCESS OF DIGESTION IN ANIMALS. 267 
 
 Strong sugar; though such a change, within certain limits, seems 
 to be, to the organic agents, just as easy, as the reducing process. 
 
 The difTerent operations of cookery, as roasting, boiling, 
 baking, &c. have all a reducing efTect ; and may, tlierefore, be 
 considered as preparatory to the solvent action of the stomach. 
 Of these operations, Man's nature has taught him to avail him- 
 self, and they constitute the chief means by which he is enabled 
 to be omnivorous : for, without such a preparation, a very large 
 portion of the matters which he now adopts as food, would be 
 completely indigestible. By different culinary processes, the 
 most refractory substances, can often be rendered nutritious. 
 Thus, by alternate baking and boiling, the woody fibre itself may 
 be converted into a sort of amylaceous pulp ; not only possessing 
 most of the properties of the amylaceous principle, but capable 
 of being formed into bread. Tlie culinary art eng-a^es no small 
 share of attention among m.ankind; but, unfortunately, cooks are 
 seldom chemists ; nor indeed do they understand the most simple 
 of the chemical principles of their art. Hence, their labour is 
 most frequently employed, not in rendering wholesome articles 
 of food more digestible, which is the true object of cookery ; but 
 in making unwholesome things palatable : foolishly imagining 
 that what is agreeable to the palate, must be also healthful to the 
 stomach. A greater fallacy can scarcely be conceived ; for, 
 though by a beautiful arrangement of Providence, what is whole- 
 some is seldom disagreeable ; the converse is by no means appli- 
 cable to man ; since those things which are pleasant to the taste 
 are not unfrequently very injurious. Animals, indeed, for the 
 most part, avoid, instinctively, all unwholesome food ; probably 
 because everytiiing tiiat would be prejudicial, is actually distaste- 
 ful to them. But as regards man, the choice of articles of nou- 
 rishment has been left entirely to his reason. 
 
 In order to illustrate the importance of a judicious adaptation of 
 cookery, we may observe, that the particular function of the 
 stomach, now under consideration, namely, the dissolving or re-' 
 ducing function, is liable to very great derangements. In some 
 individuals, the reducing pov/er is so v/eak, that their stomach is 
 almost incapable of dissolving solid food of the most simple kind. 
 In such a state of the stomach, a crude diet of the flesh of animals 
 in a hardened state, or of other compact substances, is litde else 
 than poisonous ; while the same animal and vegetable matters 
 often agree well, if reduced to a pulpy slate. On the other hand, 
 as in the disease termed Diabetes, the solvent powers of the sto- 
 mach are often inordinately increased ; and every article of food 
 is dissolved and absorbed almost as soon as it is swallowed. In 
 such cases, a diet and a mode of preparation are required, directly 
 the reverse of those which are found to be so beneficial, when 
 
268 CHEMISTRY OF ORGANIZATION. 
 
 there is a debility of the solvent powers ; and aliments which are 
 firm and solid, but at the same time nutritious, must be chosen. 
 
 Regarding the intimate nature of the agency, by which the 
 combination of alimentary substances with water is effected in 
 the stomach, we cannot be said to possess much certain know- 
 ledge. This combination appears to be chiefly owing to the 
 agency of a fluid, secreted by the stomach ; the glands for the 
 formation of which fluid, are most numerous toward the pyloric 
 orifice. The aliment having been previously broken down by 
 mastication, and havinjj received an admixture of saliva and of 
 other fluids, is brought into contact with the fluid secreted by the 
 stom.ach ; by which secretion, or by some other energy there in 
 operation, the food that has been introduced into the stomach is 
 associated with water ; and thus becomes itself more or less a 
 fluid. Of this important secretion of the stomach, chlorine , in 
 some state or other of combination, is an ingredient ; it would 
 seem a necessary ingredient ; for the secretion in its healthy 
 slate, always contains more or less of chlorine, the powerful in- 
 fluence of which elementary principle, seems mainly to contribute 
 towards efTccting the union of the food with water. The chlo- 
 rine, thus so indispensable to the reducing process, is perhaps 
 more frequently the subject of derangement, than anything con- 
 cerned with the assimilation of the food. It often happens that 
 instead of chlorine, or a little free muriatic acid, a large quantity 
 of free muriatic acid is elicited ; which not only gives rise to much 
 secondary uneasiness, but more or less retards the process of re- 
 duction itself. The source of this chlorine or muriatic acid, must 
 be the common salt which exists in the blood : to suppose that it 
 is generated, is quite an unnecessary hypothesis. Tiie chlorine 
 is therefore secreted from the blood ; and it may be demanded, 
 what is the nature of the agency, capable of separating that ele- 
 ment from a fluid so heterogeneous as the blood? We are ac- 
 quainted with one agent that exerts such a power, namely, elec- 
 tricity ; and this agent, as we formerly observed, seems to be 
 employed by the animal economy for its operations, in the same 
 manner, and on the same principles, as the materials themselves 
 are employed, from whicli the animal body is constructed. Per- 
 haps, therefore the decomposition of the salt of the blood may be 
 fairly referred to the immediate agency of this princi])le, elec- 
 tricity. But here the question arises, What becomes of the soda 
 from which the muriatic acid has been disunited ? The soda re- 
 mams behind, of course, in the blood, and a portion of it no doubt, 
 is requisne to preserve the weak alkaline condition essential to 
 the fluidity of the blood, liut the larger part of this soda is pro- 
 bably directed to the liver, and is elicited with the bile in the 
 duodenum, where it is thus again brought into union with the 
 acid, tiiat had been separated from the blood, by the stomach. 
 
PROCESS OF DIGESTION IN ANIMALS. 269 
 
 These observations, illustrating the importance of common salt in 
 the animal economy, seem to explain, in a satisfactory manner, 
 that instinctive craving after this substance, which is shown by 
 all animals. 
 
 Admitting that the decomposition of the salt of the blood is 
 owing to the immediate agency of galvanism ; we have, in the 
 principal digestive organs, a kind of galvanic apparatus, of which 
 the mucous membrane of the stomach, and perhaps that of 
 the intestinal canal generally, may be considered as the acid or 
 positive pole ; while the hepatic system may, in the same 
 view, beconsidered as the alkaline or negative pole. Whether 
 such galvanic action be admitted or not ; and the admission is 
 of no very great importance ; what we have above stated may be 
 received as a simple expression of the facts, in so far as they 
 relate to the saline constituents of the blood. Moreover, be the 
 nature of the energies what they may, by which these changes 
 are effected; along with these changes, and probably by the aid 
 of the same energies, other very important changes or processes 
 are carried on, to some of which we shall presently have occa- 
 sion to allude. In the mean time, we may close this section by 
 observing that there is strong reason to believe, that the solvent 
 power, which we have described, or some power having a great 
 resemblance to it, exists not only in the stomach, but m every 
 part of an animal body. In all animals there are minute tubes, 
 called absorbents, which originate in every part of their bodies, and 
 at length uniting, enter the sanguiferous system along with the 
 chyle. Now, the office of these tubes, is to remove all those 
 portions of the animal frame, which after having performed their 
 several functions, require to be withdrawn. Of course, before 
 solid parts can be thus removed, they must be dissolved, {digested 
 in fact ;) and such solution, in many instances, is probably eliected, 
 as it is in digestion, by combining these solid parts with water. 
 This supposed analogy between the solvent powers of the sto- 
 mach, and those which must prevail all over the body, seems to 
 be strongly confirmed by that similarity of structure and of func- 
 tion existing between the lacteals and the absorbents : they in- 
 deed form but one system. We shall resume this subject here-- 
 after. 
 
 2. Of the Poivers of Conversion possessed by the Stomach. — ^ 
 Though the proportions of the ditTerent ingredients of the chyle, 
 as ultimately formed, are liable to be much varied, according to 
 the nature of the food ; yet, whatever the nature of the food may 
 be, the general composition and character of the chyle, remain al- 
 ways the same. The stomach must, therefore, be endowed with 
 a power or faculty, the agency of which is to secure this uniform 
 composition of the chyle, by appropriate action upon such mate- 
 
 23* 
 
270 CHEMISTRY OF ORGANIZATION. 
 
 rials, as circumstances may bring within its reach. Two, indeed, 
 of the chief materials from which chyle is formed, namely, the 
 albuminous and the oleaginous principles, may be considered to 
 be already fitted for the purposes of the animal economy, without 
 undergoing any essential change in their composition. But the 
 saccharine class of aliments, which form a very large part of the 
 food of all animals, except of those subsisting entirely on flesh, 
 are by no means adapted for such speedy assimilation. Indeed, 
 one or more essential changes must take place in saccharine ele- 
 ments, previously to their conversion, either into the albuminous, 
 or into the oleaginous principles. Most probably, under ordinary 
 circumstances, these essential clianges are altogether chemical; 
 that is to say, they are such as do take place, or rather, such as 
 would take place, if the elements of the substances thus changed 
 in the stomach, could, out of the body, be so collocated, as to bring 
 into action the affinities necessary to produce these changes. Thus, 
 as we know, the saccharine principle spontaneously becomes al- 
 cohol; M'hich, as has been stated, is merely an oleaginous body 
 of a weak kind. When, therefore, in the stomach, it is requisite 
 that sugar be converted into oil, it is probable that the sugar passes 
 through precisely the same series of changes it undergoes, out of 
 the body, during its conversion into alcohol. We cannot trace 
 the conversion of sugar into albumen ; because we are ignorant 
 of the relative composition, and of the laws which regulate the 
 changes, of these two substances. The origin of the azote in the 
 albumen, is likewise at present unknown to us ; though \n all or- 
 dinary cases, it seems to be appropriated from some external source. 
 That the oleaginous principle may be converted into most, if not 
 into all the matters necessary for the existence of animal bodies, 
 seems to be proved by the well-known fact, that the life of an ani- 
 mal may be prolonged by the absorption of the oleaginous matter, 
 contained within its own body. Thus, many hybernating animals, 
 when they retire in autumn, to sleep during the winter, are enor- 
 mously I'ai. But while tlicy sleep, their fat is gradually removed ; 
 till they awake in the spring quite divested of it, and in a state of 
 inanition. 
 
 Tlie reader will have remarked that we have made use of the 
 term onlinury circumstances ; and perhaps it may not be amiss 
 to explain what meaning we attach to that term. 
 
 Wlien an animal is duly fed according to that diet which is na- 
 tural to it, and for which its organization has been adapted ; a re- 
 gular and urdimirij series of changes takes place within the animal, 
 and the alimentary matters are converted into chyle. But one 
 general characteristic of organized beings is that within certain 
 limits, and for a certain lime, they possess the power of varying 
 their habits, and of accommodating themselves to circumstances. 
 Under cxtraordinanj circumstances, therefore, extraordinary 
 
PROCESS OF DIGESTION IN ANIMALS. 271 
 
 changes must, and do, take place. In some instances, these changes 
 out of the ordinary course, are to an extent altogether astonish- 
 ing ; and such as defy our utmost calculation. The assimilating 
 organs appear even to decompose principles which are still con- 
 sidered as elementary, nay, to form azote or carbon ; so that it is 
 impossible to define what, on an emergency, these organs are ca- 
 pable of doing. But what is thus done by these organs on an 
 emergency, will usually, be found to constitute an exception to 
 what they do in ordinary ; their ordinary mode of action being al- 
 ways that which is most simple, and which is thus to be consi- 
 dered as the rule. 
 
 3. Of the Organizing and Vitalizing Powers of the Sto- 
 mach. — In this part of our investigation, we meet the real diffi- 
 culties we have to overcome in explaining the operations of living 
 beings. The whole of the great and essential changes which ali- 
 mentary substances undergo, may, and perhaps will be, traced by 
 care and attention ; but all beyond, will probably remain for ever 
 unknown to us. Now at least, it may be truly said, that though 
 we understand, in some degree, the chemical changes ; of the vi- 
 talizing influence Ave know absolutely nothing. There is, how- 
 ever, every reason to believe that vitality is imparted through the 
 agency of the living animal itself. For though, from the natural 
 composition of alimentary substances, they be to a certain extent, 
 fitted for the purposes of the animal economy ; yet, alone, they 
 are incapable of uniting themselves with the animal frame ; and 
 unless the living economy contribute likewise its share of the la- 
 bour, the future work of assimilation wdll be incomplete. 
 
 Of the Changes the lood undergoes in the Duodenum. — We 
 alluded in general terms to the bile and the pancreatic fluids, when 
 we were treating of the organs by which they are secreted. We 
 have now to consider, more particularly, the nature of these se- 
 cretions, and their share in the performance of the functions of the 
 duodenum. 
 
 With the yellow colour, and the intensely bitter taste of the 
 hile, all are familiar: we need not, therefore, dwell on the sensible 
 properties of the secretion, but proceed to notice its chemical com- 
 position. The chemical composition of the bile is very heteroge- 
 neous, though not perhaps so heterogeneous as has been repre- 
 sented ; since it is probable that many of the ingredients said to be 
 contained in the secretion, are products that have resulted from the 
 methods employed in its analysis. Bile, like all animal fluids, is 
 composed essentially of water ; but the solid matters contained in 
 the bile, are nearly altogether formed from one or more proximate 
 principles, in which carbon and hydrogen predominate. These 
 proximate principles exist simultaneously, if not in conjunction 
 with soda, and with various salts of soda, besides other substances. 
 The properties of the bile vary somewhat in different animals ; 
 
272 CHEMISTRY OF ORGANIZATION. 
 
 but in all animals its essential characters remain wonderfully si- 
 milar. 
 
 We are much less acquainted with the properties of the pan- 
 creatic J^uid, than with those of the bile. The nature of the pan- 
 creatic fluid was formerly supposed to be very analogous to that 
 of the saliva; but recent observations have shown that it contains 
 albumen, and a curdy substance. The pancreatic fluid is, for the 
 most part, in a slight degree acid, and holds in solution matters 
 of a saline nature, closely resembling those found in all animal 
 fluids. 
 
 When the food that has undergone the first process of digestion 
 in the stomach, quits that organ, and enters the duodenum, some 
 other clianges of a very remarkable kind take place. If the food 
 originally contained no albuminous matter, no albumen is deve- 
 loped in the stomach; but immediately on the entrance of the 
 semi-fluid mass into the duodenum, and its mixture with the bile 
 and the pancreatic fluids ; albuminous, and other chylous matters, 
 become distinctly perceptible. At the same instant, those fluid 
 parts, which in the stomach were acid, are so far altered, by the 
 addition of the bile, and the pancreatic fluids, as to become neu- 
 tral, or almost neutral : some gas is frequently extricated ; and 
 that portion of the food which is destined to be excrementitious, 
 is evidently separated. The albumen, which is tlius found to 
 exist in the chyme, (as the food is termed, after it has been acted 
 on by the stomach, and has entered the duodenum), may be partly 
 derived from the pancreatic fluid, which, as we have already 
 mentioned, has been said to contain albumen. But the quantity 
 of albumen, and of other proximate principles of the chyle, that 
 are found in the contents of the duodenum, at some distance on- 
 ward from the pylorus, is much too great to be explained in 
 this manner. Indeed, the properties, as well as the quantity, of 
 the albuminous matters, show, beyond a doubt, tliat the albumi- 
 nous matters are developed from the food, and constitute the chyle, 
 which is subsequently taken up by the lacteals. 
 
 Such are those most interesting, and at the same time obvious, 
 phenomena, that are observed in different animals, in which the 
 changes produced on the food by the action of the duodenum have 
 been examined. These phenomena appear to vary considerably, 
 according to the nature of the food ; but so far as we can under- 
 stand the phenomena, under every change of food, the essential 
 chiiracter of the chanjies which the food underscoes in the duode- 
 nuiii, remains unaltered. That is to say : the acid formed in the 
 stomach, combines, in the duodenum, with the alkali of the bile; 
 the albuminous principles are developed; and the excrementitious 
 matters arc, more or less perfectly, separated. Of the nature of 
 the more recondite and vitalizing changes which take place in the 
 
PROCESS OF DIGESTION IN ANIMALS. 273 
 
 duodenum ; we are in the same slate of complete ignorance, as 
 we are of the similar changes which lake place in the stomach, 
 and probably shall long so remain. 
 
 In the preceding remarks on the different processes which take 
 place in the stomach and duodenum, and which are necessary for 
 the conversion of the food of an animal into the living material 
 of its body ; we have endeavoured to distinguish between what, to 
 a certain extent, is within our powers of comprehension, and 
 what is completely beyond them. It remains to be observed in 
 conclusion, that though the three great and essential processes of 
 digestion, namely, the reducing, the converting, and the organi- 
 zing processes be sufficiently distinct from each other ; yet it is 
 not to be understood that they take place in succession, or in the 
 order in which they have been described. The fact is, that all 
 these processes go on at the same time ; and as soon as a portion 
 of food begins to be dissolved, its future changes seem to be de- 
 termined. If it be necessary that the portion of food undergo an 
 essential change, that change is accordingly begun. If no such 
 change be required, the organizing process itself begins simulta- 
 neously with the reducing process. The consequence of this 
 union of the digestive processes is, as we have stated, that the 
 staminal principles are all developed in the chyle ; as soon as the 
 excreraentitious matters are separated by the biliary and pancrea- 
 tic fluids. 
 
 Of the Fiindions of the JUimentary Canal, beyond the Duo- 
 denum. — Compared with the functions of the stomach and duo- 
 denum, the functions of the succeeding portions of the alimentary 
 canal, as far as we can judge, are unimportant. The digested 
 mass passes from the duodenum into the jejimum, and ilium ; 
 though before the food reaches the end of the ilium, the whole of 
 the chyle contained in it, has been absorbed into the apertures of 
 the numerous tubes named lacteals. These tubes open in greater 
 or less number, into the whole interior surface of the three por- 
 tions of the alimentary canal, along which the food is moved from 
 the stomach to the colon. From the ilium, the undigested or 
 excremenlitious matters proceed into the coecura ; in which cavity, 
 in some animals, as for example, in the horse, even these excre- 
 menlitious matters appear to undergo a second digestion ; but in 
 all animals, the contents of the coecum have a very different as- 
 pect from those of any part of the alimentary canal, nearer to the 
 stomach. The mass of excremenlitious matters continue their 
 course from the coecum into the colon, where thev are still further 
 changed. The nature of these changes, however, is not well 
 understood, thougii they are probably of no small importance in 
 the animal economy. Finally, all the nutritious portions of the 
 
274 CHEMISTRY OF ORGANIZATION. 
 
 food, liaving entered into the system of the animal, nothing re- 
 maitis but what is entirely excrcmenlitious. 
 
 Such is a short sketch of the phenomena of digestion and assi- 
 milation, in as far as these processes are effected by the stomach 
 and th.e alimentary canal. The phenomena suggest the following 
 reflections : 
 
 First. With regard to the nature and the choice of aliments, 
 and the modes of their culinary preparation; it follows from the 
 observations we have offered ; that, under similar circumstances, 
 those articles of food, which are the least organized, must be the 
 most difficult to be assimilated : consequently, that the assimila- 
 tion of crystallized, or very pure substances, must be more diffi- 
 cult, than the assimilation of any others. Thus, pure sugar, pure 
 alcohol, and pure oil, are much less easy to be assimilated, than 
 substances purely amylaceous ; or than that peculiar condition or 
 mixture of alcohol existing in natural wines; or than butter. In 
 these forms, the assimilation of the saccharine and the oleaginous 
 principles is comparatively easy. Of all crystallized matters, 
 pure sugar is perhaps the most easily assimilated ; but every one 
 is taught by experience, that much less can be eaten of articles 
 composed of sugar, than of those composed of amylaceous mat- 
 ters. In some forms of dyspepsia, the effect of pure sugar is 
 most pernicious; perhaps fully as pernicious as that of pure al- 
 cohol. Nature has not furnished either pure sugar or pure starch ; 
 and these substances are always the results of artificial processes, 
 more or less elaborate ; in which, as in many of the processes of 
 cookery, man has been over-officious ; and has studied the grati- 
 fication of his palate, rather than followed the dictates of his reason. 
 In many dyspeptic individuals, the assimilating and preservative 
 powers of the system, are already so much weakened, as to be 
 unable to resist the crystallization of a portion of their fluids. 
 Thus in gouty invalids, how often do we see chalk-stones formed 
 in every joint? Now, with so little control over their own fluids, 
 how can they reasonably hope to assimilate extraneous crystal- 
 lizations? If, therefore, such an invalid, on sitting down to 
 a luxurious modern banquet, composed of sugar, and oil, and 
 albumen, in every state of combination, except those best adapted 
 for food, would pause a moment, and ask himself the question ; 
 Is this debilitated and troublesome stomacii of mine, endowed 
 with the alchemy requisite for the conversion of all these things 
 into wholesome flesh and blood ? He would probably adopt a 
 simpler repast, and would thus save himself from much uneasi- 
 ness. The truth is, that many of the elaborate dishes of our in- 
 genious continental neighbours, are scarcely nutritious, or designed 
 to be so. Th(?y are mere vehicles for dilferent stimuli — diflerent 
 ways, in short, of gratifying that low animal propensity, by which 
 
PROCESS OF DIGESTION IN ANIMALS. 275 
 
 SO many are urged to the use of ardent spirits, or of various nar- 
 cotics. In one respect indeed, namely, tiiat of reducing to a state 
 of pulp those refractory substances which we have before men- 
 tioned, the culinary processes of our neighbours are much supe- 
 rior to ours ; but in nearly every other respect, and most of all, 
 in tlie general use of pure sugar and pure oil, their cookery is 
 eminently injurious to all persons who have weak digestion. On 
 the other hand, in this country, we do not in general pay suffi- 
 cient attention to the reducing processes of the culinary art. Every- 
 thing is firm and crude ; and though the mode of preparation be 
 less captivating ; the quantity of indigestible aliment is quite as 
 great in our culinary productions, as in those of France. 
 
 We are not, however, writing a treatise on cookery or dietetics ; 
 but in treating of the function of digestion, it is im{)ossib!e alto- 
 gether to pass over these important subjects. The foregoing ob- 
 servations are merely intended as illustrations of those general 
 principles which often regulate the choice, and the preparation of 
 the food of mankind, in a state of civilized society. Reason is 
 too little followed, the indulgence of the palate is the sole object ; 
 so that the organs of digestion already enfeebled, and incapacitated 
 for the assimilation, even of the most proper nourishment, are 
 daily oppressed with a task for which they are altogether unequal. 
 The consequence is, that though for a time the labourbe sustained, 
 the digestive energies are at length overcome. The dyspeptic 
 being passes half his days in misery ; his offspring inherit their 
 parents' constitution ; and if they persist in a like course of slow 
 poison ; after a few generations, the race becomes extinct, — " his 
 name even is cut off from among men!" Providence has gifted 
 man with reason ; to his reason, therefore, is left the ehoice of his 
 food and drink, and not to instinct, as among the lower animals : 
 it thus becomes his duty to apply his reason to that object ; to 
 shun excess in quantity, and what is noxious in quality ; to ad- 
 here, in short, to the simple and the natural ; among which the 
 bounty of his Maker has afforded him an ample selection ; and 
 beyond which if he deviates, sooner or later, he will suffer the 
 penalty. 
 
 Secondly. The view we have now taken of the processes of 
 digestion, removes in some degree that mysterious character v/ith 
 which they have been invested; and by lessening the field of our 
 inquiry, brings us nearer to our object. We had previously known, 
 that the articles employed as food by animals are essentially com- 
 posed of three or four elements. But we have now learnt, that 
 all the more perfect of those matters on which animals subsist, 
 are compounds of three or four proximate principles ; the whole 
 of which compounds, except one, are, in their essential charactes, 
 identical with those composing the fiameof the animals themselves. 
 
276 CHEMISTRY OF ORGANIZATION. 
 
 We have also learnt, that owhig to this identity of composition, 
 many animals are saved the labour of forming these proximate 
 principles from their elements; and have only to re-arrange them, 
 as their exigencies may require. The task of forming the proxi- 
 mate principles is thus left to the inferior animals or to plants; 
 which are endowed with the capacity of compounding them from 
 matters still lower than themselves, in the scale of organization. 
 Hence there is a series, from the lowest being that derives its 
 nourishment from carbon and carbonic acid, up to the most perfect 
 animal existing. Each individual in the series preferring to assi- 
 milate those immediately below itself; but having on extraordinary 
 occasions, and in a minor degree, the power of assimilating all, 
 not only below, but above itself, in the system of organized crea- 
 tion. 
 
 We stated that the immediate influence employed by the organic 
 agent is probably galvanism, or the common agents that operate 
 among inorganic matters ; and that the digestive apparatus, viewed 
 as a whole, seems to be arranged on galvanic principles. AVe 
 wish, however, our readers clearly to understand, that we con- 
 sider the organic agent residing in the ganglionic system of nerves, 
 and employing the electric agency, to be not electricity itself; 
 though the agency is probably the lowest kind existing in animal 
 bodies, and only, as it were, one degree above the agencies of in- 
 animate matter. We dwell on this point the more, because from 
 deficient recollection of what electricity is, and what are the living 
 powers acting through the nervous system of animals, it has been 
 maintained, nay, has even been endeavoured to be experimentally 
 proved, that these nervous powers are identical witli the powers 
 of electricity. It is impossible to imagine a greater fallacy. Ad- 
 mitting that electricity, properly directed, could change the proxi- 
 mate elements of the food into those of chyle : can we imagine 
 this principle to vary spontaneously its mode of operation, so as 
 to produce the same chyle from every sort of aliment — that elec- 
 tricity is an inteUigent agency acting with a certain object ? 
 Besides, if the nervous agency be identical with electricity, how 
 different must be its functions in different nerves ; in one nerve, 
 for example, digesting and assimilating tlie food; in another con- 
 veying sight ; in a third conveying sound; in the brain itself, shall 
 we say, actually thinking! As to the experiments, on which it 
 has been attempted to rear this most untenable opinion, they prove 
 nothing whatever; and are easily explained on other principles. 
 Sucii explanation would be foreign to our present object, were 
 we to introduce it here. But there is one observation, which has 
 always appeared to us conclusive against this fancied identity of 
 the nervous energy with electricity ; and with which, we shall 
 close what we have to offer, regarding the present subject. Most 
 
ABSORPTION OF THE CHYLE, ETC. 277 
 
 persons are aware that there arc certain fishes endowed with the 
 power of evolving electricity, and of communicating a smart shock 
 to other animals. Now, in all the fishes in which this power re- 
 sides, as in the Torpedo, there is a complicated apparatus, extend- 
 ing over a large portion of the fish's body, expressly for the pur- 
 pose of forming the electricity, which the fish communicates ; 
 thus, proving beyond a doubt, that mere nerves are not suflicient 
 to develope electricity; and ihat, when electricity is wanted, aa 
 express and peculiar organ is as requisite for its secretion or for- 
 mation, as for the secretion and formation of any other product of 
 the animal economy. 
 
 The reflections suggested by the facts we have now detailed, 
 will be given in conjunction with those suggested by the facts to 
 be detailed in the next chapter. 
 
 CHAPTER IV. 
 
 OF THE PROCESSES OF ASSIMILATION SUBSEQUENT TO THOSE IN THE STO- 
 MACH AND ALIMENTARY CANAL ; PARTICULARLY OF THE CONVERSION OF 
 THE CHYLE INTO BLOOD. OF RESPIRATION, AND ITS USES. OF SECRE- 
 TION. OF THE FINAL DECOMPOSITION OF ORGANIZED BODIES. GENERAL 
 REFLECTIONS, AND CONCLUSION. 
 
 1. Of the Passage of the Chyle from the Alimentary Canal 
 into the Sanguferous System; and of the Function of Absorp- 
 tion generally. — The Chyle, as we have already said, is taken 
 up from the alimentary canal, by numerous minute tubes, named 
 lacteals ; these lubes being part of the system of similar tubes, 
 which arise from all parts of the body, and are termed absorbents. 
 The whole of the absorbing tubes, after passing through various 
 glands, at length unite into one or two of larger size ; that on the 
 left side being by far the largest, and known by the appellation 
 of the thoracic duct. These larger absorbent tubes pour their 
 contained fluids into the veins named the sub-clavian ; and thus 
 into the general mass of the blood. The exact nature of the 
 changes which the chyle and the lymph undergo in their passage 
 through these tubes, is not well understood. One change appears 
 to be, that the chyle, as first formed in the alimentary canal, is 
 to a certain extent, completed^ or freed from water, during its 
 course through the lacteals : for though, when the chyle is mixed 
 with the blood, its albuniinous principles are much less perfectly 
 developed than those of tiie blood itself; yet their developement, 
 on their mixture with the blood, is more perfect, than when the 
 chvle is first taken up from the alimentary canal. 
 
 24 
 
278 CHEMISTRY OF ORGAMZATIOX. 
 
 The matters conveyed from the other parts of the body, by the 
 tubes of the general absorbent system, have, by most physiolo- 
 gists, been supposed to be of an excrementitious character. That 
 some of the absorbed matters are excrementitious, is very proba- 
 ble ; arguments may, however, be adduced, to show, that the 
 whole of ihe matters absorbed are by no means excrementitious ; 
 but that they are repeatedly consigned to the uses of the vital 
 agency : every new organization raising them, as it were, a step 
 liio^her, and quaiifving them for those refined and ulterior pur- 
 
 o'l^^O ••11 
 
 poses ; for which the crude chyle can hardly be imagined to be 
 at once adapted. 
 
 The circumstances favouring the above opinion, which we are 
 now desirous to mention, are — 
 
 First. It is unreasonable, and contrary to every thing we 
 know respecting the operations of the animal economy, to sup- 
 pose that the chyle should be separated from one kind of excre- 
 mentitious matter, in the alimentary canal ; in order to be imme- 
 diately mixed again with other excrementitious matters, in the 
 chyliferous tubes. It is, therefore, a just inference, that if the 
 matters contained in the absorbents are really and wholly excre- 
 mentitious, they would be carefully kept apart ; and would be 
 removed from the system by some other means, than by tubes 
 united with those conveying the nutritious fluids. 
 
 Secondly. By admitting that the fluids contained in the absor- 
 bent tubes possess a highly animalized character, the design of 
 their union with the crude and imperfectly animalized chyle, be- 
 comes apparent : the fluid in the absorbents will be seen to exe- 
 cute an important and necessary oflice ; by raising the vital cha- 
 racter of the chyle, and qualifying it, for becoming a part of the 
 general mass of the blood. We thus obtain a cogent reason, why 
 the fluids taken up from the internal surface of the alimentary 
 canal, should be mingled with those that are absorbed from other 
 parts of the body ; a mixture which is inexplicable, on the hypo- 
 tliesis of these absorbed fluids being wholly excrementitious. 
 
 Thirdly. The gradual developement of the staminal princi- 
 ples of animal bodies, by repeated organizing processes, fully 
 accords with those general views of the operations of nature 
 wliich, throughout this work, we have endeavoured to illustrate ; 
 and which lead to the general conclusion, that the operations of 
 nature are never abrupt, but always slow and gradual. Further, 
 it is more reasonable to conceive, that matters already assimilated 
 to the animal body, arc better fitted for its immediate uses ; than 
 those which, like the chyle, have only received an imperfect 
 assimilation. 
 
 Fourthly. Many animals can and do live, for a considerable 
 time, on substances cantained in their own bodies. Thus hyber- 
 natlng animals, as previously stated, have the ability to assimilate 
 
BLOOD. 279 
 
 principles of the blood, gelatine is not mentioned. In fact, thongli 
 further, those matters which have already become part of them- 
 selves ; consequently, such a faculty of progressive organization 
 as we have supposed, actually exists ; and a sort of dif^estion is 
 carried on in all parts of the body, to fit for absorption and 
 future appropriation, those matters that have been already assi- 
 inilated. Were it necessary, other arguments to the same effect 
 might be added : but we shall at present delay t!ie further consi- 
 deration of the assimilating character of the whole absorbent sys- 
 tem ; that we may recur to it again, in a succeeding part of the 
 present chapter. 
 
 2. Of the Blood. — The blood is that well-known fluid pervad- 
 ing the tubes, named from their function the blood-vessels ; which 
 tubes are extended more or less over every part of an animal. 
 We have already described the general distribution of the blood- 
 vessels ; and shall now confine ourselves chiefly to the properties 
 of the blood itself. 
 
 The chyle, as we have stated, is poured into the general mass 
 of the blood near the heart ; and from the heart is almost immedi- 
 ately propelled through the lungs. The chyle, thus set in motion, 
 is not only united thoroughly with the blood ; but undergoes those 
 other important changes, by which its final conversion into blood 
 is accomplished. The exact nature of these changes is unknown ; 
 but they are evidently of a completing character — that is to say, 
 the weak hydrated ingredients of the chyle, are freed from a por- 
 tion of the water with which they were associated ; and are trans- 
 muted into the strong albuminous matter of the blood. 
 
 The chief constituents of the blood are essentially albuminous. 
 Blood contains albumen in three states of modification : namely, 
 albumen, properly so called ; fibrin ; and the red particles. In 
 addition there are oily matters ; besides various minute portions 
 of other animal matters, and saline matters, all dissolved, or 
 rather suspended, in a large quantity of water. The following 
 short table exhibits the relative proportions of the constituents of 
 human blood to each other, as they exist in most individuals. 
 
 ONE THOUSAND PARTS OF HUMAN BLOOD CONTAIN 
 
 Of Water 783,37 
 
 Fibrin ... - - 2,83 
 
 Albumen ... - - 67,25 
 
 Colouring- matters - - - - 126,31 
 
 Fatty matters, in various states - - 5,16 
 
 Various undefined animal matters, and salts- 15,08 
 
 1000,00* 
 The reader will not fail to remark, that among these constituent 
 * Le Canu ; mean of two analyses. 
 
280 CHEMISTRY OF ORGANIZATION. 
 
 existinff most abundantly in various animal structures, s^elatlne 
 is never found in the blood, or in am/ product of glandular se- 
 cretion. We formerly noticed that gelatine appears to rank lower 
 than albumen in the scale of organized substances : and we may 
 now add, that a given weight of gelatine, contains at least three 
 or four per cent, less carbon, than an equal weight of albumen. 
 The production of gelatine from albumen must, therefore, be a 
 reducing process. VVe shall presently have occasion to revert to 
 these facts. In the mean time we subjoin ihe few observations 
 we have to offer, on the organization or structure of the blood. 
 
 The organization of the blood is even more wonderful tban its 
 chemical composition, and is still less understood. The red por- 
 tion of the blood, .Hor example, is composed of innumerable minute 
 globules, varying in size in different animals ; and in all instances, 
 highly organized : the real structure indeed of these globules is 
 very imperfectly known ; but they are generally supposed to be 
 formed of solid colourless nuclei, within red vesicles. The 
 fibrin, also, is diffused through the mass of the blood in a state of 
 equally minute subdivision ; though t!ie particles of the fibrin 
 are colourless, and their magnitude much less than that of the red 
 particles. From this inferiority in size, some physiologists have 
 been led to think, that the colourless particles of the Tibrin, are 
 identical with the nuclei of the red particles. During the life of 
 an animal, the particles of the fibrin, as well as the red particles 
 of its blood, seem to be in a state of extreme self-repulsion ; by 
 which self-repulsion, the union of these particles is prevented ; 
 except as the economy of the animal may require, and may de- 
 termine. After death, however ; or in blood withdrawn from the 
 body of a living animal, the property of self-repulsion, more 
 especially among the fibrinous particles of the blood, ceases, and 
 they readily cohere : this cohesion is termed the coagulation of 
 the blood. Much beautiful design is probably concealed under 
 that peculiar organization of the blood, to which it owes its coag- 
 ulating tendency. One result of the coagulation of the blood, in- 
 deed, is as obvious as it is important ; namely, the prevention of 
 haemorrhage. If the blood did not coaorulate, the existence of 
 animals would be most precarious ; as on the slightest injury, they 
 •would be liable to bleed to death. 
 
 3. Of Respiration. — The function of Respiration, or breath- 
 ing, is one of the most important in the animal economy, and 
 cannot, like many of the other functions, be suspended ; the in- 
 tcrrupiion of that function being immediately destructive of life. 
 When we described the phenomena of the circulation of the blood, 
 we observed, that the blood, in passing through the lungs, is ex- 
 posed to the action of the atmospheric air. Now, during this 
 exposure of the blood to the atmospheric air, it undergoes certain 
 changes. The blood from the right side of the heart, when it 
 
RESPIRATION. 281 
 
 enters the lungs, is of a dark red colour; it is then dispersed, in 
 a state of most minute subdivision, through the ultimate vessels 
 of the lungs, and in these vessels is brought into contact with the 
 atmospheric air, and becomes of a bright red colour. In other 
 words, the blood changes in the lungs its venous appearance, and 
 assumes the character of arterial blood. The blood thus arterial- 
 ized, returns to the left side of the heart, and from that organ, is 
 propelled through the whole arteries of the body. In the minute 
 terminations of the arteries, the blood again loses its llorid hue, 
 and, reassuming its dark red colour, is returned to the veins, to the 
 right side of the heart ; to be exposed as before to the influence 
 of the atmospheric air, and to undergo the same succession of 
 chang-es. 
 
 On examining the respired air, a remarkable alteration of its 
 properties is found to have taken place ; a portion of its oxygen 
 ^ has disappeared, and a similar bulk of carbonic acid gas, has been 
 substituted. With respect to the origin of this carbonic acid gas, 
 there have been various opinions. Formerly, the greater number 
 of physiologists maintained, that carbon, in some form, was ex- 
 creted by the lungs ; and that this excreted carbon, uniting with 
 the oxygen of the inspired air, was converted into carbonic acid 
 gas. No one imagined that oxygen gas could be passing inwards 
 through the membrane of the lungs, while carbonic acid gas was, 
 at the same time, passing outwards, through the same membrane. 
 Accurate observations have, however, demonstrated, that such a 
 simultaneous passage of gases really takes place through the mem- 
 brane of the lungs; and the observations are not confined to the 
 two gaseous bodies in the lungs ; but are applicable to all gases 
 whatever, under similar circumstances. In consequence of these 
 observations, it seems now to be generally admitted, that the 
 oxygen of the atmospheric air is absorbed by the blood, and, in 
 some unknown state of combination, reaches the extreme subdi- 
 visions of the arteries ; where it is united with a portion of carbon, 
 and forms carbonic acid gas : that this carbonic acid gas is retained 
 in some unknown state of combination in the venous blood ; till, 
 in the lungs, it is expelled, and oxygen is absorbed in its stead ; 
 according to the laws which regulate the diff'usion of gaseous bo- 
 dies, formerly explained. Further, with the carbonic acid gas, 
 a large quantity of aqueous vapour, as we have stated, is at the 
 same time separated. 
 
 It would be foreign to the objects of this treatise, were we to 
 enter further into the reasons for the view we have given of the 
 phenomena of respiration. These reasons are many and strong; 
 and seem indeed to prove clearly, that the changes which the 
 blood undergoes, during its circulation through the body, are as 
 we have described them. We shall, therefore, assume that our 
 
 24* 
 
282 CHEMISTRY OF ORGANIZATION. 
 
 view of respiration is correct; and shall ofier a few remarks on 
 the attendant circumstances, and on the consequences of respira- 
 tion. 
 
 First. To what influence are we to ascribe tlie different colours 
 of arterial and of venous blood ? The opinion formerly held, was, 
 that the arterial colour arose from the absorption of oxygen ; and 
 the venous colour from the presence of carbon. But recent ob- 
 servations seem to show that the change in tlie colour of the 
 blood during its circulation, if not entirely independent of oxygen, 
 is much influenced by the saline matters ; particularly by the com- 
 mon salt, wliich the blood contains : and that the dark colour of 
 venous blood, is principally owing to the presence of carbonic acid 
 
 Secondly. What is the source of the carbonic acid in venous 
 blood, and of the aqueous vapour that is expelled from the lungs ? 
 These questions cannot be answered with certainty. But some 
 observations lately made, have induced us to believe, that the 
 conversion of albuminous matters into gelatine, is one great 
 source of the carbonic acid in venous blood. Gelatine, which, 
 as before observed, contains three or four per cent, less of carbon 
 than albumen contains, enters into the structure of every part of 
 the animal frame, and especially of the skin : the skin indeed con- 
 sists of little else besides gelatine : it is most probable, therefore, 
 that a large part of the carbonic acid of venous blood is formed in 
 the skin, and in the analogous textures. Indeed, we know that 
 the skin of many animals gives off* carbonic acid, and absorbs oxy- 
 gen ; in other words, performs all the offices of the lungs ; a func- 
 tion of the skin perfectly intelligible, on the supposition that near 
 the surface of the body, the albuminous portions of the blood are 
 always converted into gelatine. With respect to the aqueous va- 
 pour thrown off^ from the lungs : we have every reason to believe, 
 as before stated, that much of this vapour is derived from the 
 c/ii/le, in its passage through these organs ; and that by such se- 
 paration of water, the iveak and delicate albumen of the cliyle, is 
 converted into the strong and perfect albumen of the blood ; ac- 
 cording to the principles detailed at the commencement of this 
 chapter. 
 
 'I'hirdly. What are the uses of the continual extrication of car- 
 bonic acid from living animals ; and could not a litde superfluous 
 carbon have been thrown off" from their bodies in a more simple 
 manner? The precise use of the constant evolution of carbonic 
 acid, or how it is effected, we know not ; but one great use which 
 lias been assigned to this evolution, is, the formation of the heat 
 of the body ; and not only the power of forming that heat ; but 
 also the power of varying it according to circumstances — a power 
 so characteristic of oriranized life. Out of the bodv, carbon does 
 
SECRETION. 283 
 
 certainly give off heat on combination with oxygen. Hence, it 
 has been maintained with great plausibility, that the same com- 
 bination, within a living body, may give origin to its heat ; though 
 it must be confessed, that there are some difficulties about this 
 view of the origin of animal heat, which detract considerably from 
 its likelihood. Moreover, it is exceedingly probable, that though 
 the evolution of carbonic acid gas, may be one of the means pos- 
 sessed by the animal economy for generating heat ; there are yet 
 other means, the nature of which at present are quite unknown. 
 
 The quantity of carbon thrown off by the lungs, is very abun- 
 dant ; but has probably been much overrated. Philosophers have, 
 for instance, calculated that the lungs of a man of ordinary size 
 expel, in the course of twenty-four hours, eleven ounces of car- 
 bon ; a quantity more than equal to that contained in six pounds 
 of beef.* If carbon be indeed thrown off from the lungs so co- 
 piously; it must be produced within the body. It is difficult to 
 account for the quantity of carbon thrown off, even on the lowest 
 estimate. We are, therefore, necessarily obliged to conclude, that 
 more solid matter is every day expelled from the body by the 
 lungs, than in any other manner. Hence the probability of the 
 opinion formerly noticed, that the matters taken up by the absor- 
 bents, and by the veins, enter successively into the formation of 
 various parts of the animal frame ; instead of being removed, im- 
 mediately after their absorption, as at present is generally sup- 
 posed. For it seems hardly possible to reconcile, with the quan- 
 tity of food, the great quantity of carbon that is expelled from the 
 lungs alone ; much less, what must be expelled if all the matter 
 taken up by the absorbents be likewise considered excrementitious. 
 
 4. Of Secretion. — From the blood, are formed, by means of 
 peculiar apparatus, all those numerous products termed Secre- 
 tions ; not only so unlike each other, but so unlike the fluid 
 from which they are originally separated. Some of these se- 
 creted products appear to be little else, than a separation of cer- 
 tain matters already existing in the blood. Other secretions have 
 no resemblance to any ingredient of the blood : consequently, in 
 the glandular structure, by which these secretions, so dissimilar 
 to the blood, are formed, the blood must undergo some essential 
 change. In the present state of our information, however, we 
 must content ourselves with a limited insight into the nature and 
 
 * According' to an elaborate analysis, by Berzelius, the muscle of an ani- 
 mal contains 77 per cent, of water, and 23 per cent, of other matters. 
 Supposing-, what is near the truth, that 22 of these 23 parts consist of al- 
 bumen, and that this albumen contains half its weight of carbon ; which in 
 round numbers is a sufficiently neat approximation ; it foUowa, that 100 
 parts of the muscular fibre of animals, contain about 11 parts of carbon ; 
 so that 11 ounces of carbon must represent 100 ounces of beef; that is, 
 upwards of six pounds as stated in the text. 
 
284 CHEMISTRY OF ORGANIZATION. 
 
 the pauses of secretory action. We see that secreted products 
 are of two kinds ; that some of the maiters separated by animal 
 bodies are evidendy thrown oft', on account of their noxious quali- 
 ties ; are, in fact, excretions ; which could not be retained with- 
 out proving fatal to the life of the animal from which they are 
 detaclied : while others again, are as obviously intended for furtlier 
 objects, and for the performance of various subordinate actions in 
 the living system ; are in fact, secretions ; properly so called. But 
 as we have stated, we are still perfecdy unacquainted with the 
 intimate nature of these changes ; though it is probable that a 
 careful examination of the phenomena, would throw much light 
 on their general character ; and display evidence of the most 
 consummate design. 
 
 5. Spontaneous decciy of Organized Bodies. — It remains 
 finally to ch)se this work with a few observations on the sponta- 
 neous, and inevitable decay, of all those things that are produced 
 by organization; after they have been removed from the influence 
 of the organic agents, by which the combination of their consti- 
 tuent principles was eflTected. 
 
 The organized beings that inhabit this globe, however nume- 
 rous, have a very small relation to the magnitude of the globe, 
 and seem to occupy its surface only. We have seen that the ele- 
 ments forming the structure of these beings, are not only com- 
 bined in diilereiU proportions, but that they appear, in many in- 
 stances, to undergo further decomposition into ultimate forms of 
 matter, which, out of a living body do not, and perhaps, in the 
 present constitution of the universe, cannot, exist in an isolated 
 state. Owing to this diversity in the composition of organized 
 beuisfs from that of inoro^anic matter, and to other causes which 
 will readily occur to the reader, organized beings and their laws, 
 are in continual opposition to the general laws, by which inor- 
 ganic matter is governed. To counteract, therefore, these oppo- 
 site laws, and to maintain the existence of organized beings, 
 recjuire the unremitting eflbrts of the organic agency. But at length 
 these efforts are exhausted ; the contest ceases ; when the gene- 
 ral laws of inorganic nature prevail, and speedily reduce, to their 
 original stale of existence, the atoms which had been incarce- 
 rated in the living frame. 
 
 The spontaneous decay of organized beings is usually termed 
 the putrefactive process ; and some substances are much more 
 prone than others, to undergo that change. As miglit be ex- 
 pected ; those substances whose constitution is most simple, as 
 the oils, and Ixxhes of a like nature, are also the most permanent; 
 ■wliile sul).si;inces more compounded, especially those which in- 
 clude azote, are exceedingly liable to putrescent change. For 
 such changes a certain degree of heat and of moisture appear to 
 
RECAPITULATION AND REFLECTIONS. 285 
 
 be necessary : since in a temperature below the freezing point of 
 water, or in a perfectly dry state of the atmosphere, even animal 
 substances njay be preserved uiichan<.{ed (hiring any length of time. 
 The ]>henomena attending the dissoluiion of different kinds of or- 
 ganized matters are of course dill'erent ; but in every instance, the 
 tendency is toward the formation of compounds more simple 
 than the matter decomposed ; that is to say, of compounds whose 
 existence, out of a living body, is not incompatible with the pre- 
 sent state of the globe. Those matters which, in a warm and damp 
 air, seem first to be loosened from organic combination, are those 
 foreign bodies we formerly mentioned, as existing, in every part 
 of the structure of organized beings, in some unknown but active 
 self-repulsive state. Hence, during putrescent action, arises the 
 formation of sulphuretted and phosphoretted hydrogen, and of other 
 undefined compounds of the same elements: and these gaseous 
 compounds, chiefly, produce the very offensive odour of putre- 
 faction. At the same time, there are formed, carburetted hydro- 
 gen, oil, acetic acid, ammonia, and last of all, carbonic acid gas 
 and water; while the azote is extricated in a gaseous condition. 
 Finally, both vegetable and animal matters, but vegetable matters 
 more especially, are reduced to the state of mould. The mould 
 from vegetable matters, consists principally of carbon, in combi- 
 nation with a Hide oxygen or hydrogen : the mould from animal 
 products, consists of similar matters, mixed with a litde azote, 
 and the usual saline ingredients of organized substances. In this 
 form of mould, the remains of vegetables and of animals, as was 
 before stated, constitute the food of plants ; by which they are 
 again organized, and thus go through the same series of changes. 
 
 We may here pause for a moment, and, on account of the ge- 
 neral reader, briefly recapitulate the most striking facts, that iiave 
 been detailed in the present, and in the preceding chapters. 
 
 In the first place, the mcchanicMl arrcmgcmtnts for reducing 
 the food of animals to the proper degree of comminution, are 
 wonderfully varied, according to the peculiar qualities of that food. 
 In the graminivorous and granivorous tribes, for example, the 
 teeth are literally instruments for grinding or triturating herbaceous 
 matters, and seeds. In carnivorous animals, such a structure * 
 would be useless : the teeth, therefore, are suited only for cutting, 
 or tearing. In knawing animals, the teeth present a totally differ- 
 ent structure, but at the same time are admirably fitted to the ha- 
 bits of the animal. Occasionally, as in the fowl trihe of birds, 
 the grinding apparatus is placed, not in the mouth, but in the 
 stomach itself; this organ being, as it were, expressly contrived 
 for trituration ; while some of the functions it performs in other 
 animals, are transferred to contiguous parts. 
 
 The structure and mechanism of the stomach, and of the all- 
 
286 CHEMISTRY OF ORGANIZATION*. 
 
 mentary canal, then claim our particular attention. In carnivorous 
 animals, whose food requires comparatively little assimilation, 
 the alimentary canal is short, and of a simple structure. On the 
 other hand, in vegetable feedets, that canal is long and compli- 
 cated ; but perfectly adapted for macerating their food, and f(U" 
 extracting from it, everything that can be converted into nourish- 
 ment. Nor is there an adherence to any model, but the whole 
 is throughout varied ; as if in order to demonstrate the power and 
 the wisdom of llim by whom they were contrived. Thus the 
 alimentary canals of the cow, and of the horse, are formed on en- 
 tirely different models ; though the food of both animals be nearly 
 the same. 
 
 We proceed in the next place, to the consideration of the che- 
 mical changes, which the food undergoes in the stomach and 
 duodenum. In these chano-es we discover arrangements not less 
 wonderful, indeed more wonderful, than in those of structure and 
 of mechanism. The variety of forms, assumed by bodies having 
 the same essential composition, produces a latitude, in the choice 
 of diet, which is almost infinite : at the same time, the organs being 
 endowed with the power to discriminate all these differences, and 
 to act on the ultimate principles of bodies ; elaborate, from all 
 these various forms of matter, the same uniform resulting chyle. 
 The povver by which the stomach is enabled to effect these asto- 
 nishing changes, is the power which it possesses, of associating 
 the different alimentary substances with water; the power, in 
 sliort, of dissolving or digesting them. This dissolving power 
 seems to be exerted through the agency of chlorine, derived from 
 the common salt in the blood; at least, chlorine is always present 
 in the stomach, during the act of the solution of the food ; though 
 the precise mode in which it operates, is stdl unknown. Con- 
 tem})oraneously with the act of solution of the food, such essen- 
 tial changes take place in its composition, as are requisite for 
 perfecting the fviture chyle. 
 
 'J'iie stomach having accomplished its office, the digested mass 
 enters the duodenum ; where the scries of chanffes is continued 
 in a manner equally wonderful. In the duodenum, the digested 
 mass is brought in contact with the biliary and the pancreatic 
 fluids. The alkali of the bile unites with the acid, with which 
 the food had been mingled during its digestion in the stomach; 
 the excrementitious parts, both of the food, and of the bile, are 
 separated or precipitated ; while at the same time, the proper 
 chylous princi[)les are eliminated, in a condition appropriate for 
 their absorption by the lacteals. 
 
 'IMiere are two divisions of those minute tubes, that compose 
 what is termed the absorbent system of animals ; — the lacteals — 
 and the absorbents properly so called. The ultimate ramifications 
 of the lacteals, originate from the internal surface of the alimcn- 
 
RECAPITULATION AND REFLECTIONS. 287 
 
 tary canal, M^here they take up the digested, and partly assimilated, 
 element or chyle. The ultimate ramifications of the proper absor- 
 bents, originate from all parts of the body ; and are enabled to 
 take up, by some peculiar process, every component of the body, 
 solid as well as fluid, in the same manner as the chyle is taken 
 up by the lacteals. 
 
 Tlie fluid obtained from the lacteals, and that obtained from the 
 proper absorbents, are both alike albuminous. Tiie albumen of 
 the chyle, as we have formerly shown, is produced in the stomach 
 and duodenum, while the food is undergoing the process of 
 digestion. But whence is the albumen derived, that is found in 
 the proper absorbents ? The animal body we know to be com- 
 posed of a great variety of matters, among which gelatine pre- 
 dominates. Now, since albumen only is found in the absorbents, 
 it follows, that before the gelatine of the body is taken up by the 
 absorbents, it is re-converted into albumen : in other words, the 
 absorbed gelatine undergoes a process, entirely analogous to that 
 which gelatine, and other matters, undergo in the stomach and 
 duodenum, during the process of digestion. Hence, the diges- 
 tive process, instead of being confined to the stomach and duode- 
 num, is actually carried on without intermission, in all parts of a 
 living animal body. 
 
 The two kinds of fluid albumen derived from these two sources; 
 that is to say, the crude chyle in the lacteals, and the highly 
 animalized lymph in the absorbents, are at length commingled; 
 and form one uniform fluid of an intermediate character, adapted 
 for becoming a part of the general mass of the blood. The cha- 
 racter however of this fluid, when it becomes part of the blood, 
 though albuminous, is still very weak ; that is to say, the fluid 
 consists of albumen, holding a large proportion of water in a 
 stale of essential combination. By a beautiful arrangement, as 
 soon as this weak albuminous fluid is mingled with the blood, it 
 is hurried through the lungs ; where it undergoes a remarkable 
 change. In the lungs, the water, which is in essential union 
 with the weak albuminous matter of the chyle, is separated and 
 expelled along with the carbonic acid gas, which is continually 
 escaping from these organs ; and at the same lime, the weak 
 and delicate albuminous matter of the chyle, is converted into the 
 strong and firm albuminous matter of the blood. We are thus 
 brought to consider the process of respiration. 
 
 The blood, in its course through the lungs, emits carbonic acid 
 gas, and assumes a florid arterial colour. At the same time, ac- 
 cording to the principles of gaseous diffusion, the blood absorbs, 
 in the lungs, a portion of oxygen from the air of the atmosphere. 
 The oxygen thus absorbed, remains in some peculiar state of 
 union witli the blood, (Query, as oxygenated water, or some 
 analogous compound ?) till the blood reaches the ultimate termi- 
 
288 CHEMISTRY OF ORGANIZATION. 
 
 nations of the arteries. In these minute tubes the oxygen changes 
 its mode of union; it com.bines with a portion of carbon, and is 
 converted into carbonic acid ; which carbon must be derived from 
 the albuminous principles of the blood. Two distinct alterations 
 take place during the union of the carbon with the oxygen : a 
 portion of the albumen contained in the blood is sujiposed to be 
 reduced to the state of gelatine ; w^hich gelatine is appropriated 
 toward the renovation of those textures wliose composition is 
 chiclly gelatinous : at tlie same time, the carbonic acid which 
 had been formed from t!ie reduced albumen, nnites with the blood, 
 communicates to that fluid its dark venous colour, and is trans- 
 ferred to the lungs ; where it is expelled from the system, along 
 with a portion of aqueous vapour, derived principally from the 
 weak albumen of the chyle ; as formerly explained. 
 
 The blood is the source, not only of all the constituent princi- 
 ples of animal bodies, but likewise of all the various secretions ; 
 many of which difler altogether, in their properties, from those 
 of llie primary fluids, and perform secondary offices, of great im- 
 portance in the animal economy. Other products separated from 
 the blood, are purely excretions; as, for instance, the carbonic 
 acid gas from the lungs ; which could not be retained in the ani- 
 mal system without destroying life. 
 
 Finally, the life of the animal becoming extinct, the essential 
 properties of the matter of which it is composed, resume their 
 natural action, and speedily restore the elements to their original 
 condition. 
 
 Sucli is a summary of those operations of living bodies, which, 
 in the present and in the preceding chapters, we have endeavoured 
 to illustrate ; and though our insight into those operations be 
 ver}^ imperfect, it is amply sutficient to satisfy us, of the infinite 
 wisdom by which they are directed ; and that the unknown, must 
 be far more wonderful than what has been disclosed. Most of 
 the facts on which we have dwelt, are of a character so obvious, 
 that they require only to be understood, in order to be admitted 
 among the proofs of the great argument of design ; at least, by all, 
 but those who alTect to deny that argument. We therefore leave 
 to the reader, the application of facts, so obviously demonstrative 
 of design ; and proceed to ofi'or a few remarks on certain general 
 arrangements of organized and living beings, relatively to those 
 of inorganic matter. 
 
 First. In considering the economy of organized beings, one of 
 the circumstances most calculated to arrest our attention, is the 
 cxtraordiuiiry skill manifested in the disposal of the various parts 
 of the organized system, with regard to each other. As an in- 
 stance, on the great scale, may be noticed, the mutual relation 
 and dependance of plants and animals. Thus, as we formerly 
 pointed out, carbonic acid gas constitutes the chief food of plants; 
 
RECAPITULATION AND REFLECTIONS. 289 
 
 and we now see, that nearly the whole of the superfluous carbon 
 produced by the operations of the animal system, is actually 
 thrown off in the form of carbonic acid. Plants, therefore, on 
 the one hand, supply the chief nourishment to animals ; while 
 that gaseous matter which is separated by the animal economy, 
 and which if retained within animals, would to them be fatal, 
 constitutes, on the other hand, the chief food of plants. Nor in 
 these two respects only, are the two great systems of organiza- 
 tion mutually dependent ; for unless plants consumed the carbonic 
 acid gas which is formed by animals ; this deleterious compound 
 would probably accumulate in the atmosphere, so as to destroy 
 animal life ; while it is doubtful, whether the present races of 
 vegetables could exist, if carbonic acid gas were not formed 
 by animals. Again, the general scheme of Providence, for the 
 nourishment of animals, claims our especial notice. Animals 
 have not only been destined to prey on each other : but all created 
 beings are the food of those progressively higher than themselves, 
 in the scale of organization. By this wise arrangement, the 
 labour of the assimilating power has been greatly diminished ; 
 and by the same means, that accumulation of dead animal re- 
 mains which soon would be overwhelming, is entirely prevented. 
 Even in the fabric of individual animals, and in the operations 
 carried on within them, the same wise purposes of mutual rela- 
 tion and dependance are observable. Thus, whether we contem- 
 plate the repeated employment of the same materials ; or the 
 various important ends, in many instances accomplished by the 
 same process ; we discover, throughout, the utmost abridgement 
 of labour ; so that the greatest possible effect, is every where 
 produced, by the simplest possible means. 
 
 Secondly. The general subserviency, of the mechanical ar- 
 rangements of the frame of organized beings, to the chemical ope- 
 rations that are carried on within them, is of still greater interest 
 and importance, than even those arrangements have been shown 
 to be. Wemay view an organized being as a piece of intricate 
 machinery, adapted to the physical, and the chemical properties 
 of matter. The adaptation of this machinery to the physical pro- 
 perties of matter, belongs to another department. Our attention 
 is directed solely to the chemical adaptations. The performance 
 of the chemical changes within organized beings, through the in- 
 terposition of mechanical arrangements, as has been stated in a 
 former part of this work, establishes, beyond a doubt, that these 
 chemical changes have a real existence. Thus, when we wit- 
 ness such a display of elaborate arrangements, as are exhibited in 
 the mechanism of the digestive organs, and of the circulating 
 system ; the purpose of which arrangements is merely to produce 
 a few chemical changes in the food, and in the blood ; it is evi- 
 
 25 
 
290 CHEMISTRY OF ORGANIZATION. 
 
 dent that the chemical changes so produced, must be at least as 
 real, as the mechanical structure, by means of which they are ef- 
 fected. Hence the adaptations of mechanical arrangements, in 
 the structure of organized beings, to the pre-existing chemical 
 properties of matter, affords an evidence of design, not less im- 
 pressive than unequivocal. The most determined sceptic can- 
 not assert that there is any necessary relation, or indeed any re- 
 lation whatever, between the mechanical arrangements, and the 
 chemical properties to which they administer. There is no rea- 
 son why the chemical changes of organization, should result from 
 the mechanical arrangements, by which they are accomplished : 
 neither is there the slightest reason, why the mechanical arrange- 
 ments in the formation of organized beings, should lead to the 
 chemical changes of which they are the instruments. From what 
 cause, then, arose the association of the chemical changes with 
 the mechanical arrangements ? How were the chemical opera- 
 tions of digestion and of respiration brought into union with the 
 mechanical apparatus of digestion, and with the circulating sys- 
 tem ? The co-existence of things so entirely dissimilar, and hav- 
 ing no kind of mutual relation, can be explained only on the sup- 
 position that a ivill exists somewhere ; and also 3. jwiver to exe- 
 cute that ivill. The existence is thus unavoidably acknowledged 
 of a Being, who knowing every pre-existing chemical property of 
 matter, and willing to direct these properties to a specific object, 
 has contrived for that purpose an apparatus admirably fitted to 
 attain His object. Such is the explanation — the only possible 
 explanation, of the subserviency of mechanism to chemistry, in 
 the processes of organic life. And what is this explanation, but 
 our argument of design, in terms that seem absolutely irresisti- 
 ble ? 
 
 Thirdly. That perpetual renovation and decay to which all or- 
 ganized beings arc liable, may be considered as a part only of the 
 great round of changes, which we witness in everything that has 
 been created. The world itself, as we have seen, appears to 
 have been, at intervals, subjected to changes involving even the 
 fundamental laws by which it is governed. Nothing, therefore, 
 belonging to the world, can reasonably be expected to be perma- 
 nent. Had there been even an approach to such permanence, the 
 beautiful adaptations of organized beings to the pre-established laws 
 of inanimate matter, and all the other wonderful arrangements we 
 have described, could not have been manifested as they now are. 
 Besides, to the changes we ourselves undergo, we are nidebted for 
 the greater part of the enjoyments of our life. If none died, none 
 could be born ; and the present arrangements of human society 
 could have no existence. There would be none of the pleasing 
 relations of parent and offspring ; none of the agreeable variety of 
 childhood, of youth, of maturity, and of age, experienced by 
 
RECAPITULATION AND REFLECTIONS. 291 
 
 every individual ; which, with all the other numerous relations 
 of society, incidental to the persons of different individuals, con- 
 tribute so largely to human happiness. Were man exempt from 
 change ; whether the rest of the world were supposed to be pro- 
 gressive, as it is ; or whether it were stationary, as regards him ; 
 the same uniform and dull monotony would prevail, the same 
 want of motive. In short, with our present constitution and feel- 
 ings, perpetuity and uniformity would be physically and morally 
 impossible. 
 
 But why, it has a thousand times been asked, why has the 
 world been so constituted ? AV-hy this unceasing round of change ? 
 Whence its origin? AVhat its object? — Such questions, the 
 Great Author of the universe alone can answer. But as within 
 those narrow limits by which our observations are bounded, 
 wherever we can trace His desii^ns, we see that His works are 
 never without an object ; we cannot doubt that in determining 
 their perpetual change, there is no less an object ; though it be 
 above our comprehension. By placing immaterial and intelligent 
 beings, for a time, in personal connection with matter, He has 
 indeed communicated to them a knowledge of those properties of 
 matter which so strikingly display His wisdom and power; and 
 this may have been one of His objects :~but to speculate further 
 on points so utterly beyond our capacity, would be presumptuous : 
 for who can "know the mind of God, or who hath been His 
 counsellor ?" 
 
 We have thus given a brief outline of what has been denomi- 
 nated the Chemistry of organization ; in other words, an account 
 of those changes and combinations which, through the operation 
 and. the agencies of inorganic matter, organic agents are capable 
 of effecting. The information it has been in our power to give, 
 though imperfect, we have shown to be amply sufficient, not only 
 to demonstrate the astonishing wisdom, and foresight, with which 
 organized beings, in as far as we can understand them, have been 
 contrived and formed ; but the infinitely higher perfection of both 
 these attributes, requisite to impart to organization that vitality, 
 the nature of which so entn*ely surpasses our conception'. 
 
 We shall now close this volume with a few observations on 
 the future progress of chemistry ; on the means by which this 
 science may be applied to physiological research ; and on the 
 tendency of physical knowledge in general. 
 
 Chemistry, as we pointed out in the introduction to this treatise, 
 forms the connecting link between those branches of human 
 knowledge which are founded on quantity, and those which are 
 derived solely from experience. All our experimental knowledge 
 that is not chemical ; for instance, all that physiology which re- 
 
292 CHEMISTRY OF ORGANIZATION. 
 
 lates to the phenomena of life, is wholly removed from the logic 
 of quantity, and depends entirely on observation. Now so far as 
 the logic of quantity is applicable, so far are we certain of our 
 conclusions, as certain at least as we are of our own existence, or 
 that we see and hear. But when this logic cannot be applied, 
 our conclusions are no longer such as imist be — no longer follow 
 from our premises a necessary consequence ; but are only, for the 
 most part, such as may be ; that is to say, have no more than 
 that degree of probability which arises from the evidence we have 
 of the truth of the phenomena or events, forming our premises. 
 
 In all knowledge depending on mere observation or experiment, 
 what we know, is grounded on our own observation and experi- 
 ence, or on the observation and experience of others. What 
 we ourselves observe, we too often observe very imperfectly; or 
 do not understand, wdien observed. But phenomena or events, 
 the knowledge of which we are obliged to receive at second hand, 
 on the testimony of others ; and which may have been observed 
 through the distorted medium of ignorance or of prejudice — may 
 even have been wilfully misrepresented — of these we have a still 
 less assurance. If a phenomena or event has happened only once, 
 and be therefore historical; we are under the necessity of acquies- 
 cing in its truth, or of estimating its probability, according to the 
 rules of evidence. If the phenomenon or event be of frequent oc- 
 currence, or if its nature be such, that it is capable of being brought 
 under our own observation ; in order to remove our uncertainty, 
 we endeavour to observe it ourselves ; in short, we make an ex- 
 periment. Such is the method we pursue, in obtaining all that 
 knowledge which is the result of mere observation. The differ- 
 ent events succeed one another, but we know not wherefore ; we 
 see not their mutual connexion. We believe that an event will, 
 probably, follow another event ; because the one event has always 
 followed the other, or because of some other probability ; but we 
 cannot discover that 7iecc55o?'?/ connexion between the two events, 
 which so irresistibly leads us to determinate conclusions, where 
 we can apply the laws of quantity. 
 
 The foregoing remarks may be viewed as a continuation of 
 those offered in the introduction to this volume, and chiefly relate 
 to the progress of chemistry. Chemistry being a science of ob- 
 servation, we can form but a very imperfect conception of its fu- 
 ture progress; because, we cannot, by reasoning, anticipate the 
 discovery of those chemical facts which are yet concealed. The 
 progress that chemistry, within these k\v years, has made, is truly 
 astonishing ; and when a more rigorous mode of observation shall 
 be adopted — in short, when chemistry shall be brought more under 
 the control of the laws of quantity — a control that will be exer- 
 
CONCLUSION. 293 
 
 cised, at least indirectly — it is impossible to foretell the degree of 
 perfection which chemistry, as a science, may attain. But, for 
 many years yet to come, the progress of chemistry must depend 
 solely on experiment ; and its cultivators must be satisfied with 
 the comparatively humble oflice, of discovering the actual chemi- 
 cal changes, which bodies effect on each other. 
 
 Since, then, in knowledge derived from observation, an acquaint- 
 ance with what exists, and with ivhat is done, is indispensable ; 
 to obtain a clear, accurate, and unequivocal conception of these 
 things, is the first duty of every observer, and of every experimen- 
 talist. Nor is there any observer, or experimentalist, however 
 unpretending, who may not add to the stock of ascertained facts ; 
 so varied and inexhaustible are the stores of nature. Another duty 
 of every one who engages in observation or experiment, is to be- 
 come the faithful historian of what he witnesses ; to narrate the 
 event or phenomenon in plain and intelligible language, employ- 
 ing only terms of a definite meaning ; so as to convey to others a 
 just notion of what he has seen. We say a just notion; in the 
 greater number of instances, a perfect notion is impossible ; be- 
 cause what is seen, cannot be expressed by language. But to give 
 a just notion ; that is to say, a notion which, though incomplete, 
 has 710 foreign or false gloss, is within the power of every ob- 
 server ; and to give such a notion of the facts he narrates, ought 
 to be his chief study. One testimony of so faithful a witness is 
 often invaluable, and worth a thousand vague and inaccurate ob- 
 servations ; which are only calculated to bewilder, or to mislead ; 
 and thus are worse than useless. 
 
 The next rule which an interpreter of nature should bear in 
 mind, is not to attempt too much at first ^ but in order to estab- 
 lish a sure foundation for his succeeding labours, he ought to be 
 content with obvious and unexceptionable facts ; and so to arrange 
 these facts, as to lead to others. To elicit novel and prominent 
 facts, is the lot of few ; and any one may happen to be so success- 
 ful. But all, as before stated, may investigate truth ; and thus 
 contribute more or less towards the advancement of knowledgfe. 
 Moreover the humblest contributors may rest assured, that they 
 imperceptibly raising a structure, which will sooner or later in- 
 clude the conspicuous labours of their more fortunate coadjutors ; 
 in which structure, these labours will indeed still appear conspi- 
 cuous ; though their importance will be diminished as the fabric 
 is extended around them. 
 
 The remarks just made, have especial reference to the applica^ 
 tion of chemistry to physiology. The cautious and judicious ap- 
 plication of chemistry to physiology has already effected much, 
 and is capable of effecting still more. Indeed it is hardly possible 
 to say, how far chemistry may extend physiological knowledge, 
 
 25* 
 
294 CHEMISTRY OF ORGANIZATION. 
 
 But chemistry, in its present state, in order to be made really use- 
 ful, must'be applied in a manner the most guarded and sparing- 
 must, indeed, be rigidly confined to the ascertainment of what the 
 living principle does ; and how it operates on inorganic princi- 
 ples. With the living, the animative properties of organized bo- 
 dies, chemistry has not the smallest alliance ; and probably will 
 never, in any degree, elucidate these properties. The phenomena 
 of life, are not, even remotely, analogous to anything we know in 
 chemistry, as exhibited among inorganic agents. The great error 
 of chemists, therefore, has been their attempting to apply that 
 science to explain phenomena, for the explanation of which, che- 
 mistry, as we have said, is totally valueless. Such perversion of 
 the reasoning powers, has too much prevailed among physiologists 
 in all ages. In the earlier ages, heat was considered the principle 
 or life. In later times, electricity has been discovered ; and to 
 electricity, the same functions have been ascribed. Life, accord- 
 ing to other philosophers, is motion. But the progress of science 
 has dispelled all these illusions : the origin of the obscure and eva- 
 nescent principle of life, must be sought elsewhere. By heat, for 
 example, many wonderful things may be accomplished; but heat 
 will not act itself. The powers of electricity are still more won- 
 derful than those of heat : but electricity, we know to be governed, 
 in its mode of action, by certain laws, and that it gives no sign of 
 intelligence. In the same manner, life, as we are acquainted with 
 it, cannot exist without motion ; but motion can exist without life. 
 Life and motion, consequently, are not synonymous terms ; nor 
 can we conceive the existence of motion, without a mover. In 
 short, the living principle, as already pointed out, is something 
 difierent from, and superadded to the common agencies of matter; 
 over which, to a certain extent, it has a control. Thus, the phe- 
 nomena exhibited by the mysterious agency of life, are strictly 
 comparable only with one another ; and have no relation to any 
 inorganic phenomena. 
 
 But the desire of the Physiologist to ascribe to the agencies of 
 inorganic matter, those operations carried on wiiliin living bodies, 
 is merely a display of that innate propensity of the human mind, 
 which leads us to seek after First Causes. The conceptions of 
 the physiologist regarding the principle of life are the same, there- 
 fore, as the conceptions of mankind in all ages regarding the Great 
 First Cause — the Deity himself. The poor untutored savage 
 *' sees God in every cloud, and hears him in the wind." The 
 complacent philosopher smiles at the credulity of the savage, and 
 perhaps defies " the laws of nature !" Both are alike ignorant; 
 nor is the imagined Supreme Being of the untaught savage, in any 
 degree, more absurd, than the imagined Pantheism of the philo- 
 sopher. The winds we know can be referred to other causes, to 
 
CONCLUSION. 295 
 
 which they are immediately owing : so with the progress of know- 
 ledge, the "laws of nature," have been found to merge, and will 
 continue to be found to merge, into other laws, still more general ; 
 thus proving that these laws are, all alike, mere delegated agencies. 
 Hence the tendency of knowledge, and of its due application, is 
 to abstract the attention from inferior things, and to fix the mind 
 on the source of all knowledge and of all power — the Great First 
 Cause ; who exists and acts throughout the universe ; whom we 
 can approach only, by studying His works ; and whose works, an 
 eternity, will be inadequate to explore. 
 
APPENDIX 
 
 CONTAINING 
 
 ADDITIONAL NOTES AND EMENDATIONS. 
 
 Page 33. " Forces of Gravitation." — Many objections have 
 been offered to the term vis inertise adopted by Newton. In- 
 deed, to speak of mere inertia, or inactivity, as a force, is ob- 
 viously absurd. We have always agreed with those who think 
 that the term inertia has been unfortunately chosen ; since inertia 
 expresses only one quality, as it were, of that which is attracted, 
 or which reacts, in nature. But, we fully acquiesce in the 
 opinion, that whatever resists attraction or reacts, is as appro- 
 priately named a force, in a certain sense of that term, as that 
 which attracts or acts ; and such resistance is in all instances, 
 virtually considered as a force by the mathematician, however he 
 may choose to designate it. 
 
 Page 42. We fear the terms chemical and cohesive axes are 
 not quite legitimate. We have employed these and other familiar 
 modes of expression, such as ^^ forces of gravitation," "polar- 
 izing forces,'^ &c. above alluded to, either on account of the 
 general reader, for whom this work is principally intended, or 
 for the sake of analogy. 
 
 Page 50. — Elementary form of electrical energies, &c. 
 Throughout this work, as just observed, we have adhered as 
 much as possible to the common language ot chemistry. We 
 conceive, however, that chemical, and the allied, phenomena 
 admit of being expressed in terms of hypotheses, of which the 
 chief are the following : — 
 
 1. That every portion of matter attracts, and is attracted by, 
 every other portion of matter, according to laws which have ob- 
 tained universal assent. 
 
 2. That all matter, as it is known to us, exists in the condition 
 of molecules ; which molecules we consider to be virtually 
 spheres or spheroids. 
 
 3. That all the spherical or spheroidal molecules, when unim- 
 peded, revolve on their axes, with velocities, which in molecules 
 having the same weight, are under similar circumstances, fixed 
 and definite ; but which velocities, in molecules of different 
 
298 APPENDIX. 
 
 weights, increase, according to a law which need not be here 
 specified, as the weights of the molecules diminish. 
 
 4. That the molecules of the imponderable matters,, liglit and 
 heat, are vastly less than those of any ponderable substance ; 
 hence, that the velocities of the molecules composing these im- 
 ponderable matters, are inconceivably rapid ; further, that the 
 substance of these molecules is either fluid or elastic, so that 
 they become more or less oblate, in proportion to the intensity 
 of their motion. 
 
 5. That the imponderable molecules of light and heat obey the 
 same laws by which ponderable matters are governed ; but that 
 these imponderable molecules are capable of pervading and ope- 
 rating within ponderable molecules, whose motions they influ- 
 ence by the intensity of their own motion; and that the mole- 
 cules of imponderable matters thus appear in the character of 
 agents. 
 
 Page 64, note. — The term "homogeneous" light is a mis- 
 print : we mean the unaltered light of the sun. Light and heat, 
 and indeed all self-repulsive fluids may be supposed to possess 
 two kinds of self-repulsive power: that which is common to 
 them as fluids ; and that which depends upon the action of indi- 
 vidual molecules of such fluids when in certain positions, and 
 which positions, these molecules are naturally inclined to assume 
 under certain circumstances, particularly when in motion. Hence 
 the marshalling of the individual molecules of light, supposed in 
 this note, probably do not exist, at least so as to become apparent, 
 till the light approaches, or passes through some ponderable me- 
 dium. These phenomena of light, may perhaps, be rendered 
 more intelligible, by what appears to happen with respect to 
 gaseous bodies. The rapidity of the motion of gaseous bodies, 
 through any permeable medium, increases as their specific gravity 
 diminishes. Thus the force with which, the lightest of these 
 bodies, hydrogen, struggles to escape through any porous matter, 
 is almost incredible ; according to Mr. Graham's experiments, 
 suflicient to raise a column of water from 20 to 30 inches. This 
 rapidity of motion seems only explicable on the supposition, that 
 the individual molecules of the gas, in their passage through nar- 
 row canals, are guarded from external and lateral influence ; and 
 are thus enabled to assume that position which is natural to them, 
 and in which their mutual self-repulsion is the greatest possible. 
 Hence, a single row of self-repulsive molecules of gas (or other 
 self-repulsive fluid) passing through the minute apertures of a 
 porous vessel into a vacuum, or what is analogous, into another 
 gas liaving diflerent self-repulsive powers, may be compared to a 
 row of bullets urged by an elastic fluid, in quick succession 
 through a gun barrel : but with this difl'erence, that the gaseous 
 
APPENDIX. 299 
 
 molecules propel each other ; instead of being, like the bullets, 
 propelled by a foreign agency. The explanation now offered of 
 the passage of the molecules of a gas through a narrow canal, or 
 through any porous matter, may, as we have said, be applied, 
 not only to the passage of light and heat through various media; 
 but also to the passage of liquids through various bodies, by the 
 processes which have been termed endosmose and exosmose. 
 Do these forces operate also in capillary attraction ? 
 
300 
 
 APPENDIX. 
 
 Page 131 TABLE OF TEMPERATURES.— (from 
 
 Isother- 
 mal 
 
 Zones. 
 
 o 
 
 o 
 
 ♦J 
 
 o 
 
 CO 
 
 o 
 o 
 
 c 
 o 
 
 O 
 
 o 
 o 
 
 ttl 
 
 <y 
 C 
 o 
 
 
 o 
 
 Names of Places. 
 
 Position. 
 
 Latitude 
 Nortli. 
 
 Longitude. 
 
 Height 
 In Feet. 
 
 Nain - - - 
 *Enontekies - - 
 Hospice de St. ^ 
 Gothard - 5 
 North Cape 
 *Uleo - - - 
 *Umeo - - - 
 *St. Petersburg - 
 Drontheim - - 
 Moscow - - 
 Abo - - - - 
 
 *Upsal - - - 
 
 ^Stockholm - - 
 
 Quebec - - - 
 
 Christiana - - 
 ^Convent of ? 
 
 Peysenburg 3 
 *Copenliagen 
 
 *Kendal - - - 
 
 Malouine Islands 
 
 * Prague - - - 
 
 Goltingen - - 
 
 ■'^Zurich - - - 
 
 'Edinburgh - - 
 
 Warsaw - - 
 
 *Coire - - - 
 
 Dublin - - - 
 
 Berne - - - 
 
 ^Geneva - - - 
 
 ^Manlieini - - 
 
 Vienna - - - 
 
 57^ 
 
 ' 8' 
 
 68 
 
 30 
 
 46 
 
 30 
 
 71 
 
 
 
 65 
 
 3 
 
 63 
 
 50 
 
 59 
 
 56 
 
 63 
 
 24 
 
 55 
 
 45 
 
 60 
 
 27 
 
 59 
 
 51 
 
 59 
 
 20 
 
 46 
 
 41 
 
 59 
 
 55 
 
 47 
 
 47 
 
 55 
 
 41 
 
 54 
 
 17 
 
 51 
 
 25 
 
 50 
 
 5 
 
 51 
 
 32 
 
 47 
 
 22 
 
 55 
 
 57 
 
 52 
 
 14 
 
 46 
 
 50 
 
 53 
 
 21 
 
 46 
 
 5 
 
 46 
 
 12 
 
 49 
 
 29 
 
 48 
 
 12 
 
 17 
 
 18 
 71 
 10 
 
 10 
 
 12 
 2 
 
 59 
 
 14 
 9 
 8 
 3 
 
 21 
 9 
 6 
 7 
 6 
 8 
 
 16 
 
 Mean 
 Tempe- 
 rature 
 of the 
 Year. 
 
 61°20'w 
 
 
 
 20 47 E 
 
 1356 
 
 8 23 E 
 
 6390 
 
 25 50 E 
 
 
 
 25 26 E 
 
 
 
 20 16 E 
 
 
 
 30 19 E 
 
 
 
 10 22 E 
 
 
 
 37 32 E 
 
 970 
 
 22 18 E 
 
 
 
 38 E 
 
 
 
 3 E 
 
 
 
 10 w 
 
 
 
 48 E 
 
 
 
 34 E 
 
 3066 
 
 35 E 
 
 
 
 46 w 
 
 
 
 59 w 
 
 
 
 24 E 
 
 
 
 53 E 
 
 456 
 
 32 E 
 
 1350 
 
 10 w 
 
 
 
 2 E 
 
 
 
 30 E 
 
 1876 
 
 19 w 
 
 
 
 26 E 
 
 1650 
 
 8 E 
 
 1080 
 
 28 E 
 
 432 
 
 22 E 
 
 420 
 
 26.42° 
 26.96 
 
 30.38 
 
 32.00 
 35.08 
 33.26 
 
 38.84 
 39.92 
 40.10 
 
 40.28 
 
 42.80 
 42.26 
 41.74 
 42.08 
 
 42.98 
 
 45.68 
 46.22 
 46.94 
 49.46 
 46.94 
 47.84 
 47.84 
 48.56 
 48.92 
 49.10 
 49.28 
 49.28 
 50.18 
 50.54 
 
 (*) At the Places thus distinguished, the Ten^.peratures 
 
APPENDIX. 
 
 301 
 
 ENCYCLOPfEDIA METROPOLITANA. — ARTICLE METEOROLOGY.) 
 
 given are the result of at least 8000 observations. 
 
 26 
 
 
 
 
 
 Maximum 
 
 Distribution of Heat in the different Seasons. 
 
 and 
 Minimum. 
 
 Mean temp, 
 of Winter. 
 
 Mean temp. 
 
 of Spring. 
 
 * 
 
 Mean temp, 
 of Summer. 
 
 Mean temp, 
 of Autumn. 
 
 Mean temp. 
 
 of warmest 
 
 Month. 
 
 Mean temp. 
 
 of coldest 
 
 Month. 
 
 —0.60° 
 
 23.90° 
 
 48.38° 
 
 33.44° 
 
 51.80° 
 
 — 11.28° 
 
 + 0.68 
 
 24.98 
 
 54.86 
 
 27.32 
 
 59.54 
 
 —0.58 
 
 18.32 
 
 26.42 
 
 44.96 
 
 31.82 
 
 46.22 
 
 + 15.08 
 
 23.72 
 
 29.66 
 
 43.34 
 
 32.08 
 
 46.58 
 
 22.10 
 
 11.84 
 
 27.14 
 
 57.74 
 
 35.96 
 
 61.52 
 
 7.70 
 
 12.92 
 
 33.80 
 
 54.86 
 
 33.44 
 
 62.60 
 
 11.48 
 
 17.06 
 
 38.12 
 
 62.06 
 
 38.66 
 
 65.66 
 
 8.60 
 
 23.72 
 
 35.24 
 
 61.24 
 
 40.10 
 
 64.94 
 
 19.58 
 
 10.78 
 
 44.06 
 
 67.10 
 
 38.30 
 
 70.52 
 
 6.08 
 
 20.84 
 
 38.30 
 
 61.88 
 
 40.64 
 
 
 
 
 
 24.98 
 
 39.38 
 
 60.26 
 
 42.80 
 
 62.42 
 
 22.46 
 
 25.52 
 
 38.30 
 
 61.88 
 
 43.16 
 
 64.04 
 
 22.82 
 
 14.18 
 
 38.84 
 
 68.00 
 
 46.04 
 
 73.40 
 
 13.81 
 
 28.78 
 
 39.02 
 
 62.69 
 
 41.18 
 
 56.74 
 
 28.41 
 
 28.58 
 
 42.08 
 
 58.46 
 
 42.98 
 
 59.36 
 
 30.20 
 
 30.74 
 
 41.18 
 
 62.60 
 
 48.38 
 
 65.66 
 
 27.14 
 
 30.86 
 
 45.14 
 
 56.84 
 
 46.22 
 
 58.10 
 
 34.88 
 
 39.56 
 
 46.58 
 
 53.06 
 
 48.46 
 
 55.76 
 
 37.40 
 
 31.46 
 30.38 
 
 47.66 
 44.24 
 
 68 90 
 
 ^0 1ft 
 
 
 
 VIO *v7\J 
 
 64.76 
 
 tl v - X o 
 
 48.74 
 
 66.38 
 
 29.66 
 
 29.66 
 
 4820 
 
 64.04 
 
 48.92 
 
 65.66 
 
 26.78 
 
 38.66 
 
 46.40 
 
 58.28 
 
 48.56 
 
 59.36 
 
 38.30 
 
 28.76 
 
 47.48 
 
 69.08 
 
 49.46 
 
 70.34 
 
 27.14 
 
 32.36 
 
 50.00 
 
 63.32 
 
 50.30 
 
 64.58 
 
 29.48 
 
 39.20 
 
 47.30 
 
 59 54 
 
 50.00 
 
 61.16 
 
 35.42 
 
 32.00 
 
 48.92 
 
 66.56 
 
 49.82 
 
 67.28 
 
 30.56 
 
 34.70 
 
 47.66 
 
 64.94 
 
 50.00 
 
 66.56 
 
 34.16 
 
 38.80 
 
 49.64 
 
 67 10 
 
 49.82 
 
 68.72 
 
 33.44 
 
 32.72 
 
 51.26 
 
 69.26 
 
 50.54 
 
 70.52 
 
 26.60 
 
302 
 
 APPENDIX. 
 
 TABLE OF TEMPERATURES. 
 
 Isother- 
 
 
 
 Posit 
 
 ion. 
 
 
 Mean 
 Tempe- 
 
 
 
 
 
 
 Names of Places. 
 
 
 
 
 Height 
 
 rature of 
 
 Zones. 
 
 
 Latitude. 
 
 Longitude. 
 
 the 
 Year. 
 
 
 
 
 
 
 in feet 
 
 
 
 *Clermont - - 
 
 45°46' 
 
 3° 
 
 5'e 
 
 1260 
 
 50.00° 
 
 
 *Buda - - - 
 
 47 29 
 
 19 
 
 lE 
 
 494 
 
 51.08 
 
 o* 
 
 Cambridge, (U. S.) 
 
 42 25 
 
 71 
 
 3 w 
 
 
 
 50.36 
 
 05 
 
 *Paris - - - 
 
 48 50 
 
 2 
 
 20 E 
 
 222 
 
 51.08 
 
 O 
 
 ^London - - 
 
 51 80 
 
 
 
 5 w 
 
 
 
 50.36 
 
 o 
 o 
 
 Dunkirk - - 
 
 51 2 
 
 2 
 
 22 E 
 
 
 
 50.54 
 
 s 
 
 o 
 
 «J2 
 
 Amsterdam - - 
 
 52 22 
 
 4 
 
 50 E 
 
 
 
 51.62 
 
 Brussels - - 
 
 50 50 
 
 4 
 
 22 E 
 
 
 
 51.80 
 
 09 
 
 *Franeker - - 
 
 52 36 
 
 6 
 
 22 E 
 
 
 
 51.80 
 
 c 
 o 
 
 Philadelphia 
 
 39 56 
 
 75 
 
 16 w 
 
 
 
 53.42 
 
 N 
 
 New York 
 
 40 40 
 
 73 
 
 58 w 
 
 
 
 53.78 
 
 13 
 
 '^Cincinnati - - 
 
 39 6 
 
 82 
 
 40 w 
 
 510 
 
 53.78 
 
 
 St. Malo - - 
 
 48 39 
 
 2 
 
 1 w 
 
 
 
 54.14 
 
 o 
 
 Nantes - - - 
 
 47 13 
 
 1 
 
 32 w 
 
 
 
 54.68 
 
 1— < 
 
 Pekin - - - 
 
 39 54 
 
 116 
 
 27 E 
 
 
 
 54.86 
 
 
 *Milan - - - 
 
 45 28 
 
 9 
 
 11 E 
 
 390 
 
 55.76 
 
 
 Bordeaux - - 
 
 44 50 
 
 
 
 34 w 
 
 
 
 56.48 
 
 a> o 
 
 Marseilles - - 
 
 43 17 
 
 5 
 
 22 E 
 
 
 
 59.00 
 
 
 Montpellier 
 
 43 36 
 
 3 
 
 52 E 
 
 
 
 59.36 
 
 2 o 
 
 *Rome - - - 
 
 41 53 
 
 12 
 
 27 E 
 
 
 
 60.44 
 
 1- »o 
 
 Toulon - - - 
 
 43 7 
 
 5 
 
 50 E 
 
 
 
 62.06 
 
 
 Nangasacki 
 
 32 45 
 
 129 
 
 55 E 
 
 
 
 60.80 
 
 o 2 
 
 *Natchez - - 
 
 31 28 
 
 90 
 
 30 w 
 
 180 
 
 04.76 
 
 
 *Funchal - - 
 
 32 37 
 
 16 
 
 56 w 
 
 
 
 68.54 
 
 ^ CO ^ 
 
 Algiers - - - 
 
 36 48 
 
 3 
 
 1 E 
 
 
 
 69.98 
 
 
 
 
 
 
 
 
 3 s 
 
 *Cairo - - . 
 
 30 2 
 
 31 
 
 18e 
 
 
 
 72.32 
 
 §-2 • 
 
 ^Vera Cruz - - 
 
 19 11 
 
 96 
 
 1 w 
 
 
 
 77.72 
 
 
 *Havannah - - 
 
 23 10 
 
 82 
 
 13w 
 
 
 
 78.08 
 
 00 o 
 
 ^Cumana - - - 
 
 10 27 
 
 65 
 
 15 w 
 
 
 
 81.86 
 
 At the places thus distinguished, the Temperatures 
 

 
 APPENDIX. 
 
 
 3US 
 
 
 
 (continued.) 
 
 
 
 
 
 
 1 
 
 Maximum 1 
 
 Distribution of Heat 
 
 in Different Seasons. | 
 
 an 
 
 d 
 
 
 
 
 
 Minimum. 
 
 Mean temp. 
 
 Mean temp. 
 
 Mean temp. 
 
 Mean temp. 
 
 Mean temp. 
 ofwarinest 
 
 Mean temp, 
 of coldest 
 
 of winter. 
 
 of spring. 
 
 of summer. 
 
 of autumn. 
 
 Month. 
 
 Month. 
 
 34.52° 
 
 50.54° 
 
 64.40° 
 
 51.26° 
 
 60.20° 
 
 28.04° 
 
 33.98 
 
 51.08 
 
 70.52 
 
 52.34 
 
 71.60 
 
 27.78 ■ 
 
 33.98 
 
 47.66 
 
 70.70 
 
 49.82 
 
 72.86 
 
 29.84 
 
 38.66 
 
 49.28 
 
 64.58 
 
 51.44 
 
 65.30 
 
 36.14 
 
 39.56 
 
 48.56 
 
 63.14 
 
 50.18 
 
 64.40 
 
 37.76 
 
 38.48 
 
 48.56 
 
 64.04 
 
 50.90 
 
 64.76 
 
 37.75 
 
 36.86 
 
 51.62 
 
 65.84 
 
 51.62 
 
 66.92 
 
 35.42 
 
 36.68 
 
 53.24 
 
 66.20 
 
 51.08 
 
 67.28 
 
 35.60 
 
 36.68 
 
 51.08 
 
 67.28 
 
 54.32 
 
 69.08 
 
 32.90 
 
 32.18 
 
 51.44 
 
 73.94 
 
 56.48 
 
 77.00 
 
 32.72 
 
 29.84 
 
 51.26 
 
 79.16 
 
 54.50 
 
 80.78 
 
 25.34 
 
 32.90 
 
 54.14 
 
 72.86 
 
 54.86 
 
 74.30 
 
 30.20 
 
 42.26 
 
 52.16 
 
 66.02 
 
 55.76 
 
 66.92 
 
 41.74 
 
 40.46 
 
 54.50 
 
 68.54 
 
 55.58 
 
 70.52 
 
 39.02 
 
 26.42 
 
 56.30 
 
 82.58 
 
 54.32 
 
 84.38 
 
 24.62 
 
 36.32 
 
 56.12 
 
 73.04 
 
 56.84 
 
 74.66 
 
 36.14 
 
 42.08 
 
 56.48 
 
 70.88 
 
 56.30 
 
 73.04 
 
 41.00 
 
 45.50 
 
 57.56 
 
 72.50 
 
 60.08 
 
 74.66 
 
 44.42 
 
 44.06 
 
 56.66 
 
 75.74 
 
 60.98 
 
 78.08 
 
 42.08 
 
 45.86 
 
 57.74 
 
 75.20 
 
 62.78 
 
 77.00 
 
 42.26 
 
 48.38 
 
 60.80 
 
 75.02 
 
 64.40 
 
 77.00 
 
 46.40 
 
 39.38 
 
 57.56 
 
 82.94 
 
 64.22 
 
 86.90 
 
 37.40 
 
 48.56 
 
 65.48 
 
 79.16 
 
 66.02 
 
 79.70 
 
 46.94 
 
 64.40 
 
 65.84 
 
 72.50 
 
 72.32 
 
 75.56 
 
 64.04 
 
 61.52 
 
 65.66 
 
 80.24 
 
 72.50 
 
 82.76 
 
 60.08 
 
 58.46 
 
 73.58 
 
 85.10 
 
 71.42 
 
 85.82 
 
 56.12 
 
 71.96 
 
 77.90 
 
 81.50 
 
 78.62 
 
 81.86 
 
 71.06 
 
 71.24 
 
 78.98 
 
 83.30 
 
 78.98 
 
 83.84 
 
 69.98 
 
 80.24 
 
 83.66 
 
 82.04 
 
 80.24 
 
 84.38 
 
 79.16 
 
 ■ 
 
 o-iven are the result of at least 8000 observations. 
 
304 APPENDIX. 
 
 Page 163, Note. — We have stated that the diffusion of the 
 same air, and of the same vapour at different temperatures, are 
 inferences only from the supposed general law of the diffusion of 
 gaseous bodies; and have alluded to the existence of modifica- 
 tions of that general law. To those who feel an interest in such 
 inquiries, the following additional remarks may be not unaccepta- 
 ble, as pointing out the grounds from which we infer such diffu- 
 sion of the same air and vapour ; and the modifications, to which 
 we have no doubt, it will be found to be liable. 
 
 Let us suppose a flexible air-tight bag to be furnished with a 
 stop-cock ; and to be filled with hydrogen gas, under exactly 
 the same pressure, and having the same temperature as the sur- 
 rounding atmosphere. Let us now suppose the stop-cock to be 
 opened. Lumediately, the hydrogen in the bag, and the exterior 
 atmospheric air, will begin to commingle, with a force and velo- 
 city proportional to the quantity of the gas diffused ; and which 
 quantity varies inversely as the square roots of the specific gravi- 
 ties of hydrogen gas, and of atmospheric air ; that is to say, the 
 volume of atmospheric air diffused inwards, being supposed to be 
 equal to J, the volume of hydrogen diffused outwards, will be 
 equal to 3.8 nearly. The diffusion of hydrogen and atmospheric 
 air of the same temperature, and under the same pressure, is an 
 instance of the simplest form of gaseous diffusion ; and is, we 
 believe, the only form of diffusion, which has been experimentally 
 investigated. The phenomena attending the diffusion of these 
 two bodies show, that, all other circumstances being supposed to 
 be alike, the diffusion of gases is influenced solely by the differ- 
 ence of their specific gravities. 
 
 We have stated the case of the diffusion of two gaseous bodies 
 having the same temperature. Their temperature however, may 
 vary within any limits ; and though the law of diffusion may be 
 modified, diffusion will continue to take place, (except at those tem- 
 peratures at which the specific gravities of the two gases become 
 equal, at which temperatures there will be no tendency to diffu- 
 sion) ; provided difference of specific gravity alone be the cause 
 of diffusion. But if the diflusion of diflerent gases at different 
 temperatures be admitted, it seems to follow, that different por- 
 tions of the same gaseous body under the same pressure, but 
 having different temperatures, and consequently different specific 
 gravities, will likewise have a tendency to diffusion. 
 
 The case we shall next suppose is dissimilar to the two fore- 
 going cases, but is deducible from the same premises ; it is the 
 case of the diffusion of the same vapour, as of the vapour of water, 
 which may be illustrated in the following manner: 
 
 Let us suppose our apparatus to contain atmospheric air, 
 having the temperature of 100°, and saturated with water; while 
 
APPENDIX. 305 
 
 the exterior atmospheric air is at the temperature of 60°, and is 
 likewise saturated with water ; and that the pressure on the air 
 confined in the bag, is the same as the external pressure. We 
 suppose the presence of air in the apparatus, in order that it may 
 be able to sustain the atmospheric pressure ; for, as we formerly 
 stated, vapour alone, at ordinary temperatures, exerts elastic forces 
 very different from, and far inferior to the elastic force of air at 
 these temperatures. Such being supposed to be the state of the 
 air contained in our apparatus, what will happen on the opening 
 of the stop-cock ? The air within the bag will have the same 
 tendency to diffusion, as the contents of the bag supposed in the 
 last case ; but the vapour with which the air is associated will have 
 an opposite tendency. The warmer vapour within the apparatus, 
 instead of being, like the warmer air, lighter; will have a greater 
 specific gravity than the colder vapour associated with the ex- 
 ternal air. Consequently, the inv/ard tendency to diffusion, 
 that is to say, the tendency of the colder vapour without the 
 apparatus, to diffuse itself among the molecules of the warmer 
 vapour within will be greater than the outward diffusive ten- 
 dency of the vapour in the apparatus. Such will be the op- 
 posing diffusive tendencies of warm vapour and of warm air in 
 a state of commixture; and if the air were absent, the diffusive 
 tendency of vapour alone would have a similar diffusive tendency 
 to that which it has, when mixed with air ; though that tendency 
 would, of coarse, be not exactly the same as when modified by 
 the influence of the air. The vapour within, and the vapour 
 without the apparatus, would each exert the elastic forces peculiar 
 to their respective temperatures as vapour. 
 
 There would, however, be a striking difference between the 
 phenomena attending the diffusion of vapour, (whether mixed or 
 unmixed with air), and that of air itself at different temperatures. 
 Two portions of air at different temperatures would cease to have 
 any diffusive tendencies as soon as their temperatures became 
 uniform. The temperature of two portions of vapour becoming 
 uniform, would, of course, produce, in the same manner, a cessa- 
 tion of their diffusive tendencies ; but the circumstances accompa- 
 nying that cessation would be altogether different. The colder 
 vapour v/ithout the apparatus, being the lighter, would move with 
 accelerated velocity into, or toward, the heavier warm vapour 
 within the apparatus ; while that warm vapour, in moving out- 
 ward, would be instantly condensed ; and thus its diffusive pow- 
 ers would be annihilated. On these grounds we advanced the 
 opinion, that probably, there may, under certain circumstances, 
 exist in the atmosphere, a tendency to diffusion from above down- 
 wards ; the vapour in the higher regions of the atmosphere, being 
 relatively lighter than the vapour below. 
 
306 APPENDIX. 
 
 The observations that have been offered in this note, regard the 
 only circumstance which is yet known to cause a difference in 
 this diffusive tendency of gaseous bodies, namely, the difference 
 of their specific gravities. If there be other causes of such differ- 
 ence ; and it is ahnost certain that there is one other cause ; the 
 effects produced by these causes may be very different. The dif- 
 ference in the diffusive power of the same gaseous body, is not 
 perliaps, under any circumstances, very remarkable ; but there 
 will probably be found to be a much greater difference in the dif- 
 fusive power of vapours ; though it is not easy to form even a 
 conjecture as to the extent of that difference. In the present state 
 of uncertainty therefore on those points, we have thought it right 
 to speak of a tendency to diffusion, rather than of diffusion, as a 
 thing actually existing. The diffusive powers of elastic fluids 
 are at present very little understood or appreciated. They con- 
 stitute, however, as we have said, one of the most interesting and 
 important subjects in physics, and would amply repay whoever 
 would take the trouble to investigate them. 
 
 Page 207. — The table follows, illustrating the distribution of 
 plants over the globe, to which we have referred in the text. 
 It has been copied immediately from Lindiey's Introduction to 
 Botany. 
 
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