SMITHSONIAN MISCELLANEOUS COLLECTIONS. 1072 HODGKIXS FUISTD. THE ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. BY FRAISTOIS ALBERT ROLLO RUSSELL, Vice-President of the Royal Meteorological Society, Fellow of the Sanitary Institute of Great Britain, Member of the Boyal Institution of Great Britain, CITY OF WASHINGTON: PUBLISHED BY THE SMITHSONIAN INSTITUTION. 1896. RECAP fiA7^Z R intljeCitpofMfWgork College of ^fj^giciang aniJ ^urgeonji Xibrarp Digitized by the Internet Archive in 2010 with funding from Open Knowledge Commons http://www.archive.org/details/atmosphereinrelaOOruss ii;Dax PART I page Constituents and conditions of the air 3-50 Oxygen 5 Ozone 9 nitrogen 10 Carbon dioxide 11 Vapor of water 16 Pog, smoke, gaseous and solid im- purities in the air 31 Fog 31 Particles suspended in the air 37 living germs in the air .... 38 Sewer air . 41 Air of mines 41 Ground air 42 Org?.nisms, etc. in the open air 4S Microorganisms in rooms .... 42 Sev/er air 43 Vapor and organic matter from living bodies 44 Organic emanations from the sick 45 Organic emanations from the skin 45 Sulphuric and hydrochloric acids^6 Arsenious acid in rain 47 Ammonia in the air 47 ITitric acid in the air 48 Local gaseous impurities — sulphur eted hydrogen -- sewer and drain air 49 Sulphurous acid 49 Carbureted hydrogen 49 Hydrochloric acid 49 Carbon bisulphide 49 Organic vapors 50 Solid artificial impurities . . 50 ? II - Climate, air and health Ilalarious and infectious diseases: their connection with and destruction "by the atmosphere -- the influence of climate Page on national health 51-86 Insiifflation of anthrax, .etc. ... 54 Tuberculosis 54 Typhus 58 The plague 58 | Cholera 59 Diarrhea 60 Typhoid fever , • . 61 , Halaria 62 Yellow fever 63 i Diphtheria 64 i Pneumonia 65 j Bronchitis 66 | Rheumatism and rheumatic fever . . .66 ; I lea si es and v/ho oping cough 67 ] Dengue 67 | Smallpox 67 Influenza 68 Colds 70 I Seasonal and geographical distribu- | tion of infectious diseases . . 72 \ Conditions of infection through the air 73 ] Prevention of spread and j prevalence of various i maladies 77 \ Ilalaria class .... 77 ' Cholera " .... 77 i Typhus " .... 77 Measles " .... 78 Importance of fresh air to horses aiid cattle ... .78 , Influence of climate on mental and ; physical qualities and on nation- 1 al health 79 j ! Kental and physical quali- i ties in relation to cli- ! mate 83 i Mode of attck of miasmatic I diseases 84 PART III Page Various atmospheric conditions and phe- nomena 87-117 Temperature and health 87 Dry climates and health 87 Health at high altitudes 88 Sea air and health 88 The improvement of climate v/ith slight elevation 89 Effect of impurities in the air of tov/ns on mental and bodily health 90 Wind force and health in a large town 94 Dew and frost — exhalation of vajjor from the earth 95 Exhalation of gases and particles from the earth 96 Ground air ► . . 98 Emanation of organic particles from evaporating fluids 99 Permeation of "building materials by air and vapor 100 Mechanical ventilation in schools . 101 Aeration and self -purification of rivers 102 Action of bacteria and of the air in connection with decomposition and plant growth 104 Influence of weather on insect pests 106 Action of plants on the air .... 107 The influence of forests on climate 107 Certain physical qualities of the at- mosphere , 108 Propagation of sound in air 109 Aurora borealis and australis . . . .110 Meteors and aerolites 112 Atmospheric tides 112 The zodiacal light 113 Height of the atmosphere 113 Atmospheric dust and the reflection of light 113 Sunlight and earth's atmosphere -- absorption and reflection .... 114 Winds and temperature at great heights 115 Range of temperature at great heightsll6 Electricity at high altitudes • • . ..116 Atmospheric currents above 40,000 i'eet • 116 PART IV Page Subjects for research 117-148 The bearing of atmospheric influ- ences on plants 125 A'bsorx)tion and emission of water from the leaves of plants . . . .128 I.Ialaria , 129 Cholera 130 Yellow fever 130 The plague, typhus, typhoid and pneu- monia 130 Diphtheria 131 Scarlet fever, measles, whooping- cough, influenza, and smallpox . 131 Infectious, contagious, epidemic, and endemic diseases in general 131 Exploration of the atmosphere in con- nection with weather forecasts and a more exact knowledge of atmospheric conditions 136 Electricity, clouds, and rain , . . 137 Overcooling, etc 138 Distribution of vapor clouds . . . .139 Sound in air 140 Position of the planets, sun spots, aurorae, weather, and crops . , .140 Aerolites 140 Limits of the atmosphere 141 Absorption of the spectrum 141 Combined forecasting 141 On some possible modifications of climate by human agency 142 Symon's British rainfall ..... .145 SMITHSONIAN MISCELLANEOUS COLLECTIONS. hodgki:ns fui^d. THE ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH, BY FRANCIS ALBERT ROLLO RUSSELL, Vice-President of the Royal Meteorological Society, Fellow of the Sanitary Institute of Great Britain, Member of the Royal Institution of Great Jiritain. per\ • 4li orbbH? CITY OF WASHINGTON: PUBLISHED 1!Y THE SMITHSONIAN INSTITUTION. 1896. THE ATMOSPHERE IIT RELATION TO HUMAK LIFE AND HEALTH. By Francis Albert Rollo Russell,* Vice-President of the Boyal Meteorological Society, Fellow of the Sanitary Institute of Great Britain, Member of the Royal Institution of Great Britain. [Memoir Hubmitted in the Hodgkins Fund Prize competition of the Smitlisoniaa Institution, and awarded honorable ruentioa with a silver medal.] Part I. — Constitution and Conditions of the Air. The atmosphere has been compared to a great ocean, at the bottom of which we live. But the comparison gives do idea of the magnitude of this ocean, without definite bounds, and varying incessantly in den- sity and other important qualities from depth to height and from place to place. Uninterrupted by emergent continents and islands, the atmosphere freely spreads high above all mountains and flows ever in mighty cur- rents at levels beyond the most elevated regions of the solid earth. What is the composition of this encompassing fluid, and what its char- acter? The work of the present century has gathered in a rich store of knowledge to answer the inquiry. The atmosphere consists in the main of two gases, oxygen and nitro- gen, and these are intimately mixed in the proportion of about 20.9 of oxygen to 79.1 of nitrogen by volume, and 23.1 of oxygen to 76.9 of nitrogen by weight. ^ These gases, which are each of them chemical ele- ments, are not chemically combined with one another, but only mixed; each preserves its qualities, modified only by solution in the other. Gases have the property of diffusing among each other so comj^letely, that no portion which could be conveniently taken, however small, would fail to represent the two gases in a proportion corresponding with that which they maintain in the whole atmosphere. Another valuable constituent of the atmosphere, though varying greatly in amount at different times and places, is of no less impor- ' Author of "Lonilon Fogs," "Epidemics, Plagues, and Fevers; their Causes and Prevention," " The Spread of Influenza," "Observations on Dew and Frosts," etc. -M. Leduc gives the weights as follows: Oxygen, 23.58; nitrogen, 76.42. Dumas and Boussingault give the density of nitrogen as 0.09725. (Comptes Eendus, 1890.) 3 4 ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. tance to maakind than the two elemeutary gases which ruake up by ftir the greater part of the vohinie and weight of the whole. This is vapor of water, the result of the process of evaporation of those vast watery surfaces which are always in contact with the lower strata of the air. Deprive the air of auy one of these three main constituents and human life becomes impossible. !^ext in rank from the human point of view is carbon dioxide, or car- bonic acid gas, which, though comparatively very small in amount, exists throughout at least all the lower ranges of the atmosphere, and has the same close and necessary relations with plant life as oxygen has, or ratlier as food has, with the life of animals. It presents on a great scale an exam^jle of the wonderful law of gaseous diffusion; for, though much heavier than air, in the proportion of about 2 to 1, it diffuses under natural conditions nearly equably through every part, whether the region of its origin be near or distant. Stated in tons, the following are the calculated weights of the chief substances composing the whole atmosphere: Billions of tons. Oxygen 1,233,010 Nitrogen 3,994,593 Carbon dioxide 5, 287 Vapor 54,460 In addition to the above, we find in the air a variable and very small quantity of ammonia, chlorides, sulphates, sulphurous acid, nitric acid, and carburetted hydrogen, but some of these depend, where detected, to a great extent on manufacturing operations and on aggregations of men and animals. Liquids and solids in great variety are also very important, widely diffused, and constant ingredients in the atmosphere. The solids are everywhere present in the condition of very minute microscopic or ultra- microscox)ic motes or dust, composed chiefly of sea salt, or chloride of sodium, sand, or fine silicious particles, various dusts derived from volcanoes, factories, towns, and the remains of meteors set on fire in their passage through the upper air. Some of the most beneficent functions of these microscopic and invisible motes will be considered later. Other solids present in the upper air over a large part of the globe and in the lower strata, especially in the Arctic regions, are small particles of ice, condensed either in clouds or in air which appears nearly clear. Explorers in high latitudes relate that on fine cold days the air is frequently sprinkled with shining crystals of ice which seem to fall from a blue sky, and, on the other hand, in heavy gales and stormy Aveather the lower air is filled with a fine icy dust, resulting from the freezing of the spray torn from the sea waves. In temperate climates very much of the rain which falls on the surface of the earth has existed i)reviously at high levels in the state of snow or ice i^articles. The experience of mountaineers and balloon voyagers, and, in a moun- tainous country, the sight of peaks covered with fresh snow after a ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. day's iJiiii on the low ^loiiiul, prove how eoiiiuionly iiiiii is melted iee or snow. Other solid partieles always present in f^reat ii inn hers in 1 he lower air, andotj;reat iinportaiiee in relation to human, animal, and plant life, are various kinroportion, by weight, of oxygen in the air has l)een determined by Leduc as 23.58 per cent.^ The volume of oxygen in the air in different localities and conditions has been tested by various observers. On the western seashore of Scotland the percentage was found to be 20.991; on the tops of hills, 20.98; in a sitting room (close), 20.89; at the backs of houses, 20.70j at the bottom of shafts in mines, 20.44. 1 See Comptcs Rendus, 1890. M. Muller. 'Coniptes Rendus, 1890. A. Leduc. ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 7 The accurate determinations of Bunsen of the oxygen in the general air gave a mean of 20.93 per cent. Two hundred and three analyses by lieiset gave nearly the same result. Hempel found the amount at Tronso to be L'0.!>2; at Dresden, 20.i)0; at Taris, 20.89. Those amounts must be received with qualilication, because in comparing one town with another more depends on the position in the town than on the situation of the town. The average proportion of oxygen in the ojien country or at sea may be stated at about 20.95 per cent. In large, open spaces in Lon- don the amount of oxygen is nearly normal; in the streets, about 20.885; in Manchester, in fog and frost, 20.91; in the suburbs in wet weather, 20.90 to 20.98. These figures are merely approximate. In the air of mines an average of 20 has been observed, and in extreme cases the amount was no highet than 18.6. In the midst of vegetation on open ground, especially in the daytime, there is an excess of oxygen. Angus Smith and others found the following quantities of oxygen in air in different situations: On t]io Atlantic (Regnanlt) 20.918 In tho Andes on Picbinclia, about (Regnanlt) 20. 949 Tops of hills, Scotland 20.98 Northeast shore and open heath, Scotland 20.999 Stockholm (Petersson and Plogland) 20. 94 Suburb of Manchester, wet day 20. 98 Middle of Manchester, inclosed space 20. 652 Manchester, fog and frost 20. 91 Manchester, backs of houses and closets 20. 70 Manchester, dense fog 20. 86 Heidelberg (Bunsen) 20. 924 Low parts of Perth 20.935 Swampy places, France and Switzerland | 90 q-"' Bengal Bay, over bad water (Eegnault) 20.387 Sitting room, rather close 20.89 Small room with petroleum lamp 20. 84 Gallery of a theater, lO.SO p. m 20. 86 Pit of a theater, 11.30 p. m 20. 74 Court of Queen's Bench 20. 65 Chemical Theater, Sorbonne, before lecture 20.28 Chemical Theater, Sorbonne, after lecture 19.86 In cow houses 20. 75 In sumps or pits in mines 20. 14 Worst in a miuo 18.227 Very difficult to remain in many minutes 17.2 Eecent experiments by Messrs. Smith and Haldane on impure air contained in a leaden chamber showed that with oxygen 20.19 and carbon dioxide 3.84 two men instantly got headaches on entering. Oxygen is the breath of life, the element without which no human being could exist for a single hour. Brought into contact by every inhalation of the lungs, it revivifies the loaded blood, spreads over the 8 ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. body the warmth resulting from its combustion with the carbon con- tained in the blood and tissues, and gives to the whole physical being a vigor and freshness which is impossible where the element is deficient. Thus to mankind it is life-giver, warmth-maker, and puri- fier. Unlike food, which may be taken irregularly and at long inter- vals, oxygen is a necessity at all times and in all conditions, in every hour of the day and night 5 and upon its reaching or approaching the normal quantity in the air around us, our health and enjoyment directly depend. 3y the law of diffusion of gases, which causes the interchange of position of gases separated by a thin porous partition, the carbonic acid gas brought by the blood to the lungs passes out and is then exhaled, while the oxygen breathed into the air cells passes in through the walls of these cells to the blood. The heart sends the imj)ure blood derived from the circulation through the body to the lungs 5 this dark blood is loaded with carbonic acid gas; the lungs return the aerated and purified red blood through their blood vessels to another division of the heart, which again drives the vivifying blood through the sys- tem. Experiments have shown that a similar change in appearance from dark to bright red blood can be caused by j)assiug a stream of oxygen through the dark venous blood of an animal. That a process of combustion, or, otherwise put, chemical union, goes on at the same time, is shown by the fact that the blood is raised one or two degrees by its contact with oxygen. The oxygen in its course through the body combines with the effete or waste products presented to it by the tissues, and so the heating effect of combustion maintains the tempera- ture of the whole body at the normal, about 98.6. The waste gases given off by the lungs consist of carbonic acid gas, water vapor, and a very small quantity of ammonia and other organic matters. The average volume of air breathed in at each breath is about 30 cubic inches, and the volume of air which may be easily breathed in by an effort, and by expanding the chest, is about 130 cubic inches, or about four times as much. After a very full inspiration about 230 cubic inches can be expired by a man of average height and in good health. The total capacity of the lungs, however, is much more than this — about 330 cubic inches. Thus in ordinary quiet breathing we only fill about one-tenth of the available air space of the lungs. After every outbreath, or expiration, a quantity of air is left in the lungs. This residual air amounts to about 100 cubic inches. An adult at rest breathes about 686,000 cubic inches in the course of twenty-four hours; a laborer at full work, about 1,580,900 cubic inches — more than double. The amount of air passing into the lungs has been estimated at 400 cubic feet in a state of rest, 600 in exercise, 1,000 in severe exertion. The number of air cells in the lungs is esti- mated at 5,000,000 or 6,000,000, and their surface at about 20 square feet. The epithelium or membranous film between the blood and air is exceedingly thin, and in many x)arts the capillaries are exposed, in the ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 9 dividing walls of cells, to air on both sides. The weight of air inhaled in the conrso of the day is seven or eight times that of the food eaten. Tlie mechanical work of bieathing represents energy expressed by the lifting of 21 tons 1 foot in 24 hours.* From every volume of air inspired about ih per cent of oxygen is abstracted, and a somewhat smaller ({uantlty of carbonic acid gas is at the same time added to tlie expired air. Experiments on animals show that the amount of oxygen absorbed is very little if at all increased by an excess in the air surrounding them. OZONE. Ozone is an imx)ortant constituent of the atmosphere, greatly con- tributing to its purity and freshness and to the vigor of human life. It is a form of oxygen in which the molecule is considered to be composed of three molecules of the gas. Although existing in small quantity in the air, rarely exceeding 1 part in 10,000, the activity of ozone is so great and its function so beneficial that its presence in normal quantity is, in ordinary sur- roundings, a fair guaranty of the purity of the air and of healthy con- ditions so far as breathing is concerned. JSTo ozone is found in the streets of large towns, in most inhabited rooms, near decomposing organic matter, and in confined spaces generally. In very large, well- ventilated rooms it is sometimes, though rarely, detected. Ozone is found in very small quantity a little to leeward of a large town. Even at Brighton, a town of about 110,000 inhabitants, ozone was barely discoverable on the pier when the wind blew from the town, but abundant when the wind was from another direction. Ozone has the power of oxidizing to a much higher degree than oxy- gen, and vigorously attacks organic matter in a fine state of division. It is therefore a strong disinfectant. Its oxidizing power is the reason of its absence from confined spaces where organic matter, dust, or smoke is present, for such matter quickly uses up the small portion of ozone which enters with the fresh air. The walls, furniture, etc., are also covered with fine dust, which the ozone attacks. The difference we feel in going from a furnished room, however large, into the oi)en air, is thus i^artly accounted for. There is somewhat more ozone on moun- tains than on plains, and most of all near the sea. Water is said by Carius to absorb 0.8 of its volume of ozone. An examination of sea water with a view to detect the amount contained in it would be diffi- cult, but might give interesting results. A great excess of ozone is destructive to life, and oxygen containing one two hundred and fortieth part of ozone is rapidly fatal. The ordinary quantity even has bad effects in exacerbating bronchitis and bronchial colds and some other affections of the lungs. • ' Professor Hangliton, Carpenter's Principles of Human Physiology. 10 ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. Ozone is formed by the passage of the electric spark, and especially of the brisk discharge through oxygen, and is therefore found in unusual quantity after thunderstorms. It may also be formed by the slow oxidation of phosphorus, and of essential oils in the presence of moisture; also by the decomposition of water by a galvanic current. When formed by electric discharge in air, it is quickly turned back again into oxygen, either by further discharges or by the action of high temperature, about 230° C; at the temperature of boiling water it is slowly decomposed in moist air. Its pungency of odor is said to make it easily perceptible when only present to the extent of 1 volume in 2,500,000 volumes of air, and the smell may sometimes be noticed on the seabeach. It has been liquefied at 100° C. under 127 atmospheres pressure. In this form it shows a dark indigo-blue color; gaseous ozone looked at in a tube 1 meter long also shows a blue color. Thus there can be little doubt that, in conjunction with oxygen and fine dust, it contributes to the azure hue of the sky. NITROGEN. Mtrogen, the gas which constitutes four-fifths of the volume of the atmosphere, takes no direct part in the sustenance of human life, but has two great functions to perform: first, the dilution of oxygen to the proper and tolerable strength for respiration, and secondly, the supply of food material to plants. Although life is possible for many hours in pure oxygen, it is hardly conceivable that the human constitution could be so modified as to endure for long an atmosphere of so actively combustible a character. At any rate, nitrogen is indispensable in present conditions to the human race. Plants, with few exceptions, do not absorb nitrogen from the air, and, indeed, in the case of most of these exceptions the supply of nitrogen is in a transitional compound form. JSTitrogeu is brought to the j)laiits in general by processes of decay, and by the action of microbes in the soil, which rearrange organic elements, forming nitrates and nitrites. These nitrogen compounds are largely api)lied to the roots of plants as inanure. Only one or two classes of plants can take up nitrogen from the air. Certain low algae, freely exposed to light and air, seem to absorb nitrogen directly. Leguminous plants, such as peas, vetches, lupins, beans, clover, etc., absorb nitrogen from the air in a very curious way. Nodules or swellings are found on the roots; these contain minute fungi or microbes; the bacteria absorb nitrogen from the air, and, probably at the expense of the energy of the carbo- hydrates, etc., which they oxidize, supply this nitrogen in the form of comi)ounds to the plant. These recently discovered facts open out the prospect of obtaining scientifically from the air, in some cases at least, the nitrogen whick is now applied in combination with oxygen, soda, etc., as manure. If by the aid of special bacteria parasitic upon the plant we can systematically obtain the chief element of manurial ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 11 stuffs from the fitmospliere itself, a great advance will have been made in agriculture and in the cheapening of food. CARBON DIOXIDE. Carbonic acid gas, or carbon dioxide, is found in small quantities everywhere in the air, and in about the same proportion at 11, ()()() feet as at the sea level. It is a colorless, traiisi)arent gas and does not sup- port combustion or animal life. At 0° C. it may be liquefied under a pressure of 38.5 atmospheres. When liquefied and then allowed to escape it freezes into a snow-white solid in the air, and In a vessel under the vacuum of the air pump freezes into a transparent mass like ice. One liter of carbonic dioxide at 0"^ C. and 760 mm. pressure weighs 1.97714, nearly double the weight of air, taken as 1. At the ordinary temperature and pressure water dissolves about its own volume of the gas. Dissolved in rain it exerts in the course of time a very powerful disintegrating effect on rocks and minerals, so that the crust of the earth is greatly modified by the constant action of the solution. The chief sources of carbonic dioxide in the air are the respiration of animals and the burning of fuel. A large quantity emerges from the earth in certain places, as in the Poison Valley of Java, and in many mineral springs, where it effervesces out of water escaping from pressure. Saussure found the amount per cent in a wood near Geneva to be 0.0504 in the day and 0.0576 at night; in January, 0.0423; in August, 0.0508. In Geneva he found an average amount of 0.0468, compared with 0.0437 in the wood. Schulze, Eeiset, Levy, Armstrong, and Muntz, in different places, made several thousand observations, and the mean of all these showa during the day 0.0299, and during the night 0.0317. Eeiset's long con- tinued observations in the country 4 miles from Dieppe gave an average of 0.02942; and in June, above the crop of red trefoil, 0.02898; in July, above barley, 0.02829; near a flock of sheep, 0.03178. Thorpe's very carefully conducted experiments agree well with the above values, and give for the air over the sea 0.03011. Armstrong, at Grasmere, obtained during the day 0.0296, and during the night 0.033. At the Montsouris Observatory the mean during 1877-1882 was 0.03. In an unventilated barrack the following amounts have been re- corded as the result of careful observations: 0.1242, 0.189, 0.195; in a hospital at jSTetley, 0.06 to 0.08; in the General Hospital, Madrid, 0,32 to 0.43; in a boys' school, 4,640 cubic feet and 67 boys," 0.31; in a crowded meeting, 0.365; in a schoolroom at Madrid, 10,400 cubic feet and 70 girls, 0.723; in a stable at Hilsea, cubic space 655 feet per horse, 0.1053. It is not easily explained why the normal amount of carbonic dioxide in the free air has been so long assumed in scientific articles and text- books as 0.04 per cent, or 4 volumes per 10,000, when the best recent 12 ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. observations show an average not exceeding 0.0317 per cent, even at night, and a general mean of about 0.0308, or 3.08 volumes in 10,000. All the most recent works on hygiene, however generally accurate, repeat this error. Considering the value of small quantities in these measurements, . especially where they affect human life, it is most desirable that the standard should be taken rather as 3 than 4 volumes per 10,000. Although carbon dioxide does not itself support animal life, and we could do very well without it in the atmosphere so far as breathing is concerned, it is necessary to the growth of plants, and therefore through them an indispensaMe substance for the existence of the human race. The vegetable world not only needs a supply of this gas for its own sustenance, but by the selective action of its leaves keeps the air con- tinually pure enough for the life of animals. Under the influence of sunlight every green plant absorbs the carbonic dioxide at its surface, breaks it up into carbon and oxygen, and returns some free oxygen to the atmosphere. In this way the two great kingdoms, the vegetable and the animal, mutually contribute, each to the other, the elements of Hie. The carbon drawn from the air, together with hydrogen and oxygen, forms the wood of the tree, the stalk of the plant, and the flesh of the fruit, and these, when burnt or eaten, again result in carbon dioxide and water. The change from the compound gas to carbon and oxygen is brought about by small openings or pores filled with a green substance, chlorophyll, which during the daytime has the power to extract the carbon and set free the oxygen. At night, on the contrary, there is a slight expiration of carbonic dioxide, so that there is a real reason against keeping large green plants in a bedroom during the night. But the amount is very small compared with that exhaled by one person. It is now known that plants, like animals, breathe oxygen from the air, while they use the carbonic acid as food. About 1,346 cubic inches of carbonic dioxide are exhaled by a healthy man per hour. An adult gives oft' in repose about 0.7 cubic foot, and in active work about 1 cubic foot per hour. (Pettenkofer.) It is a remarkable fact that this amount is much reduced when the air is already fouled with this gas; experiments showed that where the same air was rebreathed, as it often is, the reduction was from 32 to 0.5 inches per minute. Thus it appears that the elimination of waste products from the system is seriously checked by the presence in the air breathed of an excess of carbonic dioxide. Otherwise stated, air in crowded places may continue to sustain life while it fails to remove any but a very inadequate portion of the poisons with which the blood is charged. The general surface of the skin of the body also gives out a consid- erable quantity of carbon dioxide, though, of course, very much less than the lungs. ATMOSPHERE IN RELATION TO IITMAN LIFE AND HEALTH. 13 About G7, 200 cubic feet of cjirbou dioxide" are ):;iven off by the burn- iuji' of every ton of coal. Since about 405,480 toius are burnt daily in England on an average (the quantity is much larger in winter), the air over the country receives daily about L'4,728,25<),00() cubic; feet of the gas, or 1,200,000 tons. The i)erfe(!t burning of ordinary coal gas gives rise to 200 cubic feet of carbonic dioxide for every 100 (nibi(; I'eet of gas consumed. Pi-acti- cally evei-y cubic foot of gas burnt vitiates as much air as the respira- tion of one person. So that in a large town during the evening hours in winter the vitiation of the air is in main streets and in rooms many times larger than during the daytime. Angus Smith, whose methods were not quite so precise as those later in use, found the following amounts of the gas in air in the situation described: Hills in Scotland, 1,000 to 4,406 feet high 0.0832 Bottom of eamo bills 0o31 In tlio subniLis of Duuid passage of the hailstone through very cold air speedily and continuously dissipates the heat thus set free. The appearance of spaces between successive tiers of dense cumulus cloud and the almost invariably excessive display of electric phenomena are characteristic of great hailstorms. It is very probable that between the dense clouds lie masses of saturated, or even sui)ersaturated, almost dust-free air. A cold hailstone falling through these would accumulate ice in clear, alternate zones surrounding the nucleus. Large hailstones are gen- erally spheroidal, small ones conical, with icy bases and a softer apex. The large hailstones are probably more dependent on electric attrac- tion, and the small on the impact of descent, for their form and icy accumulations. In a thunderstorm or shower, the lower clouds are generally nega- tively and the upi)er positively electrified. Before a hailstorm clouds of great significance may be observed, which may be described as tur- reted cumulus or cumulo-stratus. They are quite distinctive of hail- storm weather, though of course the hailstorm may not occur in the district where they are seen. They consist of hard-looking, sharply defined, generally white, and rather small masses of cloud, with pro- jections towering upward and rather broader at the top than at the base, or equally broad. These peculiar clouds are worthy of note with the view of forecasting the probable occurrence of hailstorms. Vapor, when it ceases to exist as a gas in the air, assumes several 'The height of cumulus cloud may often be well observed and measured not only from the plain, but on mountains. The tower of cumulus cloud often exceeds 10,000 or 15,000 feet, and in great storms may be 25.000 to 40.000 feet from base to summit. Both observations from the earth and balloon ascents supply evidence to this effect. 26 ATMOSPHERE IN RELA.TION TO HUMAN LIFE AND HEALTH. different forms which are only obscurely understood. There seems to be a stage between the gaseous and the misty in which vapor is condensed into very minute transi)arent motes or into a condition corresponding to the critical state, the viscous interval, observed by Andrews in carbon dioxide under great pressure. Just above this critical point this gas behaved to some degree like its vapor and liquid below it with regard to pressure. The behavior of water vapor under varying pressure and when near saturation at different temperatures would be an interesting though difficult subject for research. Dry vapor is regarded by some experimental observers as diathermanous, like air; yet we certainly find that what seems to be invisible trans- parent vapor does largely arrest radiation from the earth. Therefore, it would seem much of the vapor of the air, when near saturation, must be in a condition bordering on mist or finely divided water. Only beyond a certain size, maybe, or when dust is thick, do the particles become large enough to give the effect of haze. It often happens that a thermometer freely exposed to the sky on a fine night suddenly ceases to fall, and rises several degrees without any apparent cloudiness or diminution of the luster of the stars, but this rise, in the present writer's experience, is a good indication of approaching rain after dry weather. Whether the screen in the upper air which reflects the radiation from the earth be a thin cloud or else vapor in a state of inchoate condensa- tion, has not yet been ascertained. Haze, fogs, and clouds are caused by the tendency of vapor to con- dense upon solid particles below a certain temperature. A change of state from vapor to liquid or liquid to solid occurs much earlier in the presence of "free surfaces" of other bodies than where these are absent. Saturated air, as we call it, can hold no more vapor in ordinary condi- tions, but apart from solids and dust particles it could contain much more vapor without j)recipitation. Similarly, if water could be heated by itself apart from solids and contained gases, it would rise high above the boiling point without boiling, and would eventually explode; so also the droplets of a cloud do not freeze, though many degrees below the freezing point, until they touch a solid object. Dust in the air offers the free surface which is required for condensation. Differ- ent kinds of dust differ greatly in the power of compelling deposition. Sulphur, magnesia, and common salt are, in the laboratory, at any rate, powerful fog producers. In the open air sulphur seems to have little appreciable effect; but salt, which is hygroscopic, or damp-attracting, and pervades the atmosi^here, plays an important part. Smoke, again, or finely divided tarry matter, greatly favors fog formation, owing, I)robably, to its strong radiative capacity and to its coating the water globules so as to prevent evaporation. Suppose the motes of dust or salt in heterogeneous air to be radiat- ing freely, and therefore to be colder than the air, and suppose each of them to be frequently brought in contact with filaments of air and ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 27 vapor at a higher temperature tliaii the average, then it is conceivable that momentary deposition and reevaporation may occur. The result would be haze. With fairly homogeneous masses of air, as with a west wind, the contact of warm and cool air occurs here and there on a much larger scale and at once produces massive clouds, owing to the (juick growth of particles in a moist air brought in block below the dew-point by ascent or otherwise. The interchange between differing air masses is in this case by large columns instead of by infiltration and filaments. The steam leaving the escape valve of a boiler at high pressure is at first invisible, then bluish and semitransparent, like haze, then opaque and white, like cloud. The influences which cause haze maintain the vapor in the second stage; it passes perpetually from molecular invisibility to the verge of particulate visibility and back to invisibility by swift evaporation. Clouds, on the contrary, result from cooling in large masses, as by ascent, and the humidity is too great to permit so rapid a return to the condition of vapor within their borders. When they evaporate they become invisible at the edge without per- ceptibly passing through the stage of haze. Why the process of change of size of the particles differs so much in ditTerent states of weather is by no means clear. Haze has long been a meteorological problem. If it be vapor, why does it so frequently occur in the driest weather? If it be dust, why should dust continue to affect the atmosphere in such excessive quantities during particular periods, often in calm weather, and with a gentle wind from uninhabited areas, either sea or land? The moistest winds are generally the clearest, the driest are the haziest.' More- over, there is a thick haze which sometimes persists for many days in spring or summer in England, and neither increases nor diminishes per- ceptibly during the night, when radiation is active. In such weather the air is dry, and the wind, if any, commonly a light air from between east and north. Since neither the sun's heat nor the nocturnal cold affects it, we must ascribe it to one of two things — the presence of a large quantity of dry dust in an unusual state, or the development of vapor condensation in some unusual way, so as to depend little on the general temperature. On the top of Snowdon, 3,300 feet, the present writer has observed haze as thick as on the ground level, and extend- ing 1,000 or 2,000 feet above the summit. It was similar, though less in degree, to the obscuration described in the annals of last century as iiaving covered Europe for months after the great eruption of a volcano in Iceland in 1783. Mr. Conway has recently observed high above the Himalayas a sudden haze overspreading the sky like the smoky haze seen near a large city in England. The explanation prob- ably is that the haze depends on the relative temperature of mixed portions of strata of air, and much less on the general air temperature. Aitkeu has shown that when the wind blows from inhabited places 1 In Eugland. 28 ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. there is both more haze and more dust than when it blows from the sea or from uninhabited country, and in Switzerland a thick veil of haze seemed to hang in the air between the observer and the mountains on all days when the number of particles was great, and it became very faint when the number was small. When the wind blew from the plains the air was thick ; when from the Alps, clear. Similarly, at Ben Nevis, on the northwest coast of Scotland, a northwest wind was clearest, a southeast wind haziest, and the dust particles were gen- erally more numerous according to the amount of haze. " Of 'purify- ing areas' the Mediterranean gave for lowest values 891, the Alps 381, the Highlands 141, and the Atlantic 72 particles per cubic centimeter. Dampness of the air was found to increase the effect of dust, so that nearly double the number of particles are required to produce the same amount of haze when it is dry than when it is dampish." When the depressioD of the wet-bulb thermometer below the dry bulb was 2° or more the transparency was roughly proportional to the wet bulb depression; that is, to the dryness of the air. "The nearness of the vapor to the dew-point seems to enable the dust particles to condense more vapor by surface attraction and otherwise, and thus by becoming larger they have a greater hazing effect." The number of dust parti- cles in square centimeter lengths of 10 to 250 miles required to pro- duce complete haze in air giving different wet-bulb deiDressions was calculated to be as follows : Wet-bnlb depression. Nnmber of parti- cles to produce complete haze. Degrees. 2 to 4 4 to 7 7 to 10 12, 500, 000, 000 17, 100, 000, 000 22, 600, 000, 000 Since more particles are required to produce haze in dry than in damp weather, it becomes the more remarkable that thick haze is so common in dry weather and generally absent in a moist atmosphere. The observations of the present writer for many years have shown that haze is most apt to occur when there is infiltration or mixture of differing air currents, and indeed that it generally expresses the juxta- position and mixture of winds. A steady wind extending to the upper clouds is very seldom hazy, and, on the other hand, haziness may be taken as a sign of the existence of another wind above that pre- vailing near the ground, or of variable currents. So much is this the case that in southern England a hazy or misty east wind signifies gen- erally a rather short period of its jjrevalence, but a clear east wind means continuance. Of course care must be taken to be situated on the windward side of thickly inhabited districts in making such fore- casts. It seems, thereforCj that when haze is not due to a large amount ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 29 of dust, it must arise from some eflect of the Diixturo of ditrGrent cur- rents. A wiud from the Atlantic on the west coast of Great Britain generally has a west wind above it, and is fairly liomogeneous, but an east wind generally lias to encounter and drive back a westerly or southerly wind, and has an opposing current within 3 to 7 miles above. There must in these cases be a great deal of mixture of portions of air of ditlerent humidity, temperature, and electrical tension. The contig- uous parcels of air j^roduce at a number of points momentary dei)osi- tion of vapor on dust particles, and the resulting effect is haze. The dew point is attained in the molecular environment by momentary contact of cold, dry, dust bearing with moist, warmer, less dusty air. It is well to bear in mind the large extent and small depth of tlie whole of the lower region of winds. Currents of air, say within 25,000 feet of the surface, extended over a territory 400 miles square, would be represented by a layer of. water an inch deep in a basin 80 inches square. On the east coast of Scotland an east wind often brings a thick haze which may last two or three days, and is followed by rainy weather. But a much less thick blue haze prevails during fine weather, with light or variable easterly breezes, both in Scotland and England. The density of the haze in these conditions depends less on the number of dust particles than on the mixture of differing currents and on the moisture and warmth of the one current, the coldness and moisture of the other. There is no reason for supposing that a wind blowing from the polar regions and over the breadth of the North Sea is heavily charged with dust, yet the haziness is as great looking seaward as over the land of Berwickshire or Fife. The clear air of continental climates, such as the European and North American, is partially explained by the moderate amount of dust, the infrequency of a condition approaching saturation in the lower air, and the absence generally of local winds such as are x^roduced by a varied distribution of land and sea. Haze is very often the result of the pas- sage of air over water of a lower temperature, and the difference of the temperatures may decide whether the obfuscation shall be haze, fog, mist, or fine rain. No amount of dust is in general competent in a dry, uniform air to produce apppreciable haze beyond what is due to its own particles. Thus in Colorado there is often a great deal of dust in the air, but the air is clearer at such times than it commonly is in England; in the Punjaub dust winds obscure the air for a long dis- tance ; in the Sahara Desert there is often thick dust, but the hazing is not great except with strong wind; when, however, this dust is blown far out over the Atlantic, the haze becomes very considerable, and is a common phenomenon about the Cape de Verde Islands. Towns, again, such as Paris and Pittsburg, which produce a great deal of dust, by the test of the dust counter, are not affected by haze in clear, dry weather, and even London, in some states of the air and very often at 30 ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. aight, is only covered by a barely perceptible ligbt haze. But coal smoke, commonly lias the effect of causing a very persistent liaze, and this, in the case of London, spreads consx)icuously with the wind to places distant 100 miles or more. Coal smoke, we must remember, is accompanied by a good deal of water vapor and sulphurous acid. Gas and wood, when burned in large towns, produce no fog and very little haze, though the dust counter might show as many particles as where coal is burned. Dust in general may therefore be acquitted of taking an important part in producing any but a light, thin haze, except where there is a mixture of currents at different temperatures, and then some haze would in most instances be produced in any case by the normal average amount of very fine dust which exists everywhere in the atmos- phere. In clear, homogeneous air, even near saturation, much dust or smoke may be added to the air without causing haze; in dry, hazy air much dust may be added without much intensifying the haze. In cer- tain conditions of wind and weather much haze may exist without an abnormal quantity of dust, and, except on rare occasions, there is always enough dust, maybe of almost molecular dimensions, in the lower strata of the air to admit of precipitation of moisture where con- ditions are otherwise favorable.^ A great deal of this dust probably consists of chloride of sodium, or sea salt. The following instances may serve to show how haze and cloud are successively formed by a conflict of differing currents of air. St. Fil- lans Hill is a small, steep, isolated, conical hill about 300 feet in height, standing in the middle of the valley of the upper Earn, in Perthshire, about 2 miles from the lower end of Loch Earn, and flanked by moun- tains about 2,000 feet high on each side of the valley. The author was on the summit about 5 o'clock one evening in August,^ when the breeze, which had been blowing freshly from the west, with a clear air, sud- denly began to slacken, and in about five minutes dropped altogether. Then down the valley, eastward, a blue haze began swiftly to climb the glens tributary to Strathearn, and the whole air eastward grew obscure. The calm only lasted a little more than two minutes, and then suddenly a strong wind from the east set in, and soon the air westward as well as eastward had turned thick. The east wind continued, and in a few minutes the tops of the hills rising precipitously from Strathearn to a height of about 2,000 feet were obscured with cloud banners which grew continuously, and descended till in about two hours not only the hills above alevel of about 1,000 feet, but the whole sky, was covered with gray clouds. The duration of the neutral calm corresponded with the time usually occupied, according to my observations in the neighbor- hood of London, by a moderate east wind in driving back the opposing current. At Eichmond, and between Eichmond and London,, such a ' These observations are derived from many years' attention to the conditions of prevalence of haze and fog in and near Londou, 2 About 1877 or 1878. ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 31 change is signalized in the neutral band of calm by a dense yellow haze, i)rodu<;ing great darkness in winter, the result of a bunking up of sniok(> to some altitude, together with the condensation of vapor b}' the mixture of currents differing in temperature. The darkness in such a, band lasts much longer with lighter winds, and I have known a Avest wind to i)revail at lliclimond simultaneously with an east wind in London, botli without fog, while at Wandsworth a calm continued for many minutes with dense, almost nocturnally black smoke fog, the pressure in each direction being apparently e(]ual. FOG, SMOKE, GASEOUS AND SOLID IMPURITIES IN THE AIR. Fog is the result of one or both of two principal causes. The first is active radiation into space from the earth and from the air contiguous to it, and the second is a mixture of winds and currents, or of vapor and air at different temperatures. 1. Radiation fogs occur commonly when the atmosphere above the lowest stratum is cold, dry, and nearly still, and when the lowest stratum is greatly cooled by contact with the cold radiating earth, and therefore precipitates vapor into the form of minute globules of water. These globules themselves have a large radiative capacity, so that they tend further to reduce the temperature of the air in which they float, which has no such capacity. The stratum of fog so formed, not extending very many feet above the ground, fails to reflect much of the heat radi- ated from below, and quickly disperses, by radiation into space, what- ever heat it absorbs. Thus earth and fog continue rapidly to part with their heat through the clear sky into space. The stratum of fog often grow^ in height and density through the night, and continues till about noon of the following day, or disperses in the late hours of the morn- ing. If extended over a plain and watched from a height above the upper level, a fog of this character, in somewhat damp and not typical radiation weather, may be seen gradually to move irregularly upward under the influence of the morning sun, and in various directions to present prominences like thobe of the upper edge of cumulo-stratus. Smoke issuing from a tall factory chimney rises through and above the fog, but in a very short time falls back upon its surface and meanders like a dark river on a white ground.^ The persistence of the fog depends upon the coldness of the ground, which is shielded from the sun, and upon the very large diflerence of temperature, sometimes 10 degrees or more, between the fog and the stratum of air a few feet above it. When, however, the sun's heat absorbed by the water particles exceeds the heat lost by radiation, the fog lifts, that is, its upjiermost stratum rises, owing to diminished specific gravity, and ' These observations were taken during the prevalence of a ground fog, in the country surrounding the Malvern Hills, in February, 1890. 32 ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. either clears at once or remains for some time as a light blue haze.^ The strata below it, submitted to the same influence, successively rise and take its place, and the evaporated moisture mingles with the gen- eral air. Fogs of this kind locate themselves in low-lying valleys, basins, and plains, for the air, chilled by contact with the radiating ground, sinks by gravitation into such situations and in them is least likely to be disturbed. Sometimes a white fog may be seen pouring down an open and rather steep ravine like water.^ Slopes of hills, especially their southern sides, some hundreds of feet above the j^lain, are com^jaratively free from these fogs, and are much drier and warmer during their prevalence than lower places in the neighborhood. Such an elevation is more favorable on this account to the human constitution ; both the daily and yearly thermometric range is much smaller. Dense fog and frost often remain throughout the day on the northern side of hills when the southern slope is bathed in sunshine. This has been observed on several occasions on Hindhead, Surrey, the air in the fog keeping much colder than the air above it and on the southern slope. In the still air which precedes and accompanies radiation fogs the number of dust particles is high above the average, owing partly to their becoming gathered by undisturbed iDrecipitation into the lowest strata. On several occasions when the dust particles were counted they amounted to between 45,000 and 80,000 per cubic centimeter. Each of these is a nucleus for the deposition of vapor. The water particles are so small that they evaporate before touching solid objects during the daj^time, the objects being warmer than themselves. For this reason these fogs have no wetting efl'ect. In a fog, when objects were invisible at 100 yards distance, 19,350 droplets sometimes fell on a square inch per minute, but the average was much less than this, and the smallest number about 1,900 per minute.^ The . large number of particles favors the formation of fog. Considerable numbers of living organisms no doubt exist among the water particles of the fog, but are not known to be a cause of ill-health in the country remote from towns. Nor is great cold combined with fog productive of much illness in the country. In smoky towns the case is far d'ifferent. Thus, in London the death rate was raised in a single fortnight, from January 24 to February 7, 1880, from 27.1 to 48.1 per thousand. The fatality and prevalence of respiratory diseases were enormously increased. The excess of deaths over the average in the three weeks ending February 14 was 2,994, and in the week ending February 7 the deaths from whooping cough were unprecedent«dly numerous — 248 — and from bron- chitis numbered 1,223. At least 30,000 persons must have been ill 'This haze may be taken to be caused by the aggregated nuclei of dust left after evaporation of the water which condensed upon them. -This was seen by the author with remarkable distinctness near Alum Bay, in the Isle of Wight. ^ Aitkeu. ATMOSPHERE IN RELATION TO HUMAN LIFE ANIJ HEALTH. 33 from the coinbiiiod cttect of smoky fo^^f and cold. Tho present author was in London dnriii*;" the wliohj period, and noted csi)ecially the unus- ual number of days during whi(;h the darkness and stillness continued, and the tenacity with which tlu^ foj;* chiiij^* to the cohl {ground on the shady sides of s(in;ires and stre<'ts, when a warm, gentle cmrent from the south improved and cleared the air above'a lieightof 20 or 30 feet.' The large excess of carbonic acid, of sul])linrous acid, and of micro- organisms and etiete organic ])roducts was partly concerned in these ill effects, but the factor of greatest importance was the finely divided and thickly distributed carbon or carbonaceous matter, which irritated the breathing passages and lungs. The results corres[)onded ratlier closely with the more gradual ill effects of dusty trades. The lungs of a man who has spent his life in London or jNfanchester are found, i)OSt mortem, to be choked with black matter. In some parts of London there is sometimes no more light at noon than in the darkest night. After a fortnight of dense fog the deaths in London for one week, end- ing January 2, 1892, exceeded by 1,484 the average number, being at the rate of 42 per 1,000. Increases took i)lace in the following diseases : Measles, 114 per cent; whooping cough, 173; X'^thisis, 42; old age, 3G; apoplexy, 58; diseases of the circulatory system, lOG; bronchitis, 170; pneumonia. 111; other respiratory diseases, 135; accidents, 103. These results are in the main attributable to the concentration of the ordinary constituents of London air, with moisture and intense cold to help their deadly work. The majority of the fatal cases were in "weakeiked constitutions, though many were among the robust. The experience of large towns always is that the power of recovery after illness is much less within their confines than in the country. In the fog the evil influences of town air are many times multiplied. The blackest fogs, which are local, are the result of variable or opposing currents which carry up the discolored mass to a height of hundreds of feet, where they condense their moisture in a stratum of unusual thickness or height. By a converging flow of currents, a huge column of blackened fog particles rises vertically to a height where it may remain or whence it may move slowly from place to place. A fog need Dot always be resting on the ground, but may hang after the manner of stratus cloud at some level, often a few hundred feet above it. This happens when the ground is not much colder than the air. The smoke of a steamer may be seen sometimes thus to form a dark streak, remain- ing about the same level for an hour or more. That domestic fires at least rival manufacturing works in the production of dark fogs is proved by the intense darkness which has prevailed in London on Sun- days, and once on Christmas Day. Factory fires are out on Sundays, but domestic fires are larger and more numerous. Smoky fogs invade houses and even warm rooms, showing that many of the nuclei are solid particles large enough visibly to obstruct light even when dry. ' London Fogs. E. Eussell. Published by Stanford, London, 1880. 230A 3 34 ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. At a distance of 10 miles from London, tlie smoky particles are small and slio\v quite a tliick haze in a room with a fire, wlieu a geutle cur- rent is moving" from tlie town. Professor Frankland lias shown that if a little smoky air be blown across the surface of water evaporation is retarded 80 ])er cent. The water globules may be similarly coated with tarry matter, which hinders the warmth of the sun from evaporat- ing them. Moreover, every i:)article of carbon is a good radiator and in the early morning tends to increase the cold in the air around it; moisture is deposited upon it, in the opinion of the present writer, and can only with difficulty evaporate, so long as radiation is active and while the heat and light of the sun are stopped by smoke. The efi'ect of finely divided carbon in stopping light may be tested by holding a piece of glass for a few moments above the flame of a candle; the black film deposited enables us to look at the sun easily, and it appears well defined, like a red orange, as in a fog. The imperfect combustion of coal is the cause not only of fogs being specially dangerous to life, but of their persistence in duration far beyond those of the surrounding country. The removal of coal smoke would mean much less fog and much less evil in that w^hich remained. Cities which use wood as fuel, or anthracite, or gas, or oil, are no more visited by fogs than the surrounding country, although the fine "dust" above them is, according to Aitken, very greatly in excess of the normal. Pittsburg had a black climate till it used natural gas, and thencefor- ward has had a clear air, and no special liability to darkness and fog. In London, of 9,709,000 tons of coal used annually, about 1 per cent escapes into the air unburnt and 10 ijer cent is lost in other volatile compounds of carbon. The bright sunshine, compared with that of Kew, 9 miles distant, was, in the four years 1883-1886, 3,925 hours, against 5,713 at Kew, and about G,880 at St. Leonards, about 80 miles distant. From November, 1885, to February, 1886, inclusive, the sun- shine in London was 62 hours, at Kew 222, and at Eastbourne 300. Town fogs contain an excess of chlorides and sulphates, and about double the normal, or more, of organic matter and ammonia salts. During the last fortnight of February, 1891, the previously washed roofs of the glass houses at Chelsea and Kew, the former just within, and the latter just outside, London, received a deposit from the fog, which was analyzed and gave the following results: Substances. Carbon Hydrocarbons Organic bases (pyridines, etc.) Sulpburic acid (fiOs) Hydroclilorio acid (HCE) Ammonia Metallic iron and magnetic oxide of iron ilineral matter (chieliy silica and ferric oxide) Water, not determined (say difference) Cbclsea. Kew. Per cent. 39 Percent. 42.5 12.3 4.8 2 4.3 4 1.4 .8 1.4 i.l 2.0 31.2 41.5 5.8 5.3 ATMOSPHERE IN RELATION TO HUMAN LIFE ANIJ JIEALTH. 35 Tli(^ weij^lit of the deposit was at Kew 30 <;ram.s in I'O yards. At Chelsea the same area j^ave 40 j>;rams, which is ecjuivaleiit to 2^5 ])(nmds to the acre, or C tons to tlie scjuare mile. A large ])roi)ortioii of the deposits of fo^' in smoky towns clearly arises from the imperfect combustion of coal. On j)lants the deposit is sticky, like brown ])aint, and is not washed otfby water. A country fog is harndess in a green- house; a town fog most destructive, killing soft-wooded plants, and greatly damaging others. A very large number of plants will not thrive in smoky towns. In Manchester, the deposit colh^^ted from aucubii leaves gave C to 9 per cent of sulphuric, and 5 to 7 per cent of hydrochloric acid, mostly in a state of combination. Tiiree days' fog deposited per square mile li liundredweigLts of sul])huric acid and 13 hundredweights of blacks. Among the results of smoky air in towns may be mentioned: The discouragement of cleanliness and ventilation; the constant deficiency of light; the damage to plant life, so that only a few trees and plants can live; the destruction and disfigurement of stone, cement, iron, paint, wall papers, clothing, etc., and the depressing effect of dirt and bla(;kened streets on the peoi)le; losses to artists of all kinds who depend on light; the lowered vitality of a large portion of the poi)ula- tion, and a contributory influence toward the rapid degeneration and extinction of town families. In London the extra expenditure entailed is about £1 a head, or more than the value of all the coal burnt in houses. The extra wash- ing, painting, aud repairs, and the loss of unburned carbon, etc., are among the principal items in the account. The intensity of the ground fog depends largely on the amount of cooling which the earth has previously undergone. At the beginning of February, 1880, the ground in London was hard frozen with the intense frost which had i)revailed for some days. A moist southerly current supervened and the temperature rose several degrees above the freezing point. On the shady side of squares the fog then pro- duced between the ground and 10 or 20 feet above it was so dense that at 10 a. m. a lamp-post 4J yards distant was invisible. In an ordinary thick fog, such as that of January 11, 1888, objects are visible at thir- teen times that distance. Above the shallow stratum of ground fog the air was nearly clear aud the smoke escaped. Such fogs are due partly to radiation into space, but also lai*gely to the mixture of the warm current with air which has become cold by contact with the ground, and to radiation toward the ground. All radiation fogs disperse or greatly diminish when the sky becomes clouded and reflects some of the warmth radiated from the ground. They are not formed under a cloud}- sky. 2. Fog is frequently produced, sometimes ou an euormous scale, cov- ering an area exceeding that of the British Isles, by the mixture of opposite currents of small velocity. The condition of atmosphere often 36 ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. resembles that which produces haze in summer; a slow infiltration of currents of different temperatures brings different laminaB into contact. A cold earth and a sky clear above the low clouds increase the inten- sity of such a fog, but are not necessary to its existence. A southerly wind is too warm to produce fog by itself unless it meets with a cold surface, and a northerly wind is too dry by itself to be reduced below the dew-point. When, however, two opposite currents, one of which is colder than the other, diffuse into each other slowly, as when the colder current over an extensive area sinks into the warmer current below it, a fog may be produced which is less thick than a radiation fog, but may continue with little change through several days and nights, and commonly declares its character by the height to which, it extends and by its moisture. It deposits much more moisture on trees, etc., than most radiation fogs, and, though no visible mist or rain may fall, the ground under trees often becomes very wet. Thus precipitation of moisture is increased in forests. In cold climates or at high levels every exposed object accumulates ice. A wet or mixture fog disap- pears under cover, and is thinner in large towns than in the country, for the particles of which it is composed are almost pure water and evaporate when the air is a little raised in temperature. On moun- tains in Great Britain wet fogs are very common, and may occur with strong wind; moisture or ice is deposited on the windward side of ail objects. Continuous damp mist may be produced in Great Britain by a northeast wind blowing beneath a damp southwest or south current, and such mists produce very disagreeable weather. In September and the first half of October, 1894, southern England was immersed for weeks in a mist so produced. The northeast wind was not of very distant origin, and, not being dry, its mixture with the very damp southerly current overlying it produced dense mist, cloud, and occa- sional rain. Many fogs, such as those over rivers or valleys, and over the cold ocean current near the Bank of ITewfoundland, are due partly to mix- ture and partly to radiation. The sea fog originates in the cooling of air by contact with the colder surface of water and by mixture with the cold air which lies near the water. At many coast places on a hot summer day a sea fog frequently comes up on a cool breeze which mixes with the warm air above it from the land. On the other hand, when a sheet of water is much warmer than the air above it, a thick mist or fog may be formed, which is largely condensed steam. Fog is less common in summer in the interior of continents or of large islands than on the coast, but in winter, owing to the greater loss of heat by the surface of the earth than by the surface of the sea, fog is more common inland. In many countries in the temperate zone the stratum of cloud or fog does not lie often upon the ground, but at a height of hundreds or thousands of feet; the sky remains quiet and overcast for days and weeks together. The elevation of the cloud, ATMOSPHERE IN RELATION TO HUMAN LIFE AXI) UKALTIl. 37 whicli would be fog on the grcmnd, (Icpeiids on the lieight at which the de\v-i)(iint of the air is reached, or else on the hi-i.uht of the boundaries of a lower and upper current dilferiiij^ in temperature. The h)\ver air is too dry to permit the condensation of vapor within its l>orders. A warmer and moister ni)i)er- current coner hectare per annum. Bcav contains about 6 milli- grams, equal to about 29 kilograms per hectare per annum; fog, about 50 milligrams, and' in Paris, 138 milligrams. Water dissoh'es from 700 to 1,000 times its volume of ammonia, according to the temperature. Eepresenting the quantity of ammonia in rain at Yalentia, in Western Ireland, by 1, the quantity inland in England was 5.94, at Glasgow 50.55. The albuminoid ammonia was: A'alentia 1, Manchester 7.38, London G.23. ' Pierre. 48 ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. In summer the amount in the air is highest, in winter lowest. In large coal-burning towns it is considerably more abundant than in the country, and is deposited with carbonaceous, sulphurous, and organic matter on exposed surfaces during the prevalence of fogs. Foggy air in these towns contains an excess of sulphates and chlorides, but a stiil greater excess of organic matter and ammonia salts, often double the normal. The ammonia contained in the deposit on glass roofs in Chelsea and Kew after fogs was respectively 1.4 and 1.1 per cent. The processes of combustion, both in manufiictories and in domestic fires, of coal and of coal gas, give rise to ammonia. Only traces of ammonia are evolved from the lungs, and a little from the skin and in i)erspiration. The smell of ammonia is distinguishable in most stables, but where strong we may be sure that ventilation is deficient. Main streets, especially where wooden iDavements are used, often smell offensively of ammonia; on still, dry days the ammoniacal dust is thick in the air, and in windy weather is blown about in clouds. Analysis has shown that 95 per cent of the dust from wooden jjavements in main London thoroughfares, consists of horse dung. This is breathed into the lungs and often produces sore eyes and sore throat. Such pavements should either be kept scrupulously clean throughout the day or be properly watered, in order to reduce harmful dust, and an occasional coating of tar would not only prevent the emanation of noxious matter, but would preserve the wood. Ammonia, being everywhere present in the air and extremely soluble in water, may truly be said to be attached to all exposed surfaces where moisture is also i3resent; in the neighborhood of human habitations and decaying animals or vegetable matter it has been found on all objects; in a room, if a perfectly clean glass be suspended, traces of it appear after an hour and a half. Evolved in small quantities from the skin and lungs, it must be deposited with condensed vapors on the walls, ceilings, and floors of dwelling houses. NITRIC ACID IN THE AIR. Nitric acid also pervades tlie air in minute quantity, and, with ammo- nia, plays a great part in the development of plants. It results partly from the combination of nitrogen and oxygen in the atmosj)here caused by thunder storms and partly by the oxidation in loamy soil of the ammonia of decomposing organic matter. It seems probable that many forms of bacteria or molds may be favored in their growth by the presence, with moisture, of these two nitrogenous substances. Within human habitations, cow sheds, etc., we must regard the walls, and all surfaces as covered with a thin top-dressing of moist organic dust and ammonia. Within the soil ammonia appears to be oxidized to nitrites by one set of microorganisms, while another set oxidizes nitrites to nitrates. To the latter the presence of ammonia is a hindrance. ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 49 LOCAL GASKOUS IMPUIUTIKS— SUI.I'UUHKTKI) IIYDIfiOGKN — SKWKIl AND DRAIN AIU. When certain :iiiiiii;il :iiise who have some tissue delicacy or i>i'edis])ositioii. lint another very(;omnion cause, especially in thclargely fatal tuberculosis of infants, is the use of milk from infected cows. Now, these cows are themselv^es diseased Ihrougii media veiy similar to thosi; which disarm the human subject, rebreathcil foul air and dirty places; in fact, want of cleanli- ness, arid, above all, want of fresh air. Well-ventilated cow sheds, and immediate separation of sick animals, prevent the spread of tuberculosis among cows; thus children are saved from the danger of tuberculous milk. The breath of the con- sumptive in well-ventilated rooms may be considered harndess. Animals have been infected by breathing the dust of sputum dissem- iiuited in the air, and no doubt the same mode of infection is very common among mankind, but only in close association with the sick or in stuffy apartments. The State board of health of oNIaine has issued valuable instructions to i)revent the practice of expectoration except in spittoons, which may be wooden or pasteboard, and should either be burned daily or cleansed Avith boiling water and potash soa^). The reduction of consumption by such means and by better regard for ventilation is not only probable, but certain. In England the death rate has considerably declined with sanitation. From 1851 to 18G0 it was 2,G79 per million per annum. In 1888 it was 1,541. In New Hampshire, United States, the deaths from the several diseases named were as follows: From 1881 to 1888, consumption, 4,039; diphtheria and croup, 98,); ty])hoid, 750; scarlatina, 187; measles, 100; whoop- ing cough, 109; smallpox, 2. Here the very large proportion of deaths due to consumption, and the importance of effecting a reduction, are strikingly shown; but a similar ])roportion exhibits itself in every thickly inhabited State, both in Europe and America. Booms occupied by consumptives should be j)eriodically disinfected and always kept clean. The danger is there, but it can be averted. The experience of the Brompton Hospital shows that with jiroper hygienic precautions cases of infection from patients are very rare. Koch has shown that enormous multitudes of bacilli may be distributed on the ground and in the air from only one patient, and how infection is explained by their long survival in a moist or dry state. Cornet showed how the walls and carpets, cornices, etc., retain them still potentially virulent. Thus certain houses remain for a long while centers of infection, and newcomers are attacked out of all propor- tion to the cases among neighboring uninfected dwellings. Prisons, barracks, etc., w4iich when crowded and badly ventilated were very fatally affected with consumption have been rendered whole- some by thorough ventilation and greater cleanliness. Out of an average prison population of 4,807 in the year 1890 in England, only 9 died of i)hthisis, excluding cases in which sick prisoners were removed home. 56 ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. The mortality of the British army in barracks from consumption in the ten years 1837 to 1840 was 11.9 j)er thousand. After the report of a royal commission in 1858, ventilation and air space were greatly extended, and the mortality immediately and rapidly fell; in 1888 the consumption rate was only 1.2 -per thousand. The disease prevails more on wet, cold, clayey ground and damp places generally than on liigh and dry sites, and all causes of chills and colds give an opportunity to the infection of the specific bacilli wliere they are x)resent in sufficient numbers and strength. Cold countries are rather less subject to the disease than temperate and warm climates, but everywhere the most important factors are the habitsof thepeople. A moist atmosphere, with wide daily range of tem- perature, favors its prevalence. In Greenland, Labrador, Iceland, Spitz- bergen, ^ISTova Zembia, Finland, Siberia, and the northern parts of North America the disease has been rare; also especially on mountain ranges, high plateaus, and little-visited districts, such as the Soudan. In Algeria the nomad Arabs were free from it. The Bedouins who exchange their tents for stone-built houses suffer to some extent. Many uncivilized tribes are exempt until they adopt the clothes and way of living of civilization. Outdoor life in the free air, and clean, spacious sleeping quarters almost or quite annihilate consumption if animal sources are excluded. Soldiers on campaign, fishermen, hunters, engine drivers, gardeners, and farm laborers are least attacked ; workers in gritty stone or metallic dust, in hot, close, crowded, and damp rooms or factories or mines, and dwellers in damp houses, back-to-back houses, and close courts furnish the largest numbei of victims. In the old town of Havre, with its airless, narrow streets, the mortality is three times as great as in other parts of the town. It has been shown that in proportion as a population, male and female, is drawn to indoor occupations, the death rate from consumption increases. An elaborate investigation for official purposes by Dr. Ogle showed the mortality from phthisis and lung diseases of men from 45 to 65 years of age working in pure and vitiated air in England, to be as fol- lows: Pbtliisis. other lung dis- eases. Total, Pure air: Fishermf n 55 52 61 62 84 152 144 233 45 50 56 79 59 65 94 84 100 Farmers 102 Gardeners 117 Agricultural laborers 141 Confiued air : Grocers 143 Drapers 217 Highly vitiated air: Tailors 238 Printers 317 ATMOSPHKRE IN RKLATION TO HUMAN LIFE AND IIKALTII. ;j7 From these lijiuics tlu; oHect of the luciithin*^ of foul air on res- piriitoiy diseases is (;oiisj)icuous. ]>iit tlie (linereiiccs nipnsseiilcMl would have been imich j;reatei' if llie class described as livinj;' in ])iirc air h;inrity of air in and around dwellings abolishes plague altogether, as h;is been proved locally in the Himalayas and generally in the retrogiession of the disease from Europe. CHOLERA. Cholera is to a great extent a disease of air poisoning. It arises from the soil in certain districts of India, where it is endemic, and from which it occasionally has the opportunity, through favoring climatic influences and the movements of travelers, of invading temperate regions, in which it may cause great mortality in a few seasons, but can hardly establish itself permanently in the soil or water. It does not, as was long supposed, travel from jdace to place through the air, and has no epidemic existence beyond its breeding places apart from human agency. The cholera microbe, the comma in all probability, thrives in a damj), organically polluted soil, such as that of the delta of the (Janges and the tiat lands around Madras, Bombay, and Shang- hai; of the valleys of the Brahmaputra, the Nerbudda, the Tapti, the Indus, and the Euphrates, and in a temperature of from 25° to 40° C. In the delta of the Ganges the temperature of soil and air ajipears to be so favorable that it never dies down ; at Shanghai it regularly infects the air and water after the heat of July and August. It is aerobic. A freezing temperature prevents its growth, but does not destroy it. Kept moist, it may live for months after growth has ceased; dried for a few hours, it dies. In temperate climates it is spread by the entrance into water and air of the organisms derived from growth in the dejections of cholera patients, some cases being only recognized as diarrhea, but still being capable of spreaaing the poison. The destruction of the dejecta is, therefore, the safeguard in all cases. The power of exten- sion of cholera through the air alone in the neighborhood of cholera l>atients where due hj^gienic precautions are observed is very small, but every article used mut?t be washed or sterilized. The general atmosphere does not convey it either from person to person or from soil to soil, unless, possibly, in rare cases and for a short distance. In fact, free air, unless very humid, soon kills it. The atmosphere of the Gan- getic delta, the chief endemic area of cholera, is remarkably damp. There are probably a number of places in India where the soil is to some extent infected, but where mischief arises only in certain seasons. The conditions of soil and air favorable to the growth and exhala- tion of the cholera germ may be concisely summed up as follows; 60 ATMOSPHERE IN EELATION TO HUMAN LIFE AND HEALTH. Permeability of soil to air, moisture of soil not excessive, average soil heat at G feet deep about 79°, a moderate amount of contained organic matter, and little putrefaction or ordinary decomposition; mean annual temperature of air about 72° F. The minimum water level, otherwise the maxiunim ol soil ventilation, and the maximum of cholera coincide. Dry or saturated soil are unsuitable for the continuous growth of the bacillus. DIARRHEA. In an inquiry conducted about thirty-five years ago^ regarding the prevalence of diarrhea, a disease which in England is fatal to very large numbers of children, it was found that there are districts in ■which endemic diarrhea is unknown, and others in which it i)revails extensively every year. The excess of mortality coincided in all cases with one of two local conditions, the tainting of the atmosphere with the products of organic decomposition, especially human excrement, or the habitual drinking of impure water. Since the time of the report a large amount of evidence has accumulated which goes to prove that summer or inftmtile diarrhea is caused by the infection of air and food by emanations from a damp organically contaminated soil raised above a certain temperature. Houses built on or near a subsoil con- taining decomposing organic matter, or where sewers leak, are particu- larly subject to diarrhea. The nature of the soil is important. Sand, loose fine gravel, deep mold, and permeable soils generally, where organic matter is abundant, are productive of the disease; houses built upon rock, without fissures, are generally altogether exempt. "Made ground," containing organic rubbish, on which so many houses in the outskirts of large towns are built, emits products of decomposition into the interior of houses and is a fruitful source of sufiering. The prac- tice of burlding on rubbish heaps should be made a criminal offense. The absence of free ventilation within and around houses greatly increases the mortality from this cause. Deep drainage has been fol- lowed by a marked fall in the prevalen(;e of the disease. Paving, impervious flooring in houses, cleanliness in the storage of food, with ventilation, are important measures for its reduction. Purity of air, indeed, in this as in so many other cases, is the remedy to be sought. Diarrhea in the epidemic form arises under conditions very similar to those of cholera. It jnay be in fact a very near relation of that microorganism, but is milder in its effects and has the quality of developing at lower temperatures. When x)olluted, damp soil at 3 or 4 feet deep reaches about 50"^ to 60° C, as it generally does in England in June or July, the cases of diarrhea mount up rapidly, for the diar- rheal microbe is then multiplying in the subsoil and emerging through the upper stratum, and may indeed be develoiied in decaying organic matter on the surface. Settling upon articles of food and drink, such as vegetables, water, and milk, it multiplies and develops the poison * Second Eeport to the Privy Council, London, 1859, ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. Gl wliicli b(']()iij;s to fnii,u()i(l growtli. When invested with food, and even wiieu breathed with the air, it causes the disease. The air of that part of a town which was subject to diarrhea lias been proved to con- tain germs wliicli cause the disease, and to (;ontain 1{,()0() to 7,((()() bac- teria and micrococci in the cubic meter. The deatlis in tliis part of tlie town, containing one-third of the population, were 21G out of a total of 25(). The remedies for diarrhea are principally draining (he ground to a considerable depth, paving, ventihitioii of dwellings and of i)laces where milk and food are ke})t with air from some height above ground, cleanliness generally, and a good water supply. Cows, faim- yaids, and dairies need sindlar attention. Diarrhea is much less common among the Irish population of laige towns, owing to their infants being almost invariably suckled by their mothers and not from the bottle. The general air soon nullifies the danger from strata near the infected ground, and the germ seems to be incapable of enduring con- veyance in a potent state through any (considerable distance in the free atmosphere. TYPHOID FEVER. Typhoid fever, like cholera and diarrhea, depends to a great extent on the growth and cultivation in neglected human refuse by human agency (unwilling but effectual) of germs which thrive in damp, pol- luted soil or in foul water. Warmth and exclusion from free air favor the development of the bacillus, supposed to be the cause of typhoid. It can grow, however, in the presence of free oxygen, and then develops the saprophytic habit and great resistant power. In direct sunlight it is killed in six to seven hours, and in diffuse daylight growth is very slow. The mode of entrance of typhoid is both through air and water contaminated with the products of the intestinal discharges of persons sick with the disease. During twenty years preceding 1883, the average annual number of i)ersons who died of typhoid in England was about 13,000, the number of those who suffered from it about 130,000. In many conti- nental cities, tlie proportion is much higher. Although bad water accounts for a large number of cases, bad air, the emanations from drains through defective traps and waste pipes, also infects in very many instances. Eecent experiments of great interest have shown that sewer air is capable of so poisoning the system as to lay it open to the attacks of the typhoid bacillus, which is doubtless frequently present either in the foul air or in the intestines. In this way many outbreaks are cansed by the coml)ined influence of drain air and spe- cific microbes. The condition of farmyards near dairies whence milk is supplied to cities is too often so filthy that both air and water are poisoned. Milk has a remarkable power of absorbing gases and vapors, and is also a cultivating medium of various fungi and bacteria. Typhoid germs, Uke so many others, are soon rendered innocuous by G2 ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. mixture with fresh air, and there is some evidence to show that oxida- tion by the air in running water has a good effect where the noxious matter is largely diluted and the stream pure. In London, New York» Paris, Berlin, and perhaps the majority of places in the northern tem- perate zone, typhoid fever is most prevalent in the late summer or autumn, when the ground at a little depth, and water in shallow wells, are at their highest temperature. In India it occurs mostly in the hot, dry months beforo and after the rains, and may in part be attributed to the wind blowing up the dust of filth deposited in the fields, but chiefly to the same conditions as prevail in England and to the intro- duction of the virus, often from slight and unsuspected cases. The great majority of houses in civilized places resemble inverted, slightly ventilated bell jars, connected with a system of pipes on which deadly organisms may grow, and from which they may be conveyed by the poisonous gases to the bodies of the inmates. It should be a pri- mary object to make the entrance of these gases difficult and of the outer air easy. The bacillus concerned in typhoid fever is probably widely diffused, but, whether often present or not in an innocuous form in the human intestines, does not attack life where air and diet are pure. With the aid of impure air from drains, middens, and foul sinks it acquires deadly power. Cleanly disposal of refuse and abundance of fresh air are the great securities against this disease. MALARIA. Malaria is the most general, constant, and destructive of endemic diseases in tropical climates and over a very large proportion of the inhabited globe. Millions die of it every year in India, and in Africa and South America it is terribly prevalent and fatal. Vast numbers )f people are crippled and diseased for life in consequence of the fever, and in many districts the whole population looks debilitated and anpem ic. It depends on the emission of living organisms, probably amcebiform, from warm, damp soil, rich mold, sand, or other suitable ground con- taining a little organic matter. It haunts open and narrow valleys, dried water courses, the country at the foot of many mountain ranges, sandy coasts in certain climates, mangrove swamps, deltas, marshes, and even in certain districts dry, sandy plains at a considerable eleva- tion. The organism appears to exist either in an active or latent form in nearly all hot countries where the soil contains sufficient organic matter, and that need not be much. Where soil is efficiently drained, naturally or artificially, malaria is rare or absent; and where irrigation works increase the dampness of the soil, there also malaria increases or develops itself. Cultivation, with the exception of rice growing, in general diminishes or abolishes malaria within the area cultivated. Lowering of the water level and aeration of the soil reduce malaria notably. Drainage in East Anglia has almost exthignished ague, which is a similar or the same disease. Some sandy, semidesert districts, such ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. G3 as "Western Kajpootaiui, are subje(!t to miliaria, althouj^h the water is several hundred feet below the surface, liut here the sand is found to be dani}) a short distance below the surfa(;e, and probably the same condition ju'evails elsewhere in sandy tra(;ts where malaria is ])resent. The rainfall is scanty, but the great range of temi)erature ])robably causes a good deal of dew-condensation on the sand. Sometimes, though rarely, rocky surfaces emit malaria, but ])rol)ably the habitat of the organisms in these cases is in clefts or disintegrated rocky detritus. The eflicieney of attack 07i the human body depends in great measure on the concentration of the organisms within a fciW feet of the surface of the eartli in the evening hours, the diirereiice between day and night temi)erature, the high temperature of the soil, and the suddenness of the fall of temperature. Although the strong- est men in the best of health nuiy be stricken, yet, in most nuilariuus countries, the avoidance of fatigue, of indigestion, and of any chilling of the surface of the body, is an important safeguard. The conditions in which malarious germs are emitted from the soil and concentrated in the nethermost strata of the air are further considered in relation to the emanation of vajior from the earth and the deposition of dew. YELLOW FEVER. Yellow fever results, in all probability, from a fungoid or raicrobic growth, but the jiarticular microbe concerned has not been certainly identified. It prevails habitually in the West Indies and on the coasts of the Gulf of Mexico, and these have been regarded as the original breed- ing grounds. But it has also long been endemic on the west coast of Africa, especially at Sierra Leone. It is easily capable of transi)orta- tion, especially in the case of particular outbreaks and in particular seasons, and it has in several years, like cholera, attained almost a world-wide prevalence. When transplanted to favorable places (and these are mostly seaports with very poor sanitary conditions) it takes root and breaks out in succeeding years as if it were multiplying on the polluted soil. As a matter of fact, it thrives on damp organically contaminated soil, on the walls of houses, and on the wood of ships, in foul holds. It haunts the vicinity of drains, banks of rivers occasion- ally dry, harbors, and crowded rooms or houses. The manner of its growth a good deal resembles that of cholera, but its areas of iireva- lence are smaller, and it is more largely communicated through the air, each case of yellow fever becoming a focus of prevalence in tropical and foul conditions. It requires a high temperature for its propaga- tion, and is arrested, but not destroyed, by frost. Strangers are much more liable to attack than residents, but residents are not always immune. The living cause of the disease clings with great tenacity to ships, walls, etc., for a long time, and is conveyed, in very many instances, by tlie air to persons who approach the infected object. The organic poison seems to multiply outside the body, upon foul surfaces, 64 ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. and thence to infect. It is not transported by the wind — at any rate to a distance — but depends on human movements, on overcrowding, neglected refuse, and absence of proper ventilation. It seems j)robable, from its persistence on the coast, on the banks of tidal rivers, and on ocean-going ships, that it finds a favorite pabulum in slightly saline deposits. DIPHTHERIA. Diphtheria, now one of the most fatal maladies of children, both in Europe and America, is equally preventable by purity of air; but since it is commonly caught by infection, and susceptible persons are attacked through slight doses, absolute j^revention is difficult. Its propagation deiDends to a great extent on schools and close aggregations of children, some of whom may be affected by the disease in a mild form, such as slight sore throat. Some cases arise from a disease of the cow, which is not easily identified, but the great majority of cases of the disease are certainly due to the emission into confined air of the microbes from persons already suffering with sore throat or diphtheria, and therefore the great majority of cases would not occur if schools and dwelling houses were well cleansed and ventilated, and if children with sus- pected throats were as far as possible isolated. The gradual growth of diphtheria in villages and towns and its frequent recurrence indi- cate an infection of the air in houses either from a contaminated sur- face soil, from floor or walls, or from the breath of persons who have had the disease and in whose throats the microbe lingers after their recovery. Diphtheria does not occur at all in clean, dry places, unless introduced by some person or imported article carrying the infective organism. The germ is certainly not present in a potent condition in the outer air. Newly inhabited countries and places have always remained free from diphtheria until the germ has been introduced by human agency. Diphtheria and scarlet fever are among the most widely and con- stantly prevalent, and most fatal, of all diseases in temperate climates. They are both communicable through the air in proximity to a patient, and this is a very common mode of conveyance. But they have never been known to pass across any considerable space through the outside air. The evidence leads very strongly to the conclusion that they are rarely if ever caught by exj^osure to infected air which has been very largely diluted in the free atmosphere. Predisposition to dii)htheria, and probably to a less extent to scarlet fever, is favored by drain air, sewer air, and the emanations from heaps of decaying animal or vege- table matter, dust heaps, and by the various causes of sore throat. And it is probable that the microbe of diphtheria, which has been iden- tified, frequently infects the surfaces whence the foul emanations pro- ceed. It is certainly present in very many places, especially in houses and localities where the disease has formerly prevailed. Measles are often followed by diphtheria, though no source of infection can be ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. G5 discovered. Many persons after recovering from diplitberia are still capable of giving infection by the breath, for the bacillus may remain for months in the mouth and throat. Oases of sore throat which may be slight often communicate to other persons, in consequence of aggre- gation iu foul air, severe sore throats and dii)htheria. It seems that the disease may bo a slight one until by the effects of rebreathed air it develops fatal virulence. For this reason, and owing als(j to the opi)or- tunities of ordinary infection in confined air, diphtheria is a disease which largely depends on schools for increase and i)r(jpagation. It haunts the surfaces of objects which have been exposed to it, and thorough disinfection is required to remove it. The autumn and winter season, damp dwellings, damp soil, dirty farmyards, privies, etc., favor its development; but its continual increase has been due to increased school attendance, meetings, etc., and to the increase in the number of infected places, and iu the means of quick traveling. Ventilation, much more thorough than any now generally practiced, combined with the better disposal of refuse, must be the principal hygienic measure to reduce its prevalence. Investigation of the conditions under which it survives in places and houses, and of the effect of ventilation and proper space in schools in preventing its propagation, is much needed. PNEUMONIA. Two or more difTerent diseases are known under the name of pneu- monia. The temperature of the air is an important factor in its pro- duction, but all countries are subject to it. The maximum number of deaths from this infection occur in December, the minimum in August. Cold is a strong predisposing, but not the ultimate cause. Overcrowd- ing, the want of ventilation, emanations from sewer and filth, play an important part in epidemic outbreaks. Certain bacilli or micrococci are concerned in the production of epidemic pneumonia, and possibly the commonest form of pneumonia is due to the opportunity given by cold or by foul gases for the attack on the body of an organism fre- quently present in the breathing organs. There is little evidence as to the exemption of persons living entirely in the open air and thoroughly well- ventilated dwellings, and not exposed to infection from others, but the i^robability appears to be that many persons have in themselves a cause of a certain sort of pneumonia which may attack them through a chill, but that the breathing of purer air and the prevention of infection through the breath would greatly reduce the number of victims. The typhoidal character of some forms of pneumonia and their mode of origin and spread suggest a connection with soil poisoning and contamination of superjacent air. On these points investigation is needed. Pneumonia is very apt to occur after colds, measles, t^^lioid, malaria, and especially influenza. If it be due to a particular micrococcus, the organism must be very widely disseminated. But probably several dif- ferent organisms are capable of thus affecting the weakened constitution, 230A 5 66 ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. and tlie disease named pneumonia is tlie result of different causes which need more distinct classification than they have yet received. Dusty trades and smoky fogs favor the incidence of pneumonia. BRONCHITIS. Bronchitis, one of the most prevalent and fatal of all diseases in cold and temperate climates, is often directly due to the effect of cold and of a sudden fall of temperature. Altliough much less common and fatal among people living in healthy conditions, it nevertheless often attacks strong constitutions, even in the purest atmosphere. Fatigue predis- poses. A great deal of preventable bronchitis results from imprudence in clothing and in diet — for instance, alcoholic excess — but much also from breathing dusty and smoky air. A smoky fog of some days' dura- tion in cold weather in London causes a heavy mortality, while a fog in the country has little effect. Much bronchitis results from weakness and chill following illness and fatigue. Changes in the blood and accumu- lation of waste products are apt to follow excessive exertion. The importance of warm clothing and of breathing air free from smoke and dust, especially the dust given off in the manufacture of hardware, pot- tery, lead mining, etc., is great in the prevention of this disease. Close rooms where gas is burned contribute largely to bronchial attacks, and in general x)urity of air is one of the first conditions tending to immu- nity. But cold and damp seem to be quite sufficient to produce bron- chitis in some constitutions, and in young children and old people, apart from anything like infection from outside. Indeed, it seems likely that an excess of ozone, or else a cold, bracing air, often determines an attack, and these qualities are beyond doubt sufficient greatly to exacerbate symptoms resulting from a slight cold or chest weakness. A soothing, soft, warm, damp air, on the contrary, quickly ameliorates the condition of a sufferer from bronchitis, cold, or cough; the extraor- dinary power of a whiff of cool, fresh air to increase the malady, and the ill effect of even a glass of cold water, seem to show that the bron- chial tubes, capillaries, and air passages are in a highly sensitive state and that temperature is a matter of extreme importance. Experimental investigation of the tem^Derature and condition of air most tending to rapid recovery from bronchitis might disclose facts of importance in the connection of inflammatory states with the atmosphere. It seems not unlikely that an absence of ozone, deficiency of oxygen, and excess of vapor of water, and of nitrogen or carbon dioxide, might prove favorable. RHEUMATISM AND RHEUMATIC FEVER. Few diseases are more common or cause more suffering than rheu- matism, acute or chronic. A great deal has still to be discovered respecting its external causes. It prevails much more in some districts than in others, and certainly in many cases the mischief is brought into the human system through the air. Damj) and cold in soil and air, ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 67 and cliill in the body, especially when feeble or fatigued, are main fac- tors. As in so many other maladies, the sjteeific cause in rheumatic fever may be the entrance of a micrococcus or other germ by means of a chill, either in hot or cold weather. An inquiry into the distribution of rheiinuitism, with regard especially to soil, climate, air, and dwell- ings, and eliminating as far as i)Ossible predisposing human habits, would furnish results of much value. There is some indication, as in the case of malaria, that air near the ground in low places has much to do with the incidence of the disease. Damp dwellings and clothes conduce to an attack, and to the chronic form. It seems very probable that it would be found that persons removed from ground air, as in the attics of high buildings, are exempt from attack, excei)t through food and drink. MEASLES AND WHOOPINa COUGH. Measles and whooping cough are spread chiefly through the air to persons in the immediate neighborhood of the sick, and of articles, especially clothing, which have been exposed to the infective matter. Segregation, ventilation, and avoidance and disinfection of materials which may disseminate the disease are effective in prevention, where they can be carried out. In the early stage of measles, as of influenza, even while the symptoms are slight, the germs of the disease may infect through the air, and therefore measures of precaution are difficult. The best preventives against widespread and severe attacks are habitual ( regard for sufficient air space and warmth and immediate isolation, DENGUE. Dengue is a disease somewhat resembling influenza in its symptoms, but i)revalent only as an occasional epidemic in tropical countries. It is apparently spread by infection in the air from case to case, but not through the general atmosphere. The reason of its failure to extend beyond hot climates is quite obscure, but it would seem as if it required, like yellow fever, a high temperature outside the body in order to grow and disseminate germs fitted for infection. SMALLPOX. Smallpox has been ascertained by several careful investigations to be capable of passing through long distances, at least half a mile or a mile, of fresh air without losing its power of infecting susceptible per- sons. The ex]3erience of hospitals in London and Paris is well known. Kecent observations on the spread of smallpox from a hospital near Leicester, containing 49 jiatients, showed that a number of cases which occurred in a suburb about 300 yards distant were in all probability due to transport by the wind. The epithelial scales and dust of smallpox cases are rather peculiarly protected from atmospheric influences, and the conditions of the survival of exposed germs need inquiry. 68 ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. INFLUENZA. No disease of the epidemic character has seemed to depend more on the constitution and infection of the general atmosphere than influenza. Its rapid spread, its apparently capricious outbreaks at places wide apart, the almost simultaneous attack, as it seemed, upon a large fraction of the population of a country, masked the true method of progress. But when its track and behavior were carefully followed, these facts became clear — that it never traveled faster than human beings J that many mild cases existed in every large town long before it was generally recognized ; that it took at least six weeks to attain its maximum after the occurrence of the first cases; that its rapidity of advancement from east to west and from town to village corresponded roughly and generally with the rapidity of means of transit ; that large numbers of people not exposed to personal infection escaped; that islands un visited through the period, deep-sea fishermen, and light- house keepers escaped, except in a very few instances where they had been ashore or received communications from infected places; tliat susceptible persons very easily caught the pest within a few days after exposure to infection in the ordinary sense; that inl'ection was some- times conveyed by parcels, letters, clothing, etc., from patients or infected places ; that ships which had cases on board were the means of starting it in islands at which they stopped; and that in previous epi- demics the spread was often so very slow as to be quite unaccountable by any atmospheric quality. Moreover, when the bacillus of influenza was identified, it became easy to comprehend how the countless multi- tudes of exceedingly small organisms alive in the sputum and saliva might be disseminated in the air of buildings and of public conveyances and transmitted from place to -place by commerce and the post. The general atmosphere either diffused them to harmlessness or killed them, for there was no evidence of influenza reaching an isolated community by means of wind blowing from a place where it was prevalent. But in confined or foul air they were capable of passing through many feet without losing their capacity of infection. They were experimentally shown to thrive abundantly on the gum of an envelope,^ and since many patients wrote letters, this must have been rather a common mode of transmission, the organic motes flying upward to the breathing organs of the recipient on his breaking the fastening. There is no difficulty in explaining the quick diffusion of an epidemic having the qualities of influenza among a susceptible population. The miuuteness of the bacilli, their vast numbers in the breathing organs, the short period of incubation, and the early infectiveness, and in mod- ern times the immense daily communications between distant i)laces, have to be taken into consideration. If examination of matter of the *Dr. Klein, British Medical Journal, February, 1894. ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. G9 tenuity of smoke particles, or of the miiiut(ist microbes, could bo under- taken, with a view to determine the rate and extent of its diffusion by human communications, it would po-obably be found that very few dis- tricts in the country are out of microbic touch, as it were, with all the chief centers of ])opulation for a single day, and none for so long as a week; and certainly the air inclosed in a packet from an infected place, when suddenly liberated, would be likely to bear with it active seeds of mischief. But the great majority of cases of influenza were due to proximity to a person already attacked. Most people in the course of a day come into association with ten or twenty others in more or less confined spaces of air. If only one in five catches the influenza, and so on in the same proportion, a fourth part of a large city may be struck down in a very few weeks. In general, one-half or three-fourths escape, being insusceptible, or less suscei)tible than others, or less exposed to the virus. AVhere large numbers of persons work together in one ill- ventilated building, the proportion of attacks is much higher, other things being equal, than where people work at their own homes. But the frequent opportunities of infection at meetings, social gatherings, public houses, in public conveyances, churches, and chapels tend to reduce the inequalities which would otherwise be conspicuous. The distance of air through which influenza can stril^e has not been well ascertained, circumstances being very different, and some forms, such as the catarrhal, being apparently more easily diffused than others. The maximum distance in the recent epidemics, for susceptible persons, could hardly have been less than 100 feet in close air, and 4 feet in the open. Isolation, where practiced, was successful in so far as it was strict. Eiut tbe intercourse of ordinary life makes isolation imi)ossible for the general poi^ulation when once an epidemic of influenza has been allowed to attack a number of centers. Strong measures against impor- tation from other countries and immediate isolation and supervision of the few cases which would occur might succeed in staving off a national infliction, for the precautionary measures would not need enforcement beyond the brief period of its prevalence in neighboring countries. !N"ot only the high mortality, but the enfeeblement of millions of breadwinners for months, years, and even for life has to be consid- ered in connection with the expense of preventive measures. This expense would oidy be a small fraction of the losses incurred by per- mitting the pestilence to rage unchecked. As regards weather and climate, cold is distinctly conducive to the spread of influenza, probably for several reasons : (1) The stillness which often prevails in frost; (2) the closing of windows, etc., and the closer association; (3) the greater prevalence of colds, bronchitis, etc., laying open the breathing organs to attack. The first epidemic in London, at the end of December, 1889, was ushered in by fog and frost, and api)ar- ently rapidly reduced in severity by the mild and strong winds of the latter half of January, 1890. The epidemics in succeeding years were 70 ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. mucli more severe, altLougli tliey came upon a population to some extent protected. At the same time there can be no doubt that an epidemic may occur in any climate and in any weather. The tropics are not exempt. An instructive instance of the subtle diffusion of influenza occurred in a village of Central Africa, which was attacked immediately after the arrival of two natives from an infected place far distant. But outdoor life and less constant communications prevent the quick diffusion and wide i^revalence which belong to civilized nations in temperate climates. The manifest, at present the only iDracticable and yet difficult, meas- ures for i^reventing these great and very destructive epidemics are: Precautions against the introduction of the pest by travelers and by articles sent from infected districts; immediate comx)u]sory notification, without fee, of all cases occurring in a district to the medical officer of the district and through him to the central board ; isolation so far as can be arranged of all the early cases in a district at the homes of the patients ; prohibition of attendance of infected persons at any assem- blage; and publication of the importance of ventilation, and of living, warmly clothed, as much as possible in the open air, unless actually stricken. During the period of illness, and for some time after recov- ery, the greatest care is required to avoid chill, which often induces pneumonia or other evils. The fresh outer air can only be safely breathed when the symptoms have subsided and when the strength has partially returned. It is remarkable that cold air alone, however pure, seems capable of causing a relapse when the system has been greatly enfeebled and the breathing organs left in a highly sensitive condition. COLDS. Colds and sore throat have never received the attention they deserve from an etiological point of view, owing probably to the slight character of the majority of cases. Yet they are important, first for their wide diffusion, endemicity, and frequency, and secondly for their effect in giving opportunity for the attack of more serious disorders, among which may be mentioned diphtheria, measles, pneumonia, bronchitis, and consumption. Close observation for many years has led the jires- ent writer to the conclusion that though primarily a chill, that is exposure, insufficiently clad, to a draft or cold air, is very frequently sufficient to give a slight cold or sore throat, or the feeling of one, yet severe colds are caught in general either (1) in marshy or low and damp situations, or in conditions somewhat similar to those which produce malaria; or (2) by infection from persons after the manner of other infectious diseases. It would appear as if the microorganism, or one species of microorganisms, which sets up a sore throat and severe cold, inhabits the upper layer of earth, especially in damp or marshy places, where decaying vegetable matter abounds, and i)asses into the air, especially in summer and autumn evenings when the earth and water ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 71 are still warm and the air is rapidly cooling. When the microbes are dense in the humid and misty low stratum of air, and when the human body is being ([uickly chilled, tliey are able to attack successfully. The microbe is probably a very common and widely diffused one, and may be ijresent in comparatively small projxjrtion and in less vigor in the lower air generally over the land. At sea it would be absent, and indeed there is good evidence tluit it does Tiot bear long transport in a virulent state in the free air. Colds are scarcely ever caught on the o])en sea, even if the clothes be Avet with salt water, and breezes straight from the Atlantic do not seem ca[)able of inducing sore throat or cold. But, of course, to make an experiment crucial, i)revious life in the oi>en air, disinfection of clothes and if ijossible of the breathing organs, would be necessary. It is not improbable that the microbe of colds, like that of pneumonia, may be freipiently present in the mouth. The experience of St. Kilda,' which used to be absolutely free from colds until the annual boat arrived from the mainland, points to the ordinary presence of the infective particles on clothes or in the breath. The islanders were nearly all struck down with severe colds within a day or two after welcoming their visitors. Probably a similar dose of infection would be quite insufficient to prostrate jiersons on the mainland who were accustomed to the petty assaults of the microbe, and protected by scarcely noticed symptoms of catarrh. An exactly similar thing occurs in the case of influenza. Hundreds of instances were observed in which the proximity of persons who had had inlluenza or had been near cases of influenza gave it to others, and often persons lately arrived in a place which had passed through the epidemic were struck down while the great majority of the resident population remained protectew; the mere iiei;,Mibor- hood (>r a Hw:ini|), witliout any pDlliitioii of wal«'r supply, is olteii siifli- cieiit to i)r()str;it(' tr()()|)s. Tiicre can indeed be no doiibf that air infe(!ted IVom the •iroiiiid very coiiiinoiily eauses awidespn-atl epiih-mic of malaria. When the watiirs of a lh)()d subside, tluj l"ever extends over a wide area anil beyond the limits of tlni Hood; an:(U's are increased by voyaging in a fair climate. Much depends, of course, upon tin- accommodation and diet, as well as upon the atmosjiheric conditions, TIIK IM1M{()VEMKNT OF CLIMATK WITH SLKiHT ELEVATION. From a cerrain number of experiments and from a review of observa- tions taken by meteorologists of differences between temperature and humidity at different heights above the ground, the ])resent writer came to the following conclusions,' shortly stated: The mean temperature at a height of about 100 feet above the ground does not differ sensibly from the mean temperature at 5 feet, but seems to be slightly in excess. The means of daily maxima at heights of (Jl) and 128 feet fall short of the mean maxima at 10 feet, and still more of the maxima at 4 feet. The means of daily minima at the greater heights exceed the mean minima at the smaller heights. There is a certain altitude, apparently' al)out 150 feet above the ground, al which, while the mean temperature is equal to that at 4 feet, the maxima are lower and the minima higher than at any lower point. On an average of nineteen mouths, the mean of maxima was about 1.5° F. lower at 128 feet 10 inches than at 10 feet, and the niean of minima about 0.55° higher. In cyclones the higher, and in anticyclones the lower, points gen- erally have the lowest mean tem])erature. The mean night temperature is always highest at the higher points, and the mean day temperature always lowest. About sunset in clear or foggy weather, when calm, temperature falls much faster near the ground than at some height above it. Equality of lower and upper temperature seems to occur about two hours V)efore suiiset and after suniise, but varies witli tlie season. In clear weather and low fogs, betwecm sunset and sunrise, temi)era- ture is always, or nearly always, higher at heights varying from 50 to 300 feet above the ground than at heights from 2 to 22 feet. In bad weather the higher points are coldest by day and night. In foggy weather, especially with ground or radiation fogs, temperature is very much the lowest near the ground, and within the fog nuich lower than above it. ' Trans. Sanit. Inst, of Great Britain. 90 ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. The mean daily range at 128 feet approaches closely that of the English seacoast, and at 69 feet is about midway between that of coast and inland stations. Mean humidity is more than 1° less at 69 and 128 feet than at 10 feet surrounded by trees. Humidity by day is a little greater, by night much less, 2° or 3°. Places on hills or slopes from 150 to 700 feet above a plain or valley, especially with a southern aspect, have a much smaller annual range, and also a smaller daily range than places on the flat. At 545 feet a superiority of 12° or 13° in the extreme minimum has been registered. Thus we find that at a height about equal to that of the upper rooms of a high house a more equable and drier climate prevails than near the ground, and that conditions on sloping or well-chosen natural elevations are on the whole similar. The importance to delicate persons, and indeed to the majority of people, of living at some height above the ground, especially in places which, are damp, subject to fog, or to unwholesome emanations from the ground, has yet to be appreciated. EFFECT OF IMPURITIES IN THE AIR OF TOWNS ON MENTAL AND BODILY HEALTH. A dense population in manufacturing and other large towns is accus- tomed to breathe a compound mixture in the air which in course of time profoundly affects the health of the race. The oxygen is deficient, the ozone absent, carbon dioxide in excess, hydrocarbons, animal and mineral dust, sulphurous acid, chlorides, ammonia, and microorganisms in pernicious abundance. The small tenements or crowded rooms produce the high death rate, an enormous proportion of deaths in childhood, and of diseases of the lungs at all ages. The best model dwellings, on the contrary, have a lower death rate than the mean of the town, although the population to the acre is dense.^ In New York, about twenty-five years ago, 495,000 persons lived in tenement houses and cellars, most of them dark, damp, and unventilated. By hygienic measures, largely by ventilation, the death rate was reduced in twelve years from 1 in 33 to 1 in 38. Townspeople spend much, more of their lives indoors than the peas- antry. At their work and in their rooms they breathe dust of many sorts, particles of skin, organic poisons, and often many pathogenic germs which, would develop in their bodies if they had not already passed through the specific disorder. The air being deprived of its exhilarating power, they seek stimulants in food and drink, and go to mischievous excess in the consumption of animal flesh and alcohol. Hence many internal diseases. Children are never seen of the right sturdiness and color which is common in the country. Most children 'The corrected death rate of infants in the dwellings, chiefly blocks, of the Metro- politan Association for Improving the Dwellings of the Industrious Classes in Lon- don, has been for some years past much below the average. ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 01 born and bred in the crowded parts of towns are sickly, pale, feeble, unnaturally sliarj) and wizened, tbeir voices are of bad quality, and their height and weif^ht delicient. The elder people become reckless, often depraved, diity, and scjircely ever free from ailments. Their whole bodily, mental, and moral nature deteriorates. Asaconsequence, it is ditticult for native townsfolk to obtain employment in competition with iminifirants from the country. In geneial, policemen, laborers, domestic servants, and several other classes of emiiloyees are found to be most fitted for their duties if country born, and thus perpetual immi- gration is stimulated. The best and strongest people are constantly migratiiifi' to the great towns, brinj;ing their health and youth to sup- ply the demand for good work, and reducing the death rate, so that the true proportion of victims of town air and town conditions fails to be realized. As a matter of fact, it has been ascertained that very few families survive in central London for more than four generations, and that Tnany die out in two or three generations. A true Londoner of the fifth and even of the fourth generation is rare. A very large pro- portion, probably the majority, lose the fine stock of liealth they brought with them from the country within two generations.^ This is a matter of national and international importance, and the fact should be clearly understood by the public and by legislators that the desertion of the country by the best blood involves the rapid consumption of the finest physical, mental, and moral qualities. We have, in fact, in our midst areas — climates, if we may so strain the term — of which the properties come into close competition with the influ- ences of the tropics in bringing about the decline and extirpation of families. If the inner circle of a great city were to exclude immigra- tion for a generation, the poverty of its health resources would stare it in the face, and the falling value of a day's labor would startle it into the promotion of hygienic reform. Eoom and space would be demanded as a necessity for the proper development of human beings. The rate of mortality is greatly increased by the bad air of towns, and especially by the close, foul air of dwellings and workshops. But the rate of sickness is still more increased above that of the breezy country. In one part of the parish of St. George's-in-the-East, in Lon- don, there are nine cases of sickness to one death, but in the worst part of the same district there are twenty known cases of sickness to one death, and a sickness rate of 620 per 1,000. There is, in fact, no good health in the people of the crowded streets, unless it may be for • Defining a Londoner as one who habitually resides in London, with only few holidays, and whose great-grandparents, grandparents, and parents were Londoners, it is exceedingly ditticnlt to find such a specimen among 5,000,000 people. Even true Londoners of the third generation are very disproportionately small in numbers and feeble in health and strength. These facts, however, do not prove that the inhabitants of large towns must of necessity decay unless recruited from without, for with better homes, houses, more air, reduced hours of work, more holidays, and better hygienic conditions of suburban as compared with central quarters, the pros- pect of continued vitality greatly improves. 92 ATMOSPHERE IX RELATION TO HUM AX LIFE AXD HEALTH. a short time amoug newcomers from the country. "They are perpet- ually oil the trudge to the hospitals, and get patched up again and again and live on." ^ Much of this most deplorable state of things may be owing to excess of alcoholic drink, but the excess is in many cases the result of a demand for a stimulant which pure air might have pre- vented. About 1.000.000 out of 4,000.000 persons are treated at London hospitals and dispensaries in a year, and probably this represents fairly well the sickness of great towns in general. A great amount of the lassitude and idleness of the lowest population of cities has been traced by Dr. Ifichardson to want of ventilation, in their own and former gen- erations. •• Tell them," said Mr. Chadwick, the great sanitary reformer, "that when they hear of that disease called consumption they ought to know that it comes constantly from bad administration, which per- mits dwelling houses to be built on damp and sodden and rotten sites, and which permits industrial workers to breathe, but not to live, iu foul airs, gases, vapors, and dusts. Tell them that iu model dwellings a death rate of 15 in the 1,000 has replaced one of 30 in the 1,000." Dr. Louis C. Parkes, medical officer for Chelsea, states that much of the anaemia, the pale faces and disordered digestions, and many of the wast- ing diseases of children in the great towns are to no small extent due to a condition of atmosphere which prevents the perfect action of the lungs and the complete oxygenation of the blood, and so lowers the tone of the body and the ability to repel disease. These facts ought to be impressed ui^on the population. In England it has been computed that the amount now annually spent on intoxicating liquors might double the actual house room for every family. The causes of physical degradation in towns are no doubt complex, but that bad air and want of light are very jjowerful factors, is proved by the following considerations: Children i)laced iu every respect in equally good conditions in town as they have had in the country, with the exception of the difference of town air, in many cases lose health, grow pale and weak, and iu fact do not thrive as they do in the country. Children brought up within the central area of large towns are less robust than children brought up in the country; the children of the poor especially suffer, for though they may have the chance of more flesh meat and often of more food, the air they breathe both without and within doors is inferior, and this afl'ects them not only directly, but indirectly, as through loss of appetite. Very many children in towns have poor and unwholesome appetites. Children in small, crowded towns iu various countries, e. g., Italy or Spain, where the streets are narrow and the air foul, often look unhealthy and feeble, and bad air alone, both in town and country, is known to give similar results. Children who are ailing or simply pallid and unhealthy, after the jjattern of the alley, very soon gain in health and appearance when moved to country air. The experience of very many adults is similar to that of children, and they rapidly or ' Evidence of a doctor in the East End of London. ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 93 gradually lose their aocustoined vigor dining a i»«riod of employment in crowded or badly ventilated i)lrtces. The air of workshops, printing rooms, mills, etc., sometimes changes young, vigorous lo<^»king men almost beyond recognition in the course of one or two years. Outdoor work in towns is far less pernicious, ;ind if houses and streets were more spacious, and work places m(jre airy, the phy.sical degradation would be much less perceptible. The mental and moral effect of living in l)a(l air can hardly be estimated, mixed up as it is with the various other (•(Miditions which generally accompany it. The wits are certainly dulled when oxygen is wanting and carbonic acid in excess, but social contact tends i)erhaps more powerfully to sharpen them. Sharpness, cunning, and alertness increase in towns, but great work demaixling sustained intellectual effort is not favored, but vitiated, by bad air. In schools, the loss of attention, the difficulty of keeping on long at a task, and the symi)athetic weariness, are very frequently the result of bad ventilation. The schoolmaster has great power to improve the quality, or rather the scope, of his pui)irs brains by the ak', To i)er cent compared with mortar; roiiiiiu cement permeable to liic (\vtent of ll'j jx-r cent, and Portland and hygienic cement to the extent of about 10 i)er cent. The rate of ditfusion of gases through i)or<)Us sei)ta is, by Graliam's law, in the inverse ratio of the s(iuar»', root of their gravity. If the gases in the earth l)eli)W the lk)oring be heavy compared with the air of the room, upward dill'usion through the tlooring material must be rather slow, unless other apertures for the ingress of outside air are insulli- cient to supply the draft of fires. WIumi the grounublic supi)ly which has run in the open air for various distances after contamina- tion with sewage and other impurities. The investigation is by no means a simple problem, and where the bacteria are found to have greatly diminished in number in the course of a few miles, the result is often due to other influences besides aera- tion, of which gradual dying out of the organisms is one, and sedimen- tation commonly the most eflicient. Frank's experiments on the River Spree, at Berlin, showed that, though in flowing through the city, the river contained hundreds of thousands of bacteria in the cubic centi- meter, the water some miles lower contained only 3,000 to 8,000, about the same number as in its upper course. In the Isar, below Munich, the number fell from 15,231 to 2,378 in the course of 22 miles. In the Thames and the [Ire, Franklaud did not find any considerable diminu- tion. The Massachusetts State Board of Health found in the course of 23 miles a diminution of free ammonia from 1,728 to 1,299, of albumi- noid ammonia from 826 to 382, of total nitrogen from 3,000 to 2,156, and ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 103 an increase of nitric; acid from 218 to 457. Oxidation to an important degree is shown in tliis case, but the result is not altogether favoraljle to the eOiciency of aeration. In observations made on tlic Kiver Liin- niat before and after passing through Zurich the following were the results: DiHtaiHo ill kilo- iiiutorH. Outflow from lake Station \ I 1.86 Scwcr outlets 2. 175 Station -1 2.485 stations 2.796 Station G 3. 417 station 7 5. 903 Station 8 ! 6. 21 4 Station 9 8. 078 >>uiiilic!r of liactttria per fuliic ceutimoter. 225 1,731 290, 670 12, 870 10, 892 5,902 4,218 2, 346 2,110 l\ri([uel found in the Seine above Paris a rate of 4,800,000 microbes in the liter; below I*aris, 12,800,000; in sewer water, 80,000,000. Instances of outbreaks of typhoid through the use of river water contaminated miles above the intake are not rare. Gloucester suffered by the poisoning of the river by Kidderminster, 20 miles higher up. A single case of typhoid produced the disease in a Scottish town by the drawing back up the course of the river, owing to the obstruction of a weir, of the sewage which had entered below. At Providence, E. I., an epidemic was caused by the very slight pollution of a large and rather rapid stream 3^ miles above the intake. When Lowell, Mass., has had a fever outbreak, Lawrence, lower down, has had a similar attack a little later. The Merrimac River has given several instructive examples of typhoid following pollution, and the Schuylkill, which is contaminated many miles above the intake of Philadelphia, appears to be the chief cause of the prevalence of the disease in that city. Experiments on the artificial aeration of water by the JNIassachusetts Board of Health, and on natural aeration below Is'iagara Falls by Pro- fessor Leeds, show that little or no diminution of organic particles, and no chemical i)uritication, is brought about. Dr. Percy Frankland has found that various disease-causing bacilli present no uniformity in their behavior in potable water. Many pre- serve their vitality for a considerable time — days and weeks — and some, which form spores, for an indefinite time. Gafl'key-s typhoid bacillus preserves its vitality even in distilled water for about fourteen daj's. Altogether, aeration cannot be trusted as effectual in rendering pol- luted water fit for drinking, and the diminution of organisms which to some extent does take place must be attributed to other causes. 104 ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. ACTION OF BACTERIA AND OF THE AIR IN CONNECTION WITH DECOMPOSITION AND PLANT GROWTH. Bacteria, or rDicrobes in general, of an immense nnniber of diiferent kinds are almost nbiquitous on the wliole surface of the earth and on all exposed solids. The favorite habitat of most kinds is the moist surface of some substance of organic origin undergoing decomposition. But some sorts appear to flourish on almost any kind of solid exposed to the air. Thus panes of glass, rocks, metals, tiles, and sand will furnish a crop, the richer, no doubt, for any slight deposit from organic liquids or gases. The chief work, and a very vast one, of microorgan- isms is the transformation of dead organic matter into "inorganic" substances. All the dead vegetable and animal substance lying exposed or where air has access is being transformed into mineral matter by this agency. Decomposition generally consists of oxidation by a class of microbes which take their oxygen from the air, and then the transformation and use of the oxygenized products which sink deeper into the earth by another class of microbes, the anaerobic, which not only themselves detach oxygen from its new compounds, but allow of its being united with jDroducts which are formed by chemical changes as a result of their activity. The whole process converts the nitrogenous elements into ammonia, nitrous and nitric acids, carbonic acid and water, and produces also phosphoric acid. It takes place most readily in porous, somewhat moist earth and at a high temperature. It is a necessary preparation of the soil for the life of plants. The active bacteria of this decomposition, nitrification, or mineralization do not extend to any great depth, generally not so deep as 12 feet, below which the ground is sterile. The rapid oxida- tion going on near the surface leaves little free oxygen for the use of bacteria even at the depth of a few feet. The decomposition effected chiefly by the aerobic bacteria in the upper layers enables plants to draw nutriment from the new products, and thus the presence of air and bacteria in the mold are necessary conditions for the growth of vegetation. These newly discovered facts must have a very important bearing upon agriculture. The relation of air supply, soil, tempera- ture, and moisture to the microbic life in the earth, and consequently to growing crops, will become a fruitful subject of research to chemists, bacteriologists, and scientific farmers. Most of the diseases of plants are dependent to a very great extent on conditions of weather, and many are transported by the air to new situations where they spread as from a center. Thus they differ from the spreading diseases of animals, which are not, on the whole, mainly affected by the character of a season, and are not cariied so far through the atmosphere. The number of plant diseases of an. infectious kind, depending on fungi or microbes, is very great. The vine alone is attacked by more than a hundred species. Some species live in alter- nate generations on different plants j thus the rust of wheat requires ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 105 the barberry plant for ono of its stajjes of development. The spores of mildews and mi(;roscoi)i(; fiiii<;i are j;enerally eje<'ted in j^reat num- bers and with some force into the air,.aii(l are carried from pkuit to plant, or field to field, by the air, as, for instance, the potato disease, Fcronospora infesianH^ and the mildew of the colTee i)lant. TIcut and moisture, dew and ^a-iitle rain, arc favorable to tlic },a«nvth and sj)n;ad of most diseases of plants. The fungus of dry rot grows in damp, unventilated places on badly seasoned wood, and when about to produce spores, seeks the light; its sporangia dry up and dis(;liarge innumerable spores. Tlie common ferment of grape Juice, the tSaccha- romijc<;.s eUipsoideus, grows on the surface of the grai)e, and when it gains access to the fermenting vats develops enormously by budowerful cause of 110 ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. stoppage is nonliomogeneity of atmosphere, or aerial reflection by a number of currents, columns, or laminae of clilierent density. On one day guns and sirens were heard at 10^ miles; two days later were inaudible at 3 miles. Water in the state of vapor mixed with air, in nonhomogeneous parcels, acts powerfully in wasting sounds. ]S"ot only clouds, but layers of transparent air, may produce echoes both intense and long. The power of the particles of cloud to produce aubible echoes has been doubted by Tyndall; but we may observe that a grove of trees in leaf, even of larches and pines, has a very strong eflect in reflecting sound and in heightening its pitch. Let any passen- ger by railway note the marked rise of pitch as the train i)asses between woods of beech or oak. The sound resembles that of a small cascade, or of wind among rustling leaves. The blasts of the fog siren have hitherto been found to be most effectual of all sounds tried for prolongation, x^enetration, and small cost. Its audibility is good at a range of 2 miles under all conditions. Experiments are still needed in order to attain a higher eiflciency in sound propagation for maritime and other purposes, and to ascertain the effect of air in various conditions. The transmission and collection of sound through a few miles by means of suitable exciters, polished funnels, and acoustic mirrors of large size has not been developed as it might be. ,' AURORA BOREALIS AND AUSTEALIS. The aurora borealis or australis is very far from being understood. The height of the luminous arch has been variously estimated and calculated as between 33 and 281 miles, and no doubt greatly varies in different latitudes and in different displays. The greatest height estimated was 500 miles. But in high latitudes the aurora has been observed to emerge from the tops of hills and even as a rule from the ocean, but not from ice floes. Loomis has given much information concerning the distribution of the aurora over the globe in the Smith- sonian Eeport for 1865. Near latitude 40 in the United States only 10 aurorse, on an average, are seen annually. Near latitude 42, about 20; near 45, about 40; and near 50, about 80 are seen. Between lati- tude 50 and 62 aurorae are seen almost every night, as often to the south as to the north. Farther north they are seldom seen except in the south, and from this point northward they diminish in brilliancy and fre<(uency. Near latitude 78 the number is reduced to 10 annu- ally. In the meridian of St. Petersburg the region of 80 auroras is found between 66° and 75°. The region of greatest auroral action is a zone of oval form encircling the North Pole. This zone resembles a line everywhere perpendicular to a magnetic meridian. In Europe aurorse are much rarer than in North America. Some auroral dis- plays, such as the remarkable one of March 30, 1894, are visible both in Europe and America. It seems that an exhibition around one mag- netic pole is often simultaneous with a similar exhibition around the other magnetic pole of the earth. ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. m The aurora appears to be the result of tlie agitation and vibration of particles of air under the influence of the passaj^e of an electric current, diverging from the magnetic polar regions. The current, passes where the resisting power is least, that is, in highly rarefied air, arti(;les hirger than molecules, the electric forces need not be disproportionately great to exceed by many times the force of gravitation even of the sun. If the interplanetary spaces be filled with reflecting and nonreflecting motes derived from sun, and moving at a speed much exceeding that of aeroliteSjWe must suppose that our atmosphere is always receiving within its borders multitudes of these particles which are instantly consumed by friction. Moreover, if such emission proceeds continually from the sun, a similar process takes place from the more distant stars, and the whole of recognized space is traversed by small elementary particles traveling at an enormous speed. The phenomena of the tails of comets tend to corroborate this opinion. In fact, considering the immense num- ber of comets in space, it seems impossible that such small particles can be absent. Compared with their extension, their united mass may be very small indeed within the orbits of the planets. Like meteor swarms, they do not apparently afiect the motion of comets or of plan- ets. None the less, the part they fill in the economy of the universe may be considerable. HEIGHT OF THE ATMOSPHERE. Meteors which have been calculated to pass with ignition through air at a height sometimes as great as 300 miles ; aurorae, of which the height has been estimated by careful observation sometimes to exceed 281 miles; and the duration of twilight, with polarizing effects of the sky, giving a height of 198 to 212 miles, agree in showing a much greater altitude for the extension of our atmosi^here than was formerly supposed. First 5 and then 45 miles was generally stated as the outside limit. And we have to remember that at this great altitude of about 300 miles the atmosphere is dense enough to i)roduce very palpable effects. It would be a bold proposition to assign a limit to the atmosphere within 1,000 miles. ATMOSPHERIC DUST AND THE REFLECTION OF LIGHT. Atmospheric dust, or particles large enough to arrest the movement of light waves, exercise a very important function in the illumination 230a 8 11-4 ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. of the air and sky, wliicli would otherwise be dark except in the direc- tion of the sun, moon, and stars. The beauty of land and sea and of atmospheric effects would be vastly reduced if the reflecting particles were absent, and houses not facing the direct sunshine would be incon- veniently dark. Ozone and oxygen molecules, in some state probably of aggregation, are concerned in the reflection of blue rays, so that an elimination of the coarser dust would not entirely darken the atmos- phere. A complete removal of reflected rays would slightly diminish the terrestrial warmth derived from the incidence of light rays from the general atmosphere, and slightly increase that derived from the direct rays of the sun. Invisible, or barely visible, vapor particles are probably still more efficacious in producing similar effects. SUNLIGHT AND THE EARTH'S ATMOSPHERE — ABSORPTION AND REFLECTION. The light of the sun which reaches the earth has passed through two atmospheres, one of the sun and one of the earth, and each of these atmospheres robs the light emitted from the sun's body of some of its brilliancy and an unequal proportion of color, so that the original color of the sun is modified by the successive subtractions from parts of the spectrum before it reaches our eyes. The sun's atmosphere arrests more blue rays than red, and the light from the middle of the sun's disk is more blue than that which reaches us from the limbs, for it has to traverse less of the solar atmosphere. Prof. S. P. Langley has shown that the effect of the invisible solar atmosphere is so important that its diminution by a third part would cause the temperature of the British Isles to rise above that of the torrid zone. The earth's atmos- phere, also, has the effect of scattering many rays, and principally those waves which form the most refrangible end of the visible spec- trum and gives the impression of blue. By the use of an exceedingly delicate instrument, at a height of 15,000 feet. Professor Langley was able to show that at this elevation, where nearly one-half of the absorb- ing mass of the air was got rid of, the ray 60, near D, had grown in brightness in the x)roportion 2 to 3, that the blue end of the spectrum had grown in intensity out of all proportion to the rest, and that a very great length of invisible spectrum became recognizable beyond the visible rays below the red. The amount of energy in this invisible extension is much less than that of the much shorter visible end. The conclusions to which Professor Langley arrived as the result of his investigations on the solar light was that the sun is blue, that the solar heat is greater than was supjiosed, and that the total loss by absorption in the atmosphere is nearly double what had been estimated. The sun he calculates to be competent to melt a shell of ice 60 yards thick over the whole earth annually, or to exert 1 horsepower for each square yard of the normally exposed surface. Tlie existence of life on the planet, and especially of the human race, must clearly be dependent ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 115 on the capacity of tlie atmosphere for modifying and absorbing the radiant energy of the sun. An investigation of the principal elements concerned in arresting and reflecting the sun's rays would yield results of much interest. Tlio iil»sor])tive and reflecting capacity of vapor in the free air has not been il( termined. The power of any constituents of the air, e. g., ozone and ammonia, apart from dust particles, to scatter the rays of light, is not known. The reasons of the variations in radiation from the surface of t lie earth on different days when the weatlier continues clear and appar- Proc. Roy. Soc, 1869, No. 112. 136 ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. A temperature between 30° and 42° seems to be very favorable to chills, etc., possibly owing to the humidity and conductivity of the air being greater than at lower temperatures, to the absence of the sharp, bracing action of frost, and to the greater number and vitality of microbes in the air than at lower temperatures. Dry, cold winds may have a chilling effect equal to a calm, damp air of the same tem- perature. With regard to all these matters of air and health, or season and health, a great deal might be done for the prevention of disease by the public issue of forecasts, or monitions, at appropriate times, showing the character of the maladies common at the season, or to be expected, and giving some plain directions. If this were done weekly, it is prob- able that the number of lives saved would be larger than those saved by the weather forecasts for coast purposes. EXPLORATION OF THE ATMOSPHERE IN CONNECTION WITH WEATHER FORECASTS AND A MORE EXACT KNOWLEDGE OF ATMOSPHERIC CONDITIONS. Captive balloons regularly used, weather permitting, at a number of well-distributed stations, would give valuable information in addition to the ordinary items furnished for the purposes of governmental fore- casting. Mountain observatories have already been long enough established to give results which show a different distribution of tem- perature and pressure before different types of weather. But balloons might be fitted with instruments which would show the pressure and temperature at several heights in succession during ascent and descent, and this information would very probably be important in forecasts, if the height attained were sufficient. Balloon ascents have shown the atmosphere to be frequently arranged in blocks or masses of air of very different temperatures within a short distance of each other, and occasionally in an inverse order to that which might be expected from the law of diminution with height. Thus, on July 17, 1802, the ther- mometer on the earth was 59 ; at 10,000 feet, 26 ; at 15,000 feet, 31 ; at 19,500 feet, 42; but on descent a little below this height, the tempera- ture fell with extraordinary rapidity to 16. Strata much below the freezing point may have a few hundred or thousand feet above them, currents of air at 40 or 42. The variations are often very large and rapid. The greater the height, within the limits of the cirrus cloud at least, tlie greater apparently are the differences between adjacent strata or masses of air. Irregularity of temperature and humidity dis- tribution must have a considerable influence on the consequent weather, and a series of balloon observations for a term of years at a good num- ber of stations would probably be of very considerable service both for theoretical and practical purposes. Free balloons for exploration, such as have given good results in France, might be contrived to ascend to some desired height, and then ATMOSPHERE IN RELATION TO III'MAX LIFE AND HEALTTL 137 rapidly to desceiMl, so as to be a;;iiiii availaMc Tlic liy(lro;;('ii balloon might, for instance, carry a small vessel containing a substance which wonhl combine with the oxygen and with the vapor of the air at an approximately known and arranged rate; the inereased weight ol" the contents would reverse the asec^nt at a roughly (uileulated height, and, excei)t with strong winds, the balloon would descend at no great dis- tance. In calm weather its motion (jould be watclied with a telescope and its aj)i)i()ximate height noted. Int(^lligent persons in towns and villages should i)reviously be instructed to secure the descended bal- loon and to take readings. Schoolmasters in France have received such instructions. It is i)rol)able that the condition of air immediately preceding torna- does, cyclones, and blizzards, and thunderstorms or heavy rains would frequently be of sufliciently remarkable character to give ground for generalizations from balloon records by which the advent of these phenomena could be foretold. ELE( TRICITY, CLOUDS, AND RAIN. The connection of electricity with the formation of rain, snow, and hail recpiires much fuller Investigation than it has yet received, and research in this Held is sure to yield interesting results. The upper air is positive, the lower often negative, and the almost invariable neces- sity for two or more layers of clouds for the [)roduction of anything more than misty rain over level ground seems to point to an almost invariable coexistence of oppositely electrified clouds in the formation of heavy rain. Heavy showers and snowstorms always show a large development of free electricity, but of course this may be merely a con- seqne7ice of the agglomeration of the drops, and in no important degree a cause of the preci])itation. In the heavy clouds of showers there seem to be generally several zones or areas of opposite electricities. The observations on Pikes Peak show the large development of free electricity in the rain, and hail, and snow formed at great altitudes. Howard deduced from Keed's observations that snow and liail unmixed with rain arc i)ositive almost without excejjtion. Probably if the snow and hail could have been intercepted in the u]>per air, it might have been said "without exception." On one occasion, when '^a most awful darkness filled the atmos])here" and some rain fell mixed with hail, the positive charge became ''as strong as it could iiossibly be."^ Exjjeriment on the electricity of clouds, showers, etc., does not seem to have been continued in recent years, though much might be learned from it in eonnection with the other conditions of weather. On the other hand, laboratory experiment on the electrification of steam, of smoke, and of small drops has led to most interesting results. An electrified rod, at a few thousand volts, with brush discharge, in a ' Phil. Traua., Vols. XXXI, XXXII. 138 ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. vessel filled with smoke, widened the "dust-free coat" enormously, and the whole box was cleared of smoke, A discharge from a Voss or Wimshurst machine through smoke causes a very rapid aggregation in masses or flakes along the lines of force, and the soot is left on the sides and floor of the vessel. The most effect is produced when the air itself is electrified, but a knob acts less quickly than a point. A piece of rubbed sealing wax held about a j'ard distant from a fall- ing water jet broken into small drops causes the drops at once to cease to scatter, and unites them into large drops as of a thunder shower. A cloud of steam turns into "Scotch mist;" a spherule of water amalgamates with a large mass at the first opportunity; if there be the slightest difference in size or in electrification, the repulsion is exchanged for attraction before actual contact. The opposed surfaces come into collision with considerable violence, even when the relative motion of the centers of the masses is small. Surface tension is over- come, and thus violence of contact promotes the coalescence of drops. The whole subject is of deep interest, not only in connection with the causes of rain and conditions of cloud formation, but with the physics of the atmosphere generally. OVERCOOLING, ETC. Other matters deserving fuller investigation than they have yet received, although they have been the subject of valuable memoirs by Dufour, Von Bezold, and others, are the capability of vapor existing in the atmosphere beyond the normal degree of saturation, "overcooling," as it has been termed; and, secondly, the degree of temperature and other conditions in which small drops of water and cloud globules can exist unfrozen. These questions are of great interest both meteorolog- ically and in relation to physics in general. With regard to the supersaturation of air, this has beenfjroved to be possible in the laboratory to a remarkable degree when dust is absent, but has not yet been proved in the atmosphere. It seems highly prob- able that occasionally, especially in very moist air, when much rain and cloud has been long continued, or in the intervals between thunder clouds at a great height, there may be spaces of the atmosphere iu which dust is so rare and moisture so large that the ordinary point of saturation may be passed. The accumulation upon drops or snowflakes passing through such a space would be heavy. The latent heat of condensation from vapor upon cold drops of ice Las been supposed, owing to its very considerable amount, to make the growth of such drops or hailstones to a large size by deposition from vapor impossible. But rapid passage through cold air may be found to dispose very quickly of the heat thus set free. Experiment is needed on this point. With regard to the liquidity of droplets below the freezing point, the ATMOSPIIKKE IN* RELATION TO Ill.MAN LIFE AND HEALTH. 139 fact is full}' jhovcmI, and clouds and f()