V LETTERS ON NATURAL MAGIC. Printed by John Stark, Edinburgh. LETTERS ON NATURAL MAGIC, ADDRESSED TO Sir WALTER SCOTT, Bart. BY Sir DAVID BREWSTER, K. H. LL.D. F.R.S. V.P.R.S.E. &C. &C. LONDON: JOHN MURRAY, ALBEMARLE STREET. MDCCCXXXIl. CONTENTS. LETTER I. Extent and interest of the subject — Science employed by ancient governments to deceive and enslave their subjects — Influence of the supernatural upon ignorant minds — Means employed by the ancient magicians to establish their authority — Derived from a knowledge of the phenomena of Nature — From the influence of narcotic drugs upon the victims of their delusion — From every branch of science — Acoustics — Hydro- statics — Mechanics — Optics — M. Salverte's work on the occult sciences — Object of the following Letters, 1 LETTER II. The eye the most important of our organs — Popular description of it — The eye is the most fertile source of mental illusions — Disappearance of objects when their images fall upon the base of the optic nerve — Disap- pearance of objects when seen obliquely — Deceptions arising from viewing objects in a faint light — Lumi- nous figures created by pressure on the eye either from external causes or from the fulness of the blood-vessels — Ocular spectra or accidental colours — Remarkable effects produced by intense light — Influence of the vi CONTENTS. imagination in viewing these spectra — Remarkable illusion produced by this affection of the eye — Dura- tion of impressions of light on the eye — Thauma- trope — Improvements upon it suggested — Disap- pearance of halves of objects or of one of two persons — Insensibility of the eye to particular colours — Re- markable optical illusion described, ... 8 LETTER III. Subject of spectral illusions — Recent and interesting case of Mrs A. — Her first illusion affecting the ear — Spec- tral apparition of her husband — Spectral apparition of a cat — Apparition of a near and living relation in grave-clothes seen in a looking-glass — Other illusions affecting the ear — Spectre of a deceased friend sitting in an easy chair — Spectre of a coach and four filled with skeletons — Accuracy and value of the preceding cases — State of health under which they arose — Spec- tral apparitions are pictures on the retina — The ideas of memory and imagination are also pictures on the retina — General views of the subject — Approximate explanation of spectral apparitions, ... 37 LETTER IV. Science used as an instrument of imposture — Deceptions with plane and concave mirrors practised by the an- cients — The magician's mirror — Effects of concave mirrors — Aerial images — Images on smoke — Combi- nation of mirrors for producing pictures from living objects — The mysterious dagger — Ancient miracles with concave mirrors — Modern necromancy with them, as seen by Cellini — Description and effects of the magic lanthorn — Improvements upon it — Phan- CONTENTS. vii tasmagoric exhibitions of Philipstal and others — Dr Young's arrangement of Lenses, &c. for the Phantas- magoria — Improvements suggested — Catadioptrical phantasmagoria for producing the pictures from living objects — Method of cutting off parts of the figures — Kircher's mysterious handwriting on the wall — His hollow cylindrical mirror for aerial images — Cylindri- cal mirror for reforming distorted pictures — Mirrors of variable curvature for producing caricatures, . 56 LETTER V. Miscellaneous optical illusions — Conversions of cameos into intaglios or elevations into depressions, and the reverse — Explanation of this class of deceptions — Sin- gular effects of illumination with light of one simple colour — Lamps for producing homogeneous yellow light — Methods of increasing the effects of this exhi- bition — Method of reading the inscriptions of coins in the dark — Art of decyphering the effaced inscriptions of coins — Explanation of these singular effects — Ap- parent motion of the eyes in portraits — Remarkable examples of this — Apparent motion of the features of a portrait, when the eyes are made to move — Remark- able experiment of breathing light and darkness, . 98 LETTER VI. Natural phenomena marked with the marvellous — Spectre of the Brocken described — Analogous pheno- mena — Aerial spectres seen in Cumberland — Fata Morgana in the straits of Messina — Objects below the horizon raised and magnified by refraction — Singular example seen at Hastings — Dover Castle seen through the hill on which it stands — Erect and inverted images viii CONTENTS. of distant ships seen in the air — Similar phenomena seen in the arctic regions — Enchanted coast — Mr Scoresby recognizes his father's ship by its aerial image — Images of cows seen in the air — Inverted images of horses seen in South America — Lateral images produced by refraction — Aerial spectres by re- flexion, — Explanation of the preceding phenomena, 127 LETTER VII. Illusions depending on the ear — Practised by the an- cients — speaking and singing heads of the ancients — Exhibition of the invisible girl described and explain- ed — Illusions arising from the difficulty of determin- ing the direction of sounds — Singular example of this illusion — Nature of ventriloquism — Exhibitions of some of the most celebrated ventriloquists — M. St Gille — Louis Brabant — M. Alexandre — Captain Lyon's account of Eskimaux ventriloquists, . 157 LETTER VIII. Musical and harmonic sounds explained — Power of breaking glasses with the voice — Musical sounds from the vibration of a column of air — And of solid bodies — Kaleidophone — Singular acoustic figures produced on sand laid on vibrating plates of glass — And on stretched membranes — Vibration of flat rulers, and cy- linders of glass — Production of silence from two sounds — Production of darkness from two lights — Explanation of these singular effects — Acoustic auto- maton — Droz's bleating sheep — Maillardet's singing bird — Vaucanson's flute player — His pipe and tabor player — Baron Kempelen's talking engine — Kratzen- stein's speaking machine — Mr Willis's researches, 1 79 CONTENTS. ix LETTER IX. Singular effects in nature depending on sound — Perma- nent character of speech — Influence of great elevations on the character of sounds, and on the powers of speech — Power of sound in throwing down buildings — Dog killed by sound — Sounds greatly changed un- der particular circumstances — Great audibility of sounds during the night explained — Sounds deadened in media of different densities- — Illustrated in the case of a glass of champagne — And in that of new fallen snow — Remarkable echoes — Reverberations of thun- der — Subterranean noises — Remarkable one at the Solfaterra — Echo at the Menai Suspension bridge — Temporary deafness produced in diving-bells — Inau- dibility of particular sounds to particular ears — Vocal powers of the statue of Memnon — Sounds in granite rocks — Musical mountain of El-Nakous, . . 212 LETTER X, Mechanical inventions of the ancients few in number — Ancient and modern feats of strength — Feats of Ecke- berg particularly described — General explanation of them — Real feats of strength performed by Thomas Topham — Remarkable power of lifting heavy persons when the lungs are inflated — Belzoni's feat of sustain- ing pyramids of men — Deception of walking along the ceiling in an inverted position — Pneumatic apparatus in the foot of the house-fly for enabling it to walk in opposition to gravity — Description of the analogous apparatus employed by the gecko lizard for the same purpose — Apparatus used by the Echineis remora or sucking-fish, ...... 244 X CONTENTS. LETTER XI. Mechanical automata of the ancients — Moving tripods — Automata of Daedalus — Wooden pigeon of Archy- tas — Automatic clock of Charlemagne — Automata made by Turrianus for Charles V. — Camus's auto- matic carriage made for Louis XIV. — Degennes's mechanical peacock — Vaucanson's duck which ate and digested its food — Du Moulin 's automata • — Baron Kempelen's automaton chess-player — Drawing and writing automata — Maillardet's conjuror — Benefits derived from the passion for automata — Examples of wonderful machinery for useful purposes — Duncan's tambouring machinery — Watt's statue turning ma- chinery — Babbage's calculating machinery, . 264 LETTER XII. Wonders of chemistry — Origin, progress, and objects of alchemy — Art of breathing fire — Employed by Bar- chochebas, Eunus, &c. — Modern method — Art of walking upon burning coals and red hot iron, and of plunging the hands in melted lead and boiling water — Singular property of boiling tar — Workmen plunge their hands in melted copper — Trial of ordeal by fire — Aldini's incombustible dresses — Examples of their wonderful power in resisting flame — Power of breath- ing and enduring air of high temperatures — Experi- ments made by Sir Joseph Banks, Sir Charles Blag- den, and Mr Chantry, 297 LETTER XIII. Spontaneous combustion — In the absorption of air by powdered charcoal— .And of hydrogen by spongy pla- CONTENTS. tinum — Dobereiner's lamp — Spontaneous combustion in the bowels of the earth — Burning cliffs — Burning soil — Combustion without flame — Spontaneous com- bustion of human beings — Countess Zangari — Grace Pett — Natural fire temples of the Guebres — Sponta- neous fires in the Caspian Sea — Springs of inflamma- ble gas near Glasgow — Natural light-house of Mara- caybo — New elastic fluids in the cavities of gems — Chemical operations going on in their cavities — Ex- plosions produced in them by heat — Remarkable changes of colour from chemical causes — Effects of the nitrous oxide or paradise gas when breathed — Re- markable cases described — Conclusion. . 313 LETTERS ON NATURAL MAGIC, ADDRESSED TO Sir WALTER SCOTT, Bart. LETTER I. Extent and interest of the subject — Science employed by an- cient governments to deceive and enslave their subjects — In- fluence of the supernatural upon ignorant minds — Means employed by the ancient magicians to establish their authori- ty — Derived from a knowledge of the phenomena of Na- ture — From the influence of narcotic drugs upon the vic- tims of their delusion — From every branch of science — Acoustics — Hydrostatics — Mechanics — Optics — M. Sal- verte's work on the occult sciences — Object of the following Letters. My Dear Sir Walter, As it was at your suggestion that I undertook to draw up a popular account of those prodigies of the ' material world which have received the appella- A 2 LETTERS ON NATURAL MAGIC. tion of Natural Magic, I have availed myself of the privilege of introducing- it under the shelter of your name. Although I cannot hope to produce a volume at all approaching in interest to that which you have contributed to the Family Library, yet the popular character of some of the topics which belong to this branch of Demonology may atone for the defects of the following Letters ; and I shall deem it no slight honour if they shall be considered as forming an appropriate supplement to your valuable work. The subject of Natural Magic is one of great extent as well as of deep interest. In its widest range, it embraces the history of the governments and the superstitions of ancient times, — of the means by which they maintained their influence over the human mind, — of the assistance which they derived from the arts and the sciences, and from a knowledge of the powers and phenomena of nature. When the tyrants of antiquity were un- able or unwilling to found their sovereignty on the affections and interests of their people, they sought to entrench themselves in the strongholds of supernatural influence, and to rule with the de- legated authority of heaven. The prince, the priest, and the sage, were leagued in a dark conspiracy to deceive and enslave their species ; and man, who re- fused his submission to a being like himself, became the obedient slave of a spiritual despotism, and wil- lingly bound himself in chains when they seemed to have been forged by the gods. This system of imposture was greatly favoured by the ignorance of these early ages. The human mind is at all times fond of the marvellous, and the 3 RESOURCES OF THE ANCIENT MAGIC. 3 credulity of the individual may be often measured by his own attachment to the truth. When know- ledge was the property of only one caste, it was by no means difficult to employ it in the subjugation of the great mass of society. An acquaintance with the motions of the heavenly bodies, and the variations in the state of the atmosphere, enabled its possessor to predict astronomical and meteorolo- gical phenomena with a frequency and an accuracy which could not fail to invest him with a divine character. The power of bringing down fire from the heavens, even at times when the elect: ic influ- ence was itself in a state of repose, could be regard- ed only as a gift from heaven. The power of ren- dering the human body insensible to fire was an irresistible instrument of imposture ; and in the combinations of chemistry, and the influence of drugs and soporific embrocations on the human frame, the ancient magicians found their most avail- able resources. The secret use which was thus made of scienti- fic discoveries and of remarkable inventions, has no doubt prevented many of them from reaching the present times ; but though we are very ill informed respecting the progress of the ancients in various departments of the physical sciences, yet we have sufficient evidence that almost every branch of knowledge had contributed its wonders to the ma- gician's budget, and we may even obtain some in- sight into the scientific acquirements of former ages, by a diligent study of their fables and their miracles. The science of Acoustics furnished the ancient sorcerers with some of their best deceptions. The 4 LETTERS ON NATURAL MAGIC. imitation of thunder in their subterranean temples could not fail to indicate the presence of a super- natural agent. The golden virgins whose ravish- ing- voices resounded through the temple of Del- phos ; — the stone from the river Pactolus, whose trumpet notes scared the robber from the treasure which it guarded ; — the speaking head which utter- ed its oracular responses at Lesbos ; — and the vocal statue of Memnon, which began at the break of day to accost the rising sun, — were all deceptions de- rived from science, and from a diligent observation of the phenomena of nature. The principles of Hydrostatics were equally avail- able in the work of deception. The marvellous fountain which Pliny describes in the Island of Andros as discharging wine for seven days, and water during the rest of the year ; — the spring of oil which broke out in Rome to welcome the re- turn of Augustus from the Sicilian war, — the three empty urns which filled themselves with wine at the annual feast of Bacchus in the city of Elis, — the glass tomb of Belus which was full of oil, and which, when once emptied by Xerxes, could not again be filled, — the weeping statues, and the per- petual lamps of the ancients, — were all the obvious effects of the equilibrium and pressure of fluids. Although we have no direct evidence that the phi- losophers of antiquity were skilled in Mechanics, yet there are indications of their knowledge, by no means equivocal, in the erection of the Egyptian obelisks, and in the transportation of huge masses of stone, and their subsequent elevation to great heights in their temples. The powers which they employed, and the mechanism by which they operated, have RESOURCES OF THE ANCIENT MAGIC. 5 been studiously concealed, but their existence may- be inferred from results otherwise inexplicable, and the inference derives additional confirmation from the mechanical arrangements which seem to have formed a part of their religious impostures. When in some of the infamous mysteries of ancient Rome, the unfortunate victims were carried off by the g ods, there is reason to believe that they were hurried away by the power of machinery ; and when Apol- lonius, conducted by the Indian sages to the temple of their god, felt the earth rising and falling be- neath his feet like the agitated sea, he was no doubt placed upon a moving floor capable of imitat- ing the heavings of the waves. The rapid descent of those who consulted the oracle in the cave of Trophonius, — the moving tripods which Apollo- nius saw in the Indian temples, — the walking sta- tues at Antium, and in the Temple of Hierapolis, — and the wooden pigeon of Archytas, are specimens of the mechanical resources of the ancient magic. But of all the sciences Optics is the most fertile in marvellous expedients. The power of bringing the remotest objects within the very grasp of the observer, and of swelling into gigantic magni- tude the almost invisible bodies of the material world, never fails to inspire w T ith astonishment even those who understand the means by which these prodigies are accomplished. The ancients, indeed, were not acquainted with those combinations of lenses and mirrors which constitute the telescope and the microscope, but they must have been fa- miliar with the property of lenses and mirrors to form erect and inverted images of objects. There is reason to think that they employed them to ef~ 6 LETTERS ON NATURAL MAGIC. feet the apparition of their gods ; and in some of the descriptions of the optical displays which hallow- ed their ancient temples, we recognize all the trans- formations of the modern phantasmagoria. It would be an interesting pursuit to embody the information which history supplies respecting the fables and incantations of the ancient supersti- tions, and to show how far they can be explained by the scientific knowledge which then prevailed. This task has, to a certain extent, been performed by M. Eusebe Salverte, in a work on the occult sciences, which has recently appeared ; but notwithstanding the ingenuity and learning which it displays, the individual facts are too scanty to support the specu- lations of the author, and the descriptions are too meagre to satisfy the curiosity of the reader.* In the following letters I propose to take a wider range, and to enter into more minute and popular details. The principal phenomena of nature, and the leading combinations of art, which bear the im- press of a supernatural character, will pass under our review, and our attention will be particularly called to those singular illusions of sense, by which the most perfect organs either cease to perform their functions, or perform them faithlessly ; and where the efforts and the creations of the mind pre- dominate over the direct perceptions of external nature. * We must caution the young reader against some of the views given in M. Salverte's work. In his anxiety to ac- count for every thing miraculous by natural causes, he has ascribed to the same origin some of those events in sacred history which Christians cannot but regard as the result of divine agency. GENERAL OBJECT OF THE WORK. 7 In executing this plan, the task of selection is rendered extremely difficult, by the superabundance of materials, as well as from the variety of judg- ments for which these materials must be prepared. Modern science may be regarded as one vast mi- racle, whether we view it in relation to the Al- mighty Being, by whom its objects and its laws were formed, or to the feeble intellect of man, by which its depths have been sounded, and its myste- ries explored : — And if the philosopher who is fami- liarized with its wonders, and who has studied them as necessary results of general laws, never ceases to admire and adore their author, how great should be their effect upon less gifted minds, who must ever view them in the light of inexplicable prodigies. — Man has in all ages sought for a sign from heaven, and yet he has been habitually blind to the millions of wonders with which he is surrounded. If the fol- lowing pages should contribute to abate this deplor- able indifference to all that is grand and sublime in the universe, and if they should inspire the reader with a portion of that enthusiasm of love and gra- titude which can alone prepare the mind for its final triumph, the labours of the author will not have been wholly fruitless. 8 LETTERS ON NATURAL MAGIC. LETTER II. The Eye the most important of our organs — Popular descrip- tion of it — The eye is the most fertile source of mental illu- sions — Disappearance of objects 'when their images fall upon the base of the optic nerve — Disappearance of objects when seen obliquely — Deceptions arising from viewing objects in a faint light — Luminous figures created by pressure on the eye either from external causes or from the fulness of the blood- vessels — Ocular spectra or accidental colours — Remarkable effects produced by intense light — Influence of the imagina- tion in viewing these Spectra — Remarkable illusion produced by this affection of the eye — Duration of impressions of light on the eye — Thaumatrope — Improvements upon it suggest- ed — Disappearance of halves of objects or of one of two per- sons — Insensibility of the eye to particular colours — Re- markable optical illusion described. Of all the organs by which we acquire a know- ledge of external nature the eye is the most re- markable and the most important. By our other senses the information we obtain is comparatively limited. The touch and the taste extend no fur- ther than the surface of our own bodies. The sense of smellis exercised within a very narrow sphere, and that of recognizing sounds is limited to the distance at which we hear the bursting of a meteor and the crash of a thunderbolt. But the eye enjoys a bound- less range of observation. It takes cognizance not only of other worlds belonging to the solar system, POWER AND STRUCTURE OF THE EYE. 9 but of other systems of worlds infinitely removed into the immensity of space ; and when aided by the telescope, the invention of human wisdom, it is able to discover the forms, the phenomena, and the move- ments of bodies whose distance is as inexpressible in language as it is inconceivable in thought. While the human eye has been admired by ordi- nary observers for the beauty of its form, the power of its movements, and the variety of its expression, it has excited the wonder of philosophers by the ex- quisite mechanism of its interior, and its singular adaptation to the variety of purposes which it has to serve. The eye-ball is nearly globular, and is about an inch in diameter. It is formed external- ly by a tough opaque membrane called the sclerotic coat, which forms the white of the eye, with the ex- ception of a small circular portion in front called the cornea* This portion is perfectly transparent, and so tough in its nature as to afford a powerful resist- ance to external injury. Immediately within the cornea, and in contact with it, is the aqueous hu- mour, a clear fluid, which occupies only a small part of the front of the eye. Within this humour is the iris, a circular membrane with a hole in its centre called the pupil. The colour of the eye resides in this membrane, which has the curious property of contracting and expanding so as to diminish or en- large the pupil, — an effect which human ingenuity has not been able even to imitate. Behind the iris is suspended the crystalline lens in a fine transparent capsule or bag of the same form with itself. It is then succeeded by the vitreous humour, which re- sembles the transparent white of an egg, and fills up the rest of the eye. Behind the vitreous humour, 10 LETTERS ON NATURAL MAGIC. there is spread out on the inside of the eye-ball a fine delicate membrane, called the retina, which is an expansion of the optic nerve, entering- the back of the eye, and communicating with the brain. A perspective view and horizontal section of the left eye, shown in the annexed figure, will convey a popular idea of its structure. It is, as it were, a small camera obscura, by means of which the pic- tures of external objects are painted on the retina, and in a way of which we are ignorant, it conveys the impression of them to the brain. Fig. I, This wonderful organ may be considered as the sentinel which guards the pass between the worlds of matter and of spirit, and through which all their communications are interchanged. The optic nerve is the channel by which the mind peruses the hand- writing of Nature on the retina, and through which it transfers to that material tablet its decisions and its creations. The eye is consequently the princi- pal seat of the supernatural. When the indications of the marvellous are addressed to us through the OCULAR ILLUSIONS. 11 ear, the mind may be startled without being de- ceived, and reason may succeed in suggesting some probable source of the illusion by which we have been alarmed : But when the eye in solitude sees before it the forms of life, fresh in their colours and vivid in their outline ; when distant or depart- ed friends are suddenly presented to its view ; when visible bodies disappear and reappear without any intelligible cause ; and when it beholds objects, whe- ther real or imaginary, for whose presence no cause can be assigned, the conviction of supernatural agency becomes under ordinary circumstances una- voidable. Hence it is not only an amusing but an useful occupation to acquire a knowledge of those causes which are capable of producing so strange*a belief, whether it arises from the delusions which the mind practises upon itself, or from the dexterity and sci- ence of others. . I shall therefore proceed to explain those illusions which have their origin in the eye, whether they are general, or only occasionally ex- hibited in particular persons, and under particular circumstances. There are few persons aware that when they look with one eye there is some particular object before them to which they are absolutely blind. If we look with the right eye this point is always about 15° to the right of the object which we are viewing, or to the right of the axis of the eye or the point of most distinct vision. If we look with the left eye the point is as far to the left. In order to be convinced of this curious fact, which was dis- covered by M. Mariotte, place two coloured wafers upon a sheet of white paper at the distance of three 12 LETTERS ON NATURAL MAGIC. inches, and look at the left hand wafer with the right eye at the distance of about 11 or 12 inches, taking* care to keep the eye straight above the wafer, and the line which joins the eyes parallel to the line which joins the wafers. When this is done, and the left eye closed, the right hand wafer will no longer be visible. The same effect will be pro- duced if we close the right eye and look with the left eye at the right hand wafer. When we examine the retina to discover to what part of it this in- sensibility to light belongs, we find that the image of the invisible wafer has fallen on the base of the optic nerve, or the place where this nerve enters the eye and expands itself to form the retina. This point is shown in the preceding figure by a con- vexity at the place where the nerve enters the eye. But though light of ordinary intensity makes no impression upon this part of the eye, a very strong light does, and even when we use candles or high- ly luminous bodies in place of wafers the body does not wholly disappear, but leaves behind a faint cloudy light, without, however, giving any thing like an image of the object from which the light proceeds. When the objects are white wafers upon a black ground, the white wafer absolutely disappears, and the space which it covers appears to be completely black ; and as the light which illuminates a land- scape is not much different from that of a white wafer, we should expect, whether we use one or both eyes,* to see a black or a dark spot upon every land- * When both eyes are open, the object whose image falls upon the insensible spot of the one eye is seen by the other, so that though it is not invisible, yet it will only be half as luminous, and therefore two dark spots ought to be seen. DARK SPOT ON THE RETINA, &C. 13 scape, within 15° of the point which most parti- cularly attracts our notice. The Divine Artificer, however, has not left his work thus imperfect. Though the base of the optic nerve is insensible to light that falls directly upon it, yet it has been made susceptible of receiving- luminous impressions from the parts which surround it, and the consequence of this is, that when the wafer disappears, the spot which it occupied, in place of being- black, has always the same colour as the ground upon which the wafer is laid, being white when the wafer is placed upon a white ground, and red when it is placed upon a red ground. This curious effect may be rudely il- lustrated by comparing the retina to a sheet of blot- ting-paper, and the base of the optic nerve to a cir- cular portion of it covered with a piece of sponge. If a shower falls upon the paper, the protected part will not be wetted by the rain which falls upon the sponge that covers it, but in a few seconds it will be as effectually wetted by the moisture which it absorbs from the wet paper with which it is sur- rounded. In like manner the insensible spot on the retina is stimulated by a borrowed light, and the apparent defect is so completely removed that its existence can be determined only by the experi- ment already described. Of the same character, but far more general in its effects, and important in its consequences, is another illusion of the eye which presented it- self to me several years ago. When the eye is steadily occupied in viewing any particular object, or when it takes a fixed direction while the mind is occupied with any engrossing topic of speculation or of grief, it suddenly loses sight of, or becomes 14 LETTERS ON NATURAL MAGIC. blind to, objects seen indirectly, or upon which it is not fully directed. This takes place whether we use one or both eyes, and the object which disap- pears will reappear without any change in the posi- tion of the eye, while other objects will vanish and revive in succession without any apparent cause. If a sportsman, for example, is watching with intense interest the motions of one of his dogs, his compan- ion, though seen with perfect clearness by indirect vision, will vanish, and the light of the heath or of the sky will close in upon the spot which he oc- cupied. In order to witness this illusion, put a little bit of white paper on a green cloth, and within three or four inches of it, place a narrow strip of white paper. At the distance of twelve or eighteen inches, fix one eye steadily upon the little bit of white paper, and in a short time a part or even the whole of the strip of paper will vanish as if it had been removed from the green cloth. It will again reappear, and again vanish, the effect depend- ing greatly on the steadiness with which the eye is kept fixed. This illusion takes place when both the eyes are open, though it is easier to observe it when one of them is closed. The same thing hap- pens when the object is luminous. When a candle is thus seen by indirect vision, it never wholly dis- appears, but it spreads itself out into a cloudy mass, the centre of which is blue, encircled with a bright ring of yellow light. This inability of the eye to preserve a sustained vision of objects seen obliquely, is curiously com- pensated by the greater sensibility of those parts of the eye that have this defect. The eye has the OBLIQUE VISION FEEBLE LIGHT. 15 power of seeing objects with perfect distinctness, only when it is directed straight upon them ; that is, all objects seen indirectly are seen indistinctly ; but it is a curious circumstance, that when we wish to obtain a sight of a very faint star, such as one of the satellites of Saturn, we can see it most dis- tinctly by looking away from it, and when the eye is turned full upon it, it immediately disappears. Effects still more remarkable are produced in the eye when it views objects that are difficult to be seen from the small degree of light with which they hap- pen to be illuminated. The imperfect view which we obtain of such objects forces us to fix the eye more steadily upon them ; but the more exertion we make to ascertain what they are, the greater difficulties do we encounter to accomplish our ob- ject. The eye is actually thrown into a state of the most painful agitation, the object will swell and contract, and partly disappear, and it will again be- come visible when the eye has recovered from the delirium into which it has been thrown. This phe- nomenon may be most distinctly seen when the ob- jects in a room are illuminated with the feeble gleam of a fire almost extinguished ; but it may be observed in day-light by the sportsman when he endeavours to mark upon the monotonous heath the particular spot where moor-game has alighted. Availing himself of the slightest difference of tint in the adjacent heath, he keeps his eye steadily fix- ed on it as he advances, but whenever the contrast of illumination is feeble, he will invariably lose sight of his mark, and if the retina is capable of tak- ing it up, it is only to lose it a second time. This illusion is likely to be most efficacious in 16 LETTERS ON NATURAL MAGIC. the dark, when there is just sufficient light to ren- der white objects faintly visible, and to persons who are either timid or credulous must prove a frequent source of alarm. Its influence too is greatly aided by another condition of the eye, into which it is thrown during partial darkness. The pupil expands nearly to the whole width of the iris in order to collect the feeble light which prevails ; but it is demonstrable that in this state the eye cannot accommodate itself to see near objects distinctly, so that the form of persons and things actually become more shadowy and confused when they come within the very dis- tance at which we count upon obtaining the best view of them. These affections of the eye are, we are persuaded, very frequent causes of a particular class of apparitions which are seen at night by the young and the ignorant. The spectres which are conjured up are always white, because no other co- lour can be seen, and they are either formed out of inanimate objects which reflect more light than others around them, or of animals or human beings whose colour or change of place renders them more visible in the dark. When the eye dimly descries an inanimate object whose different parts reflect different degrees of light, its brighter parts may en- able the spectator to keep up a continued view of it ; but the disappearance and reappearance of its fainter parts, and the change of shape which ensues, will necessarily give it the semblance of a living form, and if it occupies a position which is unap- proachable, and where animate objects cannot find their way, the mind will soon transfer to it a super- natural existence. In like manner a human figure shadowed forth in a feeble twilight may undergo 4 PHOSPHORESCENCE OF THE RETINA. 17 similar changes, and after being distinctly seen while it is in a situation favourable for receiving- and reflecting- light, it may suddenly disappear in a position fully before, and within the reach of, the observer's eye ; and if this evanescence takes place in a path or road where there was no side-way by which the figure could escape, it is not easy for an ordinary mind to efface the impression which it can- not fail to receive. Under such circumstances, we never think of distrusting an organ which we have never found to deceive us ; and the truth of the maxim that " seeing is believing," is too univer- sally admitted, and too deeply rooted in our nature to admit on any occasion of a single exception. In these observations we have supposed that the spectator bears along with him no fears or preju- dices, and is a faithful interpreter of the phenomena presented to his senses ; but if he is himself a be- liever in apparitions, and unwilling to receive an ocular demonstration of their reality, it is not difficult to conceive the picture which will be drawn when external objects are distorted and caricatured by the imperfect indications of his senses, and coloured with all the vivid hues of the imagination. Another class of ocular deceptions have their origin in a property of the eye which has been very im- perfectly examined. The fine nervous fabric which constitutes the retina, and which extends to the brain, has the singular property of being phospho- rescent by pressure. When we press the eye-ball outwards by applying the point of the finger bet ween it and the nose, a circle of light will be seen, which Sir Isaac Newton describes as " a circle of colours like those in the feather of a peacock's tail." He B IB LETTERS ON NATURAL MAGIC. adds, that " if the eye and the finger remain quiet, these colours vanish in a second of time, but if the finger be moved with a quavering motion they ap- pear again." In the numerous observations which I have made on these luminous circles, I have never been able to observe any colour but white, with the exception of a general red tinge which is seen when the eyelids are closed, and which is produced by the light which passes through them. The luminous circles too always continue while the pressure is applied, and they may be produced as readily after the eye has been long in darkness as when it has been recently exposed to light. When the pressure is very gently applied, so as to com- press the fine pulpy substance of the retina, light is immediately created when the eye is in total darkness ; and when in this state light is allowed to fall upon it, the part compressed is more sensi- ble to light than any other part, and consequently appears more luminous. If we increase the pres- sure, the eye-ball, being filled with incompressible fluids, will protrude all round the point of pressure, and consequently the retina at the protruded part will be compressed by the outward pressure of the contained fluid, while the retina on each side, name- ly, under the point of pressure and beyond the pro- truded part, will be drawn towards the protruded part or dilated* Hence the part under the finger which was originally compressed is now dilated, the adjacent parts compressed, and the more remote parts immediately without this dilated also. Now we have observed, that when the eye is, under these circumstances, exposed to light, there is a bright luminous circle shading off externally and inter- EFFECTS OF PRESSURE ON THE RETINA. 19 nally into total darkness. We are led therefore to the important conclusions, that when the retina is com- pressed in total darkness it gives out light ; that when it is compressed when exposed to light, its sensibility to light is increased ; and that when it is dilated under exposure to light, it becomes absolute- ly blind, or insensible to all luminous impressions. When the body is in a state of perfect health, this phosphorescence of the eye shows itself on many occasions. W T hen the eye or the head re- ceives a sudden blow, a bright flash of light shoots from the eyeball. In the act of sneezing, gleams of light are emitted from each eye, both during the inhalation of the air, and during its subse- quent protrusion, and in blowing air violently through the nostrils, two patches of light ap- pear above the axis of the eye and in front of it, while other two luminous spots unite into one, and appear as it were about the point of the nose when the eyes are directed to it. When we turn the eyeball by the action of its own muscles, the reti- na is affected at the place where the muscles are inserted, and there may be seen opposite each eye and towards the nose, two semicircles of light, and other two extremely faint towards the temples. At particular times, when the retina is more phos- phorescent than at others, these semicircles are ex- panded into complete circles of light. In a state of indisposition, the phosphorescence of the retina appears in new and more alarming forms. When the stomach is under a temporary de- rangement accompanied with headach, the pressure of the blood-vessels upon the retina shows itself, in total darkness, by a faint blue light floating be- 20 LETTERS ON NATURAL MAGIC. fore the eye, varying in its shape, and passing away at one side. This blue light increases in in- tensity, becomes green and then yelloiv, and some- times rises to red, all these colours being frequent- ly seen at once, or the mass of light shades off into darkness. When we consider the variety of dis- tinct forms which in a state of perfect health the imagination can conjure up when looking into a burn- ing fire, or upon an irregularly shaded surface, * it is easy to conceive how the masses of coloured light which float before the eye may be moulded by the same power into those fantastic and natural shapes which so often haunt the couch of the invalid, even when the mind retains its energy, and is conscious of the illusion under which it labours. In other cases, temporary blindness is produced by pressure upon the optic nerve, or upon the retina, and un- der the excitation of fever or delirium, when the * A very curious example of the influence of the imagi- nation in creating distinct forms out of an irregularly shad- ed surface, is mentioned in the life of Peter Heaman, a Swede, who was executed for piracy and murder at Leith in 1822. We give it in his own words : " One remarkable thing was, one day as we mended a sail, it being a very thin one, after laying it upon deck in folds, I took the tar brush and tarred it over in the places which I thought needed to be strengthened. But when we hoisted it up, I was astonished to see that the tar I had put upon it represented a gallows and a man under it without a head. The head was lying beside him. He was complete, body, thighs, legs, arms, and in every shape like a man. Now, I oftentimes made remarks upon it, and repeated them to the others. I always said to them all, you may depend upon it that something will happen. I afterwards took down the sail on a calm day, and sewed a piece of canvass over the figure to cover it, for I could not bear to have it always before my eyes." OCULAR SPECTRA. 21 physical cause which produces spectral forms is at its height, there is superadded a powerful influence of the mind, which imparts a new character to the phantasms of the senses. In order to complete the history of the illusions which originate in the eye, it will be necessary to give some account of the phenomena called ocular spectra, or accidental colours. If we cut a figure out of red paper, and placing it on a sheet of white paper, view it steadily for some seconds with one or both eyes fixed on a particular part of it, we shall observe the red colour to become less brilliant. If we then turn the eye from the red figure upon the white paper, we shall see a distinct green fi- gure, which is the spectrum, or accidental colour of the red figure. With differently coloured fi- gures we shall observe differently coloured spectra, as in the following table : Colour of the Colour of the Spec- Original figures. tral figures. Red, Bluish-green. Orange, Blue. Yellow, Indigo. Green, Reddish-violet. Blue, Orange-red. Indigo, Orange-yellow. Violet, Yellow. White, Black. Black, White. The two last of these experiments, viz. white and black figures, may be satisfactorily made by using a white medallion on a dark ground, and a black profile figure. The spectrum of the former will be found to be black, and that of the latter white. 22 LETTERS ON NATURAL MAGIC. These ocular spectra often show themselves without any effort on our part, and even without our knowledge. In a highly painted room illumi- nated by the sun, those parts of the furniture on which the sun does not directly fall, have always the opposite or accidental colour. If the sun shines through a chink in a red window-curtain, its light will appear green, varying, as in the above table, with the colour of the curtain ; and if we look at the image of a candle reflected from the water in a blue finger glass, it will appear yellow. Whenever, in short, the eye is affected with one prevailing co- lour, it sees at the same time the spectral or acci- dental colour, just as when a musical string is vi- brating, the ear hears at the same time its funda- mental and its harmonic sounds. If the prevailing light is white and very strong? the spectra which it produces are no longer black, but of various colours in succession. If we look at the sun, for example, when near the horizon, or when reflected from glass or water, so as to mode- rate its brilliancy, and keep the eye upon it steadily for a few seconds, we shall see even for hours af- terwards, and whether the eyes is open or shut, a spectre of the sun varying in its colours. At first, with the eye open, it is brownish-red with a sky- blue border, and when the eye is shut, it is green with a red border. The red becomes more bril- liant, and the blue more vivid, till the impression is gradually worn off ; but even when they become very faint, they may be revived by a gentle pressure on the eyeball. Some eyes are more susceptible than others of these spectral impressions, and Mr Boyle mention s OCULAR SPECTRA. 23 an individual who continued for years to see the spectre of the sun when he looked upon bright ob- jects. This fact appeared to Locke so interesting and inexplicable, that he consulted Sir Isaac New- ton respecting its cause, and drew from him the following interesting account of a similar effect upon himself : " The observation you mention in Mr Boyle's book of colours, I once made upon myself with the hazard of my eyes. The manner was this : I looked a very little while upon the sun in the looking-glass with my right eye, and then turned my eyes into a dark corner of my cham- ber, and winked, to observe the impression made, and the circles of colours which encompassed it, and how they decayed by degrees, aud at last va- nished. This I repeated a second and a third time. At the third time, when the phantasm of light and colours about it were almost vanished, intending my fancy upon them to see their last appearance, I found, to my amazement, that they began to return, and by little and little to become as lively and vivid as when I had newly looked upon the sun. But when I ceased to intend my fancy upon them they vanished again. After this, I found, that, as often as I went into the dark, and intend- ed my mind upon them, as when a man looks ear- nestly to see any thing which is difficult to be seen, I could make the phantasm return without looking any more upon the sun ; and the oftener I made it return, the more easily I could make it return again. And at length, by repeating this without looking any more upon the sun, I made such an impression on my eye, that, if I looked upon the clouds, or a book, or any bright object, I saw upon 24 LETTERS ON NATURAL MAGIC. it a round bright spot of light like the sun, and, which is still stranger, though I looked upon the sun with my right eye only, and not with my left, yet my fancy began to make an impression upon my left eye as well as upon my right. For if I shut my right eye, and looked upon a book or the clouds with my left eye, I could see the spectrum of the sun almost as plain as with my right eye, if I did but intend my fancy a little while upon it ; for at first, if I shut my right eye, and looked with my left, the spectrum of the sun did not appear till I intended my fancy upon it ; but by repeating, this appeared every time more easily. And now in a few hours time I had brought my eyes to such a pass, that I could look upon no bright object with either eye but I saw the sun before me, so that I durst neither write nor read ; but to recover the use of my eyes, shut myself up in my chamber made dark, for three days together, and used all means in my power to direct my imagination from the sun. For if I thought upon him, I presently saw his picture, though I was in the dark. But by keeping in the dark, and employing my mind about other things, I began in three or four days to have more use of my eyes again ; and by for- bearing to look upon bright objects, recovered them pretty well ; though not so well but that, for some months after, the spectrums of the sun began to re- turn as often as I began to meditate upon the phe- nomena, even though I lay in bed at midnight with my curtains drawn. But now I have been very well for many years, though I am apt to think, if I durst venture my eyes, I could still make the phantasm return by the power of my fancy. This ILLUSIONS FROM OCULAR SPECTRA. 25 story I tell you, to let you understand, that in the observation related by Mr Boyle, the man's fancy probably concurred with the impression made by the sun's light to produce that phantasm of the sun which he constantly saw in bright objects." * I am not aware of any effects that had the cha- racter of supernatural having been actually pro- duced by the causes above described ; but it is ob- vious, that, if a living figure had been projected against the strong light which imprinted these dur- able spectra of the sun, which might really happen when the solar rays are reflected from water, and diffused by its ruffled surface, this figure would have necessarily accompanied all the luminous spectres which the fancy created. Even in ordinary lights strange appearances may be produced by even tran- sient impressions, and if I am not greatly mistaken, the case which I am about to mention is not only one which may occur, but which actually happen- ed. A figure dressed in black and mounted upon a white horse was riding along exposed to the bright rays of the sun, which through a small opening in the clouds was throwing its light only upon that part of the landscape. The black figure was projected against a white cloud, and the white horse shone with particular brilliancy by its contrast with the dark soil against which it was seen. A person interested in the arrival of such a stranger had been for some time following his movements with intense anxiety, but upon his disappearance behind a wood, was surprised to observe the spectre of the mounted stranger in the form of a white rider upon a black steed, and this spectre was seen for * See the Edinburgh Encyclopaedia, Art. Accidental Colours. 26 LETTERS ON NATURAL MAGIC. some time in the sky, or upon any pale ground to which the eye was directed. Such an occurrence, especially if accompanied with a suitable combina- tion of events, might even in modern times have formed a chapter in the history of the marvellous. It is a curious circumstance, that when the image of an object is impressed upon the retina only for a few moments, the picture which is left is exactly of the same colour with the object. If we look, for example, at a window at some distance from the eye, and then transfer the eye quickly to the wall, we shall see it distinctly but momentarily with light panes and dark bars ; but in a space of time incal- culably short, this picture is succeeded by the spec- tral impression of the window, which will consist of 6/ac&panes and white bars. The similar spectrum, or that of the same colour as the object, is finely seen in the experiment of forming luminous circles by whirling round a burning stick, in which case the circles are always red. In virtue of this property of the eye an object may be seen in many places at once ; and we may even exhibit at the same instant the two opposite sides of the same object, or two pictures painted on the opposite sides of a piece of card. It was found by a French philosopher M. D'Arcet, that the im- pression of light continued on the retina about the eighth part of a second after the luminous body was withdrawn, and upon this principle Dr Paris has constructed the pretty little instrument, called the Thaumatrope, or the Wonder -turner. It consists of a number of circular pieces of card about two or three inches broad, which may be twirled round with great velocity by the application of the fore-finger and thumb of each hand to pieces of silk string at- DURATION OF LUMINOUS IMPRESSIONS. 27 tached to opposite points of their circumference. On each side of the circular piece of card is paint- ed part of a picture, or a part of a figure, in such a manner that the two parts would form a group or a whole figure if we could see both sides at once. Harlequin for example is painted on one side, and Columbine on the other, so that by twirling round the card the two are seen at the same time in their usual mode of combination. The body of a Turk is drawn on one side, and his head on the reverse, and by the rotation of the card the head is replaced upon his shoulders. The principle of this illusion may be extended to many other contrivances. Part of a sen- tence may be written on one side of a card and the rest on the reverse. Particular letters may be given on one side, and others upon the other, or even halves or parts of each letter may be put upon each side, or all these contrivances may be combined, so that the sentiment which they express can be understood only when all the scattered parts are united by the revolution of the card. As the revolving card is virtually transparent, so that bodies beyond it can be seen through it, the power of the illusion might be greatly extend- ed by introducing into the picture other figures, either animate or inaminate. The setting sun for example, might be introduced into a landscape: Part of the flame of a fire might be seen to issue from the crater of a volcano, and cattle grazing in a field might make part of the revolutionary landscape. For such purposes, however, the form of the instru- ment would require to be completely changed, and the rotation should be effected round a standing axis by wheels and pinions, and a screen placed in 28 LETTERS ON NATURAL MAGIC. front of the revolving plane with open compartments or apertures, through which the principal figures would appear. Had the principle of this instru- ment been known to the ancients, it would doubt- less have formed a powerful engine of delusion in their temples, and might have been more effective than the optical means which they seem to have employed for producing the apparitions of their gods. In certain diseased conditions of the eye effects of a very remarkable kind are produced. The fa- culty of seeing objects double is too common to be noticed as remarkable ; and though it may take place with only one eye, yet, as it generally arises from a transient inability to direct the axes of both eyes to the same point, it excites little notice. That state of the eye, however, in which we lose sight of half of every object at which we look, is more alarming and more likely to be ascribed to the dis- appearance of part of the object than to a defect of sight. Dr Wollaston, who experienced this defect twice, informs us that, after taking violent exercise, he " suddenly found that he could see but half of a man whom he met, and that, on attempting to read the name of JOHNSON over a door, he saw only SON, the commencement of the name being wholly obliterated from his view." In this instance, the part of the object which disappeared was towards his left, but on a second occurrence of the same affec- tion, the part which disappeared was towards his right. There are many occasions on which this defect of the eye might alarm the person who wit- nessed it for the first time. At certain distances from the eye one of two persons would necessarily disappear ; and by a slight change of position either INSENSIBILITY TO COLOURS. 29 in the observer or the person observed, the person that vanished would reappear, while the other would disappear in his turn. The circumstances under which these evanescences would take place could not be supposed to occur to an ordinary observer, even if he should be aware that the cause had its origin in himself. When a phenomenon so strange is seen by a person in perfect health, as it generally is, and who has never had occasion to distrust the tes- timony of his senses, he can scarcely refer it to any other cause than a supernatural one. Among the aifections of the eye which not only deceive the person who is subject to them, but those also who witness their operation, may be enume- rated the insensibility of the eye to particular co- lours. This defect is not accompanied with any imperfection of vision, or connected with any dis- ease either of a local or a general nature, and it has hitherto been observed in persons who possess a strong and a sharp sight. Mr Huddart has de- scribed the case of one Harris, a shoemaker at Mary- port in Cumberland, who was subject to this defect in a very remarkable degree. He seems to have been insensible to every colour, and to have been capable of recognizing only the two opposite tints of black and white. " His first suspicion of this de- fect arose when he was about four years old. Hav- ing by accident found in the street a child's stock- ing, he carried it to a neighbouring house to inquire for the owner : He observed the people call it a red stocking, though he did not understand why they gave it that denomination, as he himself thought it completely described by being called a stocking. The circumstance, however, remained in 30 LETTERS ON NATURAL MAGIC. his memory, and, with other subsequent observa- tions, led him to the knowledge of his defect. He observed also that, when young, other children could discern cherries on a tree by some pretended difference of colour, though he could only distin- guish them from the leaves by their difference of size and shape. He observed also that, by means of this difference of colour, they could see the cher- ries at a greater distance than he could, though he could see other objects at as great a distance as they, that is, where the sight was not assisted by the co- lour." Harris had two brothers whose perception of colours was nearly as defective as his own. One of these, whom Mr Huddart examined, constantly mistook light green for yellow, and orange for grass- green. Mr Scott has described in the Philosophical Transactions his own defect in perceiving co- lours. He states that he does not know any green in the world ; that a pink colour and a pale blue are perfectly alike ; that he has often thought a full red and a full green a good match ; that he is sometimes baffled in distinguishing a full purple from a deep blue, but that he knows light, dark, and middle yellows, and all degrees of blue except sky- blue. 66 1 married my daughter to a genteel, worthy man, a few years ago; the day before the marriage he came to my house dressed in a new suit of fine cloth clothes. I was much displeased that he should come as I supposed, in black ; and said that he should go back to change his colour. But my daughter said, No — No ; the colour is very genteel, that it was my eyes that deceived me. He was a gentleman of the law, in a fine rich claret-coloured dress, which INSENSIBILITY TO COLOURS. 31 is as much a black to my eyes as any black that ever was dyed." Mr Scott's father, his maternal uncle, one of his sisters, and her two sons, had all the same imperfection. Dr Nichol has recorded a case where a naval officer purchased a blue uniform coat and waistcoat with red breeches to match the blue, and Mr Harvey describes the case of a tailor at Plymouth, who on one occasion repaired an article of dress with crimson in place of black silk, and on another patched the elbow of a blue coat with a piece of crimson cloth. It deserves to be remarked that our celebrated countrymen the late Mr Du- gald Stewart, Mr Dalton, and Mr Troughton, have a similar difficulty in distinguishing colours. Mr Stewart discovered this defect when one of his fa- mily was admiring the beauty of the Siberian crab- apple, which he could not distinguish from the leaves but by its form and size. Mr Dalton cannot distin- guish blue from pink, and the solar spectrum con- sists only oftwocolours^Z/ow and blue. Mr Trough - ton regards red, ruddy pinks and brilliant oranges, as yellows, and greens as blues, so that he is capable only of appreciating blue and yellow colours. In all those cases which have been carefully studied, at least in three of them in which I have had the advantage of making personal observations, namely, those of Mr Troughton, Mr Dalton, and Mr Liston, the eye is capable of seeing the whole of the prismatic spectrum, the red space appearing to be yellow. If the red space consisted of homoge- neous or simple red rays, we should be led to infer that the eyes in question were not insensible to red light, but were merely incapable of discriminating between the impressions of red and yellow light. I 32 LETTERS ON NATURAL MAGIC. have lately shown, however, that the prismatic spec- trum consists of three equal and coincident spectra of red, yellow, and blue light, and consequently, that much yellow and a small portion of blue light exist in the red space; — and hence it follows, that those eyes which see only two colours, viz. yellow and blue, in the spectrum, are really insensible to the red light of the spectrum, and see only the yellow with the small portion of blue with which the red is mixed. The faintness of the yellow light which is thus seen in the red space, confirms the opinion that the re- tina has not appreciated the influence of the simple red rays. If one of the two travellers who, in the fable of the chameleon, are made to quarrel about the colour of that singular animal, had happened to possess this defect of sight, they would have encountered at every step of their journey new grounds of dissen- sion without the chance of finding an umpire who could pronounce a satisfactory decision. Under certain circumstances, indeed, the arbiter might set aside the opinions of both the disputants, and render it necessary to appeal to some higher authority to beg he'd tell 'em if he knew Whether the thing was red or blue. In the course of writing the preceding obser- vations, an ocular illusion occurred to myself of so extraordinary nature, that I am convinced it never was seen before, and I think it far from probable that it will ever be seen again. Upon directing my eyes to the candles that were standing before me, I was surprised to observe, apparently among my hair, and nearly straight above my head, and far without REMARKABLE OPTICAL ILLUSION. 33 the range of vision, a distinct image of one of the candles inclined about 45° to the horizon, as shown at A in Fig. 2. The image was as distinct and Fig. 2. perfect as if it had been formed by reflexion from a jjiece of mirror glass, though of course much less brilliant, and the position of the image proved that it must be formed by reflexion from a perfectly flat and highly polished surface. But where such a sur- face could be placed, and how, even if it were fixed, it could reflect the image of the candle up through my head, were difficulties not a little perplexing. Thinking that it might be something lodged in the eyebrow, I covered it up from the light, but the image still retained its place. I then examined the eyelashes with as little success, and was driven to the extreme supposition that a crystallization was taking place in some part of the aqueous humour of the eye, and that the image was formed by the c 34 LETTERS ON NATURAL MAGIC. reflexion of the light of the candle from one of the crystalline faces. In this state of uncertainty, and, I may add, of anxiety, for this last supposition was by no means an agreeable one, I set myself down to examine the phenomenon experimentally. I found that the image varied its place by the motion of the head and of the eyeball, which proved that it was either attached to the eyeball or occupied a place where it was affected by that motion. Upon in- clining the candle at different angles the image suffered corresponding variations of position. In order to determine the exact place of the re- flecting substance, I now took an opaque circular body and held it between the eye and the candle till it eclipsed the mysterious image. By bringing the body nearer and nearer the eyeball till its sha- dow became sufficiently distinct to be seen, it was easy to determine the locality of the reflector, be- cause the shadow of the opaque body must fall upon it whenever the image of the candle was eclipsed. In this way I ascertained that the reflecting body was in the upper eyelash, and I found, that, in con- sequence of being disturbed, it had twice changed its inclination, so as to represent a vertical candle in the horizontal position B, and afterwards in the inverted position C. Still, however, I sought for it in vain, and even with the aid of a magnifier I could not discover it. At last, however, Mrs B. who possesses the perfect vision of short-sighted persons, discovered, after repeated examinations, between two eyelashes, a minute speck, which, upon being removed with great difficulty, turned out to be a chip of red wax not above the hundredth part of an inch in diameter, and having its surface so perfectly 4 REMARKABLE OPTICAL ILLUSION. 35 flat and so highly polished that I could see in it the same image of the candle, by placing it ex- tremely near the eye. This chip of wax had no doubt received its flatness and its polish from the surface of a seal, and had started into my eye when breaking the seal of a letter. That this reflecting substance was the cause of the image of the candle cannot admit of a doubt ; but the wonder still remains how the images which it formed occupied so mysterious a place as to be seen without the range of vision, and apparently through the head. In order to explain this, let m n, Fig. 2, be a lateral view of the eye. The chip of wax was placed at m at the root of the eyelashes, and being nearly in contact with the outer surface of the cornea, the light of the candle which it reflect- ed passed very obliquely through the pupil and fell upon the retina somewhere to the left of n, very near where the retina terminates ; but a ray thus falling obliquely on the retina is seen, in virtue of the law of visible direction already explained, in a line n C perpendicular to the retina at the point near n 9 where the ray fell. Hence the candle was necessarily seen through the head as it were of the observer, and without the range of ordinary vision. The compa- rative brightness of the reflected image still surprises me; but even this, if the image really was brighter, may be explained by the fact, that it was formed on a part of the retina, upon which light had never be- fore fallen, and which may therefore be supposed to be more sensible, than the parts of the membrane in constant use, to luminous impressions. Independent of its interest as an example of the marvellous in vision, the preceding fact may be 36 LETTERS ON NATURAL MAGIC. considered as a proof that the retina retains its power to its very termination near the ciliary pro- cesses, and that the law of visible direction holds true even without the range of ordinary vision. It is therefore possible that a reflecting- surface fa- vourably placed on the outside of the eye, or that a reflecting surface in the inside of the eye, may cause a luminous image to fall nearly on the extreme margin of the retina, the consequence of which would be that it would be seen in the back of the head half way between a vertical and a horizontal line, SPECTRAL ILLUSIONS. 37 LETTER III. Subject of spectral illusions' — Recent and interesting case of Mrs A, — Her first illusion affecting the ear — Spectral ap- lU paritio?i of her husband — Spectral apparition of a cat — Apparition of a near and living relation in grave-clothes seen in a looking-glass — Other illusions affecting the ear —Spectre of a deceased friend sitting in an easy chair — Spectre of a coach and four filled with skeletons — Accu- racy and value of the preceding cases — State of health under which they arose — Spectral apparitions are pictures on the retina — The ideas of memory and imagination are also pictures on the retina — General views of the subject — Ap- proximate explanation of spectral apparitions. The preceding- account of the different sources of illusion to which the eye is subject, is not only use- ful as indicating the probable cause of any indivi- dual deception, but it has a special importance in preparing- the mind for understanding- those more vivid and permanent spectral illusions to which some individuals have been either occasionally or habitu- ally subject. In these lesser phenomena we find the retina so powerfully influenced by external impressions as to retain the view of visible objects long after they are withdrawn ; we observe it to be so excited by local pressures of which we sometimes know neither the nature nor the origin, as to see in total darkness mo v- 38 LETTERS ON NATURAL MAGIC. ihg and shapeless masses of coloured light ; and we find, as in the case of Sir Isaac Newton and others, that the imagination has the power of reviving- the impressions of highly luminous objects, months and even years after they were first made. From such phenomena, the mind feels it to be no violent transi- tion to pass to those spectral illusions which, in parti- cular states of health, have haunted the most intelli- gent individuals, not only in the broad light of day ? but in the very heart of the social circle. This curious subject has been so ably and fully treated in your Letters on Demonology, that it would be presumptuous in me to resume any part of it on which you have even touched; but as it forms a necessary branch of a Treatise on Natural Magic, and as one of the most remarkable cases on record has come within my own knowledge, I shall make no apology for giving a full account of the different spectral appearances which it embraces, and of add- ing the results of a series of observations and ex- periments on which I have been long occupied, with the view of throwing some light on this re- markable class of phenomena. A few years ago I had occasion to spend some days under the same roof with the lady to whose case I have above referred. At that time she had seen no spectral illusions, and was acquainted with the subject only from the interesting volume of Dr Hibbert. In conversing with her about the cause of these apparitions, I mentioned, that, if she should ever see such a thing, she might distinguish a genuine ghost existing externally, and seen as an external object, from one created by the mind, by merely pres- sing one eye or straining them both so as to see ob- SPECTRAL ILLUSIONS. 39 jects double ; for in this case the external object or supposed apparition would invariably be doubled, while the impression on the retina created by the mind would remain single. This observation recur- red to her mind when she unfortunately became sub- ject to the same illusions ; but she was too well ac- quainted with their nature to require any such evi- dence of their mental origin ; and the state of agi- tation which generally accompanies them seems to have prevented her from making the experiment as a matter of curiosity. 1. The first illusion to which Mrs A. was subject was one which affected only the ear. On the 26th of December 1830, about half-past four in the afternoon, she was standing near the fire in the hall and on the point of going up stairs to dress, when she heard, as she supposed, her husband's voice callingher by name, " Come here! come to me!" She imagined that he was calling at the door to have it opened, but upon going there and opening the door she was surprised to find no person there. Upon returning to the fire, she again heard the same voice calling out very distinctly and loud- ly, " Come, come here!" She thenopenedtwo other doors of the same room, and upon seeing no person she returned to the fire-place. After a few moments she heard the same voice still calling, " Come to me, come ! come away!" in a loud, plaintive, and somewhat impatient tone. She answeredas loudly, "Where are you? I don't know where you are ;" still imagining that he was some- where in search of her : but receiving no answer she shortly went up stairs. On Mr A.'s return to the house, about half an hour afterwards, she inquired 40 LETTERS ON NATURAL MAGIC. why he called to her so often, and where he was ; and she was of course greatly surprised to learn that he had not been near the house at the time. A similar illusion, which excited no particular notice at the time, occurred to Mrs A. when residing at Florence about ten years before, and when she was in perfect health. When she was undressing after a ball, she heard a voice call her repeatedly by name, and she w T as at that time unable to account for it. 2. The next illusion which occurred to Mrs A. was of a more alarming character. On the 30th of December, about four o'clock in the afternoon, Mrs A. came down stairs into the drawing-room, which she had quitted only a few minutes before, and on entering the room she saw her husband, as she supposed, standing with his back to the fire. As he had gone out to take a walk about half an hour before, she was surprised to see him there, and asked him why he had returned so soon. The fi- gure looked fixedly at her with a serious and thought- ful expression of countenance but did not speak. Supposing that his mind was absorbed in thought, she sat down in an arm chair near the fire, and within two feet at most of the figure, which she still saw standing before her. As its eyes, how- ever, still continued to be fixed upon her, she said after the lapse of a few minutes, " Why don't you speak ?" The figure immediately moved off towards the window at the farther end of the room, with its eyes still gazing on her, and it passed so very close to her in doing so, that she was struck by the circumstance of hearing no step nor sound, nor feeling her clothes brushed against, nor even any agitation in the air. Al- though she was now convinced that the figure was SPECTRAL ILLUSIONS. 41 not her husband, yet she never for a moment sup- posed that it was any thing supernatural, and was soon convinced that it was a spectral illusion. As soon as this conviction had established itself in her mind, she recollected the experiment which I had suggested, of trying to double the object ; but before she was able distinctly to do this, the figure had re- treated to the window, where it disappeared. Mrs A. immediately followed it, shook the curtains and examined the window, the impression having been so distinct and forcible that she was unwilling to believe that it was not a reality. Finding, however, that the figure had no natural means of escape, she was convinced that she had seen a spectral apparition like those recorded in Dr Hibbert's work, and she consequently felt no alarm or agitation. The ap- pearance was seen in bright daylight, and lasted four or five minutes. When the figure stood close to her it concealed the real objects behind it, and the apparition was fully as vivid as the reality. 3. On these two occasions Mrs A. was alone, but when the next phantasm appeared her husband was present. This took place on the 4th of January 1830. About ten o'clock at night, when Mr and Mrs A. were sitting in the drawing-room, Mr A. took up the poker to stir the fire, and when he was in the act of doing this, Mrs A. exclaimed, " Why there's the cat in the room!" — " Where?" asked Mr A. " There, close to you," she replied. — " Where ?" he repeated. " Why on the rug to be sure, between your- self and the coal scuttle." Mr A., who had still the poker in his hand, pushed it in the direction mention- ed, u Take care," cried Mrs A. " take care, you are hitting her with the poker." Mr A. again asked her 42 LETTERS ON NATURAL MAGIC. to point out exactly where she saw the cat. She replied, " Why sitting up there close to your feet on the rug : She is looking at me. It is Kitty — come here Kitty?" — There were two cats inthe house, one of which went by this name, and they were rarely if ever in the drawing-room. At this time Mrs A. had no idea that the sight of the cat was an illusion. When she was asked to touch it, she got up for the pur- pose, and seemed as if she were pursuing something which moved away. She followed a few steps, and then said, " It has gone under the chair." Mr A. as- sured her it was an Illusion, but she would not be- lieve it. He then lifted up the chair, and Mrs A. saw nothing more of it. The room was then search- ed all over, and nothing found in it. There was a dog lying on the hearth, who would have betrayed great uneasiness if a cat had been in the room, but he lay perfectly quiet. In order to be quite certain, Mr A. rung the bell, and sent for the two cats, both of which were found in the housekeepers room. 4. About a month after this occurrence, Mrs A., who had taken a somewhat fatiguing drive during the day, was preparing to go to bed about eleven o'clock at night, and, sitting before the dressing- glass, was occupied in arranging her hair. She was in a listless and drowsy state of mind, but fully awake. When her fingers were in active motion among the papillotes, she was suddenly startled by seeing in the mirror the figure of a near relation, who was then in Scotland, and in perfect health. The apparition appeared over her left shoulder, and its eyes met hers in the glass. It was enveloped in grave-clothes, closely pinned, as is usual with corpses, round the head, and under the chin, and SPECTRAL ILLUSIONS. 43 though the eyes were open, the features were solemn and rigid. The dress was evidently a shroud, as Mrs A. remarked even the punctured pattern usu- ally worked in a peculiar manner round the edges of that garment. Mrs A. described herself as at the time sensible of a feeling like what we conceive of fascination, compelling her for a time to gaze on this melancholy apparition, which was as distinct and vivid as any reflected reality could be, the light of the candles upon the dressing-table appearing to shine fully upon its face. After a few minutes, she turned round to look for the reality of the form over her shoulder ; but it was not visible, and it had also disappeared from the glass when she look- ed again in that direction. 5. In the beginning of March, when Mr A. had been about a fortnight from home, Mrs A. fre- quently heard him moving near her. Nearly every night as she lay awake, she distinctly heard sounds like his breathing hard on the pillow by her side, and other sounds such as he might make while turning in bed. 6. On another occasion, during Mr A.'s absence, while riding with a neighbour Mr , she heard his voice frequently as if he were riding by his side. She heard also the tramp of his horse's feet, and was almost puzzled by hearing him address her at the same time with the person really in com- pany. His voice made remarks on the scenery, improvements, &c. such as he probably should have done had he been present. On this occasion, how- ever, there was no visible apparition. 7. On the 17th March, Mrs A. was preparing for bed. She had dismissed her maid, and was sit- 44 LETTERS ON NATURAL MAGIC. ting- with her feet in hot water. Having- an ex- cellent memory, she had been thinking upon and repeating to herself a striking passage in the Edin- burgh Review, when, on raising her eyes, she saw seated in a large easy chair before her the figure of a deceased friend, the sister of Mr A. The figure was dressed, as had been usual with her, with great neatness, but in a gown of a peculiar kind, such as Mrs A. had never seen her wear, but exactly such as had been described to her by a common friend as having been worn by Mr A.'s sister during her last visit to England. Mrs A. paid particular at- tention to the dress, air, and appearance of the fi- gure, which sat in an easy attitude in the chair, holding a handkerchief in one hand. Mrs A. tried to speak to it, but experienced a difficulty in doing so, and in about three minutes the figure disap- peared. About a minute afterwards, Mr A. came into the room, and found Mrs A. slightly nervous, but fully aware of the delusive nature of the appa- rition. She described it as having all the vivid colouring and apparent reality of life ; and for some hours preceding this and other visions, she expe- rienced a peculiar sensation in her eyes, which seemed to be relieved when the vision had ceased. 8. On the 5th October, between one and two o'clock in the morning, Mr A. was awoke by Mrs A., who told him that she had just seen the figure of his deceased mother draw aside the bed-curtains and appear between them. The dress and the look of the apparition were precisely those in which Mr A.'s mother had been last seen by Mrs A. at Paris in 1824. 9. On the 11th October, when sitting in the SPECTRAL ILLUSIONS. 45 drawing-room, on one side of the fire-place, she saw the figure of another deceased friend moving towards her from the window at the farther end of the room. It approached the fire-place, and sat down in the chair opposite. As there were several persons in the room at the time, she de- scribes the idea uppermost in her mind to have been a fear lest they should be alarmed at her star- ing, in the way she was conscious of doing, at va- cancy, and should fancy her intellect disordered. Under the influence of this fear, and recollecting a story of a similar effect in your work on Demono- logy, which she had lately read, she summoned up the requisite resolution to enable her to cross the space before the fire-place, and seat herself in the same chair with the figure. The apparition remained perfectly distinct till she sat down, as it were, in its lap, when it vanished. 10. On the 26th of the same month, about two p. M. Mrs A. was sitting in a chair by the window in the same room with her husband. He heard her exclaim, " What have I seen ?" And on looking at her, he observed a strange expression in her eyes and countenance. A carriage and four had appear- ed to her to be driving up the entrance road to the house. As it approached, she felt inclined to go up stairs to prepare to receive company, but, as if spell-bound, she was unable to move or speak. The carriage approached, and as it arrived within a few yards of the window, she saw the figures of the postillions and the persons inside take the ghastly appearance of skeletons and other hideous figures. The whole then vanished entirely, when she utter- ed the above-mentioned exclamation. 46 LETTERS ON NATURAL MAGIC, 11. On the morning of the 30th October, when Mrs A. was sitting in her own room with a favour- ite dog in her lap, she distinctly saw the same dog moving about the room during the space of about a minute or rather more. 12. On the 3d December, about nine p. m. when Mr and Mrs A. were sitting near each other in the drawing-room occupied in reading, Mr A. felt a pressure on his foot. On looking up, he observed Mrs A.'s eyes fixed with a strong and unnatural stare on a chair about nine or ten feet distant. Upon asking her what she saw, the expression of her countenance changed, and upon recovering her- self, she told Mr A. that she had seen his brother, who was alive and well at the moment in London, seated in the opposite chair, but dressed in grave- clothes, and with a ghastly countenance, as if scarce- ly alive. Such is a brief account of the various spectral il- lusions observed by Mrs A. — In describing them I have used the very words employed by her husband in his communications to me on the subject ;* and the reader may be assured that the descriptions are neither heightened by fancy, nor amplified by in- vention. The high character and intelligence of the lady, and the station of her husband in society, and as a man of learning and science, would authen- ticate the most marvellous narrative, and satisfy the most scrupulous mind, that the case has been philo- sophically as well as faithfully described. In nar- rating events which we regard as of a supernatural character, the mind has a strong tendency to give * Edinburgh Journal of Science, New Series, No. iv. p. •218, 219. No. vi. p. 244, and No. viii. p. 261. SPECTRAL ILLUSIONS. 47 more prominence to what appears to itself the most wonderful ; but from the very same cause, when we describe extraordinary and inexplicable phenomena which we believe to be the result of natural causes, the mind is prone to strip them of their most mar- vellous points, and bring them down to the level of ordinary events. From the very commencement of the spectral illusions seen by Mrs A. both she and her husband were well aware of their nature and origin, and both of them paid the most minute attention to the circumstances which accompanied them, not only with the view of throwing 1 light upon so curious a subject, but for the purpose of ascer- taining their connection with the state of health under which they appeared. As the spectres seen by Nicolai and others had their origin in bodily indisposition, it becomes in- teresting to learn the state of Mrs A.'s health when she was under the influence of these illusions. Dur- ing the six weeks within which the three first il- lusions took place, she had been considerably redu- ced and weakened by a troublesome cough, and the weakness which this occasioned was increased by her being prevented from taking a daily tonic. Her general health had not been strong, and long expe- rience has put it beyond a doubt, that her indispo- sition arises from a disordered state of the digestive organs. Mrs A. has naturally a morbidly sensitive imagination, which so painfully affects her corporeal impressions, that the account of any person having suffered severe pain by accident or otherwise occa- sionally produces acute twinges of pain in the cor- responding parts of her person. The account, for example, of the amputation of an arm will produce 48 LETTERS ON NATURAL MAGIC. an instantaneous and severe sense of pain in her own arm. She is subject to talk in her sleep with great fluency, to repeat long- passages of poetry, particu- larly when she is unwell, and even to cap verses for half an hour together, never failing to quote lines beginning with the final letter of the pre- ceding one till her memory is exhausted. Although it is not probable that we shall ever be able to understand the actual manner in which a person of sound mind beholds spectral apparitions in the broad light of day, yet we may arrive at such a degree of knowledge on the subject as to satisfy rational curiosity, and to strip the phenomena of every attribute of the marvellous. Even the vision of natural objects presents to us insurmountable difficulties, if we seek to understand the precise part which the mind performs in perceiving them ; but the philosopher considers that he has given a satis- factory explanation of vision when he demonstrates that distinct pictures of external objects are paint- ed on the retina, and that this membrane commu- nicates with the brain by means of nerves of the same substance as itself, and of which it is merely an expansion. Here we reach the gulf which hu- man intelligence cannot pass ; and if the presump- tuous mind of man shall dare to extend its specu- lations farther, it will do it only to evince its in- capacity and mortify its pride. In his admirable work on this subject, Dr Hib- bert has shown that spectral apparitions are nothing more than ideas or the recollected images of the mind, which in certain states of bodily indisposition have been rendered more vivid than actual impres- sions, or, to use other words, that the pictures in PICTURES ON THE RETINA. 49 the " mind's eye" are more vivid than the pictures in the body's eye. This principle has been placed by Dr Hibbert beyond the reach of doubt ; but I pro- pose to go much farther, and to show that the " mind's eye" is actually the body's eye, and that the retina is the common tablet on which both classes of impressions are painted, and by means of which they receive their visual existence according to the same optical laws. Nor is this true merely in the case of spectral illusions : It holds good of all ideas recalled by the memory or created by the imagination, and may be regarded as a fundamental law in the science of pneumatology. It would be out of place in a work like this to adduce the experimental evidence on which it rests, or even to explain the manner in which the expe- riments themselves must be conducted ; but I may state in general, that the spectres conjured up by the memory or the fancy have always a " local ha- bitation," and that they appear in front of the eye, and partake in its movements exactly like the im- pressions of luminous objects after the objects them- selves are withdrawn. In the healthy state of the mind and body, the re- lative intensity of these two classes of impressions on the retina are nicely adjusted. The mental pictures are transient and comparatively feeble, and in ordi- nary temperaments are never capable of disturbing or effacing the direct images of visible objects. The affairs of life could not be carried on if the memory were to intrude bright representations of the past into the domestic scene, or scatter them over the external landscape. The two opposite impressions, indeed, could not co-exist : The same nervous fibre 50 LETTERS ON NATURAL MAGIC. which is carrying* from the brain to the retina the figures of memory, could not at the same instant be carrying back the impressions of external objects from the retina to the brain. The mind cannot perform two different functions at the same instant, and the direction of its attention to one of the two classes of impressions necessarily produce the ex- tinction of the other : But so rapid is the exercise of mental power, that the alternate appearance and disappearance of the two contending impressions is no more recognized than the successive observations of external objects during the twinkling of the eye- lids. If we look, for example, at the Facade of St Paul's, and, without changing our position, call to mind the celebrated viewof Mont Blanc from Lyons, the picture of the cathedral, though actually impres- sed upon the retina, is momentarily lost sight of by the mind, exactly like an object seen by indirect vision ; and during the instant the recollected image of the mountain, towering over the subjacent range, is distinctly seen, but in a tone of subdued colour- ing, and indistinct outline. When the purpose of its recall is answered, it quickly disappears, and the picture of the cathedral again resumes the ascen- dancy. In darkness and solitude, when external objects no longer interfere with the pictures of the mind, they become more vivid and distinct ; and in the state between waking and sleeping, the intensity of the impressions approaches to that of visible ob- jects. With persons of studious habits, who are much occupied with the operations of their own minds, the mental pictures are much more distinct than in ordinary persons ; and in the midst of ab- 3 PICTURES ON THE RETINA. 5] stract thought, external objects even cease to make any impression on the retina. A philosopher ab- sorbed in his contemplations experiences a tempo- rary privation of the use of his senses. His chil- dren or his servants will enter the room directly before his eyes without being- seen. They will speak to him without being- heard ; and they will even try to rouse him from his reverie without be- ing- felt ; although his eyes, his ears, and his nerves, actually receive the impressions of light, sound, and touch. In such cases, however, the philosopher is voluntarily pursuing- a train of thoug ht on which his mind is deeply interested ; but even ordinary men, not much addicted to speculations of any kind, of- ten perceive in their mind's eye the pictures of de- ceased or absent friends, or even ludicrous creations of fancy, which have no connection whatever with the train of their thoughts. Like spectral appari- tions they are entirely involuntary, and though they may have sprung- from a reg-ular series of associa- tions, yet it is frequently impossible to discover a single link in the chain. If it be true, then, that the pictures of the mind and spectral illusions are equally impressions upon the retina, the latter will differ in no respect from the former, but in the degree of vividness with which they are seen ; and those frightful apparitions become nothing- more than our ordinary ideas, ren- dered more brilliant by some accidental and tem- porary derang-ement of the vital functions. Their very vividness too, which is their only characteris- tic, is capable of explanation. I have already shown that the retina is rendered more sensible to light by voluntary local pressure, as well as by the involun- 52 LETTERS ON NATURAL MAGIC. tary pressure of the blood-vessels behind it ; and if. by looking- at the sun, we impress upon the retina a coloured image of that luminary, which is seen even when the eye is shut, we may by pressure alter the colour of that image, in consequence of having in- creased the sensibility of that part of the retina on which it is impressed. Hence we may readily un- derstand how the vividness of the mental pictures must be increased by analogous causes. In the case both of Nicolai and Mrs A. the im- mediate cause of the spectres was a deranged action of the stomach. When such a derangement is in- duced by poison, or by substances which act as poi- sons, the retina is peculiarly affected, and the phe- nomena of vision singularly changed. Dr Patouillet has described the case of a family of nine persons who were all driven mad by eating the root of the Hyoscyamus nigev or black Henbane. One of them leapt into a pond. Another exclaimed that his neigh- bour would lose a cow in a month, and a third vo- ciferated that the crown piece of sixty pence would in a short time rise to five livres. On the follow- ing day they had all recovered their senses, but re- collected nothing of what had happened. On the same day they all saw objects double, and, what is still more remarkable, on the third day every object appeared to them as red as scarlet. Now this red light was probably nothing more than the red phos- phorescence produced by the pressure of the blood- vessels on the retina, and analogous to the masses of blue, green, yelloiv, and red light, which have been already mentioned as produced by a similar pressure in headaches, arising from a disordered state of the digestive organs. GENERAL VIEWS. 53 Were we to analyse the various phenomena of spectral illusions, we should discover many circum- stances favourable to these views. In those seen by Nicolai the individual figures were always some- what paler than natural objects. They sometimes grew more and more indistinct, and became perfectly white ; and, to use his own words, " he could always distinguish with the greatest precision, phantasms from phenomena." Nicolai sometimes saw the spec- tres when his eyes were shut, and sometimes they were thus made to disappear, — effects perfectly iden- tical with those which arise from the impressions of very luminous objects. Sometimes the figures vanished entirely, and at other times only pieces of them disappeared, exactly conformable to what takes place with objects seen by indirect vision, which most of those figures must necessarily have been. Among the peculiarities of spectral illusions there is one which merits particular attention, namely, that they seem to cover or conceal objects imme- diately beyond them. It is this circumstance more than any other which gives them the character of reality, and at first sight it seems difficult of ex- planation. The distinctness of any impression on the retina is entirely independent of the accommo- dation of the eye to the distinct vision of external objects. When the eye is at rest, and is not accom- modated to objects at any particular distance, it is in a state for seeing distant objects most perfectly. When a distinct spectral impression, therefore, is be- fore it, all other objects in its vicinity will be seen indistinctly, for while the eye is engrossed with the vision, it is not likely to accommodate itself to any other object in the same direction. It is quite com- 54 LETTERS ON NATURAL MAGIC. mon, too, for the eye to see only one of two ob- jects actually presented to it. A sportsman who has been in the practice of shooting- with both his eyes open actually sees a double image of the muz- zle of his fowling-piece, though it is only with one of these images that he covers his game, having no perception whatever of the other. But there is still another principle upon which only one of two objects may be seen at a time. If we look very steadily and continuously at a double pattern, such as t hose on a carpet composed of t wo single patterns of different colours, suppose red and yelloiv ; and if we direct the mind particularly to the contempla- tion of the red one, the green pattern will sometimes vanish entirely, leaving the red one alone visible, and by the same process the red one may be made to disappear. In this case, however, the two pat- terns, like the two images, may be seen together ; but if the very same portion of the retina is excited by the direct rays of an external object, when it is excited by a mental impression, it can no more see them both at the same time than a vibrating string can give out two different fundamental sounds. It is quite possible, however, that the brightest parts of a spectral figure may be distinctly seen along with the brightest parts of an object immediately behind it, but then the bright parts of each object will fall upon different parts of the retina. These views are illustrated by a case mentioned by Dr Abercrombie. A gentleman, who was a patient of his, of an irritable habit, and liable to a variety of uneasy sensations in his head, was sitting alone in his dining-room in the twilight, when the door of the room was a little open. He saw distinctly GENERAL VIEWS. 55 a female figure enter, wrapped in a mantle, with the face concealed by a large black bonnet. She seem- ed to advance a few steps towards him, and then stop. He had a full conviction that the figure was an illusion of vision, and he amused himself for some time by watching it ; at the same time observing that he could see through the figure so as to per- ceive the lock of the door, and other objects behind it.* If these views be correct the phenomena of spec- tral apparitions are stripped of all their terror, whe- ther we view them in their supernatural character or as indications of bodily indisposition. Nicolai, even, in whose case they were accompanied with alarming symptoms, derived pleasure from the con- templation of them, and he not only recovered from the complaint in which they originated, but surviv- ed them for many years. — Mrs A., too, who sees them only at distant intervals, and with whom they have but a fleeting existence, will, we trust, soon lose her exclusive privilege, when the slight indisposi- tion which gives them birth has subsided. * Inquiries concerning the Intellectual Powers, and the Investigation of Truth. Edinburgh, 1830. 5G LETTERS ON NATURAL MAGIC LETTER IV. Science used as an instrument of imposture — Deceptions with plane and concave mirrors practised by the ancients — The magician's mirror — Effects of concave mirrors — Atrial Images — Images on smoke — Combination of mirrors for pro- ducing pictures from living objects — The mysterious dagger — Ancient miracles with concave mirrors — Modern necro- mancy with them, as seen by Cellini — Description and effects of the magic lantern — Improvements upon it — Phantasma- goric exhibitions of Philip stal and others — Dr Young's ar- rangement of Lenses, Qc.for the Phantasmagoria— Improve- ments suggested — Catadioptrical phantasmagoria for pro' ducing the pictures from living objects — Method of cutting off parts of the figures — Kircher's mysterious handwriting on the wall — His hollow cylindrical mirror for atrial images — Cylindrical mirror for reforming distorted pictures — Mirrors of variable curvature for producing caricatures. In the preceding- observations man appears as the victim of his own delusions — as the magician unable to exorcise the spirits which he has himself called into being-. We shall now see him the dupe of preconcerted imposture — the slave of his own ignorance — the prostrate vassal of power and super- stition. I have already stated that the monarchs and priests of ancient times carried on a systematic plan of imposing upon their subjects — a mode of go- vernment which was in perfect accordance with PLANE AND CONCAVE MIRRORS. 57 their religious belief : But it will scarcely be be- lieved that the same delusions were practised after the establishment of Christianity, and that even the Catholic sanctuary was often the seat of these un- hallowed machinations. Nor was it merely the low and cunning- priest who thus sought to extort money and respect from the most ignorant of his flock : Bishops and pontiffs themselves wielded the magi- cian's wand over the diadems of kings and emperors, and, by the pretended exhibition of supernatural power, made the mightiest potentates of Europe tremble upon their thrones. It was the light of science alone which dispelled this moral and intellec- tual darkness, and it is entirely in consequence of its wide diffusion that we live in times when sove- reigns seek to reign only through the affections of their people, and when the minister of religion asks no other reverence but that which is inspired by the sanctity of his office and the purity of his character. It was fortunate for the human race that the scanty knowledge of former ages afforded so few elements of deception. What a tremendous en- gine would have been worked against our species by the varied and powerful machinery of modern science ! Man would still have worn the shackles which it forged, and his noble spirit would still have groaned beneath its fatal pressure. There can be little doubt that the most common, as well as the most successful, impositions of the ancients were of an optical nature, and were practis- ed by means of plane and concave mirrors. It has been clearly shown by various writers that the an- cients made use of mirrors of st eel, silver, and a com- position of copper and tin, like those now used for 58 LETTERS ON NATURAL MAGIC. reflecting specula. It is also very probable from a passage in Pliny, that glass mirrors were made at Sidon ; but it is evident, that, unless the object pre- sented to them was illuminated in a very high de- gree, the images which they formed must have been very faint and unsatisfactory. The silver mirrors, therefore, which were universally used, and which are superior to those made of any other metal, are likely to have been most generally employed by the ancient magicians. They were made to give multiplied and inverted images of objects, that is, they were plane, polygonal or many-sided, and concave. There is one property, however, mention- ed by Aulus Gellius, which has given unnecessary perplexity to commentators. He states that there were specula, which, when put in a particular place, gave no images of objects, but, when carried to an- other place, recovered their property of reflexion. * M. Sal vert e is of opinion that, in quoting Varro, Aulus Gellius was not sufficiently acquainted with the subject, and erred in supposing that the phe- nomenon depended on the place instead of the po- sition of the mirror ; but this criticism is obvious- ly made with the view of supporting an opinion of his own, that the property in question may be ana- logous to the phenomenon of polarised light, which at a certain angle refuses to suffer reflexion from particular bodies. If this idea has any foundation, the mirror must have been of glass or some other body not metallic, or, to speak more correctly, there must have been two such mirrors, so nice- * Ut speculum in loco certo positum nihil imaginet ; alior- sum translatum faciat imagines, Aul. Gel. Noct. Attic, lib. xvi. cap. 18. magician's mirror. 59 ly adjusted not only to one another, but to the light incident upon each, that the effect could not possibly be produced but by a philosopher tho- roughly acquainted with the modern discovery of the polarisation of light by reflexion. Without seeking- for so profound an explanation of the phe- nomenon, we may readily understand how a silver mirror may instantly lose its reflecting- power, in a damp atmosphere, in consequence of the preci- pitation of moisture upon its surface, and may im- mediately recover it when transported into drier air. One of the simplest instruments of optical decep- tion is the plane mirror, and when two are com- bined for this purpose it has been called the magi- cian's mirror. An observer in front of a plane mir- ror sees a distinct image of himself; but if two per- sons take up a mirror, and if the one person is as much to one side of a line perpendicular to the mid- dle of it as the other is to the other side, they will Fig. 3. D see each other but not themselves. If we now sup- pose MC, CD, NC, CD to be the partitions of two 60 LETTERS ON NATURAL MAGIC. adjacent apartments, let square opening's be made in the partitions at A and B, about five feet above the floor, and let them be filled with plate glass, and surrounded with a picture frame, so as to have the appearance of two mirrors. Place two mirrors E, F, one behind each opening at A and B, inclined 45° to the partition MN, and so large that a person looking- into the plates of glass at A and B will not see their edges. When this is done it is obvious that a person looking into the mirror A will not see him- self but will see any person or figure placed at B. If he believes that he is looking into a common mirror at A, his astonishment will be great at see- ing himself transformed into another person, or in- to any living animal that may be placed at B. The success of this deception would be greatly increased if a plane mirror suspended by a pulley could be brought immediately behind the plane glass at A, and drawn up from it at pleasure. The spectator at A having previously seen himself in this move- able mirror, would be still more astonished when he afterwards perceived in the same place a face dif- ferent from his own. By drawing the moveable mir- ror half up, the spectator at A might see half of his own face joined to half of the face placed at B ; but in the present day the most ignorant persons are so familiar with the properties of a looking glass that it would be very difficult to employ this kind of deception with the same success which must have attended it in a more illiterate age. The optical reader will easily see that the mirror Fand the apart- ment NCD are not absolutely necessary for carry- ing on this deception ; for the very same effects will be produced if the person at B is stationed at CONCAVE MIRRORS. 6] G, and looks towards the mirror F in the direction GF. As the mirror F, however, must be placed as near to A as possible, the person at G would be too near the partition C M, unless the mirror F was extremely large. The effect of this and every similar deception is greatly increased when the persons are illuminated with a strong* light, and the rest of the apartment as dark as possible ; but whatever precautions are taken, and however skilfully plane mirrors are com- bined, it is not easy to produce with them any very successful illusions. The concave mirror is the staple instrument of the magician's cabinet, and must always perform a principal part in all optical combinations. In order to be quite perfect, every concave mirror should have its surface elliptical, so that if any object is placed in one focus of the ellipse, an inverted image of it will be formed in the other focus. This image, to a spectator rightly placed, appears suspended in the air, so that if the mirror and the object are hid from his view, the effect must appear to him al- most supernatural. The method of exhibiting the effect of concave mirrors most advantageously is shown in Fig. 3, where CD is the partition of a room having in it a square opening EF, the centre of which is about five feet above the floor. This opening might be sur- rounded with a picture frame, and a painting which exactly filled it might be so connected with a pul- ley that it could be either slipped aside, or raised so as to leave the frame empty. A large concave mir- ror MN is then placed in another apartment, so that when any object is placed at A, a distinct image of 62 LETTERS ON NATURAL MAGIC. it may be formed in the centre of the opening EF. Let us suppose this object to be a plaster cast of Fig. 4. any object made as white as possible, and placed in an inverted position at A. A strong light should then be thrown upon it by a powerful lamp, the rays of which are prevented from reach- ing the opening EF. When this is done, a specta- tor placed at O will see an erect image of the sta- tue at B the centre of the opening — standing in the air, and differing from the real statue only in being a little larger, while the apparition will be wholly invisible to other spectators placed at a little dis- tance on each side of him. If the opening EF is filled with smoke rising either from a chafing dish, in which incense is burnt, or made to issue in clouds from some opening be- low, the image will appear in the middle of the smoke depicted upon it as upon a ground, and capa- ble of being seen by those spectators who could not see the image in the air. The rays of light, in place of proceeding without obstruction to an eye MYSTERIOUS DAGGER. 63 at O, are reflected as it were from those minute particles of which the smoke is composed, in the same manner as a beam of light is rendered more visible by passing- through an apartment filled with dust or smoke. It has long been a favourite experiment to place at A, a white and strongly illuminated human skull, and to exhibit an image of it amid the smoke of a chafing dish at B ; but a more terrific effect would be produced if a small skeleton, suspended by invi- sible wires, were placed as an object at A. Its image suspended in the air at B, or painted upon smoke, could not fail to astonish the spectator. The difficulty of placing a living person in an inverted position, as an object at A, has no doubt prevented the optical conjuror from availing him- self of so admirable a resource ; but this difficulty may be removed by employing a second concave mirror. This second mirror must be so placed as to reflect towards MN, the rays proceeding from an erect living object, and to form an inverted image of this object at A. An erect image of this invert- ed image will then be formed at B, either suspend- ed in the air or depicted upon a wreath of smoke. This aerial image will exhibit the precise form and colours and movements of the living object, and it will maintain its character as an apparition if any attempt is made by the spectator to grasp its un- substantial fabric. A deception of an alarming kind, called the Mys- terious dagger^ has been long a favourite exhibi- tion. If a person with a drawn and highly polish- ed dagger, illuminated by a strong light, stands a little farther from a concave mirror than its prin- 64 LETTERS ON NATURAL MAGIC. cipal focus, he will perceive in the air between himself arid the mirror, an inverted and diminished image of his own person with the dagger similarly brandished : If he aims the dagger at the centre of the mirror's concavity, the two daggers will meet point to point, and, by pushing it still farther from him towards the mirror, the imaginary dag- ger will strike at his heart. In this case it is ne- cessary that the direction of the real dagger coin- cides with a diameter of the sphere of which the mir- ror is a part ; but if its direction is on one side of that diameter, the direction of the imaginary dag- ger will be as far on the other side of the dia- meter, and the latter will aim a blow at any person who is placed in the proper position for receiving- it. If the person who bears the real dagger is there- fore placed behind a screen, or otherwise concealed from the view of the spectator who is made to ap- proach to the place of the image, the thrust of the polished steel at his breast will not fail to produce a powerful impression. The effect of this experi- ment would no doubt be increased by covering with black cloth the person who holds the dagger, so that the image of his hand only should be seen, as the inverted picture of him would take away from the reality of the appearance. By using two mir- rors, indeed, this defect might be remedied, and the spectator would witness an exact image of the as- sassin aiming the dagger at his life. The common way of making this experiment is to place a basket of fruit above the dagger, so that a distinct aerial image of the fruit is formed in the focus of the mirror. The spectator having been desired to take some fruit from the basket ap- CONCAVE MIRRORS. 65 proaches for that purpose, while a person properly concealed withdraws the real basket of fruit with one hand, and with the other advances the dagger, the image of which, being no longer covered by the fruit, strikes at the body of the astonished specta- tor. The powers of the concave mirror have been likewise displayed in exhibiting the apparition of an absent or deceased friend. For this purpose a strongly illuminated bust or picture of the person is placed before the concave mirror, and a distinct image of the picture will be seen either in the air or among smoke in the manner already described. If the back ground of the picture is temporarily covered with lamp-black, so that there is no light- about the picture but what falls upon the figure, the effect will be more complete. As in all experiments with concave mirrors, the size of the aerial image is to that of the real object as their distances from the mirror, we may, by vary- ing the distance of the object, increase or diminish the size of the image. In doing this, however, the distance of the image from the mirror is at the same time changed, so that it would quit the place most suitable for its exhibition. This defect may be removed by simultaneously changing the place both of the mirror and the object, so that the image may remain stationary, expanding itself from a lu- minous spot to a gigantic size, and again passing through all intermediate magnitudes, till it va- nishes in a cloud of light. Those who have studied the effects of concave mirrors of a small size, and without the precautions necessary to insure deception, cannot form any idea 66 LETTERS ON NATURAL MAGIC. of the magical effect produced by this class of op- tical apparitions. When the instruments of illu- sion are themselves concealed, — when all extraneous lights but those which illuminate the real object are excluded, — when the mirrors are large and well polished and truly formed, — the effect of the repre- sentation on ignorant minds is altogether over- powering, while even those who know the decep- tion, and perfectly understand its principles, are not a little surprised at its effects. The inferiority in the effects of a common concave mirror to that of a well arranged exhibition, is greater even than that of a perspective picture hanging in an apart- ment, to the same picture exhibited under all the imposing accompaniments of a dioramic represen- tation. It can scarcely be doubted, that a concave mirror was the principal instrument by which the heathen gods were made to appear in the ancient temples. In the imperfect accounts which have reached us of these apparitions, we can trace all the elements of an optical illusion. In the ancient temple of Hercules at Tyre, Pliny mentions that there was a seat made of a consecrated stone, " from which the gods easily rose." Esculapius often exhibited himself to his worshippers in his temple at Tarsus ; and the temple of Enguinum in Sicily was cele- brated as the place where the goddesses exhibited themselves to mortals. Jamblichus actually in- forms us, that the ancient magicians caused the gods to appear among the vapours disengaged from fire ; and when the conjuror Maximus terrified his audience by making the statue of Hecate laugh, while in the middle of the smoke of burning in- 4 CONCAVE MIRRORS. 67 cense, he was obviously dealing- with the image of a living- object dressed in the costume of the sor- ceress. The character of these exhibitions in the an- cient temples is so admirably depicted in the follow- ing* passage of Damascius quoted by M. Salverte, that we recognize all the optical effects which have been already described. " In a manifestation," says he, " which ought not to be revealed there ap- peared on the wall of the temple a mass of light which at first seemed to be very remote ; it trans- formed itself in coming nearer, into a face evident- ly divine and supernatural, of a severe aspect, but mixed with gentleness, and extremely beautiful. According to the institutions of a mysterious reli- gion the Alexandrians honoured it as Osiris and Adonis." Among more modern examples of this illusion, we may mention the case of the Emperor Basil of Macedonia. Inconsolable at the loss of his son, this sovereign had recourse to the prayers of the Pontiff Theodore Santabaren, who was celebrated for his power of working miracles. The ecclesias- tical conjuror exhibited to him the image of his beloved son magnificently dressed and mounted upon a superb charger : The youth rushed towards his father, threw himself into his arms and disap- peared. M. Salverte judiciously observes, that this deception could not have been performed by a real person, who imitated the figure of the young prince. The existence of this person, betrayed by so remarkable a resemblance, and by the trick of the exhibition, could not fail to have been discover- ed and denounced, even if we could explain how 68 LETTERS ON NATURAL MAGIC. the son could be so instantaneously disentangled from his father's embrace. The emperor, in short, saw the aerial image of a picture of his son on horseback, and as the picture was brought nearer the mirror, the image advanced into his arms, when it of course eluded his affectionate grasp. These and other allusions to the operations of the ancient magic, though sufficiently indicative of the methods which were employed, are too meagre to convey any idea of the splendid and imposing exhibitions which must have been displayed. A national system of deception, intended as an instru- ment of government, must have brought into re- quisition not merely the scientific skill of the age, but a variety of subsidiary contrivances, calculated to astonish the beholder, to confound his judg- ment, to dazzle his senses, and to give a predomi- nant influence to the peculiar imposture which it was thought desirable to establish. The grandeur of the means may be inferred from their efficacy, and from the extent of their influence. This defect, however, is to a certain degree sup- plied by an account of a modern necromancy, which has been left us by the celebrated Benvenu- to Cellini, and in which he himself performed an active part. " It happened," says he, " through a variety of odd accidents, that I made acquaintance with a Si- cilian priest, who was a man of genius, and well versed in the Latin and Greek authors. Hap- pening one day to have some conversation with him when the subject turned upon the art of ne- cromancy, I, who had a great desire to know something of the matter, told him, that I had all MODERN NECROMANCY. 69 my life felt a curiosity to be acquainted with the mysteries of this art. "The priest made answer, 6 That the man must be of a resolute and steady temper who enters upon that study.' I replied, 6 that I had fortitude and re- solution enough, if I could but find an opportunity.' The priest subjoined, ' if you think you have the heart to venture, I will give you all the satisfac- tion you can desire.' Thus we agreed to enter up- on a plan of necromancy. The priest one evening prepared to satisfy me, and desired me to look out for a companion or two. I invited one Vincenzio Romoli, who was my intimate acquaintance : he brought with him a native of Pistoia, who cultivat- ed the black art himself. We repaired to the Colosseo, and the priest, according to the custom of necromancers, began to draw circles upon the ground, with the most impressive ceremonies ima- ginable : he likewise brought hither assafcetida, several precious perfumes, and fire, with some com- positions also, which diffused noisome odours. As soon as he was in readiness, he made an opening to the circle, and having taken us by the hand, or- dered the other necromancer, his partner, to throw the perfumes into the fire at a proper time, intrust- ing the care of the fire and perfumes to the rest ; and thus he began his incantations. This ceremo- ny lasted above an hour and a-half, when there ap- peared several legions of devils, insomuch that the amphitheatre was quite filled with them. I was busy about the perfumes, when the priest, perceiv- ing there was a considerable number of infernal spirits, turned to me and said, 6 Benvenuto, ask them something?' I answered, 6 let them bring me 70 LETTERS ON NATURAL MAGIC. into the company of my Sicilian mistress Angeli- ca.' That night he obtained no answer of any sort ; but I had received great satisfaction in hav- ing my curiosity so far indulged. The necroman- cer told me it was requisite we should go a second time, assuring me that I should be satisfied in whatever I asked ; but that I must bring with me a pure immaculate boy. " I took with me a youth who was in my service? of about twelve years of age, together with the same Vincenzio Romoli, who had been my compa- nion the first time, and one Agnolino Gaddi, an in- timate acquaintance, whom I likewise prevailed on to assist at the ceremony. When we came to the place appointed, the priest having made his prepa- rations as before, with the same and even more striking ceremonies, placed us within the circle?, which he had likewise drawn with a more wonder- ful art, and in a more solemn manner than at our former meeting. Thus, having committed the care of the perfumes and the fire to my friend Vincen- zio, who was assisted by Agnolino Gaddi, he put into my hand a pintaculo or magical chart, and bid me turn it towards the places that he should direct me ; and under the pintaculo I held the boy. The necromancer, having begun to make his tremendous invocations, called by their names a multitude of demons who were the leaders of the several legions? and questioned them, by the power of the eternal uncreated God, who lives for ever, in the Hebrew language, as likewise in Latin and Greek ; insomuch that the amphitheatre was almost in an instant fill- ed with demons more numerous than at the for- mer conjuration. Vincenzio Romoli was busied in MODERN NECROMANCY. 71 making a fire, with the assistance of Agnolino, and burning- a great quantity of precious perfumes. I, by the directions of the necromancer, again desired to be in the company of my Angelica. The former thereupon turning to me, said, — ' Know, they have declared that in the space of a month you shall be in her company.' " He thus requested me to stand resolutely by him, because the legions were now above a thousand more in number than he had designed ; and besides, these were the most dangerous ; so that, after they had answered my question, it behoved him to be civil to them and dismiss them quietly. At the same time the boy under the pintaculo was in a terrible fright, saying, that there were in that place a million of fierce men, who threatened to destroy us ; and that, moreover, four armed giants of enor- mous stature were endeavouring to break into our circle. During this time, whilst the necromancer, trembling with fear, endeavoured by mild and gen- tle methods to dismiss them in the best way he could, Vincenzio Romoli, who quivered like an as- pen leaf, took care of the perfumes. Though I was as much terrified as any of them, I did my utmost to conceal the terror I felt ; so that I greatly con- tributed to inspire the rest with resolution ; but the truth is, I gave myself over for a dead man, seeing the horrid fright the necromancer was in. The boy placed his head between his knees and said, 6 In this posture will I die ; for we shall all surely perish,' I told him that all these demons were under us, and what he saw was smoke and shadow ; so bid him hold up his head and take courage. No soon- er did he look up than he cried out, ' The whole 72 LETTERS ON NATURAL MAGIC. amphitheatre is burning* and the fire is just falling upon us.' So covering his eyes with his hands, he again exclaimed, 6 that destruction was inevitable, and de- sired to see no more.' The necromancer entreated me to have a good heart, and take care to burn pro- per perfumes ; upon which I turned to Romoli, and bid him burn all the most precious perfumes he had. At the same time, I cast my eye upon Agnolino Gaddi, who was terrified to such a degree that he could scarce distinguish objects, and seemed to be half-dead. Seeing him in this condition, I said, < Agnolino, upon these occasions a man should not yield to fear, but should stir about and give his as- sistance, so come directly and put on some more of these.' The effects of poor Agnolino's fear were overpowering. The boy hearing a crepitation ven- tured once more to raise his head, when, seeing me laugh, he began to take courage, and said ' That the devils" were flying away with a vengeance.' " In this condition we stayed till the bell rung for morning prayers. The boy again told us, that there remained but few devils, and these were at a great distance. When the magician had perform- ed the rest of his ceremonies, he stripped off his gown, and took up a wallet full of books which he had brought with him. " We all went out of the circle together, keeping as close to each other as we possibly could, especi- ally the boy, who had placed himself in the middle, holding the necromancer by the coat, and me by the cloak. As we were going to our houses in the quarter of Banchi, the boy told us that two of the demons whom we had seen at the amphitheatre went on before us leaping and skipping, sometimes MODERN NECROMANCY. 73 running- upon the roofs of the houses, and some- times upon the ground. The priest declared, that though he had often entered magic circles, nothing so extraordinary had ever happened to him. As we went along, he would fain persuade me to assist with him at consecrating a brook from which, he said, we should derive immense riches : we should then ask the demons to discover to us, the various treasures with which the earth abounds, which would raise us to opulence and power ; but that these love- affairs were mere follies, from whence no good could be expected. I answered, 4 That I would readily have accepted his proposal, if I understood Latin." He redoubled his persuasions, assuring me, that the knowledge of the Latin language was by no means material. He added, that he could have Latin scholars enough, if he had thought it worth while to look out for them, but that he could never have met with a partner of resolution and intrepi- dity equal to mine, and that I should by all means follow his advice. Whilst we were engaged in this conversation, we arrived at our respective houses, and all that night dreamt of nothing but devils." It is impossible to peruse the preceding descrip- tion without being satisfied that the legions of de- vils were not produced by any influence upon the imaginations of the spectators, but were actual op- tical phantasms, or the images of pictures or ob- jects produced by one or more concave mirrors or lenses. A fire is lighted, and perfumes and incense are burnt, in order to create a ground for the ima- ges, and the beholders are rigidly confined within the pale of the magic circle. The concave mirror and the objects presented to it having been so 74 LETTERS ON NATURAL MAGIC. placed that the persons within the circle could not see the aerial image of the objects by the rays di- rectly reflected from the mirror, the work of de- ception was ready to begin. The attendance of the magician upon his mirror was by no means ne- cessary. He took his place along with the spec- tors within the magic circle. The images of the devils were all distinctly formed in the air imme- diately above the fire, but none of them could be seen by those within the circle. The moment, however, that perfumes were thrown into the fire to produce smoke, the first wreath of smoke that rose through the place of one or more of the images, would reflect them to the eyes of the spectator, and they could again disappear if the wreath was not followed by another. More and more images would be rendered visible as new wreaths of smoke arose, and the whole group would appear at once when the smoke was uniformly diffused over the place occupied by the images. The " compositions which diffused noisome odours" were intended to intoxicate or stupify the specta- tors, so as to increase their liability to deception, or to add to the real phantasms which were before their eyes others which were the offspring only of their own imaginations. It is not easy to gather from the description what parts of the exhibition were actually presented to the eyes of the specta- tors, and what parts of it were imagined by them- selves. It is quite evident that the boy as well as Agnolino Gaddi, were so overpowered with terror that they fancied many things which they did not see ; but when the boy dec] ares that four armed giants of an enormous stature were threatening to MODERN NECROMANCY. 75 break into their circle, he gives an accurate de- scription of the effect that would be produced by pushing- the figures nearer the mirror, and then magnifying their images, and causing them to ad- vance towards the circle. Although Cellini de- clares that he was trembling with fear, yet it is quite evident that he was not entirely ignorant of the machinery which was at work, for in order to encourage the boy, who was almost dead with fear, he assured them that the devils were under their power, and that " what he saw was smoke and sha- dow." Mr Roscoe, from whose Life of Cellini the pre- ceding description is taken, draws a similar conclu- sion from the consolatory words addressed to the boy, and states that they " confirm him in the be- lief, that the whole of these appearances, like a phantasmagoria, were merely the effects of a ma- gic lantern produced on volumes of smoke from various kinds of burning wood." In drawing this conclusion, Mr Roscoe has not adverted to the fact, that this exhibition took place about the middle of the 16th century, while the magic lantern was not invented by Kircher till towards the middle of the 17th century, Cellini having died in 1570, and Kircher having been born in 1601. There is no doubt that the effects described could be produced by this instrument, but we are not entitled to have recourse to any other means of explanation but those which were known to exist at the time of Cellini. If we suppose, however, that the necro- mancer either had a regular magic lantern, or that he had fitted up his concave mirror in a box con- taining the figures of his devils, and that this box 76 LETTERS ON NATURAL MAGIC. with its lights was carried home with the party, we can easily account for the declaration of the boy, " that, as they were going- home to their houses in the quarter of Banchi, two of the demons whom ive had seen at the Amphitheatre, went on before us leaping and skipping, sometimes run- ning upon the roofs of the houses, and sometimes upon the ground" The introduction of the magic lantern as an optical instrument, supplied the magicians of the 17th century with one of their most valuable tools. The use of the concave mirror, which does not ap- pear to have been even put up into the form of an instrument, required a separate apartment, or at least that degree of concealment which it was dif- ficult on ordinary occasions to command ; but the magic lantern, containing in a small compass its lamp, its lenses, and its sliding figures, was pecu- liarly fitted for the itinerant conjuror, who had neither the means of providing a less portable and more expensive apparatus, nor the power of trans- porting and erecting it. The magic lantern shown in the annexed figure consists of a dark lantern, A B, containing a lamp G, and a concave metallic mirror M N, and it is so constructed that when the lamp is lighted, not a ray of light is able to escape from it. Into the side of the lantern is fitted a double tube C D, the outer half of which D, is capable of moving within the other half. A large plano-convex lens C, is fixed at the inner end of the double tube, and a small convex lens D, at the outer end ; and to the fixed tube C E, there is joined a groove E F, in which the sliders containing the painted objects are placed. MAGIC LANTERN. 77 and through which they can be moved. Each slider contains a series of figures or pictures paint - Fig. 5. v ed on glass with highly transparent colours. The direct light of the lamp G, and the light reflected from the mirror M N, falling upon the illuminat- ing lens C, is concentrated by it so as to throw a brilliant light upon the painting on the slider, and as this painting is in the conjugate focus of the convex lens D, a magnified image of it will be form- ed on a white wall or white cloth placed at P Q. If the lens D is brought nearer to E F, or to the picture, the distinct image will be more magnified, and will be formed at a greater distance from D, so that if there is any particular distance of the image which is more convenient than another, or any particular size of the object which we wish, it can be obtained by varying the distance of the lens D from E F. When the image is received on an opaque ground, as is commonly the case, the spectators are placed in the same room with the lantern ; but for the 78 LETTERS ON NATURAL MAGIC. purposes of deception, it would be necessary to place the lantern in another apartment like the mirror in Fig 4, and to throw the magnified pictures on a large plate of ground glass, or a transparent gauze screen, stretched across an opening E F, Fig. 4, made in the partition which separates the spectators from the exhibitor. The images might, like those of the concave mirror, be received upon wreaths of smoke. These images are of course always invert- ed in reference to the position of the painted ob- jects ; but in order to render them really erect, we have only to invert the sliders. The representa- tions of the magic lantern never fail to excite a high degree of interest, even when exhibited with the ordinary apparatus ; but by using double slid- ers, and varying their movements, very striking effects may be produced. A smith, for example, is made to hammer upon his anvil, — a figure is thrown into the attitude of terror by the introduc- tion of a spectral apparition, — and a tempest at sea is imitated, by having the sea on one slider, and the ships on other sliders, to which an undulatory mo- tion is communicated. The magic lantern is susceptible of great im- provement in the painting of the figures, and in the mechanism and combination of the sliders. A painted figure which appears well executed to the unassisted eye, becomes a mere daub when magnifi- ed 50 or 100 times; and when we consider what kind of artists are employed in their execution, we need not wonder that this optical instrument has degenerated into a mere toy for the amusement of the young. Unless for public exhibition, the ex- pence of exceedingly minute and spirited drawings MAGIC LANTERN. 79 could not be afforded ; but I have no doubt that if such drawings were executed, a great part of the ex- pence might be saved by engraving- them on wood, and transferring their outline to the glass sliders. A series of curious representations might be ef- fected, by inserting glass plates containing suitable figures in a trough having two of its sides parallel, and made of plate glass. The trough must be intro- duced at E F, so that the figure on the glass is at the proper distance from the object lens D. When the trough is filled with water or with any trans- parent fluid, the picture at PQ will be seen with the same distinctness as if the figure had been in- troduced by itself into the groove E F ; but if any transparent fluid of a different density from water is mixed with it, so as to combine with it quickly or slowly, the appearance of the figure displayed at P Q will undergo singular changes. If spirits of wine, or any ardent spirit, are mixed with the wa- ter, so as to produce throughout its mass partial variations of density, the figure at P Q will be as it were broken down into a thousand parts, and will recover its continuity and distinctness when the two fluids have combined. If a fluid of less den- sity than water is laid gently upon the water, so as to mix with it gradually, and produce a regular diminution of density downwards ; or if saline sub- stances soluble in water are laid at the bottom of the trough, the density will diminish upwards, and the figure will undergo the most curious elonga- tions and contractions. Analogous effects may be produced by the application of heat to the sur- face or sides of the trough, so that we may effect at the same time both an increase and a diminution 80 LETTERS ON NATURAL MAGIC. in the density of the water, in consequence of which the magnified images will undergo the most remarkable transformations. It is not necessary to place the glass plate which contains the figure within the trough. It may be placed in front of it, and by thus creating as it were an atmosphere with local variations of density we may exhibit the phe- nomena of the mirage and of looming, in which the inverted images of ships and other objects are seen in the air, as described in another letter. The power of the magic lantern has been greatly extended by placing it on one side of the transparent screen of taffetas which receives the images while the spectators are placed on the other side, and by mak- ing every part of the glass sliders opaque, excepting the part which forms the figures. Hence all the figures appear luminous on a black ground, and pro- duce a much greater effect with the same degree of illumination. An exhibition depending on these principles was brought out by M. Philipstal in 1802 under the name of the Phantasmagoria, and when it was shown in London and Edinburgh it pro- duced the most impressive effects upon the specta- tors. The small theatre of exhibition was lighted only by one hanging lamp, the flame of which was drawn up into an opaque chimney or shade when the performance began. In this " darkness visible" the curtain rose and displayed a cave with skele- tons and other terrific figures in relief upon its walls. The nickering light was then drawn up beneath its shroud, and the spectators in total darkness found themselves in the middle of thunder and light- ning. A thin transparent screen had, unknown to the spectators, been let down after the disappear- MAGIC LANTERN. 81 ance of the light, and upon it the flashes of light- ning and all the subsequent appearances were re- presented. This screen being half-way between the spectators and the cave which was first shown, and being itself invisible, prevented the observers from having any idea of the real distance of the figures, and gave them the entire character of aerial pictures. The thunder andlightning were followed by the figures of ghosts, skeletons, and known indivi- duals, whose eyes and mouth were made to move by the shifting of combined sliders. After the first fi- gure had been exhibited for a short time, it began to grow less and less, as if removed to a great distance, and at last vanished in a small cloud of light. Out of this same cloud the germ of another figure began to appear, and gradually grew larger and larger, and approached the spectators till it attain- ed its perfect developement. In this manner, the head of Dr Franklin was transformed into a skull; figures which retired with the freshness of life came back in the form of skeletons, and the retiring ske- letons returned in the drapery of flesh and blood. The exhibition of these transmutations was follow- ed by spectres, skeletons, and terrific figures, which, instead of receding and vanishing as before, sudden- ly advanced upon the spectators, becoming larger as they approached them, and finally vanished by appearing to sink into the ground. The effect of this part of the exhibition was naturally the most impressive. The spectators were not only surpris- ed but agitated, and many of them were of opinion that they could have touched the figures. M. Ro- bertson at Paris introduced along with his pictures the direct shadows of living objects, which imitated 82 LETTERS ON NATURAL MAGIC. coarsely the appearance of those objects in a dark night or in moonlight. All these phenomena were produced by varying- the distance of the magic lantern A B, Fig. 5, from the screen PQ, which remained fixed, and at the same time keeping the image upon the screen distinct, by increasing the distance of the lens D from the sliders in E F. When the lantern approached to P Q, the circle of light P Q, or the section of the cone of rays P D Q, gradually diminished, and resembled a small bright cloud, when D was close to the screen. At this time a new figure was put in, so that when the lantern receded from the screen ; the old figure seemed to have been transformed in- to the new one. Although the figure was always at the same distance from the spectators, yet, ow- ing to its gradual diminution in size, it necessarily appeared to be retiring to a distance. When the magic lantern was withdrawn from P Q, and the lens D at the same time brought nearer to E F, the image in P Q gradually increased in size, and there- fore seemed in the same proportion to be approach- ing the spectators. Superior as this exhibition was to any represen- tation that had been previously made by the magic lantern, it still laboured under several imperfec- tions. The figures were poorly drawn, and in other respects not well executed, and no attempt what- ever was made to remove the optical incongruity of the figures becoming more luminous when they retir- ed from the observer, and more obscure when they approached to him. The variation of the distance of the lens D from the sliders in E F was not ex- actly adapted to the motion of the lantern to and 3 PHANTASMAGORIC EXHIBITIONS. 83 from the screen, so that the outline of the figures was not equally distinct during their variations of magnitude. Dr Thomas Young suggested the arrangement shown in Fig. 6 for exhibiting the phantasmagoria. Fig. 6. The magic lantern is mounted on a small car H, which runs on wheels W W. The direct light of the lamp G, and that reflected from the mirror M, is condensed by the illuminating lenses C C, upon the transparent figures in the opaque sliders at E, and the image of these figures is formed at P Q, by the object lens D. When the car H is drawn back on its wheels, the rod I K brings down the point K, and, by means of the rod KL, pushes the lens D nearer to the sliders in E F, and when the car ad- vances to P Q, the point K is raised, and the rod K L draws out the lens D from the slider, so that the image is always in the conjugate focus of D, and therefore distinctly painted on the screen. The rod K N must be equal in length to I K, and 84 LETTERS ON NATURAL MAGIC* the point I must be twice the focal length of the- lens D before the object, L being- immediately un- der the focus of the lens. In order to diminish the brightness of the image when it grows small and appears remote, Dr Young contrived that the support of the lens D should suffer a screen S to fall and intercept a part of the light. This method, however, has many disadvantages, and we are sa- tisfied, that the only way of producing a variation in the light corresponding to the variation in the size of the image, is to use a single illuminating lens C, and to cause it to approach E F, and throw less light upon the figures when D is removed from E F, and to make C recede from E F when D ap- proaches to it. The lens C should therefore be placed in a mean position corresponding to a mean distance of the screen and to the ordinary size of the figures, and should have the power of be- ing removed from the slider E F, when a greater intensity of light is required for the images when they are rendered gigantic, and of being brought close to E F when the images are made small, The size of the lens C ought of course to be such that the section of its cone of rays at E F is equal to the size of the figure on the slider when C is at its greatest distance from the slider. The method recommended by Dr Young for pul- ling out and pushing in the object lens D, according as the lantern approaches to or recedes from the screen, is very ingenious and effective. It is, how- ever, clumsy in itself, and the connexion of the levers with the screen, and their interposition be- tween it and the lantern, must interfere with the operations of the exhibitor. It is, besides, suited CATADIOPTRICAL phantasmagoria. 8b only to short distances between the screen and the lantern ; for when that distance is considerable, as it must sometimes require to be, the levers K L, K I, K T would bend by the least strain, and be- come unfitted for their purpose. For these reasons, the mechanism which adjusts the lens D should be moved by the axle of the front wheels, the tube which contains the lens should be kept at its great- est distance from E F by a slender spring, and should be pressed to its proper distance by the ac- tion of a spiral cam suited to the optical relation between the two conjugate focal distances of the lens. Superior as the representations of the phantas- magoria are to those of the magic lantern, they are •still liable to the defect which we have mentioned, namely, the necessary imperfection of the minute transparent figures when magnified. This defect cannot be remedied by employing the most skilful artists. Even Michael Angelo would have failed in executing a figure an inch long with transparent varnishes, when all its imperfections were to be magnified. In order, therefore, to perfect the art of representing phantasms, the objects must be living ones, and in place of chalky ill drawn figures mi- micking humanity by the most absurd gesticulations, we shall have phantasms of the most perfect deli- neation, clothed in real drapery, and displaying all the movements of life. The apparatus by which such objects may be used may be called the cata- dioptrical phantasmagoria, as it operates both by reflexion and refraction. The combination of mirrors and lenses which seems best adapted for this purpose is shown in Fig. 7, where A B, is a living figure placed before 86 LETTERS ON NATURAL MAGIC. a large concave mirror M N, by means of which a diminished and inverted image of it is formed at a b. If P Q is the transparent screen upon which the image is to be shown to the spectators on the right hand of it, a large lens L L must be so placed before the image a b as to form a distinct and erect picture of it at A' B' upon the screen. When the image A'W is required to be the exact size of A B,the lens L L must magnify the small image a b as much as the mirror M N diminishes the figure A B. The living object A B, the mirror M N, and the lens L L, must all be placed in a moveable car for the purpose of producing the variations in the size of the phantasms, and the transformations of one figure into another. The contrivance for adjusting the lens L L to give a distinct picture at different distances of the screen will of course be required in the present apparatus. In order to give full effect to the phantasms, the living objects at A B will require to be illuminated in the strong- CATADIOPTRICAL PHANTASMAGORIA. 87 est manner, and should always be dressed either in white or in very luminous colours, and in order to give them relief a black cloth should be stretch- ed at some distance behind them. Many interest- „ ing effects might also be produced by introducing- at A B fine paintings and busts. It would lead us into too wide a field were we to detail the immense variety of resources which the science of optics furnishes for such exhibitions. One of these, however, is too useful to be passed without notice. If we interpose a prism with a small refracting angle between the image a b, Fig. 7, and the lens L L, the part of the figure immedi- ately opposite to the prism will be as it were de- tached from the figure, and will be exhibited sepa- rately on the screen P Q. Let us suppose that this part is the head of the figure. It may be de- tached vertically, or lifted from the body as if it were cut off, or it may be detached downwards and placed on the breast as if the figure were deformed. In detaching the head vertically or laterally, an opaque screen must be applied to prevent any part of the head from being seen by rays which do not pass through the prism ; but this and other practical details will soon occur to those who put the method to an experimental trial. The application of the prism is shown in Fig. 8, where a b is the inverted image formed by a concave mirror, A B C a prism with a small refracting angle B C A, placed between a b and the lens L L, s a small opaque screen, and A B the figure with its head detached. A hand may be made to grasp the hair of the head, and the aspect of death may be given to it, as if it had been newly cut off. Such a representation could be easily 88 LETTERS ON NATURAL MAGIC. made, and the effect upon the spectators would be quite overpowering*. The lifeless head might then be made to recover its vitality, and be safely repla- ced upon the figure. If the head A of the living Fig. 8. A object A B, Fig. 7, is covered with black cloth, the head of a person or of an animal placed above A might be set upon the shoulders of the figure A B by the refraction of a prism. When the figure a b, Fig. 8, is of very small di- mensions, as in the magic lantern, a small prism of glass would answer the purpose required of it ; but in public exhibitions where the image a b must be of a considerable size, if formed by a concave mirror, a very large prism would be necessary. This, how- ever, though impracticable with solid glass, may be easily obtained by means of two large pieces of plate glass made into a prismatic vessel and filled with water. Two of the glasses of a carriage win- dow would make a prism capable of doubling the whole of the bust of a living person placed as an object at A B, Fig. 7, so that two perfectly similar phantasms might be exhibited. In those cases kircher's mysterious handwriting. 89 where the images before the lens L L are small, they may be doubled and even tripled by interpo- sing* a well prepared plate of calcareous spar, that is, crossed by a thin film. These images would possess the singular character of being oppositely coloured and of changing their distances and their colours by slight variations in the positions of the plate.* In order to render the images which are formed by the glass and water prisms as perfect as possible, it would be easy to make them achromatic, and the figures might be multiplied to any extent by using several prisms, having their refracting edges paral- lel, for the purpose of giving a similarity of position to all the images. Among the instruments of natural magic which were in use at the revival of science, there was one invented by Kircher for exhibiting the mysterious Fig, 9. handwriting on the wall of an apartment from which the magician and his apparatus were excluded. The annexed figure represents this apparatus, as given * See Edin. Encyclopedia. Art. Optics, Vol. xv. p. 611, 90 LETTERS ON NATURAL MAGIC. by Schottus. The apartment in which the specta- tors are placed is between L L and G H, and there is an open window in the side next L L, G H being- the inside of the wall opposite to the window. Up- on the face of the plane speculum E Fare written the words to be introduced, and when a lens L L is pla- ced at such a distance from the speculum, and of such a focal length that the letters and the place of their representation are in its conjugate foci, a distinct image of the writing will be exhibited on the wall at G H. The letters on the speculum are of course inverted, as seen at E F, and when they are illuminated by the sun's rays S, as shown in the figure, a distinct image, as Schottus assures us, may be formed at the distance of 500 feet. In this experi- ment the speculum is by no means necessary. If the letters are cut out of an opaque card, and illuminated by the light of the sky in the day, or by a lamp during night, their delineation on the wall would be equally distinct. In the day time it would be necessary to place the letters at one end of a tube or oblong box, and the lens at the other end. As this deception is performed when the spectators are unprepared for any such exhibition, the warning written in luminous letters on the wall, or any word associated with the fate of the individual observer, could not fail to pro- duce a singular effect upon his mind. The words might be magnified, diminished, multiplied, colour- ed and obliterated, in a cloud of light, from which they might again reappear by the methods already described, as applicable to the magic lantern. The art of forming aerial representations was a great desideratum among the opticians of the 17 th century. Vitellio and others had made many un- CYLINDRICAL MIRRORS. 91 successful attempts to produce such images, and the speculations of Lord Bacon on the subject are too curious to be withheld from the reader. " It would be well bolted out/' says he, "whether great refractions may not be made upon reflexions, as well as upon direct beams. For example, take an empty basin, put an angel or what you will into it ; then go so far from the basin till you cannot see the angel, because it is not in a right line ; then fill the basin with water, and you shall see it out of its place, because of the refraction. To proceed, there- fore, put a looking-glass into a basin of water. I suppose you shall not see the image in a right line or at equal angles, but wide. I know not whether this experiment may not be extended, so as you might see the image and not the glass, which, for beauty and strangeness, were a fine proof, for then you should see the image like a spirit in the air. As, for example, if there be a cistern or pool of wa- ter, you shall place over against it the picture of the devil, or what you will, so as that you do not see the water. Then put a looking-glass in the water ; now if you can see the devil's picture aside, not seeing the water, it would look like the devil in- deed. They have an old tale in Oxford, that Friar Bacon walked between two steeples, which was thought to be done by glasses, when he walked up- on the ground. " Kircher also devoted himself to the production of such images, and he has given in the annexed figure his method of producing them. At the bottom of a polished cylindrical vessel A B he pla- ced a figure C D, which we presume must have been highly illuminated from below, and to the spectators 92 LETTERS ON NATURAL MAGIC. who looked into the vessel in an oblique direction there was exhibited an image placed vertically in the air as if it were ascending at the mouth of the vessel. Kircher assures us that he once exhibited in this manner a representation of the Ascension of our Saviour, and that the images were so perfect that the spectators could not be persuaded till they Fig. 10. c had attempted to handle them, that they were not real substances. Although Kircher does not men- tion it, yet it is manifest that the original figure AB must have been a deformed or anamorphous drawing, in order to give a reflected image of just propor- tions. We doubt, indeed, if the representation or the figure was ever exhibited. It is entirely incom- patible with the laws of reflexion. Among the ingenious and beautiful deceptions of the 17th century, we must enumerate that of the reformation of distorted pictures by reflexion from cylindrical and conical mirrors. In these re- CYLINDRICAL MIRRORS. 93 presentations the original image from which a per- fect picture is produced, is often so completely dis- torted, that the eye cannot trace in it the resem- blance to any regular figure, and the greatest de- gree of wonder is of course excited, whether the original image is concealed or exposed to view. These distorted pictures may be drawn by strict geometrical rules ; but I have shown in Fig. 11a Fig. 11. simple and practical method of executing them. Let M N be an accurate cylinder made of tin-plate 94 LETTERS ON NATURAL MAGIC. or of thick pasteboard. Out of the farther side of it cut a small aperture abed; and out of the nearer side cut a larger one A BCD, the size of the picture to be distorted. Having perforated the outline of the picture with small holes, place it on the opening A B C D so that its surface may be cy- lindrical. Let a candle or a bright luminous object, the smaller the better, be placed at S, as far behind the picture A B C D as the eye is afterwards to be placed before it, and the light passing through the small holes will represent on a horizontal plane a distorted image of the picture A' B' C D', which when sketched in outline with a pencil, and shaded or coloured, will be ready for use. If we now sub- stitute a polished cylindrical mirror of the same size in place of M N, then the distorted picture when laid horizontally at A' B' C D' will be re- stored to its original state when seen by reflexion at A B C D in the polished mirror. It would be Fig. 12. MIRRORS OF VARIABLE CURVATURE. 95 an improvement on this method to place at A B C D a thin and flexible plate of transparent mica, hav- ing drawn upon it with a sharp point or painted upon it the figure required. The projected image of this figure at A' B' C D' may then be accurate- ly copied. The effect of a cylindrical mirror is shown in Fig. 12, which is copied from an old one which we have seen in use. The method above described is equally applicable to concave cylindrical mirrors, and to those of a conical form, and it may also be applied to mirrors of variable curvature, which produce different kinds of distortions from different parts of their surfaces. By employing a mirror whose surface has a va- riable curvature like ABC, Fig. 13, we obtain an Fig. 13. instrument for producing an endless variety of caricatures, all of which are characterized by their 96 LETTERS ON NATURAL MAGIC. resemblance to the original. If a figure M N is placed before such a mirror, it will of course ap- pear distorted and caricatured, but even if the fi- gure takes different distances and positions, the va- riations which the image undergoes are neither sufficiently numerous or remarkable to afford much amusement. But if the figure M N is very near the mirror, so that new distortions are produced by the different distances of its different parts from the mirror, the most singular caricatures may be exhibited. If the figure, for example, bends for- ward his head and the upper part of his body, they will swell in size, leaving his lower extremities short and slender. If it draws back the upper part of the body and advances the limbs, the opposite effect will take place. In like manner different sides of the head, the right or the left side of it, the brow or the chin, may be swelled and con- tracted at pleasure. By stretching out the arms before the body they become like those of an orang outang, and by drawing them back they dwindle into half their regular size. All these effects, which depend greatly on the agility and skill of the performer, may be greatly increased by suitable distortions in his own features and figure. The family likeness, which is of course never lost in all the variety of figures which are thus produ- ced, adds greatly to the interest of the exhibition ; and we have seen individuals so annoyed at recog- nizing their own likeness in the hideous forms of humanity which were thus delineated, that they could not be brought to contemplate them a second time. If the figure is inanimate, like the small cast a of statue, the effect is very curious, as the MIRRORS OF VARIABLE CURVATURE. 97 swelling* and contracting* of the parts and the sud- den change of expression give a sort of appearance of vitality to the image. The inflexibility of such a figure, however, is unfavourable to its transfor- mation into caricatures. Interesting as these metamorphoses are, they lose in the simplicity of the experiment much of the wonder which they could not fail to excite if exhibited on a great scale, where the performer is invisible, and where it is practicable to give an aerial representation of the caricatured figures. This may be done by means of the apparatus shown in Fig. 7 * where we may suppose A B to be the re- duced image seen in the reflecting surface ABC, Fig. 13.-J- By bringing this image nearer the mir- ror M N, Fig. 7, a magnified and inverted image of it may be formed at a b, of such a magnitude as to give the last image in P Q the same size as life. Owing to the loss of light by the two reflexions, a very powerful illumination would be requisite for the original figure. If such an exhibition were well got up the effect of it would be very striking. * Page 86. f Page 95. G 98 LETTERS ON NATURAL MAGIC. LETTER V. Miscellaneous optical illusions — Conversions of cameos into intaglios, or elevations into depressions, and the reverse — Explanation of this class of deceptions — Singular effects of illumination with light of one simple colour — Lamps for producing homogeneous yellow light — Methods of increasing the effect of this exhibition — Method of reading the inscrip- tion of coins in the dark — Art of deciphering the effaced in- scription of coins — Explanation of these singular effects — Apparent motion of the eyes in portraits — Remarkable ex- amples of this — Apparent motion of the features of a por- trait, when the eyes are made to move — Remarkable experi- ment of breathing light and darkness. In the preceding letter I have given an account of the most important instruments of Natural Ma- gic which depend on optical principles ; but there still remain several miscellaneous phenomena on which the stamp of the marvellous is deeply im- pressed, and the study of which is pregnant with instruction and amusement. One of the most curious of these is that false perception in vision by which we conceive depres- sions to be elevations and elevations depressions, or by which intaglios are converted into cameos, and cameos into intaglios. This curious fact seems to have been first observed at one of the early meet- ings of the Royal Society of London, when one of CONVERSION OF CAMEOS INTO INTAGLIOS. 99 the members, in looking- at a guinea through a com- pound microscope of new construction, was sur- prised to see the head upon the coin depressed, while other members could only see it embossed as it really was. While using telescopes and compound micro- scopes, Dr Gmelin of Wurtemburg observed the same fact. The protuberant parts of objects ap- peared to him depressed, and the depressed parts protuberant ; but what perplexed him extremely, this illusion took place at some times and not at others, in some experiments and not in others, and appeared to some eyes and not to others. After making a great number of experiments, Dr Gmelin is said to have constantly observed the fol- lowing effects : Whenever he viewed any object rising upon a plane of any colour whatever, provid- ed it was neither white nor shining, and provided the eye and the optical tube were directly opposite to it, the elevated parts appeared depressed, and the depressed parts elevated. This happened when he was viewing a seal, and as often as he held the tube of the telescope perpendicularly, and applied it in such a manner that its whole surface almost cover- ed the last glass of the tube. The same effect was produced when a compound microscope was used. When the object hung perpendicularly from a plane, and the tube was supported horizontally and direct- ly opposite to it, the illusion also took place, and the appearance was not altered when the object hung ob- liquely and even horizontally. Dr Gmelin is said to have at last discovered a method of preventing this illusion, which was, by looking not towards the centre of the convexity, but at first to the edges of 100 LETTERS ON NATURAL MAGIC. it only, and then gradually taking- in the whole, " But why these things should so happen, he did not pretend to determine.' ' The best method of observing this deception, is to view the engraved seal of a watch with the eye- piece of an achromatic telescope, or with a com- pound microscope, or any combination of lenses, which inverts the objects that are viewed through it.* The depression in the seal will immediately appear an elevation, like the wax impression which is taken from it ; and though we know it to be hol- low, and feel its concavity with the point of our finger, the illusion is so strong that it continues to appear a protuberance. The cause of this will be understood from Fig. 14, where S is the window of the apartment, or the light which illuminates the hollow seal L R, whose shaded side is of course on the same side L with the light. If we now in- vert the seal with one or more lenses, so that it may look in the opposite direction, it will appear to the eye as in Fig. 15, with the shaded side L far- thest from the window. But as we know that the * A single convex lens will answer the purpose, provided we hold the eye six or eight inches behind the image of the seal formed in its conjugate focus. Fig. 14. CONVERSION OF CAMEOS INTO INTAGLIOS. 101 window is still on our left hand, and that the light falls in the direction R L, and as every body with its shaded side farthest from the light must neces- Fig. 15. sarily be convex or protuberant, we immediately believe that the hollow seal is now a cameo or bas-relief. The proof which the eye thus receives of the seal being raised, overcomes the evidence of its being hollow derived from our actual knowledge, and from the sense of touch. In this experiment the deception takes place from our knowing the real direction of the light which falls upon the seal ; for if the place of the window, with respect to the seal, had been inverted as w T ell as the seal itself, the illusion could not have taken place. In order to explain this better, let us suppose the seal L R, Fig. 14, to be illuminated with a candle S, the place of which we can change at pleasure. If we invert L R it will rise into a cameo, as in Fig. 15 ; and if we then place another candle D on the other side of it, as in Fig. 16, the hollow seal will be equally illuminated on all sides, and it will sink down into a cavity or intaglio. If the two candles do not illuminate the seal equally, or if any acci- dental circumstance produces a belief that the light 102 LETTERS ON NATURAL MAGIC. is wholly or principally on one side, the mind will entertain a corresponding- opinion respecting the state of the seal, regarding- it as a hollow if it be- lieves the light to come wholly or principally from the right hand, and as a cameo if it believes the light to come from the left hand. If we use a small telescope to invert the seal, and if we cover up all the candle but its flame, and arrange the experiment so that the candle may be inverted along with the image, the seal will still retain its concavity, because the shadow is still on the same side with the illuminating body. If we make the same experiments with the rais- ed impression of the seal taken upon wax, we shall observe the very same phenomena, the seal being depressed when it alone is inverted, and re- taining its convexity when the light is inverted along with it. The illusion, therefore, under our consideration is the result of an operation of our own minds, whereby we judge of the forms of bodies by the knowledge we have acquired of light and shadow. Hence the illusion depends on the accuracy and extent of our knowledge on this subject ; and while some persons are under its influence, others Fig. 16. S CONVERSION OF CAMEOS INTO INTAGLIOS. 103 are entirely insensible to it. When the seal or hollow cavity is not polished bnt ground, and the surface round it of uniform colour and smoothness, almost every person, whether young- or old, learn- ed or ignorant, will be subject to the illusion; be- cause the youngest and the most careless observers cannot but know that the shadow of a hollow is always on the side next the light, and the shadow of a protuberance on the side opposite to the light ; but if the object is the raised impression of a seal upon wax, I have found that when inverted, it still seemed raised to the three youngest of six per- sons, while the three eldest were subject to the de- ception. This illusion may be dissipated by a process of reasoning arising from the introduction of a new circumstance in the experiment. Thus, let R L Fig. 18, be the inverted seal, which consequently Fig. 17. appears raised, and let an opaque and unpolished pin A be placed on one side of the seal. Its sha- dow will be of course opposite the candle as at B. In this case the seal, which had become a cameo by its inversion, will now sink down into a cavity by the introduction of the pin and its shadow ; for as the pin and its shadow are inverted, as shown 104 LETTERS ON NATURAL MAGIC. in Fig. 18, while the candle retains its place, the shadow of the pin falling in the direction A B is a stronger proof to the eye that the light is coming from the right hand, than the actual knowledge of Fig. 18. the candle being on the left hand, and therefore the cameo necessarily sinks into a cavity, or the shadow is now on the same side as the light. This experiment will explain to us why on some occa- sions an acute observer will elude the deception, while every other person is subject to it. Let us suppose that a particle of dust, or a little bit of wax, capable of giving a shadow, is adhering to the surface of the seal, an ordinary observer will take no notice of this, or if he does, he will probably not make it a subject of consideration, and will therefore see the head on the seal raised into a cameo; but the attentive observer noticing the little protuberance, and observing that its sha- dow lies to the left of it, will instantly infer that the light comes in that direction, and will still see the seal hollow. I have already mentioned that in some cases even the sense of touch does not correct the erroneous perception. We of course feel that the part of the hollow on which the finger is placed is actu- CONVERSION OF CAMEOS INTO INTAGLIOS. 105 ally hollow ; but if we look at the other part of the hollow it will still appear raised. By using- two candles yielding- different degrees of light, and thus giving- an uncertainty to the di- rection of the light, we may weaken the illusion in any degree we choose, so as to overpower it by touch or by a process of reasoning. I have had occasion to observe a series of analo- gous phenomena arising from the same cause, but produced without any instrument for inverting the object. If AB, for example, is a plate of mother of pearl, and LR a circular or any other cavity (Fig. 19,) ground or turned in it, then if this cavity is il- Fig. 19. luminated by a candle or a window at S, in place of there being a shadow of the margin L of the hollow next the light, as there would have been had the body been opaque, a quantity of bright refracted light will appear where there would have been a shadow, and the rest of the cavity will be compa- ratively obscure, as if it were in shade. The neces- sary consequence of this is, that the cavity will ap- pear, as an elevation when seen only by the naked eye, as it is only an elevated surface that could have its most luminous side at L. Similar illusions take place in certain pieces of 106 LETTERS ON NATURAL MAGIC. polished wood, calcedony, and mother of pearl, where the surface is perfectly smooth. This arises from there being at that place a knot or growth, or no- dule of different transparency from the surrounding mass, and the cause of it will be understood from Fig. 20. Let m o be the surface of a mahogany table, Fig. 20. A mo B a section of the table, and mno, a section of a knot more transparent than the rest of the mass. Owing to the transparency of the thin edge at o, op- posite to the candle S, the side o is illuminated, while the rest of the knot is comparatively dark, so that on the principles already explained the spot mno appears to be a hollow in the table. From this cause arises the appearance of dimples in cer- tain plates of calcedony called hammered calcedo- ny, owing to its having the look of being dimpled with a hammer. The surface on which these ca- vities are seen is a section of small spherical aggre- gations of siliceous matter, which exhibit the same phenomena as the cavities in wood. Mother of pearl presents the very same phenomena, and it is indeed so common in this substance that it is near- ly impossible to find a mother of pearl button or counter which seems to have its surface flat, although they are perfectly so when examined by the touch. HOMOGENEOUS YELLOW LIGHT. 107 Owing- to the different refraction of the incident light by the different growths of the shell cut in different directions by the artificial surface, like the annual growth of wood in a dressed plank, the sur- face has necessarily an unequal and undulating- ap- pearance. Among the wonders of science there are perhaps none more surprising than the effects produced upon coloured objects by illuminating them with homo- geneous light or light of one colour. The light which emanates from the sun, and by which all the objects of the material world are exhibited to us, is compos- ed of three different colours, red, yellow, and blue, by the mixture of which in different proportions all the various hues of nature may be produced. These three colours, when mixed in the proportion in which they occur in the sun's rays, compose a pure- ly white light ; but if any body on which this white light falls shall absorb, or stop, or detain within its substance any part of any one or more of these sim- ple colours, it will appear to the eye of that colour which arises from the mixture of all the rays which it does not absorb, or of that colour which white light would have if deprived of the colours which are absorbed. Scarlet cloth, for example, absorbs most of the blue rays and many of the yellow, and hence appears red. Yellow cloth absorbs most of the blue and many of the red rays, and therefore ap- pears yellow, and blue cloth absorbs most of the yellow and red rays. If we were to illuminate the scarlet cloth with pure and unmixed yellow light, it would appear yellow, because the scarlet cloth does not absorb all the yellow rays, but reflects some of them ; and if we illuminate blue cloth with yellow 108 LETTERS ON NATURAL MAGIC. light, it will appear nearly black, because it absorbs all the yellow light, and reflects almost none of it. But whatever be the nature and colour of the bodies on which the yellow light falls, the light which it reflects must be yellow, for no other light falls upon them, and those which are not capable of reflecting yellow light must appear absolutely black, however brilliant be their colour in the light of day. As the methods now discovered of producing yellow light in abundance were not known to the ancient conjurors, nor even to those of later times, they have never availed themselves of this valuable resource. It has been long known that salt thrown Fig. 21. A into the wick of a flame produces yellow light, but this light is mixed with blue and green rays, and is, HOMOGENEOUS YELLOW LIGHT. 109 besides, so small in quantity, that it illuminates ob- jects only that are in the immediate vicinity of the flame. A method which I have found capable of producing it in abundance is shown in Fig*. 21, where A B is a lamp containing* at A a large quan- tity of alcohol and water or ardent spirits, which gradually descends into a platina or metallic cup D. This cup is strongly heated by a spirit-lamp L, in- closed in a dark lantern, and when the diluted al- cohol in D is inflamed, it will burn with a fierce and powerful yellow flame : Tf the flame should not be perfectly yellow, owing to an excess of alcohol, a proportion of salt thrown into the cup will an- swer the same purpose as a farther dilution of the alcohol.* A monochromatic lamp for producing yellow light may be constructed most effectually by em- ploying a portable gas lamp containing compressed oil gas. If we allow the gas to escape in a copious stream, and set it on fire, it will form an explosive mixture with the atmospheric air, and will no long- er burn with a white flame, but will emit a blu- ish and reddish light. The force of the issuing gas, or any accidental current of air, is capable of blow- ing out this flame, so that it is necessary to have a contrivance for sustaining it. The method which I used for this purpose is shown in Fig. 22. A small gas tube a b c, arising from the main burner M N of the gas lamp P Q, terminates above the burner, and has a short tube d e, moveable up and down within it, so as to be gas-tight. This tube d e, closed at e, communicates with the hollow ring fg, in the inside of which four apertures are per- * See Edinburgh Transactions, vol. ix. p. 435. 110 LETTERS ON NATURAL MAGIC. forated in such a manner as to throw their jets of gas to the apex of a cone, of which f g is the base. When we cause the gas to flow from the burner M, Fig. 22. P < ^ Q by opening the main cock A, it will rush into the tube abed, and issue in small flames at the four holes in the ringy^-. The size of these flames is regulated by the cock b. The inflammation, there- fore, of the ignited gas will be sustained by these four subsidiary flames through which it passes, in- dependent of any agitation of the air, or of the force with which it issues from the burner. On a projecting arm e h, carrying a ring h, I fixed a broad collar, made of coarse cotton wick, which had been previously soaked in a saturated solution of common salt. When the gas was allowed to escape at M, with such force as to produce a long and broad column of an explosive mixture of gas and '3 HOMOGENEOUS YELLOW LIGHT. Ill atmospheric air, the bluish flame occasioned by the explosion passes through the salted collar, and is converted by it into a mass of homogeneous yellow light. This collar will last a long time without any fresh supply of salt, so that the gas lamp will yield a permanent monochromatic yellow flame, which will last as long as there is gas in the reser- voir. In place of a collar of cotton wick, a hollow cylinder of sponge, with numerous projecting tufts, may be used, or a collar may be similarly con- structed with asbestos cloth, and, if thought neces- sary, it might be supplied with a saline solution from a capillary fountain. Having thus obtained the means of illuminating any apartment with yellow light, let the exhibition be made in a room with furniture of various bright colours, with oil or water coloured paintings on the wall. The party which is to witness the experiment should be dressed in a diversity of the gayest co- lours ; and the brightest coloured flowers and highly coloured drawings should be placed on the tables. The room being at first lighted with ordinary lights, the bright and gay colours of every thingthat it con- tains will be finely displayed. If the white lights are now suddenly extinguished, and the yellow lamps lighted, the most appalling metamorphosis will be exhibited. The astonished individuals will no longer be able to recognize each other. All the furniture in the room and all the objects which it contains will exhibit only one colour. The flow- ers will lose their hues. The paintings and draw- ings will appear as if they were executed in China ink, and the gayest dresses, the brightest scarlets, the purest lilacs, the richest blues, and the most 112 LETTERS ON NATURAL MAGIC. vivid greens will all be converted into one monoto- nous yellow. The complexions of the parties too will suffer a corresponding change. One pallid death-like yellow, like the unnatural hue Which autumn plants upon the perished leaf, will envelope the young and the old, and the sallow faces will alone escape from the metamorphosis. Each individual derives merriment from the cada- verous appearance of his neighbour, without being sensible that he is himself one of the ghostly as- semblage. If, in the midst of the astonishment which is thus created, the white lights are restored at one end of the room, while the yellow lights are taken to the other end, one side of the dress of every person, namely, that next the white light, will be restored to its original colours, while the other side will re- tain its yellow hue. One cheek will appear in a state of health and colour, while the other retains the paleness of death, and, as the individuals change their position, they will exhibit the most extraor- dinary transformations of colour. If, when all the lights are yellow, beams of white light are transmitted through a number of holes like those in a sieve, each luminous spot will re- store the colour of the dress or furniture upon which it falls, and the nankeen family will appear all mottled over with every variety of tint. If a magic lantern is employed to throw upon the walls or upon the dresses of the company lumi- nous figures of flowers or animals, the dresses will be painted with these figures in the real colour of 4 READING COINS IN THE DARK. 113 the dress itself. Those alone who appeared in yellow, and with yellow complexions, will to a great degree escape all these singular changes. If red and blue light could be produced with the same facility and in the same abundance as yellow light, the illumination of the apartment with these lights in successionwould add to the variety and won- der of the exhibition. The redlight might perhaps be procured in sufficient quantity from the nitrate and other salts of strontian ; but it would be difficult to obtain a blue flame of sufficient intensity for the suit- able illumination of a large room. Brilliant white lights, however, might be used, having for screens glass troughs containing a mass one or two inches thick of a solution of the ammoniacal carbonate of copper. This solution absorbs all the rays of the spec- trum but the blue, and the intensity of the blue light thus produced would increase in the same pro- portion as the white light employed. Among the numerous experiments with which science astonishes and sometimes even strikes ter- ror into the ignorant, there is none more calculat- ed to produce this effect than that of displaying to the eye in absolute darkness the legend or inscrip- tion upon a coin. To do this, take a silver coin, ( I have always used an old one, ) and after polish- ing the surface as much as possible, make the parts of it which are raised rough by the action of an acid, the parts not raised, or those which are to be rendered darkest, retaining their polish. If the coin thus prepared is placed upon a mass of red hot iron, and removed into a dark room, the inscription up- on it will become less luminous than the rest, so that it may be distinctly read by the spectator, h 114 LETTERS ON NATURAL MAGIC. The mass of red hot iron should be concealed from the observer's eye, both for the purpose of rendering the eye fitter for observing the effect, and of re- moving all doubt that the inscription is really read in the dark, that is, without receiving any light, di- rect or reflected, from any other body. If, in place of polishing the depressed parts, and roughening its raised parts, we make the raised parts polished, and roughen the depressed parts, the inscription will now be less luminous than the depressed parts, and we shall still be able to read it, from its being as it were written in black letters on a white ground. The first time I made this experiment, without be- ing aware of what would be the result, I used a French shilling of Louis XV. and I was not a little surprised to observe upon its surface in black let- ters the inscription Benedictum sit nomen Dei. The most surprising form of this experiment is when we use a coin from which the inscription has been either wholly obliterated, or obliterated in such a degree as to be illegible. When such a coin is laid upon the red hot iron, the letters and figures become oxidated, and the film of oxide ra- diating more powerfully than the rest of the coin will be more luminous than the rest of the coin, and the illegible inscription may be now distinctly read to the great surprise of the observer, who had examined the blank surface of the coin previous to its being placed upon the hot iron. The different appearances of the same coin, according as the rais- ed parts are polished or roughened, are shown in Fig. 23 and 24. In order to explain the cause of these remark- able effects, we must notice a method which has READING COINS IN THE DARK. 115 been long known, though never explained, of decy- phering the inscriptions on worn out coins. This is done by merely placing- the coin upon a hot iron : Fig. 23. Fig. 24. An oxidation takes place over the whole surface of the coin, the film of oxide changing- its tint with the intensity or continuance of the heat. The parts, however, where the letters of the inscription had existed, oxidate at a different rate from the sur- rounding parts, so that these letters exhibit their shape, and become legible in consequence of the film of oxide which covers them having a different thickness, and therefore reflecting a different tint from that of the adjacent parts. The tints thus developed sometimes pass through many orders of brilliant colours, particularly pink and green, and settle in a bronze, and sometimes a black tint, rest- ing upon the inscription alone. In some cases the tint left on the trace of the letters is so very 116 LETTERS ON NATURAL MAGIC. faint that it can just be seen, and may be entirely removed by a slight rub of the finger. When the experiment is often repeated with the same coin, and the oxidations successively remov- ed after each experiment, the film of oxide conti- nues to diminish, and at last ceases to make its ap- pearance. It recovers the property, however, in the course of time. When the coin is put upon the hot iron, and consequently when the oxidation is the greatest, a considerable smoke arises from the coin, and this diminishes like the film of oxide by frequent repetition. A coin which had ceased to emit this smoke, smoked slightly after having been exposed twelve hours to the air. I have found from numerous trials that it is always the raised parts of the coin, and in modern coins the elevated ledge round the inscription, that become first oxi- dated. In an English shilling of 1816 this ledge exhibited a brilliant yellow tint before it appeared on any other part of the coin. If we use an uniform and homogeneous disc of silver that has never been hammered or compres- sed, its surface will oxidate equally, provided all its parts are equally heated. In the process of con- verting this disc into a coin, the sunk parts have obviously been most compressed by the prominent parts of the die, and the elevated parts least com- pressed, the metal being in the latter left as it were in its natural state. The raised letters and figures on a coin have therefore less density than the other parts, and these parts oxidate sooner or at a lower temperature. When the letters of the legend are worn off by friction, the parts immedi- ately below them have also less density than the READING COINS IN THE DARK. 117 surrounding- metal, and the site as it were of the letters therefore receive from heat a degree of oxi- dation, and a colour different from that of the sur- rounding- surface. Hence we obtain an explana- tion of the revival of the invisible letters by oxida- tion. The same influence of difference of density may be observed in the beautiful oxidations which are produced on the surface of highly polished steel, heated in contact with air, at temperatures between 430° and 630° of Fahrenheit. * When the steel has hard portions called pins by the workmen, the uniform tint of the film of oxide stops near these hard portions, which always exhibit colours different from those of the rest of the mass. These parts, on account of their increased density, absorb the oxygen of atmospheric air less copiously than the surrounding portions. Hence we see the cause why steel expanded by heat absorbs oxygen, which, when united with the metal, forms the coloured superficial film. As the heat increases, a greater quantity of oxygen is absorbed, and the film in- creases in thickness. These observations enable us to explain the le- gibility of inscriptions in the dark, whether the coin is in a perfect state, or the letters of it worn off. All black or rough surfaces radiate light more copiously than polished or smooth surfaces, and hence the inscription is luminous when it is rough, and obscure when it is polished, and the letters covered with black oxide are more luminous than the adjacent parts, on account of the superior * See Edinburgh Encyclopedia, Art. Steel, vol. xviii. p. 387. 118 LETTERS ON NATURAL MAGIC. radiation of light by the black oxide which covers them. By the means now described invisible writing- might be conveyed by impressing it upon a me- tallic surface, and afterwards erasing it by grinding and polishing that surface perfectly smooth. When exposed to a proper degree of heat, the secret would display itself written in oxidated letters. Many amusing experiments might be made upon the same principle. A series of curious and sometimes alarming de- ceptions, arises from the representation of objects in perspective upon a plane surface. One of the most interesting of these depends on the principles which regulate the apparent direction of the eyes in a portrait. Dr Wollaston has thought this sub- ject of sufficient importance to be treated at some length in the Philosophical Transactions. When we look at any person we direct to them both our face and our eyes, and in this position the circular iris will be in the middle of the white of the eye- ball, or, what is the same thing, there will be the same quantity of white on each side of the iris. If the eyes are now moved to either side, while the head remains fixed, we shall readily judge of the change of their direction by the greater or less quantity of white on each side of the iris. This test, however, accurate as it is, enables us only to estimate the extent to which the eyes deviate in direction from the direction of the face to which they belong. But their direction in reference to the person who views them is entirely a different matter ; and Dr Wollaston is of opinion, that we are not guided by the eyes alone, but are uncon- Fig. 26. 118 LETTERS ON NATURAL MAGIC. radiation of light by the black oxide which covers them. By the means now described invisible writing- might be conveyed by impressing it upon a me- tallic surface, and afterwards erasing it by grinding and polishing that surface perfectly smooth. When exposed to a proper degree of heat, the secret would display itself written in oxidated letters. Many amusing experiments might be made upon the same principle. A series of curious and sometimes alarming de- ceptionS; arises from the representation of objects in perspective upon a plane surface. One of the most interesting of these depends on the principles which regulate the apparent direction of the eyes in a portrait. Dr Wollaston has thought this sub- ject of sufficient importance to be treated at some length in the Philosophical Transactions. When we look at any person we direct to them both our direction from the direction of the tace to wnicli they belong. But their direction in reference to the person who views them is entirely a different matter ; and Dr Wollaston is of opinion, that we are not guided by the eyes alone, but are uncon- MOTION OF THE EYES IN PORTRAITS. 119 sciously aided by the concurrent position of the entire face. If a skilful painter draws a pair of eyes with great correctness directed to the spectator, and deviating- from the general position of the face as much as is usual in good portraits, it is very diffi- cult to determine their direction, and they will ap- pear to have different directions to different persons. But what is very curious, Dr Wollaston has shown that the same pair of eyes may be made to direct themselves either to or from the spectator by the addition of other features in which the position of the face is changed. Thus in Fig. 25, the pair of eyes are looking intently at the spectator, and the face has a corresponding direction ; but when we cover up the face in Fig. 25 with the face in Fig. 26, which looks to the right, the eyes change their direction, and look to the right also. In like man- Fig. 25. 120 LETTERS ON NATURAL MAGIC. ner, eyes drawn originally to look a little to the right or the left of the spectator may be made to look directly at him by adding suitable features. The nose is obviously the principal feature which produces this change of direction, as it is more sub- ject to change of perspective than any of the other features ; but Dr Wollaston has shown by a very accurate experiment, that even a small portion of the nose introduced with the features will carry the eyes along with it. He obtained four exact copies of the same pair of eyes looking at the spec- tator, by transferring them upon copper from a steel plate, and having added to each of two pair of them, a nose in one case directed to the right, and in the other, to the left, and to each of the other two pairs a very small portion of the upper part of the nose, all the four pair of eyes lost their front direction, and looked to the right or to the left, according to the direction of the nose, or of the portion of it which was added. But the effect thus produced is not limited, as Dr Wollaston remarks, to the mere change in the direction of the eyes, " for a total difference of cha- racter may be given to the same eyes by a due re- presentation of the other features. A lost look of devout abstraction in an uplifted countenance may be exchanged for an appearance of inquisitive arch- ness in the leer of a younger face turned downwards and obliquely towards the opposite side," as in Fig. 27, 28. This, however, is perhaps not an exact ex- pression of the fact. The new character which is said to be given to the eyes is given only to the eyes in combination with the new features, or, what is pro- 120 LETTERS ON NATURAL MAGIC. ner, eyes drawn originally to look a little to the right or the left of the spectator may be made to look directly at him by adding- suitable features. The nose is obviously the principal feature which produces this change of direction, as it is more sub- ject to change of perspective than any of the other features ; but Dr Wollaston has shown by a very accurate experiment, that even a small portion of the nose introduced with the features will carry the eyes along with it. He obtained four exact copies of the same pair of eyes looking* at the spec- tator, by transferring them upon copper fr^- steel plate, and having added to ea^ them, a nose in one ca*" and in the otb^ other **- oe exchanged tor an appearance of inquisitive arch- ness in the leer of a younger face turned downwards and obliquely towards the opposite side," as in Fig. 27, 28. This, however, is perhaps not an exact ex- pression of the fact. The new character which is said to be given to the eyes is given only to the eyes in combination with the new features, or, what is pro- MOTION OF THE FEATURES OF A PORTRAIT. 121 bably more correct, the inquisitive archness is in the other features, and the eye does not belie it. Dr Wollaston has not noticed the converse of these illusions, in which a change of direction is Fig. 27. given to fixed features by a change in the direction of the eyes. This effect is finely seen in some magic lantern sliders, where a pair of eyes is made to move in the head of a figure which invariably follows the motion of the eyeballs. Having thus determined the influence which the general perspective of the face has upon the appa- rent direction of the eyes in a portrait, Dr Wollaston 122 LETTERS ON NATURAL MAGIC. applies it to the explanation of the well known fact , that when the eyes of a portrait look at a spectator in front of it they will follow him, and appear to look at him in every other direction. This curious fact, which has received less consideration than it merits, has heen often skilfully employed by the novelist, in alarming the fears or exciting- the courage of his hero. On returning to the hall of his ancestors, his attention is powerfully fixed on the grim por- traits which surround him. The parts which they have respectively performed in the family history rise to his mind : his own actions, whether good or evil, are called up in contrast, and as the preserver or the destroyer of his line, he stands as it we re in judg- ment before them. His imagination, thus excited by conflicting feelings, transfers a sort of vitality to the canvas, and if the personages do not " start from their frames," they will at least bend upon him their frowns or their approbation. It is in vain that he tries to evade their scrutiny. Wherever he goes their eyes eagerly pursue him ; — they will seem even to look at him over their shoulders, and he will find it impossible to shun their gaze but by quitting the apartment. As the spectator in this case changes his position in a horizontal plane, the effect which we have de- scribed is accompanied by an apparent diminution in the breadth of the human face, from only seven or eight inches till it disappears at a great obliqui- ty. In moving, therefore, from a front view to the most oblique view of the face, the change in its ap- parent breadth is so slow that the apparent motion of the head of the figure is scarcely recognized as it follows the spectator. But if the perspective MOTION OF THE FEATURES OF A PORTRAIT. 128 figure has a great breadth in a horizontal plane, such as a soldier firing- his musket, an artilleryman his piece of ordnance, a bowman drawing- his bow, or a lancer pushing* his spear, the apparent breadth of the figure will vary from five to six feet or up- wards till it disappears, and therefore the change of apparent magnitude is sufficiently rapid to give the figure the dreaded appearance of turning round, and following the spectator. One of the best examples of this must have been often observed in the fore- shortened figure of a dead body lying horizontally, which has the appearance of following the observer with great rapidity, and turning round upon the head as the centre of motion. The cause of this phenomenon is easily explain- ed. Let us suppose a portrait with its face and its eyes directed straight in front, so as to look at the spectator. Let a straight line be drawn through the tip of the nose and half way between the eyes, which we shall call the middle line. On each side of this middle line there will be the same breadth of head, of cheek, of chin, and of neck, and each iris will be in the middle of the whole of the eye. If we now go to one side, the apparent horizontal breadth of every part of the head and face will be diminish- ed, but the parts on each side of the middle line will be diminished equally, and at any position, however oblique, there will be the same breadth of face on each side of the middle line, and the iris will be in the centre of the whole of the eyeball, so that the portrait preserves all the characters of a figure looking at the spectator, and must necessar- ily do so wherever he stands. This explanation might be illustrated by a picture 124 LETTERS ON NATURAL MAGIC. which represents three artillerymen, each firing- a piece of ordnance in parallel directions. Let the gun of the middle one be pointed accurately to the eye of the spectator, so that he sees neither its right side nor its left, nor its upper nor its under side, but directly down its muzzle, so that if there was an opening- in the breech he would see through it. In like manner the spectator will see the left side of the gun on his left hand, and the right side of the gun on his right hand. If the spectator now chang- es his place, and takes ever such an oblique po- sition, either laterally or vertically, he must still see the same thing, because nothing else is present- ed to his view. The gun of the middle soldier must always point to his eye, and the other guns to the right and left of him. They must therefore all three seem to move as he moves, and follow his eye in all its changes of place. The same observa- tions are of course applicable to buildings and streets seen in perspective. In common portraits the apparent motion of the head is generally rendered indistinct by the canvas being imperfectly stretched, as the slightest concavi- ty or convexity entirely deforms the face when the obliquity is considerable. The deception is there- fore best seen when the painting is executed on a very flat board, and in colours sufficiently vivid to represent every line in the face with tolerable dis- tinctness at great obliquities. This distinctness of outline is indeed necessary to a satisfactory exhibi- tion of this optical illusion. The most perfect ex- hibition, indeed, that I ever saw of it was in the case of a painting of a ship upon a sign-board executed in strongly gilt lines. It contained a view of the BREATHING LIGHT AND DARKNESS. 125 stern, and side of a ship in the stocks, and, owing to the flatness of the board and the brightness of the lines, the gradual developement of the figure from the most violent foreshortening at great obliquities till it attained its perfect form, was an effect which sur- prised every person that saw it. The only other optical illusion which our limits will permit us to explain, is the very remarkable experiment of what may be truly called breathing light or darkness. Let S be a candle where light falls at an angle of 56° 45' upon two glass plates A, B, placed close to each other, and let the reflect- ed rays A C, B D, fall at the same angle upon two similar plates C, D, but so placed that the plane of reflexion from the latter is at right angles to the plane of reflexion from the former. An eye placed Fig. 29. B at E, and looking at the same time into the two plates C and D, will see very faint images of the candle S, which by a slight adjustment of the plates may be made to disappear almost wholly. Allowing the plate C to remain as it is, change the position of D, till its inclination to the ray BD is diminished about 3^°, or made nearly 53° 11'. When this is done, the image that had disappeared on looking into D will be restored, so that the spectator at E, upon 126 LETTERS ON NATURAL MAGIC. looking into the two mirrors C, D, will see no light in C, because the candle has nearly disappeared, while the candle is distinctly seen in D. If, while the spectator is looking into these two mirrors, either he or another person breathes upon them gently and quickly, the breath will revive the extinguish- ed image in C, and will extinguish the visible image in D. The following is the cause of this singu- lar result. The light AC, BD, is polarized by re- flexion from the plates A, B, because it is incident at the polarizing angle of 56° 45' for glass. When we breathe upon the plates C, D, we form upon their surface a thin film of water, whose polarizing angle is 53° 11', so that if the polarized rays AC, BD, fell upon the plates C, D, at an angle of 53° 1 1', the candle from which they proceeded would not be vi- sible, or they would not suffer reflexion from the plates C D. At all other angles the light would be reflected and the candles visible. Now the plate D is placed at an angle of 53° 1 V and C at an angle of 56° 45', so that when a film of water is breathed upon them the light will be reflected from the lat- ter, and none from the former : that is, the act of breathing upon the plates will restore the invisible, and extinguish the visible image. SPECTRE OF THE BROCKEN. LETTER VI. Natural phenomena marked with the marvellous — Spectre of the Brocken described — Analogous phenomena — Atrial spec- tres seen in Cumberland — Fata Morgana in the straits of Messina — Objects below the horizon raised and magnified by refraction — Singular example seen at Hastings — Dover Castle seen through the hill on which it stands — Erect and inverted images of distant ships seen in the air-Similar pheno- mena seen in the arctic regions — Enchanted coast — Mr Scores- by recognizes his father's ship by its aerial image — Images of cows seen in the air — Inverted images of horses seen in South America — Lateral images produced by refraction — Aerial spectres by reflexion — Explanation of the preceding pheno • mena. Among the wonders of the natural world which are every day presented to us, without either ex- citing our surprise or attracting our notice, some are occasionally displayed which possess all the characters of supernatural phenomena. In the names by which they are familiarly known, we re- cognize the terror which they inspired, and even now, when science has reduced them to the level of natural phenomena, and developed the causes from which they arise, they still retain their primitive importance, and are watched by the philosopher with as intense an interest as when they were deem- ed the immediate effects of Divine power. Among these phenomena we may enumerate the Spectre 128 LETTERS ON NATURAL MAGIC. of the Brocken, the Fata Morgana of the Straits of Messina, the Spectre Ships which appear in the air, and the other extraordinary effects of the Mi- rage, # The Brocken is the name of the loftiest of the Hartz Mountains, a picturesque range which lies in the kingdom of Hanover. It is elevated 3300 feet above the sea, and commands the view of a plain seventy leagues in extent, occupying nearly the 200dth part of the whole of Europe, and ani- mated with a population of above five millions of inhabitants. From the earliest periods of authen- tic history, the Brocken has been the seat of the marvellous. On its summits are still seen huge blocks of granite, called the Sorcerer's Chair and the Altar. A spring of pure water is known by the name of the Magic Fountain, and the Anemone of the Brocken is distinguished by the title of the Sorcerer s Flower. These names are supposed to have originated in the rites of the great Idol Cor- tho, whom the Saxons worshipped in secret on the summit of the Brocken, when Christianity was extending her benignant sway over the subjacent plains. As the locality of these idolatrous rites, the Brocken must have been much frequented, and we can scarcely doubt that the spectre which now so often haunts it at sunrise must have been observ- * In the Sanscrit, says Baron Humboldt, the phenome- non of the Mirage is called Mriga Trichna " thirst or desire of the antelope," no doubt because this animal Mriga, com- pelled by thirst, Trichna, approaches those barren plains where, from the effect of unequal refraction, he thinks he perceives the undulating surface of the waters. — Personal Narrative, Vol. iii, p. 554. SPECTRE OF THE BROCKEN. 129 ed from the earliest times ; but it is nowhere men- tioned that this phenomenon was in any wr.y asso- ciated with the objects of their idolatrous worship. One of the best accounts of the spectre of the Brocken is that which is given by M. Haue, who saw it on the 23d of May 1797. After having been on the summit of the mountain no less than thirty times, he had at last the good fortune of witnessing the object of his curiosity. The sun rose about four o'clock in the morning through a serene atmosphere. In the south-west, towards Achter- mannshohe, a brisk west wind carried before it the transparent vapours, which had not yet been con- densed into thick heavy clouds. About a quarter past four he went towards the inn, and looked round to see whether the atmosphere would afford him a free prospect towards the south-west, when he observed at a very great distance, towards Ach- termannshohe, a human figure of a monstrous size. His hat, having been almost carried away by a vio- lent gust of wind, he suddenly raised his hand to his head, to protect his hat, and the colossal figure did the same. He immediately made another movement by bending his body, — an action which was repeated by the spectral figure. M. Haue was desirous of making farther experiments, but the fi- gure disappeared. He remained, however, in the same position, expecting its return, and in a few minutes it again made its appearance on the Ach- termannshohe, when it mimicked his gestures as before. He then called the landlord of the inn, and having both taken the same position which he had before, they looked towards the Achtermanns- hohe but saw nothing. In a very short space of i 130 LETTERS ON NATURAL MAGIC. time, however, two colossal figures were formed over the above eminence, and after bending their bodies and imitating the gestures of the two spec- tators, they disappeared. Retaining their position, and keeping their eyes still fixed upon the same spot, the two gigantic spectres again stood before them, and were joined by a third. Every move- ment that they made was imitated by the three fi- gures, but the effect varied in its intensity, being sometimes weak and faint, and at other times strong and well defined. Fig. 30. In the year 1798 M. Jordan saw the same phe- nomenon at sunrise, and under similar circumstan- ces, but with less distinctness, and without any du- plication of the figures.* Phenomena perfectly analogous to the preceding, though seen under less imposing circumstances, * See J. F. Gmelin's Gottingischen Journal der Wissen- chqfien, Vol. i. part iii. 1798. AERIAL SPECTRES IN CUMBERLAND. 131 have been often witnessed. When the spectator sees his own shadow opposite to the sun upon a mass of thin fleecy vapour passing near him, it not only imitates all his movements, but its head is distinct- ly encircled with a halo of light. The aerial figure is often not larger than life, its size and its appar- ent distance depending, as we shall afterwards see, upon particular causes. I have often seen a simi- lar shadow when bathing in a bright summer's day in an extensile pool of deep water. When the fine mud deposited at the bottom of the pool is disturbed by the feet of the bather, so as to be dis- seminated through the mass of water in the direc- tion of his shadow, his shadow is no longer a shape- less mass formed upon the bottom, but is a regular figure formed upon the floating particles of mud, and having the head surrounded with a halo, not only luminous, but consisting of distinct radiations. One of the most interesting accounts of aerial spectres with which we are acquainted has been given by Mr James Clarke, in his Survey of the Lakes of Cumberland, and the accuracy of this ac- count was confirmed by the attestations of two of the persons by whom the phenomena were first seen. On a summer's evening in the year 1743, when Daniel Stricket, servant to John Wren of Wilton Hall, was sitting at the door along with his master, they saw the figure of a man with a dog pursuing some horses along Souterfell side, a place so extremely steep that a horse could scarce- ly travel upon it at all. The figures appeared to run at an amazing pace, till they got out of sight at the lower end of the fell. On the following morning Stricket and his master ascended the steep 132 LETTERS ON NATURAL MAGIC. side of the mountain, in the full expectation of finding" the man dead, and of picking up some of the shoes of the horses, which they thought must have been cast while galloping at such a furious rate. Their expectations, however, were disappointed. No traces either of man or horse could be found, and they could not even discover upon the turf the single mark of a horse's hoof. These strange ap- pearances, seen at the same time by two different persons in perfect health, could not fail to make a deep impression on their minds. They at first con- cealed what they had seen, but they at length dis- closed it, and were laughed at for their credulity. In the following year, on the 23d June 1744, Daniel Stricket, who was then servant to Mr Lan- caster of Blakehills, (a place near Wilton Hall, and both of which places are only about half a mile from Souterfell,) was walking, about seven o'clock in the evening, a little above the house, when he saw a troop of horsemen riding on Souterfell side in pretty close ranks, and at a brisk pace. Recol- lecting the ridicule that had been cast upon him the preceding year, he continued to observe the fi- gures for some time in silence ; but being at last convinced that there could be no deception in the matter, he went to the house and informed his master that he had something curious to show him. They accordingly went out together ; but before Stricket had pointed out the place Mr Lancas- ter's son had discovered the aerial figures. The family was then summoned to the spot, and the phenomena were seen alike by them all. The eques- trian figures seemed to come from the lowest parts of Souterfell, and became visible at a place called FATA MORGANA. 133 Knott. They then advanced in regular troops along the side of the Fell, till they came opposite to Blakehills, when they went over the mountain, after describing- a kind of curvilineal path. The pace at which the figures moved was a regular swift walk, and they continued to be seen for up- wards of two hours, the approach of darkness alone preventing them from being visible. Many troops were seen in succession ; and frequently the last but one in a troop quitted his position, galloped to the front, and took up the same pace with the rest. The changes in the figures were seen equally by all the spectators, and the view of them was not confined to the farm of Blakehills only, but they were seen by every person at every cottage within the distance of a mile, the number of persons who saw them amounting to about twenty-six. The attestation of these facts, signed by Lancaster and Stricket, bears the date of the 21st July 1785. These extraordinary sights were received not only with distrust but with absolute incredulity. They were not even honoured with a place in the records of natural phenomena, and the philo- sophers of the day were neither in possession of ana- logous facts, nor were they acquainted with those principles of atmospherical refraction upon which they depend. The strange phenomena, indeed, of the Fata Morgana, or the Castles of the Fairy Mor- gana, had been long before observed, and had been described by Kircher in the 17th century, but they presented nothing so mysterious as the aerial troopers of Souterfell; and the general characters of the two phenomena were so unlike, that even a philo- 134 LETTERS ON NATURAL MAGIC. sopher might have been excused for ascribing* them to different causes. This singular exhibition has been frequently seen in the Straits of Messina between Sicily and the coast of Italy, and whenever it takes place, the people, in a state of exultation, as if it were not only a pleasing but a lucky phenomenon, hurry down to the sea, exclaiming Morgana, Morgana. When the rays of the rising sun form an angle of 45° on the sea of Reggio, and when the surface of the water is perfectly unruffled either by the wind or the current, a spectator placed upon an eminence in the city, and having his back to the sun and his face to the sea, observes upon the surface of the water su- perb palaces with their balconies and windows, lofty towers, herds and flocks grazing in wooded vallies and fertile plains, armies of men on horseback and on foot, with multiplied fragments of buildings, such as columns, pilasters, and arches. These objects pass rapidly in succession along the surface of the sea dur- ing the brief period of their appearance. The various objects thus enumerated are pictures of palaces and buildings actually existing on shore, and the liv- ing objects are of course only seen when they hap- pen to form a part of the general landscape. If at the time that these phenomena are visible the atmosphere is charged with vapour or dense exhala- tions, the same objects which are depicted upon the sea will be seen also in the air occupying a S]3ace which extends from the surface to the height of twenty-five feet. These images, however, are less distinctly delineated than the former. If the air is in such a state as to deposit dew, and is capable of forming the rainbow, the objects OBJECTS BELOW THE HORIZON MAGNIFIED. 135 will be seen only on the surface of the sea, but they all appear fringed with red, yellow, and blue light as if they were seen through a prism. In our own country, and in our own times, facts still more extraordinary have been witnessed. From Hastings, on the coast of Sussex, the cliffs on the French coast are fifty miles distant, and they are actually hid by the convexity of the earth, that is, a strait line drawn from Hastings to the French coast would pass through the sea. On Wed- nesday the 26th July 1798, about five o'clock in the afternoon, Mr Latham, a Fellow of the Royal Society, then residing at Hastings, was surprised to see a crowd of people running to the sea side. Upon inquiry into the cause of this, he learned that the coast of France could be seen by the naked eye, and he immediately went down to witness so singu- lar a sight. He distinctly saw the cliffs extending for some leagues along the French coast, and they ap- peared as if they were only a few miles off. They gradually appeared more and more elevated, and seemed to approach nearer to the eye. The sailors with whom Mr Latham walked along the water's edge were at first unwilling to believe in the reality of the appearance, but they soon became so tho- roughly convinced of it, that they pointed out and named to him the different places which they had been accustomed to visit, and which they conceived to be as near as if they were sailing at a small dis- tance into the harbour. These appearances con- tinued for nearly an hour, the cliffs sometimes ap- pearing brighter and nearer, and at other times faint- er and more remote. Mr Latham then went upon the eastern cliff or hill, which is of considerable 136 LETTERS ON NATURAL MAGIC. height, when, as he remarks, a most beautiful scene presented itself to his view. He beheld at once Dungeness, Dover Cliffs, and the French coast all along* from Calais, Boulogne, &c. to St Vallery, and, as some of the fishermen affirmed, as far west as Dieppe. With the help of a telescope, the French fishing- boats were plainly seen at anchor, and the different colours of the land upon the heights, to- gether with the buildings, were perfectly discernible. Mr Latham likewise states that the cape of land called Dungeness, which extends nearly two miles into the sea, and is ahout sixteen miles in a straight line from Hastings, appeared as if quite close to it, and the vessels and fishing-boats which were sail- ing between the two places appeared equally near, and were magnified to a high degree. These curious phenomena continued " in the highest splendour " till past eight o' clock, although a black cloud had for some time totally obscured the face of the sun. A phenomenon no less marvellous was seen by Professor Vince of Cambridge and another gentleman on the 6th August 1806 at Ramsgate. The sum- mits v w x y of the four turrets of Dover Castle are usually seen over the hill AB, upon which it stands, lying between Ramsgate and Dover ; but on the day above-mentioned, at seven o'clock in the even- ing, when the air was very still and a little hazy, not only were the tops v w x y of the four towers of Dover Castle seen over the adjacent hill A B, but the whole of the Castle mnrs, appeared as if it were situated on the side of the hill next Ramsgate, and rising above the hill as much as usual. This phenomenon was so very singular and unexpected, SPECTRE OF DOVER CASTLE. 137 that at first sight Dr Vince thought it an illusion ; but upon continuing his observations, he became satisfied that it was a real image of the Castle, Fig. SI. Upon this he gave a telescope to a person present, who, upon attentive examination, saw also a very clear image of the castle, as the Doctor had described it. He continued to observe it for about twenty minutes, during which time the appearance remain- ed precisely the same, but rain coming on, they were prevented from making any farther observa- tions. Between the observers and the land from which the hill rises, there was about six miles of sea, and from thence to the top of the hill there was about the same distance. Their own height above the surface of the water was about seventy feet. This illusion derived great force from the remark- able circumstance, that the hill itself did not appear through the image, as it might have been expected to do. The image of the castle was very strong and well defined, and though the rays from the hill 138 LETTERS ON NATURAL MAGIC. behind it must undoubtedly have come to the eye, yet the strength of the image of the castle so far obscured the back ground, that it made no sensible impression on the observers. Their attention was, of course, principally directed to the image of the castle ; but if the hill behind had been at all visible, Dr Yince conceives that it could not have escaped their observation, as they continued to look at it for a considerable time with a good telescope Hitherto our aerial visions have been seen only in their erect and natural positions, either project- ed against the ground or elevated in the air ; but cases have occurred in which both erect and invert- ed images of objects have been seen in the air, sometimes singly, sometimes combined, sometimes when the real object was invisible, and sometimes when a part of it had begun to show itself to the spectator. In the year 1793, MrHuddart, when residing at Fig. 32. Allonby , in Cumberland, perceived the inverted image of a ship beneath the image, as shown in Fig. 32 ; INVERTED IMAGE OF A SHIP. 139 but Dr Vince, who afterwards observed this pheno- menon under a greater variety of forms, found that the ship which was here considered the real one, was only an erect image of the real ship, which was at the time beneath the horizon, and wholly in- visible. In August 1798, Dr Vince observed a great va- riety of these aerial images of vessels approaching the horizon. Sometimes there was seen only one Fig. 33. inverted image above the real ship, and this was generally the case when the real ship was full in 140 LETTERS ON NATURAL MAGIC. view. But when the real ship was just beginning to show its top-mast above the horizon, as at A, Fig. 33, two aerial images of it were seen, one at B in- verted, and the other in its natural position at C. In this case the sea was distinctly visible between the erect and inverted images, but in other cases the hull of the one image was immediately in contact with the hull of the other. Analogous phenomena were seen by Captain Scoresby when navigating with the ship Baffin the icy sea in the immediate neighbourhood of west Greenland. On the 28th of June 1820, he observed about eighteen sail of ships at the distance of ten or fifteen miles. The sun had shone during the day without the interposition of a cloud, and his rays were peculiarly powerful. The intensity of its light occasioned a painful sensation in the eyes, while its heat softened the tar in the rigging of the ship, and melted the snow on the surrounding ice with such rapidity, that pools of fresh water were formed on almost every place, and thousands of rills carried the excess into the sea. There was scarcely a breath of wind : The sea was as smooth as a mir- ror. The surrounding ice was crowded together, and exhibited every variety, from the smallest lumps to the most magnificent sheets. Bears traversed the fields and floes in unusual numbers, and many whales sported in the recesses and openings among the drift ice. About six in the evening, a light breeze at N. W. having sprung up, a thin stratus or " fog bank," at first considerably illuminated by the sun, appeared in the same quarter, and gradually rose to the altitude of about a quarter of a degree. At this time most of the ships navigating at the dis- ERECT AND INVERTED IMAGES OF SHIPS. 141 tance of ten or fifteen miles began to change their form and magnitude, and when examined by a tele- scope from the mast-head exhibited some extra- ordinary appearances, which differed at almost every point of the compass. One ship had a perfect image, as dark and distinct as the original, united to its mast head in a reverse position. Two others presented t wo distinct inverted images in the air, one of them a perfect figure of the original, and the other want- ing the hull. Two or three more were strangely distorted, their masts appearing of at least twice their proper height, the top-gallant mast forming one-half of the total elevation, and other vessels exhibited an appearance totally different from all the preceding, being as it were compressed in place of elongated. Their masts seemed to be scarcely one-half of their proper altitude, in con- sequence of which one would have supposed that they were greatly heeled to one side, or in the position called careening. Along with all the ima- ges of the ships a reflexion of the ice, sometimes in two strata, also appeared in the air, and these reflexions suggested the idea of cliffs composed of vertical columns of alabaster. On the 15th, 16th, and 17th, of the same month, Mr Scoresby observed similar phenomena, some- times extending continuously through half the cir- cumference of the horizon, and at other times ap- pearing only in detached spots in various quarters. The inverted images of distant vessels were often seen in the air, while the ships themselves were far be- yond the reach of vision. Some ships were elevated to twice their proper height, while others were com- pressed almost to a line. Hummocks of ice were sur- 142 LETTERS ON NATURAL MAGIC. prisingly enlarged, and every prominent object in a proper position was either magnified or distorted. But of all the phenomena witnessed by Mr Scoresby, that of the Enchanted Coast, as it may be called, must have been the most remarkable, This singular effect was seen on the 18th July, when the sky was clear, and a tremulous and perfectly transparent vapour was particularly sensible and profuse : At nine o'clock in the morning*, when the phenomenon was first seen, the thermometer stood at 42° Fahr. but in the preceding evening it must have been greatly lower, as the sea was in many places covered with a considerable pellicle of new ice, — a circumstance which in the very warmest time of the year must be considered as quite ex- traordinary, especially when it is known that 10° farther to the north no freezing of the sea at this season had ever before been observed. Having ap- proached on this occasion so near the unexplored shore of Greenland that the land appeared distinct and bold, Mr Scoresby was anxious to obtain a draw- ing of it, but on making the attempt he found that the outline was constantly changing, and he was in- duced to examine the coast with a telescope, and to sketch the various appearances which presented themselves. These are shown, without any regard to their proper order, in Fig. 34, which we shall describe in Mr Scoresby's own words : " The gene- ral telescopic appearance of the coast was that of an extensive ancient city abounding with the ruins of castles, obelisks, churches, and monuments, with other large and conspicuous buildings. Some of the hills seemed to be surmounted by turrets, battle- ments, spires, and pinnacles ; while others, subject- ENCHANTED COAST. 143 ed to one or two reflexions, exhibited large masses of rock, apparently suspended in the air, at a consi- derable elevation above the actual termination of the Fig. 34. mountains to which they referred. The whole exhibition was a grand phantasmagoria. Scarcelv was any particular portion sketched before it changed its appearance, and assumed the form of an object totally different. It was perhaps alter- nately a castle, a cathedral, or an obelisk ; then expanding horizontally, and coalescing with the adjoining hills, united the intermediate vallies, though some miles in width, by a bridge of a single arch, of the most magnificent appearance and ex- tent. Notwithstanding these repeated changes, the various figures represented in the drawing had all the distinctness of reality ; and not only the dif- ferent strata, but also the veins of the rocks, with 144 LETTERS ON NATURAL MAGIC. the wreaths of snow occupying ravines and fissures, formed sharp and distinct lines, and exhibited every appearance of the most perfect solidity." One of the most remarkable facts respecting* ae- rial images presented itself to Mr Scoresby in a later voyage which he performed to the coast of Greenland in 1822. Having seen an inverted image of a ship in the air he directed to it his te- lescope ; he was able to discover it to be his father's ship, which was at the time below the horizon. " It was," says he, " so well defined, that I could distin- guish by a telescope every sail, the general rig of the ship, and its particular character ; insomuch, that I confidently pronounced it to be my father's ship, the Fame, which it afterwards proved to be ; though, on comparing notes with my father, I found that our relative position, at the time, gave a dis- tance from one another very nearly 30 miles, being about seventeen miles beyond the horizon, and some leagues beyond the limit of direct vision. I was so struck with the peculiarity of the circumstance, that I mentioned it to the officer of the watch, stat- ing my full conviction that the Fame was then cruising in the neighbouring inlet." Several curious effects of the mirage were observ- ed by Baron Humboldt during his travels in South America. When he was residing at Cumana, he fre- quently saw the islands of Picuita and Boracha sus- pended in the air, and sometimes with an inverted image. On one occasion he observed small fishing- boats swimming in the air, during more than three or four minutes, above the w T ell defined horizon of the sea, and when they were viewed through a telescope, one of the boats had an inverted image accompany- 3 AERIAL SPECTRES BY REFLEXION. 145 ing it in its movements. This distinguished tra- veller observed similar phenomena in the barren steppes of the Caraccas, and on the borders of the Orinoco, where the river is surrounded by sandy- plains. Little hills and chains of hills appeared suspended in the air, when seen from the steppes, at three or four leagues distance. Palm trees stand- ing single in the Llanos appeared to be cut off at bottom, as if a stratum of air separated them from the ground ; and, as in the African desert, plains des- titute of vegetation appeared to be rivers or lakes. At the Mesa de Pavona M. Humboldt and M. Bon- pland saw cows suspended in the air at the distance of 1000 toises, and having their feet elevated 3' 20" above the soil. In this case the images were erect, but the travellers learned from good authori- ty that inverted images of horses had been seen sus- pended in the air near Calabozo. In all these cases of aerial spectres the images were directly above the real object ; but a curious case was observed by MM. Jurine and Soret on the 17th September 1818, where the image of the vessel was on one side of the real one. About 10 h p. m. a bark at the distance of about 4000 toises from Bellerive, on the lake of Geneva, was seen approaching to Geneva by the left bank of the lake, and at the same time an image of the sails was observed above the water, which, instead of following the direction of the bark, separated from it, and appeared to approach Geneva by the right bank of the lake, the image moving from east to west, while the bark moved from north to south. When the image first separated from the bark they had both the same magnitude, but the K 146 LETTERS ON NATURAL MAGIC. image diminished as it receded from it, and was re- duced to one-half when the phenomenon disappeared. A very unusual example of aerial spectres occur- red to Dr A. P. Buchan while walking on the cliff about a mile to the east of Brighton on the morn- ing of the 28th November 1804. "While watching the rising of the sun," says he, " I turned my eyes di- rectly towards the sea, just as the solar disk emerged from the surface of the water, and saw the face of the cliff on which I was standing, represented precisely opposite to me at some distance on the ocean. Cal- ling the attention of my companion to this ap- pearance, we discerned our own figures stand- ing on the summit of the apparent opposit e cliff, as well as the representation of the windmill near at hand. "The reflected images were most distinct precise- ly opposite to where we stood, and the false cliff seemed to fade away, and to draw near to the real one, in proportion as it receded towards the west. This phenomenon lasted about ten minutes, or till the sun had risen nearly his own diameter above the surface of the ocean. The whole then seem- ed to be elevated into the air, and successively dis- appeared, giving an impression very similar to that which is produced by the drawing up of a drop scene in the theatre. The horizon was cloudy, or perhaps it might with more propriety be said that the sur- face of the sea was covered with a dense fog of many yards in height, and which gradually receded before the rays of the sun.' , An illusion of a different kind, though not less interesting, is described by the Reverend Mr Hughes in his Travels in Greece, as seen from the SHADOW IMAGE OF MOUNT JETNA. 147 summit of Mount Mtna. " I must not forget to mention," says he, "one extraordinary phenomenon, which we observed, and for which I have searched in vain for a satisfactory solution. At the extremi- ty of the vast shadow which iEtna projects across the island, appeared a perfect and distinct image of the mountain itself elevated above the horizon, and diminished as if viewed in a concave mirror. Where or what the reflector could be which exhibited this image, I cannot conceive ; we could not be mistaken in its appearance, for all our party observed it, and we had been prepared for it beforehand by our Cata- nian friends. It remained visible about ten minutes, and disappeared as the shadow decreased. Mr Jones observed the same phenomenon, as well as some other friends with whom I conversed upon the sub- ject in England." It is impossible to study the preceding pheno- mena without being impressed with the conviction, that nature is full of the marvellous, and that the progress of science and the diffusion of knowledge are alone capable of dispelling the fears which her wonders must necessarily excite even in enlightened minds. When a spectre haunts the couch of the sick, or follows the susceptible vision of the inva- lid, a consciousness of indisposition divests the ap- parition of much of its terror, while its invisibility to surrounding friends soon stamps it with the im- press of a false perception. The spectres of the conjuror too, however skilfully they may be raised, quickly lose their supernatural character, and even the most ignorant beholder regards the modern ma- gician as but an ordinary man, who borrows from the sciences the best working implements of his 148 LETTERS ON NATURAL MAGIC. art. But when, in the midst of solitude, and in situations where the mind is undisturbed by sub- lunary cares, we see our own image delineated in the air, and mimicking' in gigantic perspective the tiny movements of humanity ; — when we see troops in military array performing their evolutions on the very face of an almost inaccessible precipice ; — when in the eye of day a mountain seems to become transpa- rent, and exhibits on one side of it a castle which we know to exist only on the other ; — when distant objects concealed by the roundness of the earth, and beyond the cognizance of the telescope, are ac- tually transferred over the intervening convexity and presented in distinct and magnified outline to our ac- curate examination ; — when such varied and strik- ing phantasms are seen also by all around us, and therefore appear in the character of real phenome- na of nature, our impressions of supernatural agen- cy can only be removed by a distinct and satisfac- tory knowledge of the causes which gave them birth. It is only within the last forty years that science has brought these atmospherical spectres within the circle of her dominion ; and not only are all their phenomena susceptible of distinct explanation, but we can even reproduce them on a small scale with the simplest elements of our optical apparatus. In order to convey a general idea of the causes of these phenomena, let A B C D, Fig. 35, be a glass trough filled with water, and let a small ship be placed at S. An eye situated about E, will see the top- mast of the ship S, directly through the plate of glass B D. Fix a convex lens a of short focus upon the plate of glass B D, and a little above a straight line S E joining the ship and the eye ; and EXPLANATION OF SPECTRE SHIPS. 149 immediately above the convex lens a place a con- cave one b. The eye will now see through the Fig. 35. convex lens a an inverted image of the ship at S' ? and through the concave lens Z>, an erect image of the ship at S", representing in a general way the phenomena shown in Fig. 83. But it will be ask- ed, where are the lenses in nature to produce these effects ? This question is easily answered. If we take a tin tube with glass plates at each end, and fill it with water, and if we cool it on the outside with ice, it will act like a concave lens when the cooling effect has reached the axis ; and, on the other hand, if we heat the same tube filled with water, on the outside, it will act as a convex glass. In the first case the density of the water diminishes towards the centre, and in the second it increases to- wards the centre. The very same effects are pro- duced in the air, only a greater tract of air is neces- sary for showing the effect produced, by heating and cooling it unequally. If we now remove the lenses a, and hold a heated iron horizontally 150 LETTERS ON NATURAL MAGIC. above the water in the trough ABC, the heat will gradually descend, expanding- or rendering- rarer the upper portions of the fluid. If, when the heat has reached within a little of the bottom, we look through the trough at the ship S in the direction E S', we shall see an inverted image at S', and an erect one at S", and if we hide from the eye at E all the ship S excepting the top-mast, we shall have an exact representation of the phenomenon in Fig. 33. The experiment will succeed better with oil in place of water ; and the same result may be obtained without heat, by pouring clear syrup in- to the glass trough till it is nearly one-third full, and then filling it up with water. The water will gradually incorporate with the syrup, and produce, as Dr Wollaston has shown, a regular gradation of density, diminishing from that of the pure syrup to that of the pure water. Similar effects may be obtained by using masses of transparent solids, such as glass, rock salt, &c. Now it is easy to conceive how the changes of density which we can thus produce artificially may be produced in nature. If in serene weather the surface of the sea is much colder than the air of the atmosphere, as it frequently is, and as it was to a very great degree during the phenomena de- scribed by Mr Scoresby, the air next the sea will gradually become colder and colder, by giving out its heat to the water; and the air immediately above will give out its heat to the cooler air immediately below it, so that the air from the surface of the sea, to a considerable height upwards, will gradually di- minish in density, and therefore must produce the very phenomena we have described. EXPLANATION OF SPECTRE SHIPS. 151 The phenomenon of Dover Castle seen on the Ramsgate side of the hill was produced by the air being- more dense near the ground, and above the sea, than at greater heights, and hence the rays proceed- ing from the castle reached the eye in curve lines, and the cause of its occupying its natural position on the hill, and not being seen in the air, was that the top of the hill itself, in consequence of being so near the castle, suffered the same change from the varying density of the air, and therefore, the castle and the hill were equally elevated and re- tained their relative positions. The reason why the image of the castle and the hill appeared erect was, that the rays from the top and bottom of the castle had not crossed before they reached Ramsgate ; but as they met at Ramsgate, an eye at a greater dis- tance from the castle, and in the path of the rays, would have seen the image inverted. This will be Fig. 36. better understood from the annexed diagram, which represents the actual progress of the rays, from a ship S P, concealed from the observer at E by the 152 LETTERS ON NATURAL MAGIC. convexity of the earth PQE. A ray proceeding from the keel of the ship P is refracted into the cnrve line P c x c E, and a ray proceeding- from the top-mast S, is refracted in the direction S d x d E, the two rays crossing- at and proceeding to the eye E with the ray from the keel P uppermost ; hence the ship must appear inverted as at sp. Now if the eye E of the observer had been placed near- er the ship as at before the rays crossed, as was the case at Ramsgate, it would have seen an erect image of the ship raised a little above the real ship S P. Rays S m, S n, proceeding higher up in the air, are refracted in the directions S m m E, S n n E, but do not cross before they reach the eye, and therefore they afford the erect image of the ship shown at $' p f . The aerial troopers seen at Souterfell were pro- duced by the very same process as the spectre of Dover Castle, having been brought by unequal re- fraction from one side of the hill to the other. It is not our business to discover how a troop of sol- diers came to be performing their evolutions on the other side of Souterfell ; but if there was then no road along which they could be marching, it is highly probable that they were troops exercising among the hills in secret previous to the breaking- out of the rebellion in 1745. The image of the Genevese bark which was seen sailing at a distance from the real one, arose from the same cause as the images of ships in the air, with this difference only, that in this case the strata of equal density were vertical or perpendicular to the water, whereas in the former cases they were horizontal or parallel to the water. The state of EXPLANATION OF PHENOMENA. 153 the air which produced the lateral image may he produced by a headland or island, or even rocks, near the surface, and covered with water. These headlands, islands, or sunken rocks being- power- fully heated by the sun in the day-time, will heat the air immediately above them, while the adjacent air over the sea will retain its former coolness and density. Hence there will necessarily arise a gra- dation of density varying in the same horizontal direction, or where the lines of equal density are vertical. If we suppose the very same state of the air to exist in a horizontal plane which exists in a vertical plane, in Fig. 36, then the same images would be seen in a horizontal line, viz. an invert- ed one at s p, and an erect one at s' p'. In the case of the Genevese bark the rays had not crossed be- fore they reached the eye, and therefore the image was an erect one. Had the real Genevese bark been concealed by some promontory or other cause from the observation of M.M. Jurine and Soret, they might have attached a supernatural character to the spectral image, especially if they had seen it gradually decay, and finally disappear on the still and unbroken surface of the lake. No similar fact had been previously observed, and there were no circumstances in the case to have excited the sus- picion, that it was the spectre of a real vessel pro- duced by unequal refraction. The spectre of the Brocken and other phenomena of the same kind have essentially a different origin from those which arise from unequal refraction. They are merely shadows of the observer projected on dense vapour or thin fleecy clouds, which have the power of reflecting much light. They are 154 LETTERS ON NATURAL MAGIC. seen most frequently at sunrise, because it is at that time that the vapours and clouds necessary for their production are most likely to be generated ; and they can be seen only when the sun is throwing his rays horizontally, because the shadow of the observer would otherwise be thrown either up in the air, or down upon the ground. If there are two persons looking at the phenomenon, as when M. Haue and the landlord saw it together, each observer will see his own image most distinctly, and the head will be more distinct than the rest of the figure, because the rays of the sun will be more copiously reflected at a perpendicular inci- dence ; and as from this cause, the light reflected from the vapour or cloud becomes fainter farther from the shadow, the appearance of a halo round the head of the observer is frequently visible. M. Haue mentions the extraordinary circumstance of the two spectres of him and the landlord being joined by a third figure, but he unfortunately does not inform us which of the two figures was doub- led, for it is impossible that a person could have joined their party unobserved. It is very probable that the new spectre forms a natural addition to the group, as we have represented it in Fig. 30, and if this was the case, it could only have been produced by a duplication of one of the figures produced by unequal refraction. The reflected spectre of Dr Buchan standing upon the cliff at Brighton arose from a cause to which we have not yet adverted. It was obviously no shadow, for it is certain from the locality, that the rays of the sun fell upon the face of the cliff and upon his person at angle of about 73° EXPLANATION OF PHENOMENA. 155 from the perpendicular, so as to illuminate them strongly. Now there are two ways in which such an image may have heen reflected, namely, either from strata of air of variable density, or from a vertical stratum of vapour, consisting of exceed- ingly minute globules of water. Whenever light suffers refraction, either in passing at once from one medium into another, or from one part of the same medium into another of different density, a portion of it suffers reflexion. If an object, there- fore, were strongly illuminated, a sufficiently dis- tinct image, or rather shadow of it, might be seen by reflexion from strata of air of different density. As the temperature at which moisture is deposited in the atmosphere varies with the density of the air, then at the same temperature moisture might be depositing in a stratum of one density, while no deposition is taking place in the adjacent stra- tum of a different density. Hence there would exist as it were in the air a vertical wall or stra- tum of minute globules of water, from the surface of which a sufficiently distinct image of a highly illuminated object might be reflected. That this is possible may be proved by breathing upon glass. If the particles deposited upon the glass are large, then no distinct reflexion will take place ; but if the particles be very small, we shall see a distinct image formed by the surface of the aqueous film. The phenomena of the Fata Morgana have been too imperfectly described to enable us to offer a satisfactory explanation of them. The aerial ima- ges are obviously those formed by unequal refrac- tion. The pictures seen on the sea may be either the aerial images reflected from its surface, 156 LETTERS ON NATURAL MAGIC. or from a stratum of dense vapour, or they may- be the direct reflexions from the objects them- selves. The coloured images, as described by Minasi, have never been seen in any analogous phenomena, and require to be better described before they can be submitted to scientific examina- tion. The representation of ships in the air by une- qual refraction has no doubt given rise in early times to those superstitions which have prevailed in different countries respecting- " phantom ships" as Mr Washington Irving- calls them, which al- ways sail in the eye of the wind, and plough their way through the smooth sea, where there is not a breath of wind upon its surface. In his beautiful story of the storm ship, which makes its way up the Hudson against wind and tide, this elegant writer has finely embodied one of the most inte- resting superstitions of the early American colo- nists. The Flying Dutchman had in all probabi- lity a similar origin, and the wizard beacon-keeper of the Isle of France, who saw in the air the ves- sels bound to the island long before they appeared in the offing, must have derived his power from a diligent observation of the phenomena of nature. SPEAKING AND SINGING HEADS. 157 LETTER VII. Illusions depending on the ear — Practised by the ancients — Speaking and singing heads of the ancients — Exhibition of the invisible girl described and explained — Illusions arising from the difficulty of determining the direction of sounds — Singular example of this illusion — Nature of ven- triloquism — Exhibitions of some of the most celebrated ventriloquists — M. St Gille — Louis Brabant — M. Alex- andre — Capt. Lyon's account of Eslcimanx ventriloquists. Next to the eye the ear is the most fertile source of our illusions, and the ancient magicians seem to have heen very successful in turning- to their purposes the doctrines of sound. In the laby- rinth of Egypt, which contained twelve palaces and 1500 subterraneous apartments, the gods were made to speak in a voice of thunder; and Pliny, in whose time this singular structure existed, informs us, that some of the palaces were so constructed that their doors could not be opened without per- mitting the peals of thunder from being heard in the interior. When Darius Hystaspes ascended the throne, and allowed his subjects to prostrate themselves before him as a god, the divinity of his character was impressed upon his worshippers by the bursts of thunder and flashes of lightning which accompanied their devotion. History has of course not informed us how these effects were produced ; 158 LETTERS ON NATURAL MAGIC. but it is probable that, in the subterraneous and vaulted apartments of the Egyptian labyrinth, the reverberated sounds arising- from the mere opening and shutting" of the doors themselves afforded a sufficient imitation of ordinary thunder. In the palace of the Persian king, however, a more artifi- cial imitation is likely to have been employed, and it is not improbable that the method used in our modern theatres was known to the ancients. A thin sheet of iron, three or four feet long, such as that used for German stoves, is held by one corner between the finger and the thumb, and allowed to hang freely by its own weight. The hand is then moved or shaken horizontally, so as to agitate the corner in a direction at right angles to the sur- face of the sheet. By this simple process a great variety of sounds will be produced, varying from the deep growl of distant thunder to those loud and explosive bursts which rattle in quick succes- sion from clouds immediately over our heads. The operator soon acquires great power over this instrument, so as to be able to produce from it any intensity and character of sound that may be required. The same effect may be produced by sheets of tin- plate, and by thin plates of mica ; but on account of their small size, the sound is shorter and more acute. In modern exhibitions an admirable imita- tion of lightning is produced by throwing the pow- der of rosin, or the dust of lycopodium, through a flame, and the rattling showers of rain which ac- company these meteors are well imitated by a well regulated shower of peas. The principal pieces of acoustic mechanism used by the ancients were speaking or singing heads, SPEAKING AND SINGING HEADS. 159 which were constructed for the purpose of repre- senting- the gods, or of uttering oracular responses. Among these, the speaking head of Orpheus, which uttered its responses at Lesbos, is one of the most famous. It was celebrated not only through- out Greece, but even in Persia, and it had the cre- dit of predicting, in the equivocal language of the heathen oracles, the bloody death which terminat- ed the expedition of Cyrus the Great into Scythia. Odin, the mighty magician of the north, who im- ported into Scandinavia the magical arts of the east, possessed a speaking head, said to be that of the sage Minos, which he had enchased in gold, and which uttered responses that had all the authority of a divine revelation. The celebrated mechanic Gerbert, who filled the papal chair A. D. 1000, under the name of Sylvester II., constructed a speaking head of brass. Albertus Magnus is said to have executed a head in the thirteenth century, which not only moved but spoke. It was made of earthen-ware, and Thomas Aquinas is said to have been so terrified when he saw it, that he broke it in pieces, upon which the mechanist exclaimed, " There goes the labour of thirty years." It has been supposed by some authors, that in the ancient speaking machines the deception is ef- fected by means of ventriloquism, the voice issuing from the juggler himself ; but it is more probable that the sound was conveyed by pipes from a per- son in another apartment to the mouth of the figure. Lucian, indeed, expressly informs us, that the impostor Alexander made his figure of iEscula- pius speak, by transmitting his voice through the gullet of a crane to the mouth of the statue ; and 160 LETTERS ON NATURAL MAGIC. that this method was general, appears from a pas- sage in Theodoretus, who assures us, that in the fourth century, when Bishop Theophilus broke to pieces the statues at Alexandria, he found some which were hollow, and which were so placed against a wall, that the priest could conceal himself behind them, and address the ignorant spectators through their mouths. Even in modern times, speaking-machines have been constructed on this principle. The figure is frequently a mere head placed upon a hollow pe- destal, which, in order to promote the deception, contains a pair of bellows, a sounding-board, a cy- linder and pipes supposed to represent the organs of speech. In other cases these are dispensed with, and a simple wooden head utters its sounds through a speaking trumpet. At the court of Charles II. this deception was exhibited with great effect by one Thomas Irson, an Englishman, and when the astonishment had become very general, a popish priest was discovered by one of the pages in an ad- joining apartment. The questions had been pro- posed to the wooden figure by whispering into its ear, and this learned personage had answered them all with great ability, by speaking through a pipe in the same language in which the questions were proposed. Professor Beckmann informs us that children and women were generally concealed either in the juggler's box, or in the adjacent apart- ment, and that the juggler gave them every assis- tance by means of signs previously agreed upon. When one of these exhibitions was shown at Got- tingen, the Professor was allowed, on the promise of secrecy, to witness the process of deception. He 4 THE INVISIBLE GIRL. 161 saw the assistant in another room, standing- before the pipe with a card in his hand, upon which the signs agreed upon had been marked, and he had been introduced so privately into the house that even the landlady was ignorant of his being there. An exhibition of the very same kind has been brought forward in our own day, under the name of the Invisible Girl; and as the mechanism employ- ed was extremely ingenious, and is well fitted to convey an idea of this class of deceptions, we shall give a detailed description of it. The machinery, as constructed by M. Charles, is shown in Fig. 37 in perspective, and a plan of it Fig. 37. in Fig. 38. The four upright posts A, A, A, A, are united at top by a cross rail B, B, and by two simi- lar rails at bottom. Four bent wires a, a, a, a, proceeded from the top of these posts, and termi- nated at c. A hollow copper ball M, about a foot in diameter, was suspended from these wires by four 162 LETTERS ON NATURAL MAGIC. slender ribbands b, b, b, b, and into the copper ball were fixed the extremities of four trumpets T, T, T, T, with their mouths outwards. Fig. 38. The apparatus now described was all that was visible to the spectator; and though fixed in one spot, yet it had the appearance of a piece of sepa- rate machinery, which might have occupied any other part of the room. When one of the spectators was requested by the exhibitor to propose some ques- tion, he did it by speaking into one of the trumpets at T. An appropriate answer was then returned from all the trumpets, and the sound issued with sufficient intensity to be heard by an ear applied to any of them, and yet it was so weak that it appear- ed to come from a person of very diminutive size. Hence the sound was supposed to come from an invisible girl, though the real speaker was a full grown woman. The invisible lady conversed in different languages, sang beautifully, and made the most lively and appropriate remarks on the per- sons in the room. THE INVISIBLE GIRL. 163 This exhibition was obviously far more wonder- ful than the speaking heads which we have describ- ed, as the latter invariably communicated with a wall, or with a pedestal through which pipes could be carried into the next apartment. But the ball M and its trumpets communicated with nothing- through which sound could be conveyed. The spectator satisfied himself by examination that the ribbands b, b, were real ribbands, which concealed nothing, and which could convey no sound, and as he never conceived that the ordinary piece of frame- work A B, could be of any other use than its ap- parent one of supporting the sphere M, and defend- ing it from the spectators, he was left in utter amazement respecting the origin of the sound, and his surprise was increased by the difference between the sounds which were uttered and those of ordi- nary speech. Though the spectators were thus deceived by their own reasoning, yet the process of deception was a very simple one. In two of the horizontal railings A, A, Fig. 38, opposite the trumpet mouths T, there was an aperture communicating with a pipe or tube which went to the vertical post B, and descending it, as shown at T A A, Fig. 39, went beneath the floor ff in the direction p, p, and en- tered the apartment N, where the invisible lady sat. On the side of the partition about h, there was a small hole, through which the lady saw what was going on in the exhibition room, and communica- tions were no doubt made to her by signals from the person who attended the machine. When one of the spectators asked a question by speaking into one of the trumpets T, the sound was re- 164 LETTERS ON NATURAL MAGIC. fleeted from the mouth of the trumpet back to the aperture at A, in the horizontal rail, Fig-. 38, and Fig. 39. was distinctly conveyed along the closed tube in- to the apartment N. In like manner the answer issued from the aperture A, and being reflected back to the ear of the spectator by the trumpet, he heard the sounds with that change of character which they receive when transmitted through a tube and then reflected to the ear. The surprise of the auditors was greatly increas- ed by the circumstance, that an answer was return- ed to questions put in a whisper, and also by the conviction that nobody but a person in the middle of the audience could observe the circumstances to which the invisible figure frequently adverted. Although the performances of speaking heads were generally effected by the methods now de- scribed, yet there is reason to think that the ven- triloquist sometimes presided at the exhibition, and deceived the audience by his extraordinary powers of illusion. There is no species of deception more ILLUSIONS OF SOUND. 165 irresistible in its effects than that which arises from the uncertainty with which we judge of the direc- tion and distance of sounds. Every person must have noticed how a sound in their own ears is of- ten mistaken for some loud noise moderated by the distance from which it is supposed to come ; and the sportsman must have frequently been surprised at the existence of musical sounds humming* re- motely in the extended heath, when it was only the wind sounding in the barrel of his gun. The great proportion of apparitions that haunt old castles and apartments associated with death exist only in the sounds which accompany them. The imagi- nation even of the boldest inmate of a place hal- lowed by superstition, will transfer some trifling sound near his own person to a direction and to a distance very different from the truth, and the sound which otherwise might have no peculiar com- plexion will derive another character from its new locality. Spurning the idea of a supernatural ori- gin, he determines to unmask the spectre, and grap- ple with it in its den. All the inmates of the house are found to be asleep — even the quadrupeds are in their lair — there is not a breath of wind to ruffle the lake that reflects through the casement, the reclining crescent of the night ; and the mas- sive walls in which he is inclosed forbid the idea that he has been disturbed by the warping of pan- nelling or the bending of partitions. His search is vain ; and he remains master of his own secret, till he has another opportunity of investigation. The same sound again disturbs him, and, modified probably by his own position at the time, it may perhaps appear to come in a direction slightly dif- 166 LETTERS ON NATURAL MAGIC. ferent from the last. His searches are resumed, and he is again disappointed. If this incident should recur night after night with the same result ; — if the sound should appear to depend upon his own motions, or be any how associated with himself, with his present feelings, or with his past history, his personal courage will give way, a superstitious dread, at which he himself perhaps laughs, will seize his mind, and he will rather believe that the sounds have a supernatural origin, than that they could continue to issue from a spot where he knows there is no natural cause for their production. I have had occasion to have personal knowledge of a case much stronger than that which has now been put. A gentleman, devoid of all superstitious feelings, and living in a house free from any gloomy associations, heard night after night in his bed-room a singular noise, unlike any ordinary sound to which he was accustomed. He had slept in the same room for years without hearing it, and he attribut- ed it at first to some change of circumstances in the roof or in the walls of the room, but after the strictest examination no cause could be found for it. It occurred only once in the night, it was heard almost every night, with few interruptions. It was over in an instant, and it never took place till after the gentleman had gone to bed. It was always distinctly heard by his companion, to whose time of going to bed it had no relation. It depended on the gentleman alone, and it followed him into an- other apartment with another bed, on the opposite side of the house. Accustomed to such investiga- tions, he made the most diligent but fruitless search into its cause. The consideration that the sound VENTRILOQUISM EXPLAINED. 167 bad a special reference to him alone, operated upon his imagination, and he did not scruple to acknow- ledge that the recurrence of the mysterious sound produced a superstitious feeling- at the moment. Many months afterwards it was found that the sound arose from the partial opening of the door of a wardrobe which was within a few feet of the gentle- man's head, and which had been taken into the other apartment. This wardrobe was almost always opened before he retired to bed, and the door being a little too tight, it gradually forced itself open with a sort of dull sound, resembling the note of a drum. As the door had only started half an inch out of its place, its change of place never attracted attention. The sound, indeed, seemed to come in a different direction, and from a greater distance. When sounds so mysterious in their origin are heard by persons predisposed to a belief in the mar- vellous, their influence over the mind must be very powerful. An inquiry into their origin, if it is made at all, will be made more in the hope of confirming than of removing the original impres- sion, and the unfortunate victim of his own fears will also be the willing dupe of his own judgment. This uncertainty with respect to the direction of sound is the foundation of the art of ventriloquism. If we place ten men in a row at such a distance from us that they are included in the angle within which we cannot judge of the direction of sound, and if in a calm day each of them speaks in succes- sion, we shall not be able with closed eyes to deter- mine from which of the ten men any of the sounds proceeds, and we shall be incapable of perceiving that there is any difference in the direction of the sounds emitted by the two outermost : If a man 168 LETTERS ON NATURAL MAGIC. and a child are placed within the same angle, and if the man speaks with the accent of a* child with- out any corresponding motion in his mouth or face, we shall necessarily believe that the voice comes from the child : Nay, if the child is so distant from the man that the voice actually appears to us to come from the man, we will still continue in the belief that the child is the speaker ; and this conviction would acquire additional strength if the child fa- voured the deception by accommodating its features and gestures to the words spoken by the man. So powerful, indeed, is the influence of this deception, that if a jack-ass placed near the man were to open its mouth, and shake its head responsive to the words uttered by his neighbour, we would rather believe that the ass spoke than that the sounds pro- ceeded from a person whose mouth was shut, and the muscles of whose face were in perfect repose. If our imagination were even directed to a marble statue or a lump of inanimate matter, as the source from which we were to expect the sounds to issue, we would still be deceived, and would refer the sounds even to these lifeless objects. The illusion would be greatly promoted if the voice were totally different in its tone and character from that of the man from whom it really comes; and if he occasional- ly speak in his own full and measured voice, the belief will be irresistible that the assumed voice pro- ceeds from the quadruped or from the inanimate object. When the sounds which are required to proceed from any given object are such as they are ac- tually calculated to yield, the process of deception is extremely easy, and it may be successfully ex- ecuted even if the angle between the real and the VENTRILOQUISM EXPLAINED. 169 supposed directions of the sound is much greater than the angle of uncertainty. Mr Dugald Stewart has stated some cases in which deceptions of this kind were very perfect. He mentions his having seen a person who, by counterfeiting the gesticula- tions of a performer on the violin, while he imitat- ed the music by his voice, rivetted the eyes of his audience on the instrument, though every sound they heard proceeded from his own mouth. The late Savile Carey, who imitated the whistling of the wind through a narrow chink, told Mr Stewart that he had frequently practised this deception in the corner of a coffee-house, and that he seldom fail- ed to see some of the company rise to examine the tightness of the windows, while others, more intent on their newspapers, contented themselves with put- ting on their hats and buttoning their coats. Mr Stewart likewise mentions an exhibition formerly common in some of the continental theatres, where a performer on the stage displayed the dumb show of singing with his lips and eyes and gestures, while another person unseen supplied the music with his voice. The deception in this case he found to be at first so complete as to impose upon the nicest ear and the quickest eye ; but in the progress of the entertainment, he came distinctly sensible of the imposition, and sometimes wondered that it should have misled him for a moment. In this case there can be no doubt that the deception was at first the work of the imagination, and was not sustained by the acoustic principle. The real and the mock singer were too distant, and when the influence of the imagination subsided, the true di- rection of the sound was discovered. This detec- 170 LETTERS ON NATURAL MAGIC. tion of the imposture, however, may have arisen from another cause. If the mock singer happened to change the position of his head, while the real singer made no corresponding change in his voice, the attentive spectator would at once notice this incongruity, and discover the imposition. In many of the feats of ventriloquism the per- former contrives, under some pretence or other, to conceal his face, but ventriloquists of great dis- tinction, such as M. Alexandre, practise their art without any such concealment. Ventriloquism loses its distinctive character if its imitations are not performed by a voice from the belly. The voice, indeed, does not ac- tually come from that region, but when the ven- triloquist utters sounds from the larynx without moving the muscles of his face, he gives them strength by a powerful action of the abdominal muscles. Hence he speaks by means of his belly, although the throat is the real source from which the sounds proceed. Mr Dugald Stewart has doubt- ed the fact, that ventriloquists possess the power of fetching a voice from within : he cannot con- ceive what aid could be derived from such an ex- traordinary power ; and he considers that the ima- gination, when seconded by such powers of imita- tion as some mimics possess, is quite sufficient to account for all the phenomena of ventriloquism which he has heard. This opinion, however, is strongly opposed by the remark made to Mr Stewart himself by a ventriloquist, " that his art would be perfect if it were possible only to speak distinctly without any movement of the lips at all." But, in- dependent of this admission, it is a matter of abso- VENTRILOQUISM EXPLAINED. 171 lute certainty, that this internal power is exercised by the true ventriloquist. In the account which the Abbe Chapellehas given of the performances of M. St Gille and Louis Brabant, he distinctly states that M. St Gille appeared to be absolutely mute while he was exercising his art, and that no change in his countenance could be discovered. * He affirms also that the countenance of Louis Brabant exhibit- ed no change, and that his lips were close and inac- tive. M. Richerand, who attentively watched the performances of M. Fitz- James, assures us that dur- ing his exhibition there was a distension in the epigastric region, and that he could not long conti- nue the exertion without fatigue. The influence over the human mind which the ventriloquist derives from the skilful practice of his art is greater than that which is exercised by any other species of conjuror. The ordinary magician requires his theatre, his accomplices, and the instru- ments of his art, and he enjoys but a local sove- reignty within the precincts of his own magic circle. The ventriloquist, on the contrary, has the supernatural always at his command. In the open fields, as well as in the crowded city, in the private apartment, as well as in the public hall, he can sum- mon up innumerable spirits ; and though the persons of his fictitious dialogue are not visible to the eye, yet they are as unequivocally present to the ima- gination of his auditors as if they had been shadow- ed forth in the silence of a spectral form. In order to convey some idea of the influence of this illusion, I shall mention a few well authenticated cases of successful ventriloquism. * Edinburgh Journal of Science, No. xviii. p. 254. 172 LETTERS ON NATURAL MAGIC. M. St Gille, a grocer of St Germain en Lay, whose performances have been recorded by the Abbe de la Chapelle, had occasion to shelter himself from a storm in a neighbouring- convent, where the monks were in deep mourning for a much esteemed member of their community who had been recently buried. While lamenting over the tomb of their deceased brother the slight honours which had been paid to his memory, a voice was suddenly heard to issue from the roof of the choir bewailing the condition of the deceased in purgatory, and reproving the brotherhood for their want of zeal. The tidings of this supernatural event brought the whole brotherhood to the church. The voice from above repeated its lamentations and reproaches, and the whole convent fell upon their faces, and vowed to make a reparation of their error. They accord- ingly chaunted in full choir a de prqfiindis, during the intervals of which the spirit of the departed monk expressed his satisfaction at their pious exer- cises. The prior afterwards inveighed against mo- dern scepticism on the subject of apparitions, and M. St Gille had great difficulty in convincing the fraternity that the whole was a deception. On another occasion, a commission of the Royal Academy of Sciences at Paris, attended by several persons of the highest rank, met at St Germain en Lay to witness the performances of M. St Gille. The real object of their meeting was purposely with- held from a lady of the party, who was informed that an aerial spirit had lately established itself in the neighbourhood, and that the object of the as- sembly was to investigate the matter. When the party had sat down to dinner in the open air, the VENTRILOQUISM OF M. BRABANT, &C. 173 spirit addressed the lady in a voice which seemed to come from above their heads, from the surface of the ground at a great distance, or from a consi- derable depth under her feet. Having- been thus addressed at intervals during- two hours the lady was firmly convinced of the existence of the spirit, and could with difficulty be undeceived. Another ventriloquist, Louis Brabant, who had been valet de chambre to Francis I. turned his powers to a more profitable account. Having- fallen in love with a rich and beautiful heiress, he was rejected by her parents as an unsuitable match for their daugh- ter. On the death of her father, Louis paid a visit to the widow, and he had no sooner entered the house than she heard the voice of her deceased hus- band addressing her from above, " Give my daugh- ter in marriage to Louis Brabant, who is a man of large fortune and excellent character. I endure the inexpressible torments of purgatory for having refused her to him. Obey this admonition, and give everlasting repose to the soul of your poor husband.'' This awful command could not be resisted, and the widow announced her compliance with it. As our conjuror, however, required money for the completion of his marriage, he resolved to work up- on the fears of one Cornu, an old banker at Lyons, who had amassed immense wealth by usury and ex- tortion. Having obtained an interview with the miser, he introduced the subjects of demons and spectres and the torments of purgatory, and during an interval of silence, the voice of the miser's deceas- ed father was heard complaining of his dreadful si- tuation in purgatory, and calling upon his son to rescue him from his sufferings by enabling Louis 174 LETTERS ON NATURAL MAGIC. Brabant to redeem the Christians that were enslav- ed by the Turks. The awe-struck miser was also threatened with eternal damnation if he did not thus expiate his own sins ; but such was the grasp that the banker took of his gold that the ventriloquist was obliged to pay him another visit. On this oc- casion, not only his father but all his deceased rela- tions appealed to him in behalf of his own soul and theirs, and such was the loudness of thefr complaints that the spirit of the banker was subdued, and he gave the ventriloquist ten thousand crowns to libe- rate the Christian captives. When the miser was afterwards undeceived, he is said to have been so mortified that he died of vexation. The ventriloquists of the nineteenth century made great additions to their art, and the perform- ances of M. Fitz- James and M. Alexandre, which must have been seen by many of our countrymen, were far superior to those of their predecessors. Besides the art of speaking by the muscles of the throat and the abdomen, without moving those of the face, these artists had not only studied with great diligence and success the modifications which sounds of all kinds undergo from distance, obstruc- tions and other causes, but had acquired the art of imitating them in the highest perfection. The ventriloquist was therefore able to carry on a dia- logue in which the dramatis voces, as they may be called, were numerous ; and when on the outside of an apartment he could personate a mob with its in- finite variety of noise and vociferation. Their in- fluence over an audience was still farther extended by a singular power over the muscles of the body. Mr Fitz- James actually succeeded in making the op- ESKIMAUX VENTRILOQUISTS. 175 posite or corresponding- muscles act differently from eacji other ; and while one side of his face was mer- ry and laughing", the other was full of sorrow and in tears. At one moment he was tall, thin, and me- lancholic, and after passing- behind a screen he came out " bloated with obesity and staggering with fulness." M. Alexandre possessed the same power over his face and fig-ure, and so striking- was the contrast of two of these forms, that an excellent sculptor, Mr Joseph, has perpetuated them in mar- ble. This new acquirement of the ventriloquist ena- bled him, in his own single person and with his own single voice, to represent upon the stage a dramatic composition which would have required the assis- tance of several actors. Although only one charact er in the piece could be seen at the same time, yet they all appeared during its performance, and the change of face and figure on the part of the ventriloquist was so perfect that his personal identity could not be recognized in the dramatis persona?. This de- ception was rendered still more complete by a par- ticular construction of the dresses, which enabled the performer to reappear in a new character after an interval so short that the audience necessarily believed that it was another person. It is a curious circumstance that Captain Lyon found among the Eskimaux of Igloolik ventrilo- quists of no mean skill. There is much rivalry amongst the professors of the art, who do not ex- pose each other's secrets, and their exhibitions de- rive great importance from the rarity of their oc- currence. The following account of one of them 176 LETTERS ON NATURAL MAGIC. is so interesting* that we shall give the whole of it in Captain Lyon's words. " Amongst our Igloolik acquaintances were two females and a few male wizards, of whom the prin- cipal was Toolemak. This personage was cunning and intelligent, and, whether professionally, or from his skill in the chace, but perhaps from both rea- sons, was considered by all the tribe as a man of importance. As I invariably paid great deference to his opinion on all subjects connected with his calling, he freely communicated to me his superior knowledge, and did not scruple to allow of my being present at his interviews with Tornga, or his patron spirit. In consequence of this, I took an early opportunity of requesting my friend to exhi- bit his skill in my cabin. His old wife was with him, and by much flattery and an accidental dis- play of a glittering knife and some beads, she as- sisted me in obtaining my request. All light ex- cluded, our sorcerer began chanting to his wife with great vehemence, and she in return answered by singing the Amna-aya, which was not disconti- nued during the whole ceremony. As far as I could hear, he afterwards began turning himself rapidly round, and in a loud powerful voice vocife- rated for Tornga with great impatience, at the same time blowing and snorting like a walrus. His noise, impatience, and agitation, increased every moment, and he at length seated himself on the deck, varying his tones, and making a rustling with his clothes. Suddenly the voice seemed smothered, and was so managed as to sound as if retreating beneath the deck, each moment becom- ing more distant, and ultimately giving the idea of ESKIMAUX VENTRILOQUISTS. 177 being many feet below the cabin, when it ceased entirely. His wife now, in answer to my queries, informed me very seriously, that he had dived, and that he would send up Tornga. Accordingly, in about half a minute, a distant blowing was heard very slowly approaching, and a voice, which dif- fered from that at first heard, was at times mingled with the blowing, until at length both sounds be- came distinct, and the old woman informed me that Tornga was come to answer my questions. I ac- cordingly asked several questions of the sagacious spirit, to each of which inquiries I received an an- swer by two loud claps on the deck, which I was given to understand were favourable. " A very hollow, yet powerful voice, certainly much different from the tones of Toolemak, now chanted for some time, and a strange jumble of hisses, groans, shouts, and gabblings like a turkey succeeded in rapid order. The old woman sang with increased energy, and as I took it for granted that this was all intended to astonish the Kabloona, I cried repeatedly that I was very much afraid. This, as I expected, added fuel to the fire, until the poor immortal, exhausted by its own might, asked leave to retire. " The voice gradually sunk from our hearing as at first, and a very indistinct hissing succeeded ; in its advance, it sounded like the tone produced by the wind on the bass chord of an TEolian harp. This was soon changed to a rapid hiss like that of a rocket, and Toolemak with a yell announced his return. I had held my breath at the first distant hissing, and twice exhausted myself, yet our con- juror did not once respire, and even his returning M 178 LETTERS ON NATURAL MAGIC. and powerful yell was uttered without a previous stop or inspiration of air. " Light being admitted, our wizard, as might be expected, was in a profuse perspiration, and certain- ly much exhausted by his exertions, which had continued for at least half an hour. We now ob- served a couple of bunches, each consisting of two stripes of white deer-skin and a long piece of sinew, attached to the back of his coat. These we had not seen before, and were informed that they had been sewn on by Tornga while he was below." * Captain Lyon had the good fortune to witness another of Toolemak's exhibitions, and he was much struck with the wonderful steadiness of the wizard throughout the whole performance, which lasted an hour and a half. He did not once appear to move, for he was so close to the skin behind which Captain Lyon sat, that if he had done so he must have perceived it. Captain Lyon did not hear the least rustling of his clothes, or even dis- tinguish his breathing, although his outcries were made with great exertion, f * Private Journal of Captain G. F.Lyon. Lond. 1824, p. 358, 361. f Id. Id, p. 366, MUSICAL AND HARMONIC SOUNDS. 179 LETTER VIII. Musical and harmonic sounds explained — Power of breaking glasses with the 'ooice — Musical sounds from the vibration of a column of air — And of solid bodies — Kaleidophone — Singular acoustic figures produced on sand laid on vibra- ting plates of glass — and on stretched membranes — Vibra- tion of flat rulers, and cylinders of glass — Production of si- lence from two sounds — Production of darkness from two lights — Explanation of these singular effects — Acoustic auto- maton — Droz's bleating sheep — MaillardeVs singing bird — Vaucanson's flute player — His pipe and tabor player — Baron Kempelerts talking engine — Kratzenstein 's speaking machine — Mr Willises researches. Among the discoveries of modern science there are few more remarkable than those which relate to the production of harmonic sounds. We are all familiar with the effects of musical instruments, from the deep-toned voice of the organ to the wiry shrill of the Jew's harp. We' sit entranced under their magical influence, whether the ear is charmed with the melody of their sounds, or the heart agitated by the sympathies which they rouse. But though we may admire their external form, and the skill of the artist who constructed them, we never think of inquiring into the cause of such extraordinary combinations. Sounds of all kinds are conveyed to the organ of hearing through the air ; and if this element were 180 LETTERS ON NATURAL MAGIC. to be destroyed, all nature would be buried in the deepest silence. Noises of every variety, whether they are musical or discordant, high or low, move through the air of our atmosphere at the surface of the earth with a velocity of 1090 feet in a second, or 765 miles per hour ; but in sulphurous acid gas sound moves only through 751 feet in a second, while in hydrogen gas it moves with the great velocity of 3000 feet. Along- fluid and solid bodies, its progress is still more rapid. Through water it moves at the rate of 4708 feet in a second, through tin at the rate of 8175 feet, and through iron, glass, and some kinds of wood, at the rate of 18530 feet. When a number of single and separate sounds follow each other in rapid succession, they produce a continued sound, in the same manner as a con- tinuous circle of light is produced by whirling round a burning stick before the eye. In order that the sound may appear a single one to the ear, nearly sixteen separate sounds must follow one another every second. When these sounds are exactly si- milar, and recur at equal intervals, they form a musical sound. In order to produce such sounds from the air, it must receive at least sixteen equal- ly distant impulses or strokes in a second. The most common way of producing this effect is by a string or wire A B, Fig. 40, stretched between the fixed points A, B. If this string is taken by the middle and pulled aside, or if it is suddenly struck, it will vibrate between its two fixed points, as shown in the figure, passing alternately on each side of its axis A B, the vibrations gradually dimi- nishing by the resistance of the air till the string is brought to rest. Its vibrations, however, may be MUSICAL AND HARMONIC SOUNDS. 181 kept up, by drawing a rosined fiddle-bow across it, and while it is vibrating it will give out a sound Corresponding to the rapidity of its vibrations, and Fig. 40. arising from the successive blows or impulses given to the air by the string. This sound is called the fundamental sound of the string, and its acuteness or sharpness increases with the number of vibrations which the string performs in a second. If we now touch the vibrating string A' B' lightly with the finger, or with a feather at the middle point C, Fig. 40, it will give out a more acute but fainter sound than before, and while the extent of its vibrations is diminished, their fre- quency is doubled. In like manner, if we touch the string A'' B", Fig 40, at a point C, so that A"C is one-third of A'' B", the note will be still more acute, and correspond to thrice the number of vi- brations. All this might have been expected, but the wonderful part of the experiment is, that the vibrating string A' B' divides itself at C into two 182 LETTERS ON NATURAL MAGIC. parts A'C, CB',the part A'C vibrating* round A'and C as fixed points, and the part CB' round C and B', but always so that the part A' C is at the same distance on the one side of the axis A' B' as at A m C, while the part C B is on the other side, as at C n B. Hence the point C, being always pulled by equal and opposite forces, remains at rest as if it were absolutely fixed. This stationary point is called a node, and the vibrating* portions A' m C, C n W loops. The very same is true of the string A" B", the points C and D being stationary points ; and upon the same principle a string may be divid- ed into any number of vibrating portions. In order to prove that the string is actually vibrating in these equal subdivisions, we have only to place a piece of light paper with a notch in it on different parts of the string. At the nodes C and D it will remain perfectly at rest, while at m or n in the middle of the loops it will be thrown off or violent- ly agitated. The acute sounds given out by each of the vi- brating portions are called harmonic sounds, and they accompany the fundamental sound of the string in the very same manner, as we have al- ready seen, that the eye sees the accidental or harmonic colours while it is affected with the fun- damental colour. The subdivision of the string, and consequently the production of harmonic sounds, may be effected without touching the string at all, and by means of a sympathetic action conveyed by the air. If a string A B, for example, Fig. 40, is at rest, and if a shorter string A" C, one-third of its length, fix- ed at the two points A" and C is set a- vibrating MUSICAL SOUNDS FROM VIBRATION OF AIR. 183 in the same room, the string A B will be set a- vi- brating in three loops like A" B", giving out the same harmonic sounds as the small string A" C. It is owing to this property of sounding bodies that singers with great power of voice are able to break into pieces a large tumbler glass, by singing close to it its proper fundamental note ; and it is from the same sympathetic communication of vi- brations that two pendulum clocks fixed to the same wall, or two watches lying upon the same table, will take the same rate of going, though they would not agree with one another if placed in se- parate apartments. Mr Ellicott even observed that the pendulum of the one clock will stop that of the other, and that the stopped pendulum will after a certain time resume its vibrations, and in its turn stop the vibrations of the other pendulum. The production of musical sounds by the vibra- tions of a column of air in a pipe is familiar to every person, but the extraordinary mechanism by which it is effected is known principally to philo- sophers. A column of air in a pipe may be set a- vibrating by blowing over the open end of it, as is done in Pan's pipes, or by blowing over a hole in its side as in the flute, or by blowing through an aper- ture called a reed, with a flexible tongue, as in the clarionet. In order to understand the nature of this vibration, let A B, Fig. 41, be a pipe or tube, and let us place in it a spiral spring A B, in which the coil or spire are at equal distances, each end of the spiral being fixed to the end of the tube. This elastic spring may be supposed to represent the air in the pipe, which is of equal density throughout. If we take hold of the spring at m ? 184 LETTERS ON NATURAL MAGIC. and push the point m towards A and towards B in succession, it will give us a good idea of the vibra- tion of an elastic column of air. When m is push- Fig. 41. ed towards A, the spiral spring will be compressed or condensed, as shown at m A, No. 2, while at the other end, it will be dilated or rarefied, as shown at m B, and in the middle of the tube it will have the same degree of compression as in No. 1. When the string is drawn to the other end of the tube B, the spring will be, as in No. 3, condensed at the end B, and dilated at the end A. Now when a column of air vibrates in a pipe A B, the whole of it rush- es alternately from B to A, as in No. 2, and from A to B as in No. 3, being condensed at the end A No. 2, and dilated or rarefied at the end B, while in No. 3 it is rarefied at A and condensed at B, preserving its natural density at the middle point between A and B. In the case of the spring the ends A B are alternately pushed outwards and pul- led inwards by the spring, the end A being pushed MUSICAL SOUNDS FROM VIBRATION OF AIR. 185 outwards in No. 2, and B pulled inwards, while in No. 3 A is pulled inwards and B pushed outwards. That the air vibrating- in a pipe is actually in the state now described may be shown by boring- small holes in the pipe, and putting- over them pieces of a line membrane. The membrane opposite to the middle part between A and B, where the par- ticles of the air have the greatest motion, will be violently agitated, while at points nearer the ends A and B it will be less and less affected. Let us now suppose two pipes A B, B C, to be joined tog-ether as in Fig-. 42, and to be separated by a fixed partition at B ; and let a spiral spring- be fixed in each. Let the spring- AB be now pushed to the end A, while the spring BC is pushed toC,as in No. 1, and back again, as in No. 2, Fig. 42. A. -B but always in opposite directions ; then it is obvious that the partition B is in No. 1 drawn in opposite directions towards A and towards C, and always with forces equal to each other, that is, when B is drawn slightly towards A, which it is at the begin- ning of the motion, it is also drawn slightly towards C, and when it is drawn forcibly towards A, as it is at the end of the motion of the spring, it is also drawn forcibly towards C. If the partition B, there- 186 LETTERS ON NATURAL MAGIC. fore, is moveable, it will still remain fixed during the opposite excursions of the spiral springs : Nay, if we remove the partition, and hook the end of one spiral spring to the end of the other, the node or point of junction will remain stationary during the movements of the springs, because at every instant that point is drawn by equal and opposite forces. If three, four, or Jive, spiral springs are joined in a si- milar manner, we may conceive them all vibrating between their nodes in the same manner. Upon the very same principles we may conceive a long column of air without partitions dividing it- self into two, three, or four, smaller columns, each of which will vibrate between its nodes in the same manner as the spiral spring. At the middle point of each small vibrating column, the air will be of its natural density like that of the atmosphere, while at the nodes B, &c. it will be in a state of condensation and rarefaction alternately. If, when the air is vibrating in one column in the pipe A B, as in Fig 41, No 2, 3, we conceive a hole made in the middle, the atmospheric air will not rush in to disturb the vibration, because the air within the pipe and without it has exactly the same density. Nay, if, instead of a single hole, we were to cut a ring out of the pipe at the middle point, the column would vibrate as before. But if we bore a hole between the middle and one of the ends, where the vibrating column must be either in a state of condensation or rarefaction, the air must either rush out or rush in, in order to establish the equilibrium. The air opposite the hole will then be brought to the state of the external air like that in the middle of the pipe, it will become the middle KALEIDOPHONE. 187 of a vibrating column, and the whole column of air, instead of vibrating as one, will vibrate as two co- lumns, each column vibrating with twice the velo- city, and yielding harmonic sounds along with the fun- damental sound of the whole columns, in the same manner as we have already explained with regard to vibrating strings. By opening other holes we may subdivide a vibrating column into any number of smaller vibrating columns. The holes in flutes, clarionets, &c. are made for this purpose. When they are all closed up the air vibrates in one co- lumn, and by opening and shutting the different holes in succession, the number of vibrating columns is increased or diminished at pleasure, and consequent- ly the harmonic sounds will vary in a similar man- ner. Curious as these phenomena are, they are still surpassed by those which are exhibited during the vibration of solid bodies. A rod or bar of metal or glass may be made to vibrate either longitudinally or laterally. An iron rod will vibrate longitudinally like a column of air if we strike it at one end in the direc- tion of its length, or rub it in the same direction with a wetted finger, and it will emit the same fun- damental note as a column of air ten or eleven times as long, because sound moves as much faster in iron than in air. When the iron rod is thus vibrating along its length, the very same changes which we have shown in Fig. 41, as produced in a spiral spring or in a column of air, take place in the solid metal. All its particles move alternately towards A and to- wards B, the metal being in the one case condensed at the end to which the particles move, and expanded 188 LETTERS ON NATURAL MAGIC. at the end from which they move, and retaining its natural density in the middle of the rod. If we now hold this rod in the middle, by the finger and thumb lightly applied, and rub it in the middle either of A B or B C with a piece of cloth sprinkled with powdered rosin, or with a well-rosined fiddle-bow drawn across the rod, it will divide itself into two vibrating portions A B, B C, each of which will vi- brate, as shown in Fig. 42, like the two adjacent co- lumns of air, the section of the rod, or the particles which compose that section at B, being at perfect rest. By holding the rod at any intermediate point between A and B, so that the distance from A to the finger and thumb is one-third, one-fourth, one- fifth, &c. of the whole length A C, and rubbing one of the divisions in the middle, the rod will divide it- self into 3, 4, 5, &c. vibrating portions, and give out corresponding harmonic sounds. A rod of iron may be made to vibrate laterally or transversely by fixing one end of it firmly as in a vice, and leaving the other free, or by having both ends free or both fixed. When a rod, fixed at one end and free at the other, is made to vibrate, its mode of vibrating may be rendered evident to the eye ; and for the purpose of doing this Mr Wheat- stone has contrived a curious instrument called the Kaleidophone, which is shown in Fig. 43. It con- sists of a circular base of wood A B, about nine inch- es in diameter and one inch thick, and having four brass sockets firmly fixed into it at C, D, E, and F, Into these sockets are screwed four vertical steel rods C, D, E, and F, about 13 or 14 inches long, one being a square rod, another a bent cylindrical one, V K A LEI DO PHONE. 189 and the other two cylindrical ones of different dia- meters. On the extremities of these rods are Ax- Fig. 43. ed small quicksilvered glass heads, either singly or in groups, so that when the instrument is placed in the light of the sun or in that of a lamp, bright images of the sun or candle are seen reflected on each bead. If any of these rods is set a-vibrating , these luminous images will form continuous and returning curve lines in a state of constant varia- tion, each different rod giving curves of different cha- racters. The melodion, an instrument of great power, embracing five octaves, operates by means of the vibrations of metallic rods of unequal lengths, fix- ed at one end, and free at the other. % A narrow and thin plate of copper is screwed to the free ex- tremity of each rod, and at right angles to its length ; * See Edinburgh Encyclopaedia, Art. Science, Curiosities in, Vol. xvii. p. 563. 190 LETTERS ON NATURAL MAGIC. and its surface is covered with a small piece of felt impregnated with rosin. This narrow band is placed near the circumference of a revolving- cylinder, and by touching the key it is made to descend till it touches the revolving cylinder, and gives out its sound. The sweetness and power of this instru- ment are unrivalled, and such is the character of its tones, that persons of a nervous temperament are often entirely overpowered by its effects. The vibrations of plates of metal or glass of va- rious forms exhibit a series of the most extraordi- nary phenomena which are capable of being shown by very simple means. These phenomena are dis- played in an infinite variety of regular figures as- sumed by sand, or fine lycopodium powder, strewed over the surface of the glass plate. In order to produce these figures, we must pinch or damp the plate at one or more places, and when the sand is strewed upon its surface, it is thrown into vibrations by drawing a fiddle-bow over different parts of its circumference. The method of damping or pinch- ing plates is shown in Fig. 44. In No. 1, a square plate of glass A B, ground smooth at its edges, is pinched by the finger and thumb. In No. 2 a cir- cular plate is held by the thumb against the top c of a perpendicular rod, and damped by the fingers at two different points of its circumference. In No. 3 it is damped at three points of its circumfe- rence, c and d by the thumb and finger, and at e by pressing it against a fixed obstacle a b. By a means of a clamp like that at No. 4, it may be damped at a greater number of points. If we take a square plate of glass, such as that shown in Fig. 45, No. 1, and pinching it at its 4 ACOUSTIC FIGURES. 191 centre, draw the fiddle-bow near one of its angles, the sand will accumulate in the form of a cross, as Fig. 44. shown in the figure, being thrown off the parts of the plate that are in a state of vibration, and set- tling in the nodes or parts which are at rest. If the bow is drawn across the middle of one of the edges, the sand will accumulate as in No. 2. If the plate is pinched at N, No. 3, and the bow applied at F and perpendicular to A B, the sand will arrange it- self in three parallel lines, perpendicular to a fourth passing through F and N. But if the point N where it is pinched, is a little farther from the edge than in No. 3, the parallel lines will change into curves as in No. 4. If the plate of glass is circular and pinched at its centre, and also at a point of its circumference, and if the bow is applied at a point 45° from the last 192 LETTERS ON NATURAL MAGIC. point, the figure of the sand will be as in Fig. 46, No. 1. If with the same plate, similarly pinched, Fig. 45. A E B the bow is drawn over a part 30° from the pinched point of the circumference, the sand will form six radii as in No. 2. When the centre of the plate is left free, a different set of figures is produced as shown in No. 3 and No. 4. When the plate is pinched near its edge, and the bow applied 45° from the point pinched, a circle of sand will pass through that point, and two diameters of sand at right angles to each other, will be formed, as in No. 3. When a point of the circumference is pressed against a fixed obstacle, and the bow applied 30° from that point, the figure in No. 4 is produced. 3 ACOUSTIC FIGURES. 193 If, in place of a solid plate, we strew the sand over a stretched membrane, the sand will form it- . Fig. 46. No. 1. No. 2. No. 3. No. 4. self into figures, even when the vibrations are com- municated to the membrane through the air. In order to make these experiments, we must stretch a thin sheet of wet paper, such as vegetable paper, over the mouth of a tumbler-glass with a footstalk, and fix it to the edges with glue. When the pa- per is dry, a thin layer of dry sand is strewed upon its surface. If we place this membrane upon a table, and hold immediately above it and parallel to the membrane, a plate of glass vibrating so as to give any of the figures shown in Fig. 46, the sand upon the membrane will imitate exactly the figure upon the glass. If the glass plate, in place of vibrating horizontally, is made to vibrate in an N 194 LETTERS ON NATURAL MAGIC. inclined position, the figures on the membrane will change with the inclination, and the sand will as- sume the most curious arrangements. The figures thus produced vary with the size of the mem- brane, with its material, its tension, and its shape. When the same figure occurred several times in suc- cession, a breath upon the paper will change its de- gree of tension, and produce an entirely new figure, which, as the temporary moisture evaporates, will return to the original figure, through a number of intermediate ones. The pipe of an organ at the distance of a few feet, or the notes of a flute at the distance of half a foot, will arrange the sand on the membrane into figures which perpetually change with the sound that is produced. The manner in which flat rulers and cylinders of glass perform their vibrations is very remarkable. If a glass plate about twenty-seven inches long, six-tenths of an inch broad, and six-hundredths of an inch thick, is held by the edges between the fin- ger and thumb, and has its lower surface, near either end, rubbed with a piece of wet cloth, sand laid upon its upper surface will arrange itself in paral- lel lines at right angles to the length of the plate. If the place of these lines is marked with a dot of ink, and the other side of the glass ruler is turned upwards, and the ruler made to vibrate as before, the sand will now accumulate in lines intermediate between the former lines, so that the motions of one-half the thickness of the glass ruler are precise- ly the reverse of those of the corresponding parts of the other half. As these singular phenomena have not yet been made available by the scientific conjuror, we must SILENCE FROM TWO SOUNDS. 195 be satisfied with this brief notice of them ; but there is still one property of sound, which has its analogy also in lig-ht, too remarkable to be passed without notice. This property has more of the marvellous in it than any result within the wide range of the sciences. Two loud sounds may be made to produce silence, and tivo strong lights may be made to produce darkness f If two equal and similar strings, or the columns of air in two equal and similar pipes, perform ex- actly 100 vibrations in a second, they will produce each equal waves of sound, and these waves will conspire in generating- an uninterrupted sound, double of either of the sounds heard separately. If the two strings or the two columns of air are not in unison, but nearly so, as in the case where the one vibrates 100, and the other 101 times in a se- cond, then at the first vibration the two sounds will form one of double the strength of either ; but the one will gradually gain upon the other, till at the fiftieth vibration it has gained half a vibration on the other. At this instant the two sounds will de- stroy one another, and an interval of perfect silence will take place. The sound will instantly com- mence, and gradually increase till it becomes loudest at the hundredth vibration, where the two vibra- tions conspire in producing a sound double of either. An interval of silence will again occur at the 150th, 250th, 350th vibration, or every second, while a sound of double the strength of either will be heard at the 200dth, 300dth, and 400dth vibration. When the unison is very defectiv , or when there is a great difference between the number of vibra- tions which the two strings or columns of air per- 196 LETTERS ON NATURAL MAGIC. form in a second, the successive sounds and inter- vals of silence resemble a rattle. With a power- ful organ the effect of this experiment is very fine, the repetition of the sounds wow — wow — wow, — representing the doubled sound and the in- terval of silence which arise from the total extinc- tion of the two separate sounds. The phenomena corresponding to this in the case of light, is perhaps still more surprising. If a beam of red light issues from a luminous point, and falls upon the retina, we shall see distinctly the lumi- nous object from which it proceeds ; but if another pencil of red light issues from another luminous point any how situated, provided the difference be- tween its distance and that of the other luminous point from the point of the retina, on which the first beam fell, is the 258th thousandth part of an inch, or exactly twice, thrice, four times &c. that distance ; and if this second beam falls upon the same point of the retina, the one light will increase the inten- sity of the other, and the eye will see twice as much light as when it received only one of the beams separately. All this is nothing more than what might be expected from our ordinary experience, But if the difference in the distances of the two luminous points is only one-half of the 258th thou- sandth part of an inch, or 1^, 2^, 3 J, A.\, times that distance, the one light will extinguish the other, and produce absolute darkness. If the two lumi- nous points are so situated, that the difference of their distances from the point of the retina, is inter- mediate between 1 and 1^, or 2 and 2 J, above the 258th thousandth part of an inch, the intensity of the effect which they produce will vary from DARKNESS FROM TWO LIGHTS. 197 absolute darkness to double the intensity of either light. At 1 1-, 2±, 3^ times, &c. the 258th thousandth of an inch, the intensity of the two combined lights will be equal only to one of them acting singly. If the lights, in place of falling upon the retina, fall upon a sheet of white paper, the very same effect will be produced, a black spot being produced in the one case, and a bright white one in the other, and intermediate degrees of brightness in intermediate cases. If the two lights are violet, the difference of distances at which the preceding phenomena will be produced, will be the 157th thousandth part of an inch, and it will be intermediate between the 258th and the 157th thousand part of an inch, for the in- termediate colours. This curious phenomenon may be easily shown to the eye, by admitting the sun's light into a dark room through a small hole about the 40th or 50th part of an inch in diameter, and receiving the light on a sheet of paper. If we hold a needle or piece of slender wire in this light, and examine its shadow, we shall find that the shadow consists of bright and dark stripes succeeding each other alternately, the stripe in the very middle or axis of the shadow being' a bright one. The rays of light which are bent into the shadow, and which meet in the very middle of the shadow, have exact- ly the same length of path, so that they form a bright fringe of double the intensity of either ; but the rays which fall upon a point of the shadow at a certain distance from the middle, have a difference in the length of their paths, corresponding to the difference at which the lights destroy each other, so that a black stripe is produced on each side of the middle bright one. At a greater distance from the 198 LETTERS ON NATURAL MAGIC. middle, the difference becomes such as to produce a bright stripe, and so on, a bright and a dark stripe succeeding- each other to the margin of the shadow. The explanation which philosophers have given of these strange phenomena is very satisfactory, and may be easily understood. When a wave is made on the surface of a still pool of water, by plunging a stone into it, the wave advances along the sur- face, while the water itself is never carried forward, but merely rises into a height and falls into a hol- low, each portion of the surface experiencing an elevation and a depression in its turn. If we sup- pose two waves equal and similar to be produced by two separate stones, and if they reach the same spot at the same time, that is, if the two elevations should exactly coincide, they would unite their effects and produce a wave twice the size of either ; but if the one wave should be just so far before the other, that the hollow of the one coincided with the elevation of the other, and the elevation of the one with the hollow of the other, the two waves would obliterate or destroy one another, the eleva- tion as it were of the one filling up half the hollow of the other, and the hollow of the one taking away half the elevation of the other, so as to reduce the surface to a level. These effects will be actually ex- hibited by throwing two equal stones into a pool of water, and it will be seen that there are certain lines of a hyperbolic form where the water is quite smooth, in consequence of the equal waves oblite- rating one another, while in other adjacent parts, the water is raised to a height corresponding to both the waves united. In the tides of the ocean, we have a fine example ACOUSTIC AUTOMATA. 199 of the same principle. The two immense waves aris- ing- from the action of the sun and moon upon the ocean, produce our spring-tides by their combination, or when the elevations of each coincide, and our neap-tides, when the elevation of the one wave coincides with the depression of the other. If the sun and moon had exerted exactly the same force upon the ocean, or produced tide waves of the same size, then our neap-tides would have disappeared altogether, and the spring-tide would have been a wave double of the wave produced by the sun and moon separate^. An example of the effect of the equality of the two waves occurs in the port of Batsha, where the two waves arrive by channels of different lengths, and actually obliterate each other. Now, as sound is produced by undulations or waves in the air, and as light is supposed to be produced by waves or undulations in an etherial medium, filling all nature, and occupying the pores of trans- parent bodies, the successive production of sound and silence, by two loud sounds, or of light and dark- ness by two bright lights, may be explained in the very same manner as we have explained the in- crease and the obliteration of waves formed on the surface of water. If this theory of light be correct, then the breadth of a wave of red light will be the 258th thousandth part of an inch, the breadth of a wave of green light the 207th thousandth part of an inch, and the breadth of a wave of violet light, the 157th thousandth part of an inch. Among the wonders of modern skill, we must enumerate those beautiful automata by which the motions and actions of man and other animals have been successfully imitated. I snail therefore de- 200 LETTERS ON NATURAL MAGIC. scribe at present some of the most remarkable acoustic automata, in which the production of musi- cal and vocal sounds has been the principal object of the artist. Many very ingenious pieces of acoustic mecha- nism have been from time to time exhibited in Europe. The celebrated Swiss mechanist, M. Le Droz, constructed for the King* of Spain the figure of a sheep, which imitated in the most perfect man- ner the bleating of that animal, and likewise the figure of a dog watching a basket of fruit, which, when any of the fruit was taken away, never ceased •barking till it was replaced. The singing-bird of M. Maillardet, which he exhibited in Edinburgh many years ago, is still more wonderful.* An oval box, about three inches long, was set upon the table, and in an instant the lid flew up, and a bird of the size of the humming-bird, and of the most beautiful plumage, started from its nest. After fluttering its wings, it opened its bill and performed four different kinds of the most beau- tiful warbling. It then darted down into its nest, and the lid closed upon it. The moving power in this piece of mechanism is said to have been springs which continued their action only four minutes. As there was no room, within so small a figure, for accommodating pipes to produce the great variety of notes which were warbled, the artist used only one tube, and produced all the variety of sounds by short- ening and lengthening it with a moveable piston. Ingenious as these pieces of mechanism are, they sink into insignificance when compared with the * A similar piece of mechanism had been previously made by M. le Droz. vaucanson's flute-player. 201 machinery of M. Vaucanson, which had previously astonished all Europe. His two principal automa- ta were the flute-player, and the pipe and tabor- player. The flute-player was completed in 1736, and wherever it was exhibited it produced the greatest sensation. When it came to Paris it was received with great suspicion. The French sca- vans recollected the story of M. Raisin, the organist of Troyes, who exhibited an automaton player upon the harpsichord, which astonished the French court by the variety of its powers. The curiosity of the King could not be restrained, and in consequence of his insisting upon examining the mechanism, there was found in the figure a pretty little musi- cian five years of age. It was natural, therefore, that a similar piece of mechanism should be received with some distrust ; but this feeling was soon re- moved by M. Vaucanson, who exhibited and explain- ed to a committee of the Academy of Sciences the whole of the mechanism. This learned body was astonished at the ingenuity which it displayed; and they did not hesitate to state, that the machinery employed for producing the sounds of the flute, performed in the most exact manner the very ope- rations of the most expert flute-player, and that the artist had imitated the effects produced, and the means employed by nature, with an accuracy which exceeded all expectation. In 1738, M. Vaucanson published a memoir, approved of by the academy, in which he gave a full description of the machinery employed, and of the principles of its construction. Following this memoir, I shall therefore attempt to give as popular a description of the automaton as can 202 LETTERS ON NATURAL MAGIC. be done without lengthened details and numerous figures. The body of the flute-player was about 5 J feet high, and was placed upon apiece of rock, surround- ing a square pedestal 4^ feet high by three and a half wide. When the panel which formed the front of the pedestal was opened, there was seen on the right a clock movement, which, by the aid of several wheels, gave a rotatory motion to a steel axis about 2-|- feet long, having cranks at six equi- distant points of its length, but lying in different directions. To each crank was attached a cord, which descended and was fixed by its other end to the upper board of a pair of bellows, 2-^ feet long and six inches wide. Six pair of bellows arranged along the bottom of the pedestal were then wrought , or made to blow in succession, by turning the steel axis. At the upper face of the pedestal, and upon each pair of bellows, is a double pulley, one of whose rims is 3 inches in diameter, and the other 11. The cord which proceeds from the crank coils round the smallest of these pulleys, and that which is fixed to the upper board of the bellows goes round the larger pulley. By this means the upper board of the bellows is made to rise higher than if the cords went directly from them to the cranks. Round the larger rims of three of these pulleys, viz. those on the right hand, there are coiled three cords, which, by means of several smaller pulleys, terminate in the upper boards of other three pair of bellows placed on the top of the box. The tension of each cord when it begins to raise the board of the bellows to which it is attached, vaucanson's flute-player. 203 gives motion to a lever placed above it between the axis and the double pulley in the middle and lower region of the box. The other end of this lever keeps open the valve in the lower board of the bellows, and allows the air to enter freely, while the upper board is rising to increase the capacity of the bellows. By this means there is not only power gained, in so far as the air gains easier ad- mission through the valve, but the fluttering noise produced by the action of the air upon the valves is entirely avoided, and the nine pair of bellows are wrought with great ease, and without any concus- sion or noise. These nine bellows discharge their wind into three different and separate tubes. Each tube re- ceives the wind of three bellows, the upper boards of one of the three pair being loaded with a weight of four pounds, those of the second three pair with a weight of two pounds, and those of the other three pair with no weight at all. These three tubes ascended through the body of the figure, and ter- minated in three small reservoirs placed in its trunk. These reservoirs were thus united into one, which, ascending into the throat, formed by its en- largement the cavity of the mouth terminated by two small lips, which rested upon the hole of the flute. These lips had the power of opening more or less, and by a particular mechanism, they could advance or recede from the hole in the flute. Within the cavity of the mouth there is a small moveable tongue for opening and shutting the passage for the wind through the lips of the figure. The motions of the fingers, lips, and tongue, of the figure, were produced by means of a revolving 204 LETTERS ON NATURAL MAGIC. cylinder thirty inches long, and twenty-one in dia- meter. By means of pegs and brass staples fixed in fifteen different divisions in its circumference, fifteen different levers, similar to those in a barrel- organ, were raised and depressed. Seven of these regulated the motions of the seven fingers for stop- ping the holes of the flute, which they did by means of steel chains rising through the body and direct- ed by pulleys to the shoulder, elbow, and fingers. Other three of the levers communicating with the valves of the three reservoirs, regulated the ingress of the air, so as to produce a stronger or a weaker tone. Another lever opened the lips so as to give a free passage to the air, and another contracted them for the opposite purpose. A third lever drew them backwards from the orifice of the flute, and a fourth pushed them forward. The remaining lever enabled the tongue to stop up the orifice of the flute. Such is a very brief view of the general mechanism by which the requisite motions of the flute-player were produced. The airs which it played were probably equal to those executed by a living per- former, and its construction, as well as its perfor- mances, continued for many years to delight and astonish the philosophers and musicians of Eu- rope. Encouraged by the success of this machine, M. Vaucanson exhibited in 1741 other automata, which were equally, if not more, admired. One of these was the automaton duck, which performed all the motions of that animal, and not only ate its food, but digested it ; * and the other was his pipe « See Letter XI. vaucanson's pipe and tabor-player. 205 and tabor-player, a piece of mechanism which re- quired all the resources of his fertile genius. Hav- ing* begun this machine before he was aware of its peculiar difficulties, he was often about to abandon it in despair, but his patience and his ingenuity com- bined, enabled him not only to surmount every dif- ficulty, but to construct an automaton which per- formed complete airs, and greatly excelled the most esteemed peformers on the pipe and tabor. The figure stands on a pedestal, and is dressed like a dancing shepherd. He holds in one hand a flageolet, and in the other the stick with which he beats the tambourin as an accompaniment to the airs of the flageolet, about twenty of which it is capable of.performing. The flageolet has only three holes, and the variety of its tones , depends princi- pally on a proper variation of the force of the wind, and on the different degrees with which the orifi- ces are covered. These variations in the force of the wind required to be given with a rapidity which the ear can scarcely follow, and the articulation of the tongue was required for the quickest notes, otherwise the effect was far from agreeable. As the human tongue is not capable of giving the re- quisite articulations to a rapid succession of notes, and generally slurs over one-half of them, the au- tomaton was thus able to excel the best performers, as it played complete airs with articulations of the tongue at every note. In constructing this machine M. Vaucanson ob- served that the flageolet must be a most fatiguing instrument for the human lungs, as the muscles of the chest must make an effort equal to 56 pounds in order to produce the highest notes. A single 206 LETTERS ON NATURAL MAGIC. ounce was sufficient for the lowest notes, so that we may, from this circumstance, form an idea of the variety of intermediate effects required to be produced. While M. Vaucanson was engaged in the con- struction of these wonderful machines, his mind was filled with the strange idea of constructing an automaton containing the whole mechanism of the circulation of the blood. From some birds which he made he was satisfied of its practicability ; but as the whole vascular system required to be made of elastic gum or caoutchouc, it was supposed that it could only be executed in the country where the caoutchouc tree was indigenous. Louis XVI. took a deep interest in the execution of this machine. It was agreed that a skilful anatomist should pro- ceed to Guyana to superintend the construction of the blood-vessels, and the King had not only ap- proved of, but had given orders for, the voyage. Difficulties, however, were thrown in the way : Vaucanson became disgusted, and the scheme was abandoned. The two automata which we have described were purchased by Professor Bayreuss of Helmstadt ; but we have not been able to learn whether or not they still exist. Towards the end of the seventeenth century a bold and almost successful attempt was made to con- struct a talking automaton. In the year 1779, the Imperial Academy of Sciences at St Petersburgh proposed as the subject of one of their annual prizes an inquiry into the nature of the vowel sounds, A, E, I, O and U, and the construction of an instru- ment for artificially imitating them. This prize was kempelen's talking engine. 207 gained by M. Kratzenstein, who showed that all the vowels could be distinctly pronounced by blow- ing- through a reed into the lower ends of the pipes of the annexed figures, as shown in Fig. 47, where the corresponding vowels are marked on the diffe- Fig. 47. rent pipes. The vowel I is pronounced by merely blowing into the pipe a b, of the pipe marked I, without the use of a reed. About the same time that Kratzenstein was en- gaged in these researches, M. Kempelen of Vienna, a celebrated mechanician, was occupied with the same subject. In his first attempt he produced the vowel sounds, by adapting a reed R, Fig. 48, to the bot- tom of a funnel-shaped cavity A B, and placing his hand in various positions within the funnel. This contrivance, however, was not fitted for his purpose, but after long study, and a diligent examination of the organs of speech, he contrived a hollow oval box, divided into two portions attached by a hinge as so to resemble jaws. This box received the sound which issued from the tube connected with the reed, and by opening and closing the jaws, he produced the sounds, A, O, O U, and an imperfect 208 LETTERS ON NATURAL MAGIC. E, but no indications of an I. After two years la- bour he succeeded in obtaining from different jaws Fig. 48. \ \ Pv the sounds of the consonants P, M, L, and by means of these vowels, and consonants, he could compose syllables and words, such as mama, papa, aula, lama, mulo. The sounds of two adjacent letters, however, run into each other, and an aspira- tion followed some of the consonants, so that in- stead of papa the word sounded phaa-ph-a ; these difficulties he contrived with much labour to sur- mount, and he found it necessary to imitate the human organs of speech by having only one mouth and one glottis. The mouth consisted of a funnel or bell-shaped piece of elastic gum, which approxi- mated, by its physical properties, to the softness and flexibility of the human organs.* To the mouth-piece was added a nose made of two tin * Had M. Kempelen known the modern discovery of giving caoutchouc any degree of softness, by mixing it with molasses or sugar, which is always absorbing moisture from the atmosphere, he might have obtained a still more perfect imitation of the human organs. kempelen's talking engine. 209 tubes, which communicated with the mouth. When both these tubes were open, and the mouth-piece closed, a perfect M was produced, and when one was closed and the other open, an N was sounded. M. Kempelen could have succeeded in obtaining the four letters D, G, K, T, but by using a P in- stead of them, and modifying the sound in a parti- cular manner, he contrived to deceive the ear by a tolerable resemblance of these letters. There seems to be no doubt that he at last was able to produce entire words, and sentences such as, opera, astronomy, Constantinopolis, vous etes mon ami, je vous aime de tout mon cwur, venez avec moi a Paris, Leopoldus secundus, Romano- rum imperator semper Augustus, fyc. but he never fitted up a speaking figure, and probably, from be- ing dissatisfied with the general result of his la- bours, he exhibited only to his private friends the effects of the apparatus, which was fitted up in the form of a box. This box was rectangular, and about three feet long, and was placed upon a table and covered with a cloth. When any particular word was mention- ed by the company, M. Kempelen caused the ma- chine to pronounce it, by introducing his hands be- neath the cloth, and apparently giving motion to some parts of the apparatus. Mr Thomas Collin- son, who had seen this machine in London, men- tions in a letter to Dr Hutton, that he afterwards saw it at M. Kempelen's own house in Vienna, and that he then gave it the same word to be pronoun- ced, which he gave it in London, viz. the word Ex- ploitation, which, he assures us, it again distinctly pronounced with the French accent. o 210 LETTERS ON NATURAL MAGIC. M. Kratzenstein seems to have been equally un- successful, for though he assured M. De Lalande, when he saw him in Paris in 1786, that he had made a machine which could speak pretty well, and though he showed him some of the apparatus by which it could sound the vowels, and even such syllables as papa and mama, yet there is no reason to believe that he had accomplished more than this. The labours of Kratzenstein and Kempelen have been recently pursued with great success by our ingenious countryman Mr Willis of Cambridge. In repeating Kempelen's experiment shown in Fig. 48, he used a shallower cavity, such as that in Fig. 49, and found that he could entirely dispense with the introduction of the hand, and could obtain the Fig. 49. whole series of vowels, by sliding a flat board C D over the mouth of the cavity. Mr Willis then conceived the idea of adapting to the reed cylindri- cal tubes, whose length could be varied by sliding joints. When the tube was greatly less than the length of a stopped pipe in unison with the reed, it sounded I, and by increasing the length of the tube it gave E, A, O and U in succession. But what Willis's vowel machine. 211. was very unexpected, when the tube was so much lengthened as to be 1^ times the length of a stopped pipe in unison with the reed, the vowels began to be again sounded in an inverted order, viz. U, O, A, E, and then again in a direct order, I, E, A, O, U, when the length of the tube was equal to twice that of a stopped pipe, in unison with the reed. Some important discoveries have been recently made by M. Savart respecting the mechanism of the human voice,* and we have no doubt that, be- fore another century is completed, a Talking and a Singing machine will be numbered among the con- quests of Science. * See Edinburgh Journal of Science, No. viii. p. 200, 212 LETTERS ON NATURAL MAGIC. LETTER IX. Singular effects in nature depending on sound — Permanent character of speech — Influence of great elevations on the character of sounds, and on the powers of speech — Power of sound in throwing down buildings — Dog killed by sound — Sounds greatly changed under particular circumstances — Great audibility of sounds during the night explained — Sounds deadened in media of different densities — Illustrated in the case of a glass of champagne — and in that of new fal- len snow — Remarkable echoes — Reverberations of thunder — Subterranean ?ioiscs — Remarkable one at the Solfaterra — Echo at the Menai Suspension bridge — Temporary deaf ness produced in diving bells — Inaudibility of particular sounds to particular ears — Vocal powers of the statue of Memnon — Sounds in granite rocks — Musical mountain of El-Nakous ALTHOUGHamongthephenomenaof the material world there is scarcely one, which, when well con- sidered, is not an object of wonder, yet those which we have been accustomed to witness from our infancy lose all their interest from the frequency of their occurrence, while to the natives of other countries they are unceasing- objects of astonishment and de- light. The inhabitant of a tropical climate is confounded at the sight of falling- snow, and he al- most discredits the evidence of his senses, when he sees a frozen river carrying- loaded wag-g-ons on PERMANENT CHARACTER OF SPEECH. 213 its surface. The diffusion of knowledge by books, as well as by frequent communication between the natives of different quarters of the globe, have de- prived this class of local wonders of their influence, and the Indian and the Scandinavian can visit each other's lands without any violent excitement of surprise. Still, however, there are phenomena of rare occurrence, of which no description can convey the idea, and which continue to be as deeply mark- ed with the marvellous as if they had been previ- ously unknown. Among these we may rank the remarkable modifications which sound undergoes in particular situations and under particular cir- cumstances. In the ordinary intercourse of life, we recognize individuals as much by their voice as by the fea- tures of their face and the form of their body. A friend who has been long absent will often stand before us as a stranger, till his voice supplies us with the full power of recognition. The brand imprinted by time on his outer form may have effaced the youthful image which the memory had che- rished, but the original character of his voice and its yet remembered tones will remain unim- paired. An old friend with a new face is not more common in its moral than in its physical acceptation, and though the sagacity of proverbial wisdom has not sup- plied us with the counterpart in relation to the human voice, yet the influence of its immutability over the mind has been recorded by the poet in some of his most powerful conceptions. When Manfred was unable to recognize in the hectic phantom of As- tarte the endeared lineaments of the being whom 214 LETTERS ON NATURAL MAGIC. he loved, the mere utterance of his name recalled " the voice which was his music," and invested her with the desired reality. Say on, say on — I live but in the Sound — It is thy voice ! Bvrox, The permanence of character thus impressed upon speech exists only in those regions to whose atmosphere our vocal organs are adapted. If either the speaker or the hearer is placed in air differing greatly in density from that to which they are accustomed, the voice of the one will emit different sounds, or the same sounds will produce a different impression on the ear of the other. But if both parties are placed in this new atmo- sphere, their tones of communication will suffer the most remarkable change. The two extreme posi- tions, where such effects become sufficiently strik- ing, are in the compressed air of the diving' bell, when it is immersed to a great depth in the sea, 01 in the rarefied atmosphere which prevails on the summit of the Himalaya or the Andes. In the region of common life, and even at the stillest hour of night, the ear seldom rests from its toils. When the voice of man and the bustle of his labours have ceased, the sounds of insect life are redoubled^ the night breeze awakens among the rustling leaves, and the swell of the distant ocean, and the sounds of the falling cataract or of the mur- muring brook, fill the air with their pure and so- lemn music. The sublimity of deep silence is not to be found even in the steppes of the Volga, or in the forests' of the Orinoco. It can be felt only in those lofty regions INFLUENCE OF ELEVATION ON SOUNDS. 215 Where the tops of the Andes Shoot soaringly forth. As the traveller rises above the limit of life and motion, and enters the region of habitual solitude, the death-like silence which prevails around him is rendered still more striking by the diminished den- sity of the air which he breathes. The voice of his fellow traveller ceases to be heard even at a moderate distance, and sounds which would stun the ear at a lower level make but a feeble impression. The report of a pistol on the top of Mont Blanc is no louder than that of an Indian cracker. But while the thinness of the air thus subdues the loudest sounds, the voice itself undergoes a singular change : the muscular energy by which we speak experien- ces a great diminution, and our powers of utterance, as well as our power of hearing, are thus singular- ly modified. W ere the magician, therefore, who is desirous to impress upon his victim or upon his pupil the conviction of his supernatural power, to carry him, under the injunction of silence, to breathe The difficult air of the iced mountain's top, Where the birds dare not build, nor insects wing Flit o'er the herbless granite, he would experience little difficulty in arresting his power over the elements, and still less in sub- sequently communicating the same influence to his companion. But though the air at the tops of our highest mountains is scarcely capable of transmitting sounds of ordinary intensity, yet sounds of extraordinary power force their way through its most attenuat- ed strata. At elevations where the air is three thou- 216 LETTERS ON NATURAL MAGIC. sand times more rare than that which we breathe, the explosion of meteors is heard like the sound of cannon on the surface of the earth, and the whole air is often violently agitated by the sound. This fact alone may give us some idea of the tremendous nature of the forces which such explosions create, and it is fortunate for our species, that they are confined to the upper regions of the atmosphere. If the same explosions were to take place in the dense air which rests upon the earth, our habitations and our lives would be exposed to the most immi- nent peril. Buildings have often been thrown down by vio- lent concussions of the air, occasioned either by the sound of great guns, or by loud thunder, and the most serious effects upon human and animal life have been produced by the same cause. Most per- sons have experienced the stunning pain produced in the ear, when placed near a cannon that is dis- charged. Deafness has frequently been the result of such sudden concussions, and if we may reason from analogy, death itself must often have been the consequence. When peace was proclaimed in Lon- don in 1697, two troops of horse were dismounted and drawn up in line in order to fire their vollies. Opposite the centre of the line was the door of a butcher's shop, where there was a large mastiff dog of great courage. This dog was sleeping by the fire, but when the first volley was fired, it imme- diately started up, ran into another room, and hid itself under a bed. On the firing of the second volley, the dog rose, run several times about the room trembling violently and apparently in great agony. When the third volley was fired, the dog INFLUENCE OF ELEVATION ON SOUNDS. 217 ran about once or twice with great violence, and instantly fell down dead, throwing- up blood from his mouth and nose. Sounds of known character and intensity are often singularly changed even at the surface of the earth according- to the state of the ground and the conditions of the clouds. On the extended heath, where there are no solid objects capable of reflecting or modifying sound, the sportsman must frequently have noticed the unaccountable variety of sounds which are produced by the report of his fowling--piece. Sometimes they are flat and prolong ed, at other times short and sharp, and sometimes the noise is so strange that it is referred to some mistake in the loading of the gun. These variations, however, arise entirely from the state of the air, and from the nature and proximity of the superjacent clouds. In pure air of uniform density the sound is sharp and soon over, as the undulations of the air advance without any interrupting obstacles. In a foggy atmosphere, or where the vapours produced by heat are seen dan- cing as it were in the air, the sound is dull and pro- longed, and when these clouds are immediately over head, a succession of echoes from them produces a continued or a reverberating sound. When the French astronomers were determining the velocity of sound by firing great guns, they observed that the report was always single and sharp under a perfectly clear sky, but indistinct, and attended by a long continued roll like thunder, when a cloud covered a considerable part of the horizon. It is no doubt owing to the same cause, namely, the reflexion from the clouds, that the thunder rolls through the 218 LETTERS ON NATURAL MAGIC. heavens, as if it were produced by a succession of electric explosions. The great audibility of sounds during- the night is a phenomenon of considerable interest, and one which had been observed even by the ancients. In crowded cities or in their vicinity, the effect was ge- nerally ascribed to the rest of animated beings, while in localities where such an explanation was inappli- cable, it was supposed to arise from a favourable direc- tion of the prevailing wind. Baron Humboldt was particularly struck with this phenomenon when he first heard the rushing of the great cataracts of the Ori- noco in the plain which surrounds the mission of the Apures. These sounds he regarded as three times louder during the night than during the day. Some authors ascribed this fact to the cessation of the hum- ming of insects, the singing of birds, and the action of the wind on the leaves of the trees, but M. Humboldt justly maintains that this cannot be the cause of it on the Orinoco, where the buzz of insects is much louder in the night than in the day, and where the breeze never rises till after sunset. Hence he was led to ascribe the phenomenon to the perfect transparency and uniform density of the air, which can exist only at night after the heat of the ground has been uniformly diffused through the atmo- sphere. When the rays of the sun have been beating on the ground during the day, currents of hot air of different temperatures, and consequent- ly of different densities, are constantly ascending from the ground and mixing with the cold air above. The air thus ceases to be a homogeneous medium, and every person must have observed the effects of it upon objects seen through it which SOUNDS DURING THE NIGHT. 219 are very indistinctly visible, and have a tremulous motion, as if they were " dancing in the air." The very same effect is perceived when we look at objects through spirits and water that are not perfectly mixed, or when we view distant objects over a red hot poker or over a flame. In all these cases the light suffers refraction in passing from a medium of one density into a medium of a different density, and the refracted rays are constantly changing their direction as the different currents rise in succes- sion. Analogous effects are produced when sound passes through a mixed medium, whether it con- sists of two different mediums or of one medium where portions of it have different densities. As sound moves with different velocities through me- dia of different densities, the wave which produces the sound will be partly reflected in passing from one medium to the other, and the direction of the transmitted wave changed; and hence in passing through such media different portions of the wave will reach the ear at different times, and thus de- stroy the sharpness and distinctness of the sound. This may be proved by many striking facts. If we put a bell in a receiver containing a mixture of hydrogen gas and atmospheric air, the sound of the bell can scarcely be heard. During a shower of rain or of snow, noises are greatly deadened, and when sound is transmitted along an iron wire or an iron pipe of sufficient length, we actually hear two sounds, one transmitted more rapidly through the solid, and the other more slowly through the air. The same property is well illustrated by an elegant and easily repeated experiment of Chladni's. When spark- ling champagne is poured into a tall glass till it is 220 LETTERS ON NATURAL MAGIC. half full, the glass loses its power of ringing by a stroke upon its edge, and emits only a disagreeable and puffy sound. This effect will continue while the wine is filled with bubbles of air, or as long as the effervescence lasts ; but when the effervescence begins to subside, the sound becomes clearer and clearer, and the glass rings as usual when the air- bubbles have vanished. If we reproduce the effer- vescence by stirring the champagne with a piece of bread the glass will again cease to ring. The same experiment will succeed with other efferves- cing fluids. The difference in the audibility of sounds that pass over homogeneous and over mixed media is sometimes so remarkable as to astonish those who witness it. The following fact is given on the evi- dence of an officer who observed it : When the British and the American forces were encamped on each side of a river, the outposts were so near that the form of individuals could be easily distinguish- ed. An American drummer made his appearance and began to beat his drum, but though the mo- tion of his arms were distinctly seen, not a single sound reached the ear of the observer. A coating of snow that had newly fallen upon the ground, and the thickness of the atmosphere, had conspired to obstruct the sound. An effect the very reverse of this is produced by a coating of glazed or hardened snow, or by an extended surface of ice or water. Lieutenant Foster was able to carry on a conversa- tion with a sailor across Port Bowen harbour, a distance of no less than a mile and a quarter, and the sound of great guns has been heard at distan- ces varying from 120 to 200 miles. Over hard REMARKABLE ECHOES. 221 and dry ground of an uniform character, or where a thin soil rests upon a continuous stratum of rock, the sound is heard at a great distance, and hence it is the practice among many eastern tribes to ascer- tain the approach of an enemy by applying the ear to the ground. Many remarkable phenomena in the natural world are produced by the reflexion and concentra- tion of sound. Every person is familiar with the ordinary Echo which arises from the reflexion of sound from an even surface, such as the face of a wall, of a house, of a rock, of a hill, or of a cloud. As sound moves at the rate of 1090 feet in a se- cond, and as the sound which returns to the per- son who emits it has travelled over a space equal to twice his distance from the reflecting surface, the distance in feet of the body which occasions the echo may be readily found by multiplying 545 by the number of seconds which elapse between the emission of the sound and its return in the form of an echo. This kind of echo, where the same person is the speaker and the hearer, never takes place unless when the observer is immediately in front of the reflecting surface, or when a line drawn from his mouth to the flat surface is nearly per- pendicular to it, because in this case alone the wave of sound is reflected in the very same direction from the wall in which it reaches it. If the speaker places himself on one side of this line, then the echo will be heard most distinctly by another per- son as far on the other side of it, because the waves of sound are reflected like light, so that the angle of incidence or the inclination at which the sound falls upon the reflected surface is equal 222 LETTERS ON NATURAL MAGIC. to the angle of reflexion, or the inclination at which the sound is returned from the wall. If two persons, therefore, are placed before the reflecting wall, the one will hear the echo of the sound emit- ted by the other, and obstacles may intervene be- tween these two persons so that neither of them hears the direct sound emitted by the other ; in the same manner as the same persons similarly placed before a looking-glass would see each other distinct- ly by reflexion, though objects might obstruct their direct view of each other. Hitherto we have supposed that there is only one reflecting surface, in which case there will be only one echo : but if there are several reflecting surfaces, as is the case in an amphitheatre of moun- tains, or during a thunder-storm, where there are several strata or masses of clouds ; or if there are two parallel or inclined surfaces between which the sound can be repeatedly reflected, or if the surface is curved so that the sound reflected from one part falls upon another part, like the sides of a polygon inscribed in a circle, — in all these cases there will be numerous echoes, which produce a very singu- lar effect. Nothing can be more grand and su- blime than the primary and secondary echoes of a piece of ordnance discharged in an amphitheatre of precipitous mountains. The direct or pri- mary echoes from each reflecting surface reach the ear in succession, according to their different dis- tances, and these are either blended with or suc- ceeded by the secondary echoes, which termi- nate in a prolonged growl ending in absolute silence. Of the same character are the rever- berated claps of a thunder-bolt reflected from the 4 REMARKABLE ECHOES. 223 surrounding- clouds, and dying away in the distance. The echo which is produced by parallel walls is finely illustrated at the Marquis of Simonetta's villa near Milan, which has been described by Addi- son and Keysler, and which we believe is that de- scribed by Mr Southwell in the Philosophical Tran- sactions for 1746. Perpendicular to the main body of this villa there extends two parallel wings about fifty-eight paces distant from each other, and the surfaces of which are unbroken either with doors or windows. The sound of the human voice, or rather a word quickly pronounced, is repeated above forty times, and the report of a pistol from fifty-six to sixty times. The repetitions, however, follow in such rapid succession that it is difficult to reckon them, unless early in the morning- before the equal temperature of the atmosphere is disturbed, or in a calm still evening-. The echoes appear to be best heard from a window in the main building- between the two projecting- walls, from which the pistol also is fired. Dr Plot mentions an echo in Woodstock Park which repeats seventeen syllables by day and twenty by night. An echo on the north side of Shipley church in Sussex repeats twenty-one sylla- bles. Sir John Herschel mentions an echo in the Manfroni palace at Venice, where a person standing- in the centre of a square room about twenty-five feet high with a concave roof, hears the stamp of his foot repeated a great many times, but as his position de- viates from the centre, the echoes become feebler, and at a short distance entirely cease. The same phenomenon, he remarks, occurs in the large room of the library of the museum at Naples. M. Gene- ay has described as existing- near Rouen a curious 224 LETTERS ON NATURAL MAGIC. oblique echo which is not heard by the person who emits the sound. A person who sings hears only his own voice, while those who listen hear only the echo, which sometimes seems to approach, and at other times to recede from the ear ; one person hears a single sound, another several sounds, and one hears it on the right and another on the left, the effect always changing, as the hearer changes his position. Dr Birch has described an extra- ordinary echo at Roseneath in Argyleshire, which certainly does not now exist. When eight or ten notes were played upon a trumpet they were cor- rectly repeated, but on* a key a third lower. After a short pause another repetition of the notes was heard in a still lower tone, and after another short interval they were repeated in a still lower tone. In the same manner as light is always lost by reflexion, so the waves of sound are enfeebled by reflexion from ordinary surfaces, and the echo is in such cases fainter than the original sound. If the reflecting surface, however, is circular, sound may be condensed and rendered stronger in the same manner as light. I have seen a fine ex- ample of this, in the circular turn of a garden wall nearly a mile distant from a weir across a river. When the air is pure and homogeneous, the rushing sound of the water is reflected from the hollow surface of the wall, and concentrated in a focus, the place of which the ear can easily discover from the intensity of the sound being there a maximum. A person not acquainted with the lo- cality conceives that the rushing noise is on the other side of the wall. In Whispering Galleries, or places where the low- WHISPERING GALLERY. 225 est whispers are carried to distances at which the direct sound is inaudible, the sound may be con- veyed in two ways, either by repeated reflexions from a curved surface in the direction of the sides of a polygon inscribed in a circle, or where the whisperer is in the focus of one reflecting- surface, and the hearer in the focus of another reflecting- surface, which is placed so as to receive the reflect- ed sounds. The first of these ways is exemplified in the whispering* gallery of St Paul's, and in the octagonal gallery of Gloucester Cathedral, which conveys a whisper 75 feet across the nave, and the second in the baptistery of a church in Pisa, where the architect Giovanni Pisano is said to have con- structed the cupola on purpose. The cupola has an elliptical form, and when one person whispers in one focus, it is distinctly heard by the person placed in the other focus, but not by those who are placed between them. The sound first reflected passes across the cupola, and enters the ears of the intermediate persons, but it is too feeble to be heard, till it has been condensed by a second reflexion to the other focus of ellipse. A naval officer, who travelled through Sicily in the year 1824, gives an account of a powerful whispering place in the ca- thedral of Girgenti, where the slightest whisper is carried with perfect distinctness through a distance of 250 feet, from the great western door to the cornice behind the high altar. By an unfortunate coincidence the focus of one of the reflecting sur- faces was chosen for the place of the confessional, and when this was accidentally discovered, the lovers of secrets resorted to the other focus, and thus became acquainted with confessions of the r 226 LETTERS ON NATURAL MAGIC. gravest import. This divulgence of scandal con- tinued for a considerable time, till the eager curi- osity of one of the dilettanti was punished, by hear- ing his wife's avowal of her own infidelity. This circumstance gave publicity to the whispering pe- culiarity of the cathedral, and the confessional was removed to a place of greater secrecy. An echo of a very peculiar character has been de- scribed by Sir John Herschel in his Treatise on Sound, as produced by the suspension bridge across the Menai strait in Wales. " The sound of a blow with a hammer," says he, " on one of the main piers, is returned in succession from each of t he cross beams which support the road- way, and from the opposite pier at a distance of 576 feet ; and in addition to this, the sound is many times repeated between the water and the road-way. The effect is a series of sounds which may be thus written : the first re- Fig. 50. fffffffif r unim turn is sharp and strong from the road-way over- head ; the rattling which succeeds dies away rapid- ly, but the single repercussion from the opposite pier is very strong, and is succeeded by a faint pal- pitation repeating the sound at the rate of twenty- eight times in five seconds, and which, therefore, corresponds to a distance of 184 feet, or very near- ly the double interval from the road-way to the water. Thus it appears that in the repercussion SUBTERRANEAN ECHO. 22? between the water and road-way that from the lat- ter only affects the ear, the line drawn from the auditor to the water being- too oblique for the sound to diverge sufficiently in that direction. An- other peculiarity deserves especial notice, namely, that the echo from the opposite pier is best heard when the auditor stands precisely opposite to the middle of the breadth of the pier, and strikes just on that point. As it deviates to one or the other side, the return is proportionally fainter, and is scarcely heard by him when his station is a little beyond the extreme edge of the pier, though an- other person, stationed (on the same side of the water) at an equal distance from the central point, so as to have the pier between them, hears it well." A remarkable subterranean echo is often heard when the hoofs of a horse or the wheels of a carriage pass over particular spots of ground. This sound is frequently very similar to that which is produ- ced in passing over an arch or vault, and is com- monly attributed to the existence of natural or ar- tificial caves beneath. As such caves have often been constructed in times of war as places of securi- ty for persons and property, many unavailing at- tempts have been made to discover hidden trea- sures where their locality seemed to be indicated by subterraneous sounds. But though these sounds are sometimes produced by excavations in the ground, yet they generally arise from the nature of the materials of which the ground is composed, and from their manner of combination. If the hol- low of a road has been filled up with broken rock, or with large water- worn stones, having hollows ei- ther left entirely empty, or filled up with materials 228 LETTERS ON NATURAL MAGIC. of different density, then the sound will be reflect- ed in passing from the loose to the dense materials, and there will arise a great number of echoes reach- ing- the ear in rapid succession, and forming- by their union a hollow rumbling- sound. This prin- ciple has been very successfully applied by Sir John Herschel to explain the subterranean sounds with which every traveller is familiar who has visited the Solfaterra near Naples. When the ground at a particular place is struck violently by throwing a large stone against it, a peculiar hollow sound is distinctly heard. This sound has been ascribed by some geologists to the existence of a great vault communicating with the ancient seat of the volca- no, by other writers to a reverberation from the surrounding hills with which it is nearly concen- tric, and by others to the porosity of the ground. Dr Daubeny, who says that the hollow sound is heard when any part of the Solfaterra is struck, ac- counts for it by supposing that the hill is not made up of one entire rock, but of a number of de- tached blocks, which, hanging as it were by each other, form a sort of vault over the abyss within which the volcanic operations are going on.* Mr Forbes, who has given the latest and most interest- ing description of this singular volcano,-)- agrees in opinion with Dr Daubeny, while Mr ScropeJ and Sir John Herschel concur in opinion that no such cavities exist. " It seems most probable," says the latter," that the hollow reverberation is nothing more * Description of Volcanoes, p. 1 70. f Edinburgh Journal of Science, N. Series, No. i. p. 124. | Considerations on Volcanoes, and Edinburgh Journal of Science, No. xx. p. 261, and No. xiv. p. 265. MOMENTARY DEAFNESS. 229 than an assemblage of partial echoes arising- from the reflexion of successive portions of the original sound in its progress through the soil at the in- numerable half-coherent surfaces composing it : were the whole soil a mass of sand, these reflex- ions would be so strong and frequent as to destroy the whole impulse, in too short an interval to al- low of a distinguishable after sound. It is a case analogous to that of a strong* light, thrown into a milky medium or smoky atmosphere ; the whole medium appears to shine with a nebulous undefin- ed light. This is to the eye what such a hollow sound is to the ear." * It has been recently shown by M. Savart, that the human ear is so extremely sensible as to be ca- pable of appreciating sounds which arise from about twenty-four thousand vibrations in a second, and consequently, that it can hear a sound which lasts only the twenty-four thousandth part of a second. Vibrations of such frequency afford only a shrill squeak or chirp ; and Dr Wollaston has shown that there are many individuals with their sense of hear- ing entire, who are altogether insensible to such acute sounds, though others are painfully affected by them. Nothing, as Sir John Herschel remarks, can be more surprising than to see two persons, neither of them deaf, the one complaining of the penetrat- ing shrillness of a sound, while the other maintains there is no sound at all. Dr Wollaston has also shown that this is true also of very grave sounds, so that the hearing or not hearing of musical notes at both extremities of the scale seems to depend wholly on the pitch or frequency of vibration con- * Art. Sound, Encycl. Metrop. § 110. 230 LETTERS ON NATURAL MAGIC. stituting the note, and not upon the intensity or loudness of the noise. This affection of the ear sometimes appears in cases of common deafness, where a shrill tone of voice, such as that of women and children, is often better heard than the loud and deeper tone of men. Dr Wollaston remarked, that when the mouth and nose are shut, the tympanum or drum of the ear may be so exhausted by a forcible attempt to take breath by the expansion of the chest, the pressure of the external air upon the membrane gives it such a tension that the ear becomes insen- sible to grave tones, without losing in any degree the perception of sharper sounds. Dr Wollaston found, that after he had got into the habit of mak- ing the experiment, so as to be able to produce a great degree of exhaustion, his ears were insensible to all sounds below F, marked by the base cliff. " If I strike the table before me," says he, "with the end of my finger, the whole board sounds with a deep dull note. If I strike it with my nail, there is also at the same time a sharp sound produced by quicker vibrations of parts around the point of con- tact. When the ear is exhausted it hears only the latter sound, without perceiving in any degree the deeper note of the whole table. In the same man- ner, in listening to the sound of a carriage, the deeper rumbling noise of the body is no longer heard by an exhausted ear ; but the rattle of a chain or loose screw remains at least as audible as before exhaustion." Dr Wollaston supposes that this ex- cessive tension of the drum of the ear, when pro- duced by the compressed air in the diving-bell, will also produce a corresponding deafness to low tones, DEAFNESS PRODUCED IN DIVING BELLS. 231 This curious experiment has been since made, by Dr Colladon when descending- in the diving-bell at Howth in 1 820. " We descended," says he, " so slow- ly that we did not notice the motion of the bell ; but as soon as the bell was immersed in water, we felt about the ears and the forehead a sense of pres- sure, which continued increasing- during- some mi- nutes. I did not, however, experience any pain in the ears ; but my companion suffered so much that we were obliged to stop our descent for a short time. To remedy that inconvenience, the work- men instructed us, after having- closed our nostrils and mouth, to endeavour to swallow, and to restrain our respiration for some moments, in order that, by this exertion, the internal air might act on the Eustachian tube. My companion, however, hav- ing tried it, found himself very little relieved by this remedy. After some minutes, we resumed our descent. My friend suffered considerably; he v/as pale ; his lips were totally discoloured ; his ap- pearance was that of a man on the point of faint- ing ; he was in involuntary low spirits, owing, per- haps, to the violence of the pain, added to that kind of apprehension which our situation unavoid- ably inspired. This appeared to me the more re- markable, as my case was totally the reverse. I was in a state of excitement resembling the effect of some spirituous liquor. I suffered no pain ; I expe- rienced only a strong pressure round my head, as if an iron circle had been bound about it. I spoke with the workmen and had some difficulty in hear- ing them. This difficulty of hearing rose to such a height, that during three or four minutes I could not hear them speak. I could not, indeed, hear 232 LETTERS ON NATURAL MAGIC. myself speak, though I spoke as loudly as possible ; nor did even the great noise caused by the violence of the current against the sides of the bell reach my ears." The effect thus described by Dr Colladon is dif- ferent from that anticipated by Dr Wollaston. He was not merely deaf to low tones but to all sounds whatever ; and I have found by repeated experi- ment, that my own ears become perfectly insensible even to the shrill tones of the female voice, and of the voice of a child, when the drum of the ear is thrown into a state of tension by yawning. With regard to sounds of high pitch at the other extremity of the scale, Dr Wollaston has met with persons, whose hearing was in other respects per- fect, who never heard the chirping of the Gryllus campestris, which commonly occurs in hedges dur- ing a summer's evening, or that of the house-cricket, or the squeak of the bat, or the chirping of the common house-sparrow. The note of the bat is a full octave higher than that of the sparrow; and Dr Wollaston believes that the note of some in- sects may reach one octave more, as there are sounds decidedly higher than that of a small pipe, one-fourth of an inch in length, which he conceives cannot be far from six octaves above the middle E of the piano-forte. " The suddenness of the tran- sition," says Dr Wollaston, " from perfect hearing to total want of perception, occasions a degree of sur- prise, which renders an experiment on this subject with a series of small pipes among several persons rather amusing. It is curious to observe the change of feeling manifested by various individuals of the party, in succession, as the sounds approach and INAUDIBILITY OF CERTAIN SOUNDS. 233 pass the limits of their hearing. Those who enjoy a temporary triumph are often compelled in their turn to acknowledge to how short a distance their little superiority extends." In concluding his interesting paper on this subject, Dr Wollaston conjectures that animals, like the grylli, (whose powers of hearing appear to commence nearly where ours terminate,) may have the power of hearing still sharper sounds which at present we do not know to exist, and that there may be other insects having nothing in common with us, but who are endowed with a power of exciting, and a sense of perceiving vibrations which makes no im- pression upon our organs, while their organs are equally insensible to the slower vibrations to which we are accustomed. With the view of studying the class of sounds inaudible to certain ears, we would recommend it to the young naturalist to examine the sounds emit- ted by the insect tribe, both in relation to their ef- fect upon the human ear, and to the mechanism by which they are produced. The Cicadse or locusts in North America appear, from the observations of Dr Hildreth,* to be furnished with a bag-pipe on which they play a variety of notes. " When any one passes," says he, " they make a great noise and screaming with their air bladder or bagpipes. These bags are placed under, and rather behind, the wings in the axilla, something in the manner of using the bagpipes with the bags under the arms, — I could compare them to nothing else ; and, indeed, I sus- pect the first inventor of the instrument borrowed his ideas from some insect of this kind. They play * Edinburgh Journal of Science, No. xvii. p. 158. 234 LETTERS ON NATURAL MAGIC. a variety of notes and sounds, one of which nearly imitates the scream of the tree toad." Among the acoustic wonders of the natural world may be ranked the vocal powers of the statue of Memnon, the son of Aurora, which modern disco- veries have withdrawn from among the fables of ancient Egypt. The history of this remarkable statue is involved in much obscurity. Although Strabo affirms that it was overturned by an earth- quake, yet as Egypt exhibits no traces of such a convulsion, it has been generally believed that the statue was mutilated by Cambyses. Ph. Casseli- us, in his dissertation on vocal or speaking stones, quotes the remark of the scholiast in Juvenal, "that, when mutilated by Cambyses, the statue which sa- luted both the sun and the king, afterwards saluted only the sun." Philostratus, in his life of Apollo, informs us, that the statue looked to the east, and that it spoke as soon as the rays of the rising sun fell upon its mouth. Pausanias, who saw the sta- tue in its dismantled state, says that it is a statue of the sun, that the Egyptians call it Phamenophis, and not Mem non, and that it em its sounds every morn- ing at sunrise, which can be compared only to that of the breaking of the string of a lyre. Strabo speaks only of a single sound which he heard ; but Juvenal, who had probably heard it often during his stay in Egypt, describes it as if it emitted se- veral sounds. Dimidio magicse resonant ubi Memnone chorda?. Where broken Memnon sounds his magic strings. The simple sounds which issued from the statue were in the progress of time magnified into intel- ligible words, and even into an oracle of seven VOCAL STATUE OF MEM N ON. 235 verses, and this prodigy has been recorded in a Greek inscription on the left leg- of the statue. But though this new faculty of the colossus was evi- dently the contrivance of the Egyptian priests, yet we are not entitled from this to call in question the simple and perfectly credible fact that it emit- ted sounds. This property, indeed, it seems to possess at the present day; for we learn,* that an English traveller, Sir A. Smith, accompanied with a numerous escort, examined the statue, and that at six o'clock in the morning he heard very dis- tinctly the sounds which had been so celebrated in antiquity. He asserts that this sound does not proceed from the statue but from the pedestal; and he expresses his belief that it arises from the im- pulse of the air upon the stones of the pedestal, which are arranged so as to produce this surprising effect. — This singular description is to a certain ex- tent confirmed by the description of Strabo, who says, that he was quite certain that he heard a sound which proceeded either from the base, or from the colossus, or from some one of the assistants. As there were no Egyptian priests in the escort of Sir A. Smith, we may now safely reject this last, and, for many centuries, the most probable hypothesis. The explanation suggested by Sir A. Smith had been previously given in a more specific form by M. Dussaulx, the translator of Juvenal. " The statue," says he, " being hollow, the heat of the sun heated the air which it contained, and this air, issu- ing at some crevice, produced the sounds of which the priests gave their own interpretation." Rejecting this explanation, M. Langles,in his dis- * Revue Encyclopedique, 1821, Tom. ix. p. 592, 236 LETTERS ON NATURAL MAGIC. sertation on the vocal statue of Memnon, and M. Salverte, in his work on the occult sciences, have as- cribed the sounds entirely to Egyptian priestcraft, and have even gone so far as to describe the me- chanism by which the statue not only emitted sounds, but articulated distinctly the intonations appropriate to the seven Egyptian vowels, and con- secrated to the seven planets. M. Langles conceives that the sounds may be produced by a series of hammers, which strike either the granite itself, or sonorous stones like those which have been long- used in China for musical instruments. M. Salverte im- proves this imperfect apparatus, by supposing* that there might be adapted to these hammers, a clepsydra or water-clock, or any other instrument fitted to measure time, and so constructed as to put the hammers in motion at sunrise. Not satisfied with this supposition, he conjectures that the spring of all this mechanism was to be found in the art of con- centrating the rays of the sun, which was well known to the ancients. Between the lips of the statue, or in some less remarkable part of it concealed from view by its height, he conceives an aperture to be perforated, containing a lens or a mirror capable of condensing the rays of the rising sun upon one or more metallic levers which by their expansion put in motion the seven hammers in succession. Hence he explains why the sounds were emitted only at sunrise, and when the solar rays fell upon the mouth of the statue, and why they were never again heard till the sun returned to the eastern horizon. As a piece of mechanism, this contrivance is defective in not providing for the change in the sun's ampli- tude, which is very considerable even in Egypt, for SOUNDS IN GRANITE ROCKS. 237 as the statue and the lens are both fixed, and as the sounds were heard at all seasons of the year, the same lens which threw the midsummer rays of the sun upon the hammers could not possibly throw upon them his rays in winter. But even if the ma- chinery were perfect, it is obvious that it could not have survived the mutilation of the statue, and could not, short of a miracle, have performed its part in the time of Sir A. Smith. If we abandon the idea of the whole being a trick of the priesthood, which has been generally done, and which the recent observations of Sir A. Smith authorizes us to do, we must seek some na- tural cause for the phenomena similar to that sug- gested by Dussaulx. It is curious to observe how the study of nature gradually dispels the conse- crated delusions of ages, and reduces to the level of ordinary facts what time had invested with all the cha- racters of the supernatural : And in the present case it is no less remarkable that the problem of the statue of Menmon should have been first solved by means of an observation made by a solitary traveller wan- dering on the banks of the Orinoco. " The granitic rock," says Baron Humboldt, " on which we lay, is one of those where travellers on the Orinoco have heard from time to time, towards sunrise, subterraneous sounds resembling those of the organ. The mis- sionaries call these stones loxas de musica, i It is witchcraft,' said our young Indian pilot. We never ourselves heard these mysterious sounds either at Carichana Vieja or in the upper Orinoco; but from information given us by witnesses worthy of belief, the existence of a phenomenon that seems to depend on a certain state of the atmosphere cannot be de- 238 LETTERS ON NATURAL MAGIC. nied. The shelves of rock are full of very narrow and deep crevices. They are heated during- the day to about 50°. I often found their temperature at the surface during* the night at 39°, the surrounding- atmosphere being at 28°. It may easily be con- ceived that the difference of temperature between the subterraneous and the external air attains its maximum about sunrise, or at that moment which is at the same time farther from the period of the maximum of the heat of the preceding- day. May not these sounds of an organ, then, which are heard when a person sleeps upon the rock, his ear in con- tact with the stone, be the effect of a current of air that issues out through the crevices ? Does not the impulse of the air against the elastic spangles of mica that intercept the crevices contribute to mo- dify the sounds ? May we not admit that the an- cient inhabitants of Egypt, in passing incessantly up and down the Nile, had made the same observa- tion on some rock of the Thebaid, and that the music of the rocks there led to the jugglery of the priests in the statue of Memnon ?" This curious case of the production of sounds in granite rocks at sunrise might have been regard- ed as a transatlantic wonder which was not appli- cable to Egypt ; but by a singular coincidence of observation, MM. Jomard, Jollois, and Devilliers, who were travelling in Egypt nearly about the same time that M. Humboldt was traversing the wilds of South America, heard at sunrise, in a monument of granite, situated near the centre of the spot on which the palace of Carnac stands, a noise resembling that of a breaking string, the very expression by which Pausanias characterizes SOUNDS IN GRANITE ROCKS. 239 the sound in the Memnonian granite. The tra- vellers regarded these sounds as arising from the transmission of rarefied air through the crevices of a sonorous stone, and they were of the same opin- ion with Humboldt, that these sounds might have suggested to the Egyptian priests the juggleries of the Memnonium. Is it not strange that the Prus- sian and the French travellers should not have gone a step farther, and solved the problem of two thousand years, by maintaining that the sound of the statue of Memnon was itself a natural phenome- non, or a granite sound elicited at sunrise by the very same causes which operated on the Orinoco and in the Temple of Carnac, in place of regarding it as a trick in imitation of natural sounds ? If, as Humboldt supposes, the ancient inhabitants of Egypt had, in passing incessantly up and down the Nile, become familiar with the music of the granite rocks of the Thebaid, how could the imitation of such natural and familiar sounds be regarded by the priests as a means of deceiving the people ? There could be no- thing marvellous in a colossal statue of granite giving out the very same sounds that were given out at the same time of the day by a granite rock ; and in place of reckoning it a supernatural fact, they could regard it in no other light than as the duplicate of a well known natural phenomenon. It is a mere conjecture, however, that such sounds were common in the Thebaid, and it is therefore probable that a granite rock, possessing the pro- perty of emitting sounds at sunrise, had been dis- covered by the priests, who were at the same time the philosophers of Egypt, and that the block had been employed in the formation of the Memnonian 240 LETTERS ON NATURAL MAGIC. statue for the purpose of impressing upon it a su- pernatural character, and enabling- them to maintain their influence over a credulous people. The inquiries of recent travellers have enabled us to corroborate these views, and to add another remarkable example of the influence of subterra- neous sounds over superstitious minds. About three leagues to the north of Tor in Arabia Petrsea, is a mountain, within the bosom of which the most sin- gular sounds have been heard. The Arabs of the Desert ascribe these sounds to a convent of monks preserved miraculously under ground and the sound is supposed to be that of the Nakous, a long nar- row metallic ruler suspended horizontally, which the priest strikes with a hammer for the purpose of assembling the monks to prayer. A Greek was said to have seen the mountain open, and to have descended into the subterranean convent, where he found fine gardens and delicious water ; and, in or- der to give proof of his descent, he produced some fragments of consecrated bread, which he pretended to have brought from the subterranean convent. The inhabitants of Tor likewise declare that the camels are not only frightened but rendered furi- ous when they hear these subterraneous sounds. M. Seetzen, the first European traveller who visited this extraordinary mountain, set out from Wodyel Nackel on the 17th of June at five o'clock in the morning. He was accompanied by a Greek Christian and some Bedouin Arabs, and after a quarter of an hour's walk they reached the foot of a majestic rock of hard sandstone. The moun- tain itself was quite bare and entirely composed of it. He found inscribed upon the rock several MUSICAL MOUNTAIN OF EL-NAKOUS. 241 Greek and Arab names, and also some Koptic cha- racters, which proved that it had been resorted to for centuries. About noon the party reached the foot of the mountains called JYakous, where at the foot of a ridge they beheld an insulated peaked rock. This mountain presented upon two of its sides two sandy declivities about 150 feet high, and so inclined that the white and slightly adhering sand which rests upon its surface is scarcely able to support itself ; and when the scorching heat of the sun destroys its feeble cohesion, or when it is agitated by the smallest motions, it slides down the two acclivities. These declivities unite . behind the insulated rock, forming an acute angle, and, like the adjacent surfaces, they are covered with steep rocks which consist chiefly of a white and friable freestone. The first sound which greeted the ears of the tra- vellers took place at an hour and a quarter after noon. They had climbed with great difficulty as far as the sandy declivity, a height of seventy or eighty feet, and had rested beneath the rocks where the pilgrims are accustomed to listen to the sounds. While in the act of climbing, M. Seetzen heard the sound from beneath his knees, and hence he was led to think, that the sliding of the sand was the cause of the sound, and not the effect of the vibration which it occasioned. At three o'clock the sound became louder, and continued six minutes, and after having ceased for ten minutes, it was again heard. The sound appeared to have the great- est resemblance to that of the humming top, rising and falling like that of an Eolian harp. Believing Q 242 LETTERS ON NATURAL MAGIC. that he had discovered the true origin of the sound, M. Seetzen was anxious to repeat the experiment, and with this view he climbed with the utmost dif- ficulty to the highest rocks, and, sliding down as fast as he could, he endeavoured, with the help of his hands and feet, to set the sand in motion. The effect thus produced far exceeded his expectations, and the sand in rolling beneath him made so loud a noise that the earth seemed to tremble to such a degree that he states he should certainly have been afraid if he had been ignorant of the cause. M. Seetzen throws out some conjectures respect- ing the cause of these sounds. Does the rolling layer of sand, says he, act like the fiddle-bow, which on being rubbed upon a plate of glass raises and distributes into regular figures the sand with which the plate is covered ? Does the adherent and fixed layer of sand perform here the part of the plate of glass, and the neighbouring rocks that of the sounding body ? We cannot pretend to answer these questions, but we trust that some philoso- pher competent to the task will have an opportu- nity of examining these interesting phenomena with more attention, and describing them with greater accuracy. The only person, so far as I can learn, who has visited El Nakous since the time of Seetzen, is Mr Gray of University College Oxford ; but he has not added much to the information acquired by his predecessor. During the first visit which he made to the place, he heard at the end of a quarter of an hour a low continuous murmuring sound beneath his feet, which gradually changed into pulsations as it became louder, so as to resemble the striking MUSICAL MOUNTAIN OF EL-NAKOUS. 243 of a clock, and at the end of five minutes it became so strong- as to detach the sand. Returning- to the spot next day, he heard the sound still louder than before. He could not observe any crevices by which the external air could penetrate, and as the sky was serene and the air calm, he was satisfied that the sounds could not arise from this cause. * * See Edinburgh Journal of Science, No xi. p. 153, and No. xiii. page 51. M4 LETTERS ON NATURAL MAGIC. LETTER X. Mechanical Inventions of the ancients few in number — Ancient' and modern feats of strength — Feats of Eckeberg particu- larly described — General explanation of them — Real feats of strength performed by Thomas Topham — Remarkable power of lifting heavy persons when the lungs are inflated — ■ BelzoivC s feat of sustaining pyramids of men — Deception of walking along the ceiling in an inverted position — Pneu- matic apparatus in the foot of the house-fly for enabling it to walk in opposition to gravity — Description of the analo- gous apparatus employed by the gecko lizard for the same purpose — Apparatus used by the Echineis remora or suck- ing fish. The mechanical knowledge of the ancients was principally theoretical, and though they seem to have executed some minor pieces of mechanism which were sufficient to delude the ignorant, yet there is no reason for believing, that they have ex- ecuted any machinery that was capable of exciting much surprise, either by its ingenuity or its mag- nitude. The properties of the mechanical powers, however, seem to have been successfully employed in performing feats of strength which were beyond the reach even of strong men, and which could not fail to excite the greatest wonder when exhibited by persons of ordinary size. Firmus, a native of Seleucia, who was executed by the Emperor Aurelian for espousing the cause FEATS OF ECKEBERG. 245 of Zenobia, was celebrated for his feats of strength. In his account of the life of Firmus, who lived in the third century, Vopiscus informs us, that he could suffer iron to be forged upon an anvil placed upon his breast. In doing- this he lay upon his back, and resting* his feet and shoulders against some support, his whole body formed an arch as we shall afterwards more particularly explain. Until the end of the sixteenth century the exhibi- tion of such feats does not seem to have been com- mon. About the year 1703, a native of Kent of the name of Joyce exhibited such feats of strength in London and other parts of England, that he received the name of the second Sampson. His own personal strength was very great ; but he had also discovered without the aid of theory, various positions of his body in which men even of common strength could perform very surprising feats. He drew against horses, and raised enormous weights ; but as he actually exhibited his power in ways which evinced the enormous strength of his own muscles, all his feats were ascribed to the same cause. In the course of eight or ten years, however, his methods were discovered, and many individuals of ordinary strength exhibited a number of his prin- cipal performances, though in a manner greatly in- ferior to Joyce. Sometime afterwards, John Charles Van Ecke- berg, a native of Harzgerode in Anhalt, travelled through Europe under the appellation of Sampson, exhibiting very remarkable examples of his strength. This we believe is the same person whose feats are particularly described by Dr Desaguliers. He was a man of the middle size, and of ordinary strength ; 246 LETTERS ON NATURAL MAGIC. and as Dr Desaguliers was convinced that his feats were exhibitions of skill and not of strength, he was desirous of discovering his methods, and with this view he went to see him accompanied with the Marquis of Tullibardine, Dr Alexander Stuart, and Dr Pringle, and his own mechanical opera- tor. They placed themselves round the German so as to be able to observe accurately all that he did, and their success was so great, that they were able to perform most of the feats the same evening by themselves, and almost all the rest when they had provided the proper apparatus. Dr Desaguliers exhibited some of the experiments before the Royal Society, and has given such a distinct ex- planation of the principles on which they depend, that we shall endeavour to give a popular account of them. 1. The performer sat upon an inclined board AB placed upon a frame C D E, with his feet abutting Fig. 51. against the upright board C. Round his loins was placed a strong girdle F G, to the iron ring of FEATS OF ECKEBERG. 247 which at G was fastened a rope by means of a hook. The rope passed between his legs through a hole in the board C, and several men, or two horses pull- ing at the other end of the rope, were unable to draw the performer out of his place. His hands at G, seemed to pull against the men, but they were of no advantage to him whatever. 2. Another of the German's feats is shown in Fig. 52. Having fixed the rope above-mentioned Fig. 52. to a strong post at A, and made it pass through a fixed iron eye at B, to the ring in his girdle, he planted his feet against the post at B, and raised himself from the ground by the rope, as shown in the figure. He then suddenly stretched out his legs 248 LETTERS ON NATURAL MAGIC. and broke the rope, falling- back on a feather bed at C, spread out to receive him. 3. In imitation of Firmus, he laid himself down on the ground, as shown in Fig. 53, and when an Fig. 53. anvil A was placed upon his breast, a man hammer- ed with all his force the piece of iron B, with a sledge hammer, and sometimes two smiths cut in two with chisels a great cold bar of iron laid upon the anvil. At other times a stone of huge dimensions, half of which is shown at C, was laid upon his belly, and broken with a blow of the great hammer. 4. The performer then placed his shoulders up- on one chair, and his heels upon another as in Fig. 54, forming with his back-bone, thighs, and legs, an arch springing from its abutments at A and B. One or two men then stood upon his belly, rising up and down while the performer breathed. A stone one and a half feet long, one foot broad, FEATS OF ECKEBERG. 249 and half a foot thick, was then laid upon his belly and broken by a sledge hammer, an operation which Fig. 54. may be performed with much less danger than when his back touched the ground as in Fig. 53. 5. His next feat was to lie down on the ground as in Fig. 55 : A man being then placed on his knees, he draws his heels towards his body, and raising his knees he lifts up the man gradually, till having brought his knees perpendicularly under him as in Fig. 56, he raises his own body up, and placing his arms around the man's legs, he rises with him, and sets him down on some low table or emi- nence of the same height as his knees. This feat he sometimes performed with two men in place of one. 250 LETTERS ON NATURAL MAGIC. Fig. 55. Fig. 56. FEATS OF ECKEBERG. 251 6. The last, and apparently the most wonderful, performance of the German is shown in Fig-. 57, Fig. 57. where he appears to raise a cannon A, placed upon a scale, the four ropes of the scale being fixed to a rope or chain attached to his girdle in the manner already described. Previous to the fixing of the ropes the cannon and scale rest upon two rollers B, C, but when all is ready, the two rollers are knocked from beneath the scale, and the cannon is sustained by the strength of his loins. 252 LETTERS ON NATURAL MAGIC. The German also exhibited his strength in twist- ing into a screw a flat piece of iron like A, Fig-. 58. Fig. 58. A He first bent the iron into a right angle as at B, and then wrapping- his handkerchief about its broad upper end, he held that end in his left hand, and with his right applied to the other end, twisted about the angular point, as showri at C. Lord Tulli- bardine succeeded in doing the same thing, and even untwisted one of the irons which the German had twisted. It would lead into details by no means popular, were I to give a minute explanation of the mecha- nical principles upon which these feats depend. A few general observations will perhaps be sufficient for ordinary readers. The feats No. 1, 2, and 6, depend entirely on the natural strength of the bones FEATS OF ECKEBERG. 253 of the pelvis, which form a double arch, which it would require an immense force to break, by any external pressure directed to the centre of the arch ; and as the legs and thighs are capable of sustaining four or five thousand pounds when they stand quite upright, the performer has no difficulty in resist- ing the force of two horses, or of sustaining the weight of a cannon weighing two or three thou- sand pounds. The feat of the anvil is certainly a very surpris- ing one. The difficulty, however, really consists in sustaining the anvil, for when this is done the effect of the hammering is nothing. If the anvil were a thin piece of iron, or even two or three times heavier than the hammer, the performer would be killed by a few blows ; but the blows are scarcely felt when the anvil is very heavy, for the more matter the anvil has, the greater is its inertia, and it is the less liable to be struck out of its place ; for when it has received by the blow the whole mo- mentum of the hammer, its velocity will be so much less than that of the hammer, as its quantity of matter is greater. When the blow, indeed, is struck, the man feels less of the weight of the anvil than he did before, because in the reaction of the stone all the parts of it round about the hammer rise towards the blow. This property is illustrated by the well known experiment of laying a stick with its ends upon two drinking glasses full of water, and striking the stick downwards in the middle with an iron bar. The stick will in this case be broken without breaking the glasses, or spilling the water. But if the stick is struck upwards as if to throw it up in the air, the glasses will break 254 LETTERS ON NATURAL MAGIC. if the blow be strong, and if the blow is not very quick, the water will be spilt without breaking the glasses. When the performer supports a man upon his belly as in Fig. 54, he does it by means of the strong arch formed by his backbone, and the bones of his legs and thighs. If there were room for them he could bear three or four, or, in their stead, a great stone, to be broken with one blow. A number of feats of real and extraordinary strength were exhibited about a century ago, in London, by Thomas Topham, who was five feet ten inches high, and about 31 years of age. He was entirely ignorant of any of the methods for mak- ing his strength appear more surprising, and he often performed by his own natural powers what he learned had been done by others by artificial means. A distressing example of this occurred in his attempt to imitate the feat of the German Sampson by pulling against horses. Ignorant of the method which we have already described, he seated himself on the ground with his feet against two stirrups, and by the weight of his body he succeeded in pulling against a single horse ; but in attempting to pull against two horses, he was lift- ed out of his place and one of his knees was shat- tered against the stirrups, so as to deprive him of most of the strength of one of his legs. The fol- lowing are the feats of real strength which Dr Desaguliers saw him perform. 1. Having rubbed his fingers with coal ashes to keep them from slipping, he rolled up a very strong and large pewter plate. 2. Having laid seven or eight short and strong FEATS OF STRENGTH OF TOPHAM. 255 pieces of tobacco-pipe on the first and third finger, he broke them by the force of his middle finger. 3. He broke the bowl of a strong- tobacco-pipe placed between his first and third finger, by pressing his fingers together sideways. 4. Having thrust such another bowl under his garter, his legs being bent, he broke it to pieces by the tendons of his hams, without altering the bend- ing of his leg. 5. He lifted with his teeth, and held in a hori- zontal position for a considerable time, a table six feet long, with half a hundred weight hanging at the end of it. The feet of the table rested against his knees. 6. Holding in his right hand an iron kitchen poker three feet long and three inches round, he struck upon his bare left arm, between the elbow and the wrist till he bent the poker nearly to a right angle. 7. Taking a similar poker, and holding the ends of it in his hands, and the middle against the back of his neck, he brought both ends of it together be- fore him, and he then pulled it almost straight again. This last feat was the most difficult, because the muscles which separate the arms horizontally from each other are not so strong as those which bring them together. 8. He broke a rope about two inches in circum- ference, which was partly wound about a cylinder four inches in diameter, having fastened the other end of it to straps that went over his shoulder. 9. Dr Desaguliers saw him lift a rolling stone of about 800 lbs. weight with his hands only, standing in a frame above it, and taking hold of a frame fast- 256 LETTERS ON NATURAL MAGIC. ened to it. Hence Dr Desaguliers gives the follow- ing- relative view of the strengths of individuals. Strength of the weakest men - 125 lbs. Strength of very strong men - 400 Strength of Topham - - 800 The weight of Topham was about 200. One of the most remarkable and inexplicable ex- periments relative to the strength of the human frame, which you have yourself seen and admired, is that in which a heavy man is raised with the greatest facility, when he is lifted up the instant that his own lungs and those of the persons who raise him are inflated with air. This experiment was, I believe, first shown in England a few years ago by Major H., who saw it performed in a large party at Venice under the direction of an officer of the American Navy. As Major H. performed it more than once in my presence, I shall describe as nearly as possible the method which he prescribed. The heaviest person in the party lies down upon two chairs, his legs being supported by the one and his back by the other. Four persons, one at each leg, and one at each shoulder, then try to raise him, and they find his dead weight to be very great, from the difficulty they experience in supporting him. When he is replaced in the chair, each of the four persons takes hold of the body as before, and the person to be lifted gives two signals by clap- ping his hands. At the first signal he himself and the four lifters begin to draw a long and full breath, and when the inhalation is completed, or the lungs filled, the second signal is given, for raising the person from the chair. To his own surprise and that of his bearers, he rises with the greatest facili- LIFTING HEAVY PERSONS. 257 ty, as if he were no heavier than a feather. On se- veral occasions I have observed that when one of the bearers performs his part ill, by making- the inhalation out of time, the part of the body which he tries to raise is left as it were behind. As you have repeatedly seen this experiment, and have performed the part both of the load and of the bearer, you can testify how remarkable the ef- fects appear to all parties, and how complete is the conviction, either that the load has been light- ened, or the bearer strengthened by the prescribed process. At Venice the experiment was performed in a much more imposing manner. The heaviest man in the party was raised and sustained upon the points of the fore-fingers of six persons. Major H. declared that the experiment would not succeed if the person lifted were placed upon a board, and the strength of the individuals applied to the board. He conceived it necessary that the bearers should communicate directly with the body to be raised. I have not had an opportunity of making- any ex- periments relative to these curious facts; but whe- ther the general effect is an illusion, or the result of known or of new principles, the subject merits a careful investigation. Among the remarkable exhibitions of mechani- cal strength and dexterity, we may enumerate that of supporting pyramids of men. This exhibition is a very ancient one. It is described, though not very clearly, by the Roman poet Claudian, and it has derived some importance in modern times, in consequence of its having been performed in vari- R 258 LETTERS ON NATURAL MAGIC. ous parts of Great Britain by the celebrated travel- ler Belzoni, before he entered upon the more esti- mable career of an explorer of Egyptian antiquities. The simplest form of this feat consists in placing- a number of men upon each other's shoulders, so that each row consists of a man fewer till they form a pyramid terminating in a single person, upon whose head a boy is sometimes placed with his feet upwards. Among the displays of mechanical dexterity, though not grounded on any scientific principle, may be mentioned the art of walking along the ceiling of an apartment with the head downwards. This exhibition, which we have witnessed in one of the London Theatres, never failed to excite the wonder of the audience, although the movements of the inverted performer were not such as to in- spire us with any high ideas of the mechanism by which they were effected. The following was pro- bably the method by which the performer was car- ried along the ceiling. Two parallel grooves or openings were made in the ceiling at the same dis- tance as the foot tracks of a person walking on sand. These grooves were narrower than the human foot, so as to permit a rope or chain or strong wire, attached to the feet of the performer, to pass through the ceiling, where they were held by two or more persons above it. In this way the invert- ed performer might be carried along by a sliding or shuffling motion, similar to that which is adopted in walking in the dark, and in which the feet are not lifted from the ground. A more regular mo- tion, however, might be produced by a contrivance WALKING ALONG THE CEILING. 259 for attaching the rope or chain to the sole of the foot, at each step, and subsequently detaching it. In this way, when the performer is pulled against the ceiling by his left foot, he would lift his right foot, and having made a step with it, and planted it against the grooves, the rope would be attached to it, and when the rope was detached from the left foot, it would make a similar step, while the right foot was pulled against the ceiling. These effects might be facilitated and rendered more natural, by attaching to the body or to the feet of the per- former strong wires invisible to the audience, and by using friction wheels, if a sliding motion only is required. A more scientific method of walking upon the ceiling is suggested by those beautiful pneumatic contrivances by which insects, fishes, and even some lizards are enabled to support the weight of their bodies against the force of gravity. The house-fly is well known to have the power of walking in an inverted position upon the ceilings of rooms, as well as upon the smoothest surfaces. In this case the fly does not rest upon its legs, and must there- fore adhere to the ceiling, either by some glutinous matter upon its feet, or by the aid of some appara- tus given it for that purpose. In examining the foot of the fly with a powerful microscope, it is found to consist of two concavities, as shewn in Fig. 59 and 60, the first of which is copied from a draw- ing by G. Adams, published in 1746, and the second by J. C. Keller, a painter at Nuremberg, who drew it for a work published in 1766. The author of this work maintains that these concavities are only 260 LETTERS ON NATURAL MAGIC. used when the fly moves horizontally, and that, when it moves perpendicularly or on the ceiling-, Fig. 59. they are turned up out of the way, and the progres- sive motion is effected by fixing- the claws shewn in the fig-ure into the irregularities of the surface upon which the fly moves, whether it is glass, por- celain, or any other substance. Sir Everard Home, however, supposes with great reason, that these concave surfaces are (like the leathern suckers used by children for lifting stones) employed to form a vacuum, so that the foot adheres as it were by sue- FOOT OF THE HOUSE-FLY. 261 tion to the ceiling*, and enables the insect to support itself in an inverted position. Fig. 60. This conclusion Sir Everard has been led to draw from an examination of the foot of the Lacerta Gecko. Sir Joseph Banks had mentioned to him in the year 1815, that this lizard, which is a native of the island of Java, comes out in the evening from the roofs of the houses, and walks down the smooth hard polished chunam walls in search of the flies which settle upon them, and which are its natural food. When Sir Joseph was at Batavia, he amused himself in catching this lizard. He stood close to the wall at some distance from the animal, and, by suddenly scraping- the wall with a long- flat- tened pole, he was able to bring the animal to the ground. 262 LETTERS ON NATURAL MAGIC. Having procured from Sir Joseph a very large specimen of the Gecko, which weighed 5^ ounces avoirdupois, Sir Everard Home was enabled to ascer- tain the peculiar mechanism by which the feet of this animal have the power of keeping hold of a smooth hard perpendicular wall, and carry up so heavy a weight as that of its body. The foot of the Gecko has five toes, and at the end of each of them, except the thumb, is a very sharp and highly curved claw. On the under surface of each toe, are sixteen transverse slits, leading to as many cavities or pockets, the depth of which is nearly equal to the length of the slit that forms the surface. These cavities all open forwards, and the external edge of each open- ing is serrated like the teeth of a small toothed comb. The cavities are lined with a cuticle, which also covers the serrated edges. This structure Sir Everard Home found to bear a considerable resemblance to that portion of the head of the Echineis remora, or sucking-fish, by which it attaches itself to the shark, or the bottoms of ships. It is of an oval form, and is surrounded by a broad loose moveable edge, capable of applying itself closely to the surface on which it is set. It con- sists of two rows of cartilaginous plates, connected by one edge to the surface on which th^y are placed, the other, or the external edge, being serrated like that in the cavities of the feet of the Gecko. The two rows are separated by a thin ligamentous par- tition, and the plates being raised or depressed by the voluntary muscles form so many vacua, by means of which the adhesion of the fish is ef- fected. FOOT OF THE GECKO. 263 These beautiful contrivances of Divine Wisdom cannot fail to arrest the attention and excite the ad- miration of the reader; but though there can be little doubt that they are pneumatic suckers wrought by the voluntary muscles of the animals to which they belong, yet we would recommend the farther examination of them to the attention of those who have good microscopes at their command. 264 LETTERS ON NATURAL MAGIC. LETTER XI. Mechanical automata of the ancients — Moving tripods — Auto- mata of Daedalus — Wooden pigeon of Archytas — Automa- tic clock of Charlemagne — Automata made by Turrianus for Charles V. — Camus's automatic carriage made for Louis XIV. — Degennes's mechanical peacock — Vaucanson's duck which ate and digested its food — Du Moulin'' s automata — Baron Kempclen's automaton chess-player — Drawing and writing automata — Maillardefs conjuror — Benefits derived from the passion for automata — Examples of wonderful ma- chinery for useful purposes — D uncart s tambouring machinery — Watts statue turning machinery — Babbage's calculating machinery. We have already seen that the ancients had attain- ed some degree of perfection in the construction of automata or pieces of mechanism which imitated the movements of man and the lower animals. The tripods which Homer * mentions as having- heen con- structed hy Vulcan for the banqueting hall of the gods, advanced of their own accord to the table, and again returned to their place. Self-moving tripods are mentioned by Aristotle, and Philostratus informs us, in his life of Apollonius, that this phi- losopher saw and admired similar pieces of mecha- nism among the sages of India. Daedalus enjoys also the reputation of having constructed machines that imitated the motions of * Iliad, Lib. xviii. 373—378. ARCHYTAs's WOODEN PIGEON, &C. 265 the human body. Some of his statues are said to have moved about spontaneously, and Plato, Aris- totle, and others have related that it was necessary to tie them, in order to prevent them from running away. Aristotle speaks of a wooden Venus, which moved about in consequence of quicksilver being- poured into its interior ; but Callistratus, the tutor of Demosthenes, states with some probability, that the statues of Daedalus received their motion from the mechanical powers. Beckmann is of opinion that the statues of Daedalus differed only from those of the early Greeks and Egyptians in having their eyes open and their feet and hands free, and that the reclining- posture of some, and the attitude of others, " as if ready to walk," gave rise to the exaggeration that they possessed the power of lo- comotion. This opinion, however, cannot be main- tained with any show of reason ; for if we apply such a principle in one case, we must apply it in all, and the mind would be left in a state of utter scep- ticism respecting the inventions of ancient times. We are informed by Aulus Gellius, on the autho- rity of Favorinus, that Archytas of Tarentum, who flourished about 400 years before Christ, construct- ed a wooden pigeon which was capable of flying. Favorinus relates, that when it had once alighted, it could not again resume its flight, and Aulus Gellius adds, that it was suspended by balancing, and animated by a concealed aura or spirit. . Among the earliest pieces of modern mechanism was the curious water-clock presented to Charle- magne by the Kaliph Harun al Raschid. In the dial-plate there were twelve small windows corre- sponding with the divisions of the hours. The hours 266 LETTERS ON NATURAL MAGIC. were indicated by the opening of the windows, which let out little metallic balls, which struck the hour by falling upon a brazen bell. The doors con- tinued open till twelve o'clock, when twelve little knights, mounted on horseback, came out at the same instant, and after parading round the dial, shut all the windows and returned to their apartments.* The next automata of which any distinct account has been preserved are those of the celebrated John Muller or Regiomontanus, which have been mention- ed by Kircher, Baptista Porta, Gassendi, Lana, and Bishop Wilkins. This philosopher is said to have constructed an artificial eagle, which flew to meet the Emperor Maximilian when he arrived at Nuremberg on the 7th June 1470. After soaring aloft in the air, the eagle is stated to have met the Emperor at some distance from the city, and to have return- ed and perched upon the town gate, where it waited his approach. When the Emperor reached the gate, the eagle stretched out its wings, and saluted him by an inclination of its body. Muller is like- wise reported to have constructed an iron fly, which was put in motion by wheel-work, and which flew about and leapt upon the table. At an entertainment given by this philosopher to some of his familiar friends, the fly flew from his hand, and after per- forming a considerable round, it returned again to the hand of its master. The Emperor Charles V., after his abdication of the throne, amused himself in his later years with automata of various kinds. The artist whom he employed was Janellus Turrianus of Cremona. It was his custom after dinner to introduce upon the table figures of armed men and horses. Some of these * Annales Loisiliani. Anno 807. TURRIANUS's AUTOMATA. 267 beat drums, others played upon flutes, while a third set attacked each other with spears. Sometimes he let fly wooden sparrows, which flew back again to their nest. He also exhibited corn-mills so ex- tremely small that they could be concealed in a glove, yet so powerful that they could grind in a day as much corn as would supply eight men with food for a day. The next piece of mechanism of sufficient inte- rest to merit our attention is that which was made by M. Camus for the amusement of Louis XIV. when a child. It consisted of a small coach, which was drawn by two horses, and which contained the figure of a lady within, with a footman and page behind. When this machine was placed at the ex- tremity of a table of the proper size, the coachman smacked his whip, and the horses instantly set off, moving their legs in a natural manner, and drawing the coach after them : When the coach reached the opposite edge of the table, it turned sharply at a right angle, and proceeded along the adjacent edge. As soon as it arrived opposite the place where the King sat it stopped ; the page descended and open- ed the coach door; the lady alighted, and with a curt- sey presented a petition, which she held in her hand to the King. After waiting some time she again curtsied and re-entered the carriage. The page closed the door, and having resumed his place be- hind, the coachman whipped his horses and drove on. The footman who had previously alighted, ran after the carriage and jumped up behind into his former place. Not content with imitating the movements of animals, the mechanical genius of the 17th and 18th 268 LETTERS ON NATURAL MAGIC. centuries ventured to perform by wheels and pinions the functions of vitality. We are informed by M. Lobat, that General Degennes, a French officer who defended the colony of St Christophers against the English forces, constructed a peacock, which could walk about as if alive, pick up grains of corn from the ground, digest them as if they had been submit- ted to the action of the stomach, and afterwards dis- charge them in an altered form. Degennes is said to have in vented various machines of great use in navigation and gunnery, and to have construct- ed clocks without weights or springs. The automaton of Degennes probably suggest- ed to M. Vaucanson the idea of constructing his celebrated duck, which excited so much interest throughout Europe, and which was perhaps the most wonderful piece of mechanism that was ever made. Vaucanson's duck exactly resembled the living ani- mal in size and appearance. It executed accurately all its movements and gestures, it ate and drank with avidity, performed all the quick motions of the head and throat which are peculiar to the living animal, and like it, it muddled the water which it drank with its bill. It produced also the sound of quack- ing in the most natural manner. In the anatomi- cal structure of the duck, the* artist exhibited the highest skill. Every bone in the real duck had its representative in the automaton, and its wings were anatomically exact. Every cavity, apophysis, and curvature was imitated, and each bone executed its proper movements. When corn was thrown down before it, the duck stretched out its neck to pick it up, it swallowed it, digested it, and discharged it, in a digested condition. The process of digestion was AUTOMATON CHESS-PLAYER. 269 effected by chemical solution, and not by trituration, and the food digested in the stomach was convey- ed away by tubes to the place of its discharge. The automata of Vaucanson were imitated by one Du Moulin, a silversmith, who travelled with them through Germany in 1752, and who died at Moscow in 1765. Beckmann informs us that he saw several of them after the machinery had been deranged ; but that the artificial duck, which he re- garded as the most ingenious, was still able to eat, drink, and move. Its ribs, which were made of wire, were covered with duck's feathers, and the motion was communicated through the feet of the duck by means of a cylinder and fine chains like that of a watch. Ingenious as all these machines are, they sink into insignificance when compared with the auto- maton chess-player, which for a long time astonish- ed and delighted the whole of Europe. In the year 1769, M. Kempelen, a gentleman of Presburgin Hungary, constructed an automaton chess-player, the general appearance of which is shown in the annexed figures. The chess-player is a figure as large as life, clothed in a Turkish dress sitting be- hind a large square chest or box three feet and a half long, two feet deep, and two and a half high. The machine runs on casters, and is either seen on the floor when the doors of the apartment are thrown open, or is wheeled into the room previous to the commencement of the exhibition. The Turkish chess-player sits on a chair fixed to the square chest : His right arm rests on the table, and in the left he holds a pipe, which is removed during the game, as it is with this hand that he makes the moves. A 270 LETTERS ON NATURAL MAGIC. chess-board, eighteen inches square, and bearing the usual number of pieces is placed before the figure. Fig. 61. Fig. 62. The exhibitor then announces to the spectators his intention of shewing them the mechanism of the automaton. For this purpose he unlocks the door A, Fig. 61, and exposes to view a small cupboard lined with black or dark coloured cloth, and contain- ing cylinders, levers, wheels, pinions, and different pieces of machinery, which have the appearance of occupying the whole space. He next opens the door B, Fig. 62, at the back of the same cupboard, and holding a lighted candle at the opening, he still farther displays the enclosed machinery to the spec- tators, placed in front of A, Fig. 61. When the candle is withdrawn, the door B is then locked ; and the exhibitor proceeds to open the drawer G G, Fig. 61, in front of the chest. Out of this drawer he takes a small box of counters, a set of chess -men, and a cushion for the support of the automaton's arm, as if this was the sole object of the drawer. The two front doors C, C, of the large cupboard, Fig. 4 AUTOMATON CHESS-PLAYER. 271 61, are then opened, and at the back-door D of the same cupboard, Fig. 62, the exhibitor applies a lighted candle, as before, for the purpose of shewing its interior, which is lined with dark cloth like the other, and contains only a few pieces of machinery. The chest is now wheeled round, as in Fig. 62 : The garments of the figure are lifted up, and the door E in the trunk, and another door F, in the thigh, are opened, the doors B and D having been previ- ously closed. When this exhibition of the interior of the machine is over, the chest is wheeled back into its original position on the floor. The doors A, C, C, in front, and the drawer G, G, are closed and locked, and the exhibitor, after occupying himself for some time at the back of the chest, as if he were adjust- ing the mechanism, removes the pipe from the hand of the figure, and winds up the machinery. The automaton is now ready to play, and when an opponent has been found among the company, the figure takes the first move. At every move made by the automaton, the wheels of the machine are heard in action ; the figure moves its head, and seems to look over every part of the chess-board. When it gives check to its opponent, it shakes its head thrice, and only twice when it checks the queen. It likewise shakes its head when a false move is made, replaces the adversary's piece on the square from which it was taken, and takes the next move itself. In general, though not always, the automaton wins the game. During the progress of the game, the exhibitor often stands near the machine, and winds it up like a clock after it has made ten or twelve moves. At other times he went to a corner of the room, as if 272 LETTERS ON NATURAL MAGIC. it were to consult a small square box, which stood open for this purpose. The chess-playing- machine, as thus described, was exhibited after its completion in Presburg, Vi- enna, and Paris, to thousands, and in 1783 and 1784 it was exhibited in London and different parts of England, without the secret of its movements having been discovered. Its ingenious inventor, who was a gentleman and a man of education, never pretend- ed that the automaton itself really played the game. On the contrary, he distinctly stated, " that the ma- chine was a bagatelle, which was not without merit in point of mechanism, but that the effects of it appeared so marvellous only from the boldness of the conception, and the fortunate choice of the me- thods adopted for promoting the illusion.' , Upon considering the operations of this automa- ton, it must have been obvious that the game of chess was performed either by a person enclosed in the chest, or by the exhibitor himself. The first of these hypotheses was ingeniously excluded by the display of the interior of the machine, for as every part contained more or less machinery, the spectator invariably concluded that the smallest dwarf could not be accommodated within, and this idea was strengthened by the circumstance, that no person of this description could be discovered in the suite of the exhibitor. Hence the conclusion was drawn, that the exhibitor actuated the machine ei- ther by mechanical means conveyed through its feet, or by a magnet concealed in the body of the exhibitor. That mechanical communication was not formed between the exhibitor and the figure, was obvious from the fact, that no such communi- 3 AUTOMATON CHESS-PLAYER. 273 cation was visible, and that it was not necessary to place the machine on any particular part of the floor. Hence the opinion became very prevalent that the agent was a magnet ; but even this supposition was excluded, for the exhibitor allowed a strong- and well armed loadstone to be placed upon the machine during* the progress of the game : Had the mov- ing power been a magnet, the whole action of the machine would have been deranged by the approxi- mation of a loadstone concealed in the pockets of any of the spectators. As Baron Kempelen himself had admitted that there was an illusion connected with the perfor- mance of the automaton, various persons resum- ed the original conjecture, that it was actuated by a person concealed in its interior, who either played the game of chess himself, or performed the moves which the exhibitor indicated by signals. A Mr J. F. Freyhere of Dresden published a book on the subject in 1789, in which he endeavoured to explain, by coloured plates, how the effect was produced; and he concluded, " that a well-taught boy, very thin and tall of his age, (sufficiently so that he could be concealed in a drawer almost immediately under the chess-board) agitated the whole." In another pamphlet which had been previously published at Paris in 1785, the author not only supposed that the machine was put in motion by a dwarf, a famous chess-player, but he goes so far as to explain the manner in which he could be accom- modated within the machine. The invisibility of the dwarf when the doors were opened was explain- ed by his legs and thighs being concealed in two hol- low cylinders, while the rest of his body was out of 274 LETTERS ON NATURAL MAGIC. the box, and hid by the petticoats of the automaton. When the doors were shut the clacks produced by the swivel of a ratchet-wheel permitted the dwarf to change his place and return to the box unheard; and while the machine is wheeled about the room, the dwarf had an opportunity of shutting the trap through which he passed into the machine. The interior of the figure was next shown, and the spec- tators were satisfied that the box contained no liv- ing agent. Although these views were very plausible, yet they were never generally adopted ; and when the automaton was exhibited in Great Britain in 1819 and 1820, by M. Maelzel, it excited as intense an interest as when it was first produced in Germany. There can be little doubt, however, that the secret has been discovered ; and an anonymous writer has shown in a pamphlet, entitled " An attempt to ana- lyse the automaton chess-player of M. Kempelen," that it is capable of accommodating an ordinarily sized man; and he has explained in the clearest manner how the inclosed player takes all the dif- ferent positions, and performs all the motions which are necessary to produce the effects actually ob- served. The following is the substance of his ob- servations : The drawer G G when closed does not extend to the back of the chest, but leaves a space O, behind it, (See Fig. 69, 70, and 71,) fourteen inches broad, eight inches high, and three feet eleven inches long. This space is never exposed to the view of specta- tors. The small cupboard seen at A is divided in- to two parts by a door or screen I, Fig. 68, which is moveable upon a hinge, and is so constructed AUTOMATON CHESS-PLAYER. 275 that it closes at the same instant that B is closed. The whole of the front compartment as far as I is occupied with the machinery H. The other com- partment behind I is empty, and communicates with the space O behind the drawer, the floor of this division being- removed. The back of the great cupboard C C is double, and the part P Q, to which the quadrants are attached, moves on a joint Q, at the upper part, and forms when raised an opening S, between the two cupboards, by carrying with it part of the partition R, which consists of cloth tight- ly stretched. The false back is shown closed in Fig. 69, while Fig. 70 shows the same back raised, so as to form the opening S between the chambers. When the spectator is allowed to look into the trunk of the figure by lifting up the dress, as in Fig. 70, it will be observed that a great part of the space is occupied by an inner trunk N, Fig. 70, 71, which passes off to the back in the form of an arch, and conceals from the spectators a portion of the interior. This inner trunk N opens and com- municates with the chest by an aperture T, Fig. 72, about twelve inches broad and fifteen high. When the false back is raised the two cupboards, the trunk N, and the space O behind the drawer, are all con- nected together. The construction of the interior being thus under- stood, the chess-player may be introduced into the chest through the sliding panel U, Fig. 69. He will then raise the false back of the large cupboard, and assume the position represented by the shaded figure in Fig. 63 and 64. Things being in this state, the exhibitor is ready to begin his process of deception. He first opens the door A of the small 276 LETTERS ON NATURAL MAGIC. cupboard, and from the crowded and very ingenious disposition of the machinery within it, the eye is Fig. 63. Fig. 64. unable to penetrate far beyond the opening-, and the spectator concludes without any hesitation, that the whole of the cupboard is filled, as it appears to be, with similar machinery. This false conclusion is greatly corroborated by observing the glimmer- ing light which plays among the wheel work when the door B is opened, and a candle held at the open- ing. This mode of exhibiting the interior of the cupboard satisfies the spectator also that no opaque body capable of holding or concealing any of the parts of a hidden agent is interposed between the light and the observer. The door B is now locked and the screen I closed, and as this is done at the time that the light is withdrawn it will wholly es- cape observation. The door B is so constructed as to close by its AUTOMATON CHESS-PLAYER. 277 own weight, but as the head of the chess-player will soon be placed very near it, the secret would be disclosed if, in turning round, the chest door should by any accident fly open. This accident is pre- vented by turning the key, and, lest this little cir- cumstance should excite notice, it would probably be regarded as accidental, as the keys were imme- diately wanted for the other locks. As soon as the door B is locked, and the screen I closed, the secret is no longer exposed to hazard, and the exhibit or proceeds to lead the minds of the spectators still farther from the real state of things. The door A is left open to confirm the opinion that no person is concealed within, and that nothing can take place in the interior without being observed. The drawer G G is now opened, apparently for the purpose of looking at the chess-men, cushion and counters which it contains ; but the real ob- ject of it is to give time to the player to change his Fig. 65. position, as shown in the annexed figure, and to re- place the false back and partition preparatory to 278 LETTERS ON NATURAL MAGIC. the opening* of the great cupboard. The chess- player, as the figure shows, occupies with his body the back compartment of the small cupboard, while his legs and thighs are contained in the space O, behind the drawer G G, his body being con- cealed by the screen I, and his limbs by the drawer GG. The great cupboard C C is now opened, and there is so little machinery in it that the eye instantly discovers that no person is concealed in it. To make this more certain, however, a door is opened at the back, and a lighted candle held to it, to allow the spectators to explore every corner and recess. The front doors of the great and small cupboard being left open, the chest is wheeled round to show the trunk of the figure, and the bunch of keys is allowed to remain in the door D, as the apparent carelessness of such a proceeding will help to re- move any suspicion which may have been excited by the locking of the door B. When the drapery of the figure has been raised, and the doors E and F in the trunk and thigh opened, the chest is wheeled round again into its original position, and the doors E and F closed. In the meantime the player withdraws his legs from behind the drawer, as he cannot so easily do this when the drawer G G is pushed in. In all these operations, the spectator flatters himself that he has seen in succession every part of the chest, while in reality some parts have been wholly concealed from his view, and others but im- perfectly shown, while at the present time nearly half of the chest is excluded from view. When the drawer G G is pushed in, and the AUTOMATON CHESS-PLAYER. 279 doors A and C closed, the exhibitor adjusts the machinery at the back, in order to give time to the player to take the position shown in a front view in Fig-. 66, and in profile in Fig. 67. In this po- Fig. 66. Fig. 67. sition he will experience no difficulty in executing every movement made by the automaton. As his head is above the chess-board, he will see through the waistcoat of the figure, as easily as through a veil, the whole of the pieces on the board, and he can easily take up and put down a chess man with- out any other mechanism than that of a string com- municating with the finger of the figure. His right hand being within the chest may be employ- ed to keep in motion the wheel- work for producing the noise which is heard during the moves, and to perform the other movements of the figure, such as that of moving the head, tapping on the chest, &c. A very ingenious contrivance is adopted to faci- 280 LETTERS ON NATURAL MAGIC. litate the introduction of the player s left arm into the arm of the figure. To permit this, the arm of the figure requires to be drawn backwards ; and for the purpose of concealing-, and at the same time explaining- this strained attitude, a pipe is ingeni- ously placed in the automaton's hand. For this reason the pipe is not removed till all the other arrangements are completed. When every thing has been thus prepared, the pipe is taken from the figure, and the exhibitor winds up as it were the Fig. 68. Fig. 69, rfk "L/C 1KV_ - p K inclosed machinery, for the double purpose of im- pressing upon the company the belief that the effect is produced by machinery, and of giving a signal to the player to put in motion the head of the automaton. This ingenious explanation of the chess automa- ton is, our author states, greatly confirmed by the regular and undeviating mode of disclosing the interior of the chest ; and he also shows that the facts which have been observed respecting the winding up of the machine, " afford positive proof that the axis turned by the key is quite free and AUTOMATON CHESS-PLAYER. 281 unconnected either with a spring or weight, or any system of machinery." In order to make the preceding description more intelligible, I shall add the following more detailed explanation of the figures. Fig. 70. Fig. 71. Fig. 61 is a perspective view of the automaton seen in front with all the doors thrown open. Fig. 62 is an elevation of the automaton, as seen from behind. Fig. 63 is an elevation of the front of the chest, the shaded figure representing the enclosed player in his first position, or when the door A is opened. Fig. 64 is a side elevation, the shaded figure re- presenting the player in the same position. Fig. 65 is a front elevation, the shaded figure showing the player in his second position, or that which he takes after the door B and screen I are closed, and the great cupboard opened. Fig. 66 is a front elevation, the shaded figure showing the player in his third position, or that in which he plays the game. Fig. 67 is a side elevation, showing the figure in the same position. 282 LETTERS ON NATURAL MAGIC. Fig*. 68 is an horizontal section of the chest through the line W W in Fig. 66. Fig. 69 is a vertical section of the chest through the line X X in Fig. 68. Fig. 70 is a vertical section through the line Y Y, Fig. 66 showing the false back closed. Fig. 71 is a similar vertical section showing the false back raised. The following letters of reference are employed in all the figures : A. Front door of the small cupboard. B. Back door of ditto. C C. Front doors of large cupboard. D. Back door of ditto. E. Door of ditto. F. Door of the thigh. G G. The drawer. H. Machinery in front of the small cupboard. I. Screen behind the machinery. K. Opening caused by the removal of part of the floor of the small cuj)board. L. A box which serves to conceal an opening in the floor of the large cupboard, made to facilitate the first position ; and which also serves as a seat for the third position. M. A similar box to receive the toes of the player in the first position. N. The inner chest filling up part of the trunk. O. The space behind the drawer. P Q. The false back turning on a joint at Q. R. Part of the partition formed of cloth stretch- ed tight, which is carried up by the false back to form the opening between the chambers. S. The opening between the chambers. DRAWING AND WRITING AUTOMATA. 283 T. The opening- connecting" the trunk and chest, which is partly concealed by the false back. U. Panel which is slipt aside to admit the player. Various pieces of mechanism of wonderful inge- nuity have been constructed for the purposes of drawing and writing. One of these, invented by M. Le Droz, the son of the celebrated Droz of Chaux le Fonds, has been described by Mr Collin- son. The figure was the size of life. It held in its hand a metallic style, and when a spring was touched, so as to release a detent, the figure imme- diately began to draw upon a card of Dutch vellum previously laid under its hand. After the drawing was executed on the first card, the figure rested. Other five cards were then put in in succession, and upon these it delineated in the same manner different subjects. On the first card it drew " ele- gant portraits and likenesses of the king and queen facing each other ;" and Mr Collinson remarks, that it was curious to observe with what precision the figure lifted up its pencil in its transition from one point of the drawing to another without making the slightest mistake. M. Maillardet has executed an automaton which both writes and draws. The figure of a boy kneel- ing on one knee holds a pencil in his hand. When the figure begins to work, an attendant dips the pencil in ink, and adjusts the drawing-paper upon a brass tablet. Upon touching a spring, the figure proceeds to write, and when the line is finished its hand returns to dot and stroke the letters when necessary. In this manner it executes four beau- tiful pieces of writing in French and English, and 284 LETTERS ON NATURAL MAGIC. three landscapes, all of which occupy about one hour. One of the most popular pieces of mechanism which we have seen is the magician constructed by M. Maillardet for the purpose of answering- cer- tain given questions. A figure, dressed like a ma- gician, appears seated at the bottom of a wall, hold- ing a wand in one hand, and a book in the other. A number of questions ready prepared are inscribed on oval medallions, and the spectator takes any of these which he chooses, and to which he wishes an answer, and having placed it in a drawer ready to receive it, the drawer shuts with a spring till the answer is returned. The magician then rises from his seat, bows his head, describes circles with his wand, and, consulting the book as if in deep thoug ht, he lifts it toward his face. Having thus appeared to ponder over the proposed question, he raises his wand, and striking with it the wall above his head, two folding-doors fly open, and display an appro- priate answer to the question. The doors again close, the magician resumes his original position, and the drawer opens to return the medallion. There are twenty of these medallions, all contain- ing different questions, to which the magician re- turns the most suitable and striking answers. The medallions are thin plates of brass of an elliptical form, exactly resembling each other. Some of the medallions have a question inscribed on each side, both of which the magician answers in succession. If the draw T er is shut without a medallion being put into it, the magician rises, consults his book, shakes his head, and resumes his seat. The folding-doors remain shut, and the drawer is returned empty. maillardet's conjuror. 285 If two medallions are put into the drawer together, an answer is returned only to the lower one. When the machinery is wound up, the movements con- tinue about an hour, during- which time about fifty questions may be answered. The inventor stated, that the means by which the different medallions acted upon the machinery, so as to produce the pro- per answers to the questions which they contained, were extremely simple. * The same ingenious artist has constructed vari- ous other automata representing insects and other animals. One of these was a spider entirely made of steel, which exhibited all the movements of the animal. It ran on the surface of a table during three minutes, and to prevent it from running off, its course always tended towards the centre of the table. He constructed likewise a caterpillar, a lizard, a mouse, and a serpent. The serpent crawls about in every direction, opens its mouth, hisses and darts out its tongue. Ingenious and beautiful as all these pieces of mechanism are, and surprising as their effects ap- pear even to scientific spectators, the principal ob- ject of their inventors was to astonish and amuse the public. We should form an erroneous judgment, how- ever, if we supposed that this was the only result of the ingenuity which they displayed. The passion for automatic exhibitions which characterized the 18th century, gave rise to the most ingenious me- chanical devices, and introduced among the higher orders of artists habits of nice and accurate execu- tion in the formation of the most delicate pieces * See the Edinburgh Encyclopaedia, Art. Androides, Vol, ii. p. 66. 286 LETTERS ON NATURAL MAGIC. of machinery. The same combination of the me- chanical powers which made the spider crawl, or which waved the tiny rod of the magician, con- tributed in future years to purposes of higher im- port. Those wheels and pinions, which almost eluded our senses by their minuteness, reappeared in the stupendous mechanism of our spinning-ma- chines, and our steam-engines. The elements of the tumbling puppet were revived in the chrono- meter, which now conducts our navy through the ocean ; and the shapeless wheel which directed the hand of the drawing automaton has served in the present age to guide the movements of the tam- bouring engine. Those mechanical wonders which in one century enriched only the conjuror who used them, contributed in another to augment the wealth of the nation ; and those automatic toys which once amused the vulgar, are now employed in extending the power and promoting the civi- lization of our species. In whatever way, indeed, the power of genius may invent or combine, and to whatever low or even ludicrous purposes that inven- tion or combination may be originally applied, so- ciety receives a gift which it can never lose ; and though the value of the seed may not be at once recognized, and though it may lie long unproduc- tive in the ungenial till of human knowledge, it will some time or other evolve its germ, and yield to mankind its natural and abundant harvest. Did the limits of so popular a volume as this ought to be, permit it, I should have proceeded to give a general description of some of these extra- ordinary pieces of machinery, the construction and effects of which never fail to strike the spectator mr duncan's tambouring machine. 287 with surprise. This, however, would lead me into a field too extensive, and I shall therefore confine myself to a notice of three very remarkable pieces of mechanism which are at present very little known to the general reader, viz. the tambouring- machine of Mr Duncan, the statue turning- machine of Mr Watt, and the calculating- machinery of Mr Bab- bage. The tambouring of muslins, or the art of produ- cing upon them ornamental flowers and figures, has been long known and practised in Britain, as well as in other countries ; but it was not long before the year 1790 that it became an object of general manufacture in the west of Scotland, where it was chiefly carried on. At first it was under the direction of foreigners ; but their aid was not long necessary, and it speedily extended to such a degree as to occupy, either wholly or par- tially, more than 20,000 females. Many of these labourers lived in the neighbourhood of Glasgow, which was the chief seat of the manufacture ; but others were scattered through every part of Scot- land, and supplied by agents with work and money. In Glasgow, a tambourer of ordinary skill could not in general earn more than five or six shillings a week by constant application ; but to a labouring artisan, who had several daughters, even these low wages formed a source of great wealth. At the age of five years, a child capable of handling a needle was devoted to tambouring, even though it could not earn more than a shilling or two in a week ; and the consequence of this was, that female chil- dren were taken from school, and rendered totally unfit for any social or domestic duty. The tam- bouring population was therefore of the worst kind^ 288 LETTERS ON NATURAL MAGIC. and it must have been regarded as a blessing rather than as a calamity, when the work which they per- formed was entrusted to regular machinery. Mr John Duncan of Glasgow, the inventor of the tambouring machinery, was one of those unfor- tunate individuals who benefit their species with- out benefiting themselves, and who died in the me- ridian of life the victim of poverty and of national ingratitude. He conceived the idea of bringing into action a great number of needles at the same time, in order to shorten the process by manual labour, but he at first was perplexed about the di- versification of the pattern. This difficulty, how- ever, he soon surmounted by employing two forces at right angles to each other, which gave him a new force in the direction of the diagonal of the paral- lelogram, whose sides were formed by the original forces. His first machine was very imperfect ; but after two year's study he formed a company, at whose expence six improved machines were put in action, and who secured the invention by a patent. At this time the idea of rendering the machine auto- matic had scarcely occurred to him ; but he afterwards succeeded in accomplishing this great object, and the tambouring machines were placed under the sur- veillance of a steam-engine. Another patent was taken for these improvements. The reader who desires to have a minute account of these improve- ments, and of the various parts of the machinery, will be amply gratified by perusing the inventor's own account of the machinery in the article Chain- work in the Edinburgh Encyclopaedia. At pre- sent it will be sufficient to state, that the muslin to be tamboured was suspended vertically in a frame, mr duncan's tambouring machine. 289 which was capable of being moved both in a vertical and a horizontal direction. Sixty or more needles lying- horizontal occupied a frame in front of the muslin web. Each of these working-needles, as they are called, was attended by a feeding-needle, which by a circular motion round the working- needle lodged upon the stem of the latter the loop of the thread. The sixty needles then penetrated the web, and in order that they might return again without injuring the fabric, the barb or eye of the needle, which resembled the barb of a fishing-hook, was shut by a slider. The muslin web then took a new position by means of the machinery that gave it its horizontal and vertical motion, so that the sixty needles penetrated it, at their next movement, at another point of the figure or flower. This ope- ration went on till sixty flowers were completed. The web was then slightly wound up, that the need- les might be opposite that part of it on which they were to work another row of flowers. The flowers were generally at an inch distance, and the rows were placed so that the flowers formed what are called diamonds. There were seventy- two rows of flowers in a yard, so that in every square yard there were nearly 4000 flowers, and in every piece of ten yards long 40,000. The num- ber of loops or stitches in a flower varied with the pattern, but on an average there was about thirty. Hence the number of stitches in a yard were 120,000, and the number in a piece is 1 ,200,000. The average work done in a week by one machine was fifteen yards, or 60,000 flowers, or 1,800,000 stitch- es, and by comparing this with the work done by one person with the hand, it appeared that the machine 290 LETTERS ON NATURAL MAGIC. enabled one person to do the work of twenty-four persons. One of the most curious and important applica- tions of machinery to the arts which has been sug- gested in modern times, was made by the late Mr Watt, in the construction of a machine for copy- ing- or reducing* statues and sculpture of all kinds. The art of multiplying busts and statues, by casts in plaster of Paris, has been the means of diffus- ing a knowledge of this branch of the fine arts ; but from the fragile nature of the material, the copies thus produced were unfit for exposure to the wea- ther, and therefore ill calculated for ornamenting public buildings, or for perpetuating the memory of public achievements. A machine, therefore, which is capable of multiplying the labours of the sculp- tor in the durable materials of marble or of brass, was a desideratum of the highest value, and one which could have been expected only from a ge- nius of the first order. During many years Mr Watt carried on his labours in secret, and he con- cealed even his intention of constructing such a ma- chine. After he had made considerable progress in its execution, and had thought of securing his in- vention by a patent, he learned that an ingenious individual in his own neighbourhood had been long occupied in the same pursuit ; and Mr Watt infor- med me, that he had every reason to believe that this gentleman was entirely ignorant of his labours. A proposal was then made that the two inventors should combine their talents, and secure the privi- lege by a joint patent ; but Mr Watt had experien- ced so frequently the fatal operation of our patent laws, that he saw many difficulties in the way of MR BABBAGe's CALCULATING MACHINE. 291 such an arrangement, and he was unwilling, at his advanced age, to embark in a project so extensive, and which seemed to require for its successful prosecution all the ardour and ambition of a youthful mind. The scheme was therefore abandoned ; and such is the unfortunate operation of our patent laws, that the circumstance of two individuals having made the same invention, has prevented both from bringing it to perfection, and conferring a great practical benefit upon their species. The machine which Mr Watt had constructed had actually executed some excellent pieces of work. I have seen in his house at Heathfield copies of basso relievos, and complete statues of a small size; and some of his friends have in their possession other specimens of its performance. Of all the machines which have been construct- ed in modern times, the calculating-machine is doubtless the most extraordinary. Pieces of me- chanism for performing particular arithmetical ope- rations have been long ago constructed, but these bear no comparison either in ingenuity or in mag- nitude to the grand design conceived and nearly executed by Mr Babbage. Great as the power of mechanism is known to be, yet we venture to say that many of the most intelligent of our readers will scarcely admit it to be possible that astronomi- cal and navigation tables can be accurately comput- ed by machinery ; that the machine can itself cor- rect the errors which it may commit ; and that the results of its calculations, when absolutely free from error, can be printed off, without the aid of human hands, or the operation of human intelligence. All this, however, Mr Babbage's machine can do; and as 292 LETTERS ON NATURAL MAGIC. I have had the advantage of seeing- it actually calculate, and of studying- its construction with Mr Babbage himself, I am able to make the above statement on personal observation. The calculating-machine now constructing under the superintendence of the inventor has been executed at the expence of the British Government, and is of course their proper- ty. It consists essentially of two parts, a calculat- ing part, and a printing part, both of which are ne- cessary to the fulfilment of Mr Babbage's views, for the whole advantage would be lost if the computa- tions made by the machine were copied by human hands and transferred to types by the common pro- cess. The greater part of the calculating-machin- ery is already constructed, and exhibits workman- ship of such extraordinary skill and beauty that no- thing approaching to it has been witnessed. In or- der to execute it, particularly those parts of the ap- paratus which are dissimilar to any used in ordi- nary mechanical constructions, tools and machinery of great expense and complexity have been invent- ed and constructed ; and in many instances contri- vances of singular ingenuity have been resorted to, which cannot fail to prove extensively useful in va- rious branches of the mechanical arts. The drawings of this machinery, which form a large part of the work, and on which all the contri- vance has been bestowed, and all the alterations made, cover upwards of 400 square feet of surface ', and are executed with extraordinary care and precision. In so complex a piece of mechanism, in which interrupted motions are propagated simultaneous- ly along a great variety of trains of mechanism, it might have been supposed that obstructions would 3 mr babbage's calculating machine. 293 arise, or even incompatibilities occur, from the im- practicability of foreseeing* all the possible combi- nations of the parts ; but this doubt has been entire- ly removed, by the constant employment of a sys- tem of mechanical notation invented by Mr Bab- bage, which places distinctly in view, at every in- stant, the progress of motion through all the parts of this or any other machine, and by writing down in tables the times required for all the movements, this method renders it easy to avoid all risk of two opposite actions arriving at the same instant at any part of the engine. In the printing part of the machine less progress has been made in the actual execution than in the calculating part. The cause of this is the greater difficulty of its contrivance, not for transferring the computations from the calculating part to the cop- per or other plate destined to receive it, but for giv- ing to the plate itself that number and variety of movements which the forms adopted in printed ta- bles may call for in practice. The practical object of the calculating engine is to compute and print a great variety and extent of astronomical and navigation tables, which could not be done without enormous intellectual and manual labour, and which, even if executed by such labour, could not be calculated with the requisite ac- curacy. Mathematicians, astronomers, and naviga- tors do not require to be informed of the real value of such tables ; but it may be proper to state, for the information of others, that seventeen large fo- lio volumes of logarithmic tables alone were cal- culated at an enormous expence by the French Government ; and that the British Government 294 LETTERS ON NATURAL MAGIC. regarded these tables to be of such national value that they proposed to the French Board of Lon- gitude to print an abridgement of them at the joint expence of the two nations, and offered to advance L.5000 for that purpose. Besides lo- garithmic tables, Mr Babbage's machine will calcu- late tables of the powers and products of numbers, and all astronomical tables for determining the po- sitions of the sun, moon, and planets ; and the same mechanical principles have enabled him to integrate innumerable equations of finite differences, that is, when the equation of differences is given, he can, by setting an engine, produce at the end of a given time any distant term which may be required, or any succession of terms commencing at a distant point. Beside the cheapness and celerity with which this machine will perform its work, the absolute accuracy of the printed results deserves especial notice. By peculiar contrivances, any small error produced by accidental dust, or by any slight inac- curacy in one of the wheels, is corrected as soon as it is transmitted to the next, and this is done in such a manner as effectually to prevent any ac- cumulation of small errors from producing an er- roneous figure in the result. In order to convey some idea of this stupendous undertaking, we may mention the effects produced by a small trial engine constructed by the inventor, and by which he computed the following table from the formula a? -f- x + 41. The figures as they were calculated by the machine were not exhibited to the eye as in sliding rules and similar instruments, but were actually presented to the eye on two op- MR BABBAGE's CALCULATING MACHINE. 295 posite sides of the machine, the number 383, for example, appearing in figures before the person em- ployed in copying. Table calculated by a small Trial Engine. 41 131 383 797 1373 43 151 421 853 1447 47 173 461 911 1523 53 197 583 971 1601 61 223 547 1033 1681 71 251 593 1097 1763 83 281 641 1163 1847 97 313 691 1231 1933 113 347 743 1301 2021 While the machine was occupied in calculating this table, a friend of the inventor undertook to write down the numbers as they appeared. In consequence of the copyist writing quickly, he ra- ther more than kept pace with the engine, but as soon as five figures appeared, the machine was at least equal in speed to the writer. At another trial thirty-tivo numbers of the same table were calculated in the space of two minutes and thirty seconds, and as these contained eighty-two figures, the engine produced thirty-three figures every mi- nute or more than one figure in every two seconds. On another occasion it produced forty -four figures per minute. This rate of computation could be maintained for any length of time ; and it is proba- ble that few writers are able to copy with equal speed for many hours together. Some of that class of individuals who envy all great men, and deny all great inventions, have igno- 296 LETTERS ON NATURAL MAGIC. rantly stated that Mr Babbage's invention is not new. The same persons, had it suited their pur- pose, would have maintained that the invention of spectacles was an anticipation of the telescope ; but even this is more true than the allegation, that the arithmetical machines of Pascal and others were the types of Mr Babbage's engine. The object of these machines was entirely different. Their highest functions were to perform the operations of com- mon arithmetic. Mr Babbage's engine, it is true, can perform these operations also, and can extract the roots of numbers, and approximate to the roots of equations, and even to their impossible roots. But this is not its object. Its function, in contra- distinction to that of all other contrivances for calculating, is to embody in machinery the method of differences, which has never before been done; and the effect s which it is capable of producing, and the works which in the course of a few years we expect to see it execute, will place it at an infinite dis- tance from all other efforts of mechanical genius. * * A popular account of this engine will be found in Mr Babbage's interesting volume On the Economy of Manufac- tures, just published. WONDERS OF CHEMISTRY. 297 LETTER XII. Wonders of chemistry — Origin, progress, and objects of alche* my — Art of breathing jive — Employed by Barchochebas, Eu~ nus, fyc. — Modern method — Art of walking upon burning coals and red hot iron, and of plunging the hands in melted lead and boiling water — Singular property of boiling tar — Workmen plunge their hands in melted copper—Trial of ordeal by fire — Aldin'is incombustible dresses — Examples of their wonderful power in resisting flame — Power of breathing and enduring air of high temperatures — Experiments made by Sir Joseph Banks, Sir Charles Blagden, and Mr Chantry- The science of chemistry has from its infancy been pre-eminently the science of wonders. In her la- boratory the alchemist and the magician have re- velled uncontrolled, and from her treasures was forged the sceptre which was so long and so fatally wielded over human reason. The changes which take place in the bodies immediately around us are too few in number and too remote from observation to excite much of our notice ; but when the sub- stances procured directly from nature, or formed ca- sually by art, become objects of investigation, they exhibit in their simple or combined actions the most extraordinary effects. The phenomena which they display, and the products which they form, so little resemble those with which we are familiar, 298 LETTERS ON NATURAL MAGIC. that the most phlegmatic and the least speculative observer must have anticipated from them the crea- tion of new and valuable compounds. It can scarce- ly, therefore, be a matter of surprise that minds of the highest order, and spirits of the loftiest ambi- tion, should have sought in the transmutations of che- mistry for those splendid products which were con- ceived to be most conducive to human happiness. The disciple of Mammon grew pale over his cru- cible in his ardour to convert the baser metals into gold : — The philosopher pined in secret for the uni- versal solvent which might develope the elements of the precious stones, and yield to him the means of their production ; and the philanthropist aspired after an universal medicine, which might arre&t dis- ease in its course, and prolong indefinitely the life of man. To us who live under the meridian of knowledge, such expectations must appear as pre- sumptuous as they were delusive ; but when we con- sider that gold and silver were actually produced by chemical processes from the rude ores of lead and copper ; — that some of the most refractory bodies had yielded to the disintegrating and solvent powers of chemical agents ; — and that the mercurial prepara- tions of the Arabian physicians had operated like charms^ in the cure of diseases that had resisted the feeble medicines of the times, we may find some apology for the extravagant expectations of the al- chemists. An object of lofty pursuit, even if it be one of impossible attainment, is not unworthy of philoso- phical ambition. Though we cannot scale the sum- mit of the volcanic cone, we may yet reach its heav- ing flanks, and though we cannot decompose its ORIGIN OF ALCHEMY. 299 loftiest fires, we may yet study the lava which they have melted and the products which they have su- blimed. In like manner, though the philosopher's stone has not been found, chemistry has derived rich accessions from its search ; — though the general solvent has not been obtained, yet the diamond and the gems have surrendered to science their adaman- tine strength ; — and though the elixir of life has never been distilled, yet other medicines have soothed " the ills which flesh is heir to," and prolong- ed in no slight degree the average term of our ex- istence. Thus far the pursuits of the alchemist were ho- nourable and useful ; but when his calling was follow- ed, as it soon was, by men prodigal of fortune and of character, science became an instrument of crime ; secrets unattained were bartered for the gold of the credulous and the ignorant, and books innumerable were composed to teach these pretended secrets to the world. An intellectual reaction, however, soon took place, and those very princes who had sought to fill their exhausted treasuries at the furnace of the chemist, were the first to enact laws against the frauds which they had encouraged, and to dispel the illusions which had so long deceived their subjects. But even when the moral atmosphere of Europe was thus disinfected, chemistry supplied the magi- cian with his most lucrative wonders, and those who could no longer delude the public with dreams of wealth and longevity, now sought to amuse and astonish them by the exhibition of their skill. The narrow limits of this volume will not permit me to give even a general view of those extraordi- nary effects which this popular science can display. 300 LETTERS ON NATURAL MAGIC. I must therefore select from its inexhaustible stores those topics which are most striking in their results, and most popular in their details. One of the most ancient feats of magic was the art of breathing flame, — an art which even now ex- cites the astonishment of the vulgar. During the insurrection of the slaves in Sicily in the second century before Christ, a Syrian named Eunus ac- quired by his knowledge the rank of their leader. In order to establish his influence over their minds, he pretended to possess miraculous power. When he wished to inspire his followers with courage, he breathed flames or sparks among them from his mouth, at the same time that he was rousing them by his eloquence. St Jerome informs us, that the Rabbi Barchochebas, who headed the Jews in their last revolt against Hadrian, made them believe that he was the Messiah, by vomiting flames from his mouth ; and at a later period, the Emperor Con- stantius was thrown into a state of alarm when Va- lentinian informed him, that he had seen one of the body guards breathing out fire and flames. We are not acquainted with the exact methods by which these effects were produced ; but Florus informs us, that Eunus filled a perforated nut-shell with sul- phur and fire, and having concealed it in his mouth, he breathed gently through it while he was speak- ing. This art is performed more simply by the modern juggler. Having rolled together some flax or hemp, so as to form a ball the size of a walnut, he sets it on fire, and allows it to burn till it is nearly consumed : He then rolls round it while burning some additional flax, and by these means the fire may be retained in it for a considerable WALKING ON BURNING COALS, &C. 301 time. At the commencement of his exhibition he introduces the ball into his mouth, and while he breathes through it the fire is revived, and a num- ber of burning sparks are projected from his mouth. These sparks are too feeble to do any harm, provid- ed he inhales the air through his nostrils. The kindred art of walking on burning coals or red hot iron remounts to the same antiquity. The priestesses of Diana at Castabala in Cappadocia were accustomed, according to Strabo, to walk over burning coals ; and at the annual festival, which was held in the temple of Apollo on Mount Soracte in Etruria, the Hirpi marched over burning coals, and on this account they were exempted from mi- litary service, and received other privileges from the Roman Senate. This power of resisting fire was ascribed even by Varro to the use of some lini- ment with which they anointed the soles of their feet. Of the same character was the art of holding red hot iron in the hands or between the teeth, and of plunging the hands into boiling water or melted lead. About the close of the seventeenth century, an Englishman of the name of Richardson rendered himself famous by chewing burning coals, pouring melted lead upon his tongue, and swallowing melt- ed glass. That these effects are produced partly by deception, and partly by a previous preparation of the parts subjected to the heat, can scarcely ad- mit of a doubt. The fusible metal, composed of mercury, tin, and bismuth, which melts at a low temperature, might easily have been substituted in place of lead ; and fluids of easy ebullition may have been used in place of boiling water. A solution of 302 LETTERS ON NATURAL MAGIC. spermaceti or sulphuric ether, tinged with alkanet root, which becomes solid at 50° of Fahrenheit, and melts and boils with the heat of the hand, is supposed to be the substance which is used at Naples when the dried blood of St Januarius melts spontaneously, and boils over the vessel which con- tains it. But even when the fluid requires a high tempe- rature to boil, it may have other properties, which enable us to plunge our hands into it with impuni- ty. This is the case with boiling tar, which boils at a temperature of 220° even higher than that of water. Mr Davenport informs us, that he saw one of the workmen in the King's Dock-yard at Chatham immerse his naked hand in tar of that temperature. He drew up his coat sleeves, dipped in his hand and wrist, bringing out fluid tar, and pouring it off from his hand as from a ladle. The tar remained in complete contact with his skin, and he wiped it off with tow. Convinced that there was no deception in this experiment, Mr Davenport immersed the entire length of his fore-finger in the boiling cauldron, and moved it about a short time before the heat became inconvenient. Mr Daven- port ascribes this singular effect to the slowness with which the tar communicates its heat, which he conceives to arise from the abundant volatile vapour which is evolved " carrying off rapidly the caloric in a latent state, and intervening between the tar and the skin, so as to prevent the more ra- pid communication of heat." He conceives also, that when the hand is withdrawn, and the hot tar adhering to it, the rapidity with which this vapour is evolved from the surface exposed to the air cook HANDS PLUNGED IN MELTED COPPER. 303 it immediately. The workmen informed Mr Da- venport, that, if a person put his hand into the caul- dron with his glove on, he would be dreadfully burnt, but this extraordinary result was not put to the test of observation. But though the conjurors with fire may have availed themselves of these singular properties of individual bodies, yet the general secret of their art consisted in rendering the skin of the exposed parts callous and insensible to heat, — an effect which may be produced by continually compressing or singeing, them till the skin acquires a horny consistence. A proof of this opinion is mentioned by Beckmann, who assures us that in September 1765, when he visited the copper works at Awestad, one of the workmen, bribed by a little money to drink, took some of the melted copper in his hand, and after shewing it to the company, threw it against a wall. He then squeezed the fingers of his horny hand close to each other, held it a few minutes under his arm-pit to make it perspire, as he said, and taking it again out, drew it over a ladle filled with melted copper, some of which he skimmed off, and moved his hand backwards and forwards very quickly by way of ostentation. During this performance, M. Beckmann noticed a smell like that of singed horn or leather, though the hand of the workman was not burned. This callosity of the skin may be effected by frequently moistening it with dilute sulphuric acid. Some allege that the juices of certain plants produce the same effect, while others recommend the frequent rubbing of the skin with oil. The receipt given by Albertus Magnus for this purpose was of a different nature. It consisted of a non-con- 304 LETTERS ON NATURAL MAGIC. ducting calcareous paste, which was made to adhere to the skin by the sap of the marsh-mallow, the slimy- seeds of the flea-bane, and the white of an egg. As the ancients were acquainted with the incom- bustibility of asbestos or amianthus, and the art of weaving it into cloth, it is highly probable that it was employed in the performance of some of their miracles, and it is equally probable that it was sub- sequently used, along with some of the processes already described, in enabling the victims of super- stition to undergo without hazard the trial of ordeal by fire. In every country where this barbarous usage prevailed, whether in the sanctuary of the Christian idolater, or in the pagan temple of the Bramin, or under the wild orgies of the African savage, Provi- dence seems to have provided the means of meeting it with impunity. In Catholic countries this exculpa- toryjudgment was granted chiefly to persons in weak health, who were incapable of using arms, and par- ticularly to monks and ecclesiastics who could not avail themselves of the trial by single combat. The fire ordeal was conducted in the church under the inspection of the clergy : Mass was at the same time celebrated, and the iron and the victims were consecrated by the sprinkling of holy water. The preparatory steps were also under the direction of the priests. It was necessary that the accused should be placed three days and three nights under their care, both before and after the trial. Under the pretence of preventing the defendant from pre- paring his hands by art ; and in order to ascertain the result of the ordeal, his hands were covered up and sealed during the three days which preceded and followed the fiery application ; and it has been plau- ALDINl's INCOMBUSTIBLE DRESSES. 305 sibly conjectured by Beckmann, that during the three first days the preventative was applied to those whom they wished to acquit, and that the three last days were requisite to bring- back the hands to their natural condition. In these and other cases, the accused could not have availed him- self directly of the use of asbestos gloves, unless we could suppose them so made as to imitate the human skin at a distance ; but the fibres of that mineral may have been imbedded in a paste which applied itself readily to all the elevations and depressions of the skin. In our own times the art of defending the hands a**d fctce, and indeed the whole body, from the action of heated iron and intense fire, has been applied to the nobler purpose of saving human life, and rescu- ing property from the flames. The revival and the improvement of this art we owe to the benevolence and the ingenuity of the Chevalier Aldini of Milan, who has travelled through all Europe to present this valuable gift to his species. Sir H. Davy had long ago shewn that a safety lamp for illuminating mines, containing inflammable air, might be constructed of wire-gauze alone, which prevented the flame with- in, however large or intense, from setting fire to the inflammable air without. This valuable property, which has been long in practical use, he ascribed to the conducting and radiating power of the wire- gauze, which carried ofl" the heat of the flame, and deprived it of its power. The Chevalier Aldini con- ceived the idea of applying the same material in com- bination with other badly conducting substances, as a protection against fire. The incombustible pieces of dress which he uses for the body, arms, u 306 LETTERS ON NATURAL MAGIC. and legs, are formed out of strong* cloth, which has been steeped in a solution of alum, while those for the head, hands, and feet, are made of cloth of as- bestos or amianthus. The head dress is a large cap which envelopes the whole head down to the neck, having suitable perforations for the eyes, nose, and mouth. The stockings and cap are single, but the gloves are made of double amianthus cloth, to en- able the fireman to take into his hand burning or red hot bodies. The piece of ancient asbestos cloth preserved in the Vatican was formed, we believe, by- mixing the asbestos with other fibrous substances ; but M. Aldini has executed a piece of nearly the same size, nine feet five inches long, and five feet three inches wide, which is much stronger than the ancient piece, and possesses superior qualities, in consequence of having been woven without the in- troduction of any foreign substance. In this manu- facture the fibres are prevented from breaking by the action of steam, the cloth is made loose in its fabric, and the threads are about the fiftieth of an inch in diameter. The metallic dress which is superadded to these means of defence consists of five principal pieces, viz. a casque or cap, with a mask large enough to leave a proper space between it and the asbestos cap ; a cuirass with its brassets ; a piece of armour for the trunk and thighs ; a pair of boots of double wire-gauze ; and an oval shield five feet long by 2^ wide, made by stretching the wire- gauze over a slender frame of iron. All these pieces are made of iron wire-gauze, having the interval between its threads the twenty-fifth part of an inch. In order to prove the efficacy of this apparatus, ALDINl's INCOMBUSTIBLE DRESSES. 307 and inspire the firemen with confidence in its pro- tection, he showed them that a finger first enve- loped in asbestos, and then in a double case of wire- gauze, might be held a long time in the flame of a spirit-lamp or candle before the heat became incon- venient. A fireman having his hand within a double asbestos glove, and its palm protected by a piece of asbestos cloth, seized with impunity a large piece of red hot iron, carried it deliberately to the distance of 150 feet, inflamed straw with it, and brought it back again to the furnace. On other occasions, the firemen handled blazing wood and burning substances, and walked during five minutes upon an iron grating placed over flaming faggots. In order to show how the head, eyes, and lungs, are protected, the fireman put on the asbestos and wire-gauze cap, and the curiass, and held the shield before his breast. A fire of shavings was then lighted, and kept burning in a large raised chafing- dish, and the fireman plunged his head into the middle of the flames with his face to the fuel, and in that position went several times round the chafing-dish for a period longer than a minute. In a subsequent trial at Paris, a fireman placed his head in the middle of a large brasier filled with flaming hay and wood, as in Fig. 72, and resisted the action of the fire during five or six minutes, and even ten minutes. In the experiments which were made at Paris in presence of a committee of the Academy of Sciences, two parallel rows of straw and brushwood, supported by iron wires, were formed at the dis- tance of three feet from each other, and extended thirty feet in length. When this combustible mass 308 LETTERS ON NATURAL MAGIC. was set on fire, it was necessary to stand at the dis- tance of eight or ten yards to avoid the heat. The Fig. 72. names from both the rows seemed to fill np the whole space between them, and rose to the height of nine or ten feet. At this moment six firemen, clothed in the incombnstible dresses, and marching at a slow pace behind each other, repeatedly passed through the whole length between the two rows of flame, which were constantly fed with additional combustibles. One of the firemen carried on his back a child eight years old in a wicker basket co- vered with metallic gauze, and the child had no other dress than a cap made of amianthine cloth. In February 1829, a still more striking experi- 4 EXAMPLES OF RESISTING FLAME. 309 ment was made in the yard of the barracks of St Gervais. Two towers were erected two stories high, and were surrounded with heaps of inflamed materials, consisting- of faggots and straw. The firemen braved the danger with impunity. In op- position to the advice of M. Aldini, one of them, with the basket and child, rushed into a narrow place, where the flames were raging* eight yards high. The violence of the fire was so great that he could not be seen, while a thick black smoke spread around, throwing out a heat which was un supportable by the spectators. The fireman re- mained so long invisible that serious doubts were entertained of his safety. He at length, however, issued from the fiery gulf uninjured, and proud of having succeeded in braving so great a danger. It is a remarkable result of these experiments, that the firemen are able to breathe without diffi- culty in the middle of the flames. This effect is owing not only to the heat being intercepted by the wire gauze as it passes to the lungs, in conse- quence of which its temperature becomes support- able, but also to the singular power which the body possesses of resisting great heats, and of breathing air of high temperatures. A series of curious experiments were made on this subject by M. Tillet, in France, and by Dr Fordyce and Sir Charles Blagden, in England. Sir Joseph Banks, Dr Solander, and Sir Charles Blagden, entered a room in which the air had a temperature of 198° Fahr. and remained ten mi- nutes ; but as the thermometer sunk very rapidly, they resolved to enter the room singly. Dr Solan- der went in alone, and found the heat 210°, and 310 LETTERS ON NATURAL MAGIC. Sir Joseph entered when the heat was 211°. Though exposed to such an elevated temperature, their bodies preserved their natural degree of heat* Whenever they breathed upon a thermometer it sunk several degrees : Every expiration, particu- larly if strongly made, gave a pleasant impression of coolness to their nostrils, and their cold breath cooled their fingers whenever it reached them. On touching his side, Sir Charles Blagden found it cold like a corpse, and yet the heat of his body un- der his tongue was 98°. Hence they concluded that the human body possesses the power of de- stroying a certain degree of heat when communi- cated with a certain degree of quickness. This power, however, varies greatly in different media. The same person who experienced no inconvenience from air heated to 211°, could just bear rectified spirits of wine at 130°, cooling oil at 129°, cooling water at 123°, and cooling quicksilver at 117°. A familiar instance of this occurred in the heated room. All the pieces of metal there, even their watch-chains, felt so hot, that they could scarcely bear to touch them for a moment, while the air from which the metal had derived all its heat was only unpleasant. MM. Duhamel and Tillet ob- served at Rochefoucault in France, that the girls who were accustomed to attend ovens in a bakehouse were capable of enduring for ten minutes a tempe- rature of 270°. The same gentlemen who performed the experi- ments above described ventured to expose them- selves to still higher temperatures. Sir Charles Blagden went into a room where the heat was 1° or 2° above 260°, and remained eight minutes in sir c. blagden's experiments, &c. 311 this situation, frequently walking about to all the different parts of the room, but standing still most of the time in the coolest spot, where the heat was above 240°. The air, though very hot, gave no pain, and Sir Charles and all the other gentlemen were of opinion that they could support a much greater heat. During seven minutes, Sir C. Blagden's breathing continued perfectly good, but after that time he felt an oppression in his lungs, with a sense of anxiety, which induced him to leave the room. His pulse was then 144, double its ordinary quick- ness. In order to prove that there was no mistake respecting the degree of heat indicated by the ther- mometer, and that the air which they breathed was capable of producing all the well known effects of such a heat on inanimate matter, they placed some eggs and a beef-steak upon a tin frame near the thermometer, but more distant from the furnace than from the wall of the room. In the space of twenty minutes the eggs were roasted quite hard, and in forty-seven minutes the steak was not only dressed, but almost dry. Another beef-steak, si- milarly placed, was rather overdone in thirty-three minutes. In the evening, when the heat was still more elevated, a third beef-steak was laid in the same place, and as they had noticed that the effect of the hot air was greatly increased by putting it in motion, they blew upon the steak w T ith a pair of bellows, and thus hastened the dressing of it to such a degree, that the greatest portion of it was found to be pretty well done in thirteen mi- nutes. Our distinguished countryman, Mr Chantry, has very recently exposed himself to a temperature still 312 LETTERS ON NATURAL MAGIC. higher than any which we have mentioned. The furnace which he employs for drying his moulds is about 14 feet long, 12 feet high, and 12 feet broad. When it is raised to its highest temperature, with the doors closed, the thermometer stands at 350 a , and the iron floor is red hot. The workmen often enter it at a temperature of 340°, walking over the iron floor with wooden clogs, which are of course charred on the surface. On one occasion Mr Chan- try, accompanied by five or six of his friends, enter- ed the furnace, and, after remaining two minutes, they brought out a thermometer which stood at 320°. Some of the party experienced sharp pains in the tips of their ears, and in the septum of the nose, while others felt a pain in their eyes. SPONTANEOUS COMBUSTION. 313 LETTER XIII. Spontaneous combustion — In the absorption of air by powder, ed charcoal — and of hydrogen by spongy platinum — Doberei- nefs lamp — Spontaneous combustion in the bowels of the earth — Burning cliffs — Burning soil — Combustion without flame — Spontaneous combustion of human beings — Countess Zangari — Grace Pett — Natural fire temples of the Guebres — Spontaneous fi res in the Caspian Sea — Springs of inflam- mable gas near Glasgow — Natural light-house of Maracay- bo — New elastic fluids in the cavities of gems — Chemical operation going on in their cavities — Explosions produced in them by heat — Remarkable changes of colour from die. mical causes — Effects of the nitrous oxide or paradise gas when breathed — Remarkable cases described. — Conclusion. Among the wonderful phenomena which chemistry presents to us, there are few more remarkable than those of spontaneous combustion, in which bodies, both animate and inanimate, emit flames, and are sometimes entirely consumed by internal fire. One of the commonest experiments in chemistry is that of producing inflammation by mixing- two fluids perfectly cold. Becker, we believe, was the first person who discovered that this singular effect was produced by mixing oil of vitriol with oil of tur- pentine. Borrichios shewed that aquafortis pro- duced the same effect as oil of vitriol. Tournefort proved that spirit of nitre and oil of sassafras took 314 LETTERS ON NATURAL MAGIC. fire when mixed ; and Homberg discovered that the same property was possessed by many volatile oils when mixed with spirit of nitre. Every person is familiar with the phenomena of heat and combustion produced by fermentation. Ricks of hay and stacks of corn have been fre- quently consumed by the heat generated during the fermentation produced from moisture ; and gun- powder magazines, barns, and paper-mills have been often burnt by the fermentation of the materials which they contained. Galen informs us that the dung of a pigeon is sufficient to set fire to a house, and he assures us that he has often seen it take fire when it had become rotten. Casati likewise re- lates on good authority, that the fire which consumed the great church of Pisa was occasioned by the dung of pigeons that had for centuries built their nests under its roof. Among the substances subject to spontaneous combustion, pulverised or finely powdered charcoal is one of the most remarkable. During the last thirty years no fewer than four cases of the spontaneous inflammation of powdered charcoal have taken place in France. When charcoal is triturated in tuns with bronze bruisers it is reduced into the state of the finest powder. In this condition it has the appearance of an unctuous fluid, and it occupies a space three times less than it does in rods of about six inches long. In this state of extreme division it absorbs air much more readily than it does when in rods. This absorption, which is so slow as to require several days for its completion, is accompa- nied with a disengagement of heat, which rises from 340° to 360° nearly of Fahrenheit, and which DOBEREINER S LAMP. 315 is the true cause of the spontaneous inflammation* The inflammation commences near the centre of the mass, at the depth of five or six inches beneath its surface, and at this spot the temperature is al- ways higher than at any other. Black charcoal strongly distilled, heats and inflames more easily than the orange, or that which is little distilled, or than the charcoal made in boilers. The most in- flammable charcoal must have a mass of at least 66 lbs. avoirdupois, in order that it may be suscep- tible of spontaneous inflammation. With the other less inflammable varieties, the inflammation takes place only in larger masses. The inflammation of powdered charcoal is more active in proportion to the shortness of the interval between its carbonization and trituration. The free admission of air to the surface of the charcoal is also indisj) en sable to its spontaneous combustion. Colonel Aubert, to whom we owe these interest- ing results, likewise found that when sulphur and saltpetre are added to the charcoal, it loses its power of inflaming spontaneously. But as there is still an absorption of air and a generation of heat, he is of opinion that it would not be prudent to leave these mixtures in too large masses after tritura- tion. * A species of spontaneous combustion, perfectly analogous to that now described, but produced almost instantaneously, was discovered by Professor Dobe- reiner of Jena in 1824. He found that when a jet of hydrogen gas was thrown upon recently prepar- ed spongy platinum, the metal became almost in- * See Edinburgh Journal of Science, New Series, No, viii. p. 274, 316 LETTERS ON NATURAL MAGIC. stantly red hot, and set fire to the gas. In this case the minutely divided platinum acted upon the hydrogen gas, in the same manner as the minutely divided charcoal acted upon common air. Heat and combustion were produced by the absorption of both gases, though in the one case the effect was instantaneous, and in the other was the result of a prolonged absorption. This beautiful property of spongy platinum was happily applied to the construction of lamps for producing an instantaneous light. The form given to the lamp by Mr Garden of London is shown in the annexed figure, where A B is a globe of Fig. 73. glass, fitting tightly into another glass globe C D by a ground shoulder m n. The globe A B termi- SPONTANEOUS COMBUSTION. 317 nates in a hollow tapering neck m n o p, on the lower end of which is placed a small cylinder of zinc op. A brass tube a b c, is fitted at a into the neck of the globe C D, and through this tube, which is furnished with a stop-cock d, the gas can escape at the small aperture c. A brass pin c f, carrying a brass box P, is made to slide through a hole h, so that the brass box P, in which the spongy platinum is placed, can be set at any required dis- tance from the aperture c. If sulphuric acid dilut- ed with an equal quantity of water is now poured into the vessel A B by its mouth at S, now closed with a stopper, the fluid will descend through the tube m n o p, and if the cock d is shut, it will compress the air contained in C D. The dilute acid thus introduced into C D will act upon the ring of zinc o p, and generate hydrogen gas, which after the at- mospheric air in C D is let off, will gradually fill the vessel C D, the diluted acid being forced up the tube o p m n, into the glass globe A B. The ring of zinc o p floats on a piece of cork, so that when C D is full of hydrogen, the diluted acid does not touch the zinc, and consequently is prevented from producing any more gas. The instant, however, that any gas is let off at c, the pressure of the fluid in the globe A B, and tube m n o p, overcomes the elasticity of the remaining gas in C D, and forces the diluted acid up to the zinc o p, so as to enable it to produce more gas to supply what has been used. The lamp being supplied with hydrogen in the manner now described, it is used in the following manner : The spongy platinum in P being brought near c, the cock d is turned, and the gas is thrown 318 LETTERS ON NATURAL MAGIC. upon the platinum. An intense heat is immediate- ly produced, the platinum becomes red hot, and the hydrogen enflames. A taper is then lighted at the flame, and the cock d is shut. Professor dimming of Cambridge found it necessary to cover up the platinum with a cap after every experiment. This ingenious chemist likewise found, that, with platinum foil the 9000dth part of an inch thick kept in a close tube, the hydrogen was inflamed ; but when the foil was only the GOOOdth of an inch thick, it was necessary to raise it previously to a red heat. Spontaneous combustion is a phenomenon which occurs very frequently and often to a great extent within the bowels of the earth. The heat by which it is occasioned is produced by the decomposition of mineral bodies, and other causes. This heat in- creases in intensity till it is capable of melting the solid materials which are exposed to it. Gases and aqueous vapours of powerful elasticity are generat- ed, new fluids of expansive energy imprisoned in cavities under great pressure are set free, and these tremendous agents, acting under the repressing forces of the superincumbent strata, exhibit their power in desolating earthquakes ; or, forcing their way through the superficial crust of the globe, they waste their fury in volcanic eruptions. When the phenomena of spontaneous combus- tion take place near the surface of the earth its ef- fects are of a less dangerous character, though they frequently give birth to permanent conflagrations, which no power can extinguish. An example of this milder species of spontaneous combustion has been recently exhibited in the burning cliff at Wey- mouth ; and a still more interesting one exists at COMBUSTION WITHOUT FLAME. 319 this moment near the village of Bradley, in Staf- fordshire. The earth is here on fire, and this fire has continued for nearly sixty years, and has resist- ed every attempt that has been made to extinguish it. This fire, which has reduced many acres of land to a mere calx, arises from a burning- stratum of coal about four feet thick and eight or ten yards deep, to which the air has free access, in consequence of the main coal having- been dug from beneath it. The surface of the ground is sometimes covered for many yards with such quantities of sulphur that it- can be easily gathered. The calx has been found to be an excellent material for the roads, and the workmen who collect it often find large beds of alum of an excellent quality. A singular species of invisible combustion, or of combustion without flame, has been frequently no- ticed. I have observed this phenomenon in the small green wax tapers in common use. When the flame is blown out, the wick will continue red hot for many hours, and if the taper were regular- ly and carefully uncoiled, and the room kept free from currents of air, the wick would burn on in this way till the whole of the taper is consumed. The same effects are not produced when the colour of the wax is red. In this experiment the wick, after the flame is blown out, has sufficient heat to con- vert the wax into vapour, and this vapour, being consumed without flame, keeps the wick at its red- heat. A very disagreeable vapour is produced dur- ing this imperfect combustion of the wax. Prof. Dobereiner of Jena observed, that when the alcohol in a spirit of wine lamp was nearly ex- hausted, the wick became carbonized, and though the flame disappeared, the carbonized part of the 320 LETTERS ON NATURAL MAGIC. wick became red hot, and continued so while a drop of alcohol remained, and provided the air in the room was undisturbed. On one occasion the wick continued red hot for twenty-four hours, and a very disagreeable acid vapour was formed. On these principles depend the lamp without flame which was originally constructed by Mr Ellis. It is shown in the annexed figure, where A B is Fig. 74. the lamp, and h a cylindrical coil of platinum wire, the hundredth part of an inch in diameter. This spiral is so placed that four or five of the twelve coils of which the cylinder consists are upon the wick, and the other seven or eight above it. If the lamp is lighted, and continues burning till the cy- lindrical coil is red hot, then if the flame is blown out, the vapour which arises from the alcohol will by its combustion keep the coils above the wick red hot, and this red heat will in its turn keep up the vaporisation of the alcohol till the whole of the alcohol is consumed. The heat of the wire is al- ways sufficient to kindle a piece of German fungus or saltpetre paper, so that a sulphur match may at any time be lighted. Mr Gill found that a wick com- posed of twelve threads of the cotton yarn common- SPONTANEOUS COMBUSTION. 321 ly used for lamps will require half an ounce of alco- hol to keep the wire red hot for eight hours. This lamp has been kept burning- for sixty hours ; but it can scarcely be recommended for a bed-room, as an acid vapour is disengaged during the burning of the alcohol. When perfumes are dissolved in the al- cohol, they are diffused through the apartment during the slow combustion of the vapour. A species of combustion without flame, and ana- logous to that which has been described, is exhi- bited in the extraordinary phenomenon of the spon- taneous combustion of living bodies. That animal bodies are liable to internal combustion is a fact which was well known to the ancients. Many cases which have been adduced as examples of sponta- neous combustion are merely cases of individuals who were highly susceptible of strong electrical ex- citation. In one of these cases, however, Peter Bovisteau asserts, that the sparks of fire thus pro- duced reduced to ashes the hair of a young man ; and John De Viana informs us, that the wife of Dr Freilas, physician to the Cardinal de Royas, Arch- bishop of Toledo, emitted by perspiration an inflam- mable matter of such a nature, that when the rib- bon which she wore over her shift was taken from her, and exposed to the cold air, it instantly took fire, and shot forth like grains of gunpowder. Pe- ter Borelli has recorded a fact of the very same kind respecting a peasant whose linen took fire, whe- ther it was laid up in a box when wet, or hung up in the open air. The same author speaks of a woman who, when at the point of death, vomited flames ; and Thomas Bartholin mentions this phenomenon as having often happened to persons who were x 322 LETTERS ON NATURAL MAGIC. great drinkers of wine or brandy. Ezeki-el de Cas- tro mentions the singular case of Alexandrinus Me- getius, a physician, from one of whose vertebrae there issued a fire which scorched the eyes of the behold- ers ; and Krantzius relates, that during the wars of Godfrey of Boulogne, certain people of the ter- ritory of Nivers were burning with invisible fire, and that some of them cut off a foot or a hand where the burning began, in order to arrest the ca- lamity. Nor liave these effects been confined to man. In the time of the Roman consuls Gracchus and Juventius, a flame is said to have issued from the mouth of a bull without doing any injury to the animal. The reader will judge of the degree of credit which may belong to these narrations when he ex- amines the effects of a similar kind which have taken place in less fabulous ages, and nearer our own times. John Henry Cohausen informs us, that a Polish gentleman in the time of the Queen Bona Sforza, having drunk two dishes of a liquor called brandy-wine, vomited flames, and was burned by them, and Thomas Bartholin * thus describes a similar accident : " A poor woman at Paris used to drink spirit of wine plentifully for the space of three years, so as to take nothing else. Her body contracted such a combustible disposition, that one night, when she lay down on a straw couch, she was all burned to ashes except her skull and the extremities of her fingers." John Christ. Sturmi- us informs us in the German Ephemerides, that in the northern countries of Europe flames often eva- porate from the stomachs of those who are addict- * Acta Medica et Philosophica Hafniensia, 1673. CASE OF COUNTESS ZANCARI. 323 ed to the drinking* of strong liquors ; and he adds, " that seventeen years before, three noblemen of Courland drank by emulation strong liquors, and two of them died scorched and suffocated by a flame which issued from their stomach." One of the most remarkable cases of spontane- ous combustion is that of the Countess Cornelia Zangari and Bandi of Cesena, which has been mi- nutely described by the Reverend Joseph Bianchi- ni, a prebend in the city of Verona. This lady, who was in the sixty-second year of her age, retir- ed to bed in her usual health. Here she spent above three hours in familiar conversation with her maid and in saying her prayers ; and having at last fal- len asleep, the door of her chamber w as shut. As her maid was not summoned at the usual hour, she went into the bed-room to wake her mistress ; but receiving no answer she opened the window, and saw her corpse on the floor in the most dreadful condition. At the distance of four feet from the bed there was a heap of ashes. Her legs, with the stockings on, remained untouched, and the head, half-burned, lay between them. Nearly all the rest of the body was reduced to ashes. The air in the room was charged with floating soot. A small oil lamp on the floor was covered with ashes but had no oil in it ; and in two candlesticks, which stood upright upon a table, the cotton wick of both the candles was left, and the tallow of both had disappeared. The bed was not injured, and the blankets and sheets were raised on one side as if a person had risen up from it. From an examination of all the circumstances of this case, it has been ge- nerally supposed that an internal combustion had 324 LETTERS ON NATURAL MAGIC. taken place ; that the lady had risen from her bed to cool herself, and that, in her way to open the window, the combustion had overpowered her, and consumed her body by a process in which no flame was produced which could set fire to the furniture or the floor. The Marquis Scipio Maffei was in- formed by an Italian nobleman who passed through Cesena a few days after this event, that he heard it stated in that town, that the Countess Zangari was in the habit, when she felt herself indisposed, of washing all her body with camphorated spirit of wine. So recently as 1744 a similar example of spon- taneous combustion occurred in our own country at Ipswich. A fisherman's wife of the name of Grace Pett, of the parish of St Clements, had been in the habit for several years of going down stairs every night after she was half-undressed to smoke a pipe. She did this on the evening of the 9th of April 1744. Her daughter, who lay in the same bed with her, had fallen asleep, and did not miss her mother till she awaked early in the morning. Upon dressing herself, and going down stairs, she found her mother's body lying on the right side with her head against the grate, and extended over the hearth with her legs on the deal floor, and appearing like a block of wood burning with a glowing fire with- out flame. Upon quenching the fire with two bowls of water, the neighbours, whom the cries of the daughter had brought in, were almost stifled with the smell. The trunk of the unfortunate woman was almost burned to ashes, and appeared like a heap of charcoal covered with white ashes. The head, arms, legs, and thighs, were also much FIRE TEMPLES OF THE GUEBRES. 325 burned. There was no fire whatever in the grate, and the candle was burned out in the socket of the candlestick, which stood by her. The clothes of a child on one side of her, and a paper screen on the other, were untouched ; and the deal floor was neither singed nor discoloured. It was said that the woman had drunk plentifully of gin overnight in welcoming a daughter who had recently return- ed from Gibraltar. Among the phenomenaof the natural world which are related to those of spontaneous combustion, are what have been called the natural fire temples of the Guebres, and the igneous phenomena which are seen in their vicinity. The ancient sect of the Guebres or Parsees, distinguished from all other sects as the worshippers of fire, had their origin in Per- sia ; but, being scattered by persecution, they sought an asylum on the shores of India. Those who re- fused to expatriate themselves continued to inhabit the shores of the Caspian Sea, and the cities of Ispahan, Yezd, and Kerman. Their great fire temple called Attush Kudda stands in the vicinity of Badku, one of the largest and most commodious ports in the Caspian. In the neighbourhood of this town the earth is impregnated with naphtha, an inflammable mineral oil, and the inhabitants have no other fuel, and no other light, but what is derived from this substance. The remains of the ancient fire temples of the Guebres are still visible about ten miles to the north- east of the town. The temple in which the Deity is worshipped under the form of fire is a space about thirty yards square, surrounded with a low wall, and containing many apartments. In each of 326 LETTERS ON NATURAL MAGIC. these a small volcano of sulphureous fire issues from the ground through a furnace or funnel in the shape of a Hindoo altar. On closing the fun- nel the fire is instantly extinguished, and by pla- cing the ear at the aperture a hollow sound is heard, accompanied with a strong current of cold air, which may be lighted at pleasure by holding to it any burning substance. The flame is of a pale clear colour, without any perceptible smoke, and emits a highly sulphureous vapour, which impedes respira- tion, unless when the mouth is kept beneath the level of the furnace. This action on the lungs gives the Guebres a wan and emaciated appearance, and oppresses them with a hectic cough, which strangers also feel while breathing this insalubrious atmosphere. For about two miles in circumference, round the principal fire, the whole ground, when scraped to the depth of two or three inches, has the singular pro- perty of being inflamed by a burning coal. In this case, however, it does not communicate fire to the adjacent ground : But if the earth is dug up with a spade, and a torch brought near it, an extensive, but instantaneous conflagration takes place, in which houses have often been destroyed, and the lives of the people exposed to imminent danger. When the sky is clear and the weather serene, the springs in their ebullition do not rise higher than two or three feet ; but in gloomy weather, and during the prevalence of stormy clouds, the springs are in a state of the greatest ebullition, and the naphtha, which often takes fire spontaneously at the earth's surface, flows burning in great quantities to the sea, which is frequently covered with it, in a FIRE TEMPLES OF THE GUEBRES. 3l27 state of flame, to the distance of several leagues from the shore. Besides the fires in the temple, there is a large one which springs from a natural cliff in an open situation, and which continually burns. The ge- neral space in which this volcanic fire is most abun- dant is somewhat less than a mile in circuit. It forms a low flat hill sloping to the sea, the soil of which is a sandy earth mixed with stones. Mr Forster did not observe any violent eruption of flame in the country around the Attush Kudda ; but Kinneir informs us, that the whole country round Baclku has at times the appearance of being- enveloped in flames. " It often seems," he adds, " as if the fire rolled down from the mountains in large masses, and with incredible velocity ; and during the clear moonshine nights of November and De- cember, a bright blue light is observed at times to cover the whole western range. The fire does not consume, and if a person finds himself in the mid- dle of it no warmth is felt." The inhabitants apply these natural fires to do- mestic purposes, by sinking a hollow cane or mere- ly a tube of paper, about two inches in the ground, and by blowing upon a burning coal held near the orifice of the tube, there issues a slight flame, which neither burns the cane nor the paper. By means of these canes or paper tubes, from which the fire issues, the inhabitants boil the water in their cof- fee urns, and even cook different articles of food. The flame is put out by merely plugging up the orifice. The same tubes are employed for illumi- nating houses that are not paved. The smell of naphtha is of course diffused through the house, but 328 LETTERS ON NATURAL MAGIC. after any person is accustomed to it, it ceases to be disagreeable. The inhabitants also employ this natu- ral fire in calcining- lime. The quantity of naphtha procured in the plain to the south east of Badku is enormous. It is drawn from wells, some of which yield from 1000 to 1500 lbs per day. As soon as these wells are emptied, they fill again till the naph- tha rises to its original level. # Inflammable gases issuing- from the earth have been used both in the old and the new world for do- mestic purposes. In the salt mine of Gottesgabe at Rheims, in the county of Fecklenburg-, there is a pit called the Pit of the Wind, from which a constant current of inflammable gas has issued for sixty years. M. Roeder, the inspector of the mines, has used this gas for two years not only as a light but for all the purposes of domestic economy. In the pits which are not worked, he collects the gas and conveys it in tubes to his house. It burns with a white and bril- liant flame, has a density of about 0.66, and contains traces of carbonic acid gas and sulphuretted hydro- gen, f Near the village of Fredonia in North America, on the shores of Lake Erie, are a number of burn- ing springs as they are called. The inflammable gas which issues from these springs is conveyed in pipes to the village, which is actually lighted by them. £ In the year 1828, a copious spring of inflammable gas was discovered in Scotland in the bed of a rivu- let which crosses the north road between Glasgow and Edinburgh, a little to the east of the seventh * See Forster's Travels, and Kinneir's Geog. Memoir, f Edinburgh Journal of Science, No. xv. p. 183. i Id. Id. SPRINGS OF INFLAMMABLE GAS. 329 mile-stone from Glasgow, and only a few hundred yards from the house of Bedlay. The gas is said to issue for more than half a mile along- the banks of the rivulet. Dr Thomson, who has analysed the gas, saw it issuing only within a space about fifty yards in length, and about half as much in breadth. " The emission of gas was visible in a good many places along the declivity to the rivu- let in the immediate neighbourhood of a small farm-house. The farmer had set the gas on fire in one place about a yard square, out of which a great many small jets were issuing. It had burnt without interruption during five weeks, and the soil ( which was clay ) had assumed the appearance of pounded brick all around. " The flame was yellow and strong, and resem- bled perfectly the appearance which carburetted hy- drogen gas or Jive damp presents when burnt in day-light. But the greatest issue of gas was in the rivulet itself, distant about twenty yards from the place where the gas was burning. The rivulet when I visited the place was swollen and muddy, so as to prevent its bottom from being seen. But the gas issued up through it in one place with great violence, as if it had been in a state of compression under the surface of the earth ; and the thickness of the jet could not be less than two or three inch- es in diameter. We set the gas on fire as it issued through the water. It burnt for some time with a good deal of splendour; but as the rivulet was swollen and rushing along with great impetuosity, the regularity of the issue was necessarily disturb- ed, and the gas was extinguished." Dr Thomson, found this gas to consist of two volumes of hydro- 330 LETTERS ON NATURAL MAGIC. gen gas and one volume of vapour of carbon ; and as its specific gravity was 0.555, and as it issues in great abundance, he remarks that it might be used for filling air-balloons. " Were we assured, " he adds, ' 6 that it would continue to issue in as great abundance as at present, it might be employed in lighting the streets of Glasgow." * A very curious natural phenomenon, called the Lantern or Natural Lighthouse of Maracaybo, has been witnessed in South America. A bright light is seen every night on a mountainous and uninhabit- ed spot on the banks of the river Catatumbo, near its junction with the Sulia. It is easily distinguish- ed at a greater distance than forty leagues, and as it is nearly in the meridian of the opening of the Lake of Maracaybo, navigators are guided by it as by a lighthouse. This phenomenon is not only seen from the sea coast but also from the interior of the country, — at Merida, for example, where M. Palacios observed it for two years. Some persons have ascribed this remarkable phenomenon to a thunder storm, or to electrical explosions, which might take place daily in a pass in the mountains; and it has even been asserted, that the rolling of thunder is heard by those who approach the spot. Others suppose it to be an air volcano, like those on the Caspian Sea, and that it is caused by asphaltic soils like those of Mena. It is more probable, how- ever, that it is a sort of carburetted hydrogen, as hydrogen gas is disengaged from the ground in the same district, f * Edinburgh Journal of Science, No. i. New Series, p. 71. —75. f Humboldt's Personal Narrative, Vol. iv. p. 254, note. FLUIDS IN MINERAL CAVITIES. 031 Grand as the chemical operations are which are going- on in the great laboratory of Nature, and alarming as their effects appear when they are dis- played in the terrors of the earthquake and the vol- cano, yet they are not more wonderful to the phi- losopher than the minute though analogous opera- tions which are often at work near our own persons, unseen and unheeded. It is not merely in the bowels of the earth that highly expansive elements are imprisoned and restrained, and occasionally called into tremendous action by the excitation of heat and other causes. Fluids and vapours of a similar character exist in the very gems and pre- cious stones which science has contributed to lux- ury and to the arts. In examining with the microscope the structure of mineral bodies, I discovered in the interior of many of the gems thousands of cavities of various forms and sizes. Some had the shape of hollow and regularly formed crystals : others possessed the most irregular outline, and consisted of many cavi- ties and branches united without order, but all com- municating with each other. These cavities some- times occurred singly, but most frequently in groups forming strata of cavities at one time perfectly flat and at another time curved. Several such strata were often found in the same specimen, sometimes parallel to each other, at other times inclined, and forming all varieties of angles with the faces of the original crystal. These cavities, which occurred in sapphire, chrysoberyl, topaz, beryl, quartz, amethyst, peri- dot, and other substances, were sometimes sufficient- ly large to be distinctly seen by the naked eye, but 332 LETTERS ON NATURAL MAGIC. most frequently they were so small as to require a high magnifying- power to be well seen, and often they were so exceedingly minute, that the highest magnifying powers were unable to exhibit their outline. The greater number of these cavities, whether large or small, contain two new fluids different from any hitherto known, and possessing remarkable physi- cal properties. These two fluids are in general perfectly transparent and colourless, and they exist in the same cavity in actual contact, without mix- ing together in the slightest degree. One of them expands thirty times more than water, and at a tem- perature of about 80° of Fahrenheit it expands so as to fill up the vacuity in the cavity. This will be un- derstood from the annexed figure, where A B C D is Fig. 75. the cavity, mn p o the highly expansible fluid in which at low temperatures there is always a vacuity V, like an air-bubble in common fluids, and A mn, Co p, the second fluid occupying the angles A and C. When heat such as that of the hand is applied to the specimen, the vacuity V gradually contracts in size, and wholly vanishes at a temperature of about VAPOUR CAVITIES IN MINERALS. 333 80°, as shewn in Fig. 76. The fluids are shaded, as in these two figures, when they are seen by light reflected from their surfaces. Fig. 76. When the cavities are large, as in Fig 77, com- pared with the quantity of expansible fluid m np o, the heat converts the fluid into vapour, an effect Fig. 77. TV. fi which is shewn by the circular cavity V becoming larger and larger till it fills the whole space m n op. When any of these cavities, whether they are 334 LETTERS ON NATURAL MAGIC. filled with fluid or with vapour, is allowed to cool, the vacuity V reappears at a certain temperature. In the fluid cavities the fluid contracts, and the small vacuity appears, which grows larger and larger tillit resumes its original size. When the cavities are large several small vacuities make their appearance and gradually unite into one, though they sometimes remain sepa- rate. In deep cavities a very remarkable phenome- non accompanies the reappearance of the vacuity. At the instant that the fluid has acquired the tem- perature at which it quits the sides of the cavity, an effervescence or rapid ebullition takes place, and the transparent cavity is for a moment opaque, with an infinite number of minute vacuities, which in- stantly unite into one that goes on enlarging as the temperature diminishes. In the vapour cavi- ties the vapour is reconverted by the cold into fluid, and the vacuity V, Fig 77, gradually contracts till all the vapour has been precipitated. It is curious to observe, when a great number of cavities are seen at once in the field of the microscope, that the va- cuities all disappear and reappear at the same in- stant. While all these changes are going on in the ex- pansible fluid, the other denser fluid at A and C, Fig. 75, 76, remains unchanged either in its form or magnitude. On this account I experienced con- siderable difficulty in proving that it was a fluid. The improbability of two fluids existing in a transpa- rent state in absolute contact, without mixing in the slightest degree, or acting upon each other, indu- ced many persons to whom I shewed the phenome- non to consider the lines m n, o p, Fig. 75, 76, as a partition in the cavity, or the spaces A m n, C o p y CAVITIES IN MINERALS. 335 either as filled with solid matter, or as corners into which the expanding- fluid would not penetrate. The regular curvature, however, of the boundary line m n, op, and other facts, rendered these suppo- sitions untenable. This difficulty was at last entirely removed by the discovery of a cavity of the form shewn in the annexed figure, where A , B, and C, are three por- tions of the expansible fluid separated by the inter- Fig. 78. position of the second fluid D E F. The first por- tion A of the expansible fluid had four vacuities V, X, Y, Z, while the other two portions B, C, had no vacuity. In order to determine if the va- cuities of the portions B, C, had passed over to A, I took an accurate drawing of the appearances at a temperature of 50°, as shewn in the figure, and I watched the changes which took place in raising the temperature to 83°. The portion A gradually expanded itself till it filled up all the four vacuities V, X, Y, and Z, but as the vacuities B, C, had no vacuities, they could expand themselves only by pushing back the supposed second fluid D E F. This effect actually took place. The dense fluid quitted the side of the cavity at F. The two portions B, C, of the expansible fluid instantly united, and 336 LETTERS ON NATURAL MAGIC. the dense fluid having- retreated to the limit m n n o, its other limit advanced to p q r, thus proving it to be a real fluid. This experiment, which I have often shewn to others, involves one of those rare combinations of circumstances which nature sometimes presents to us in order to illustrate her most mysterious operations. Had the portions B, C, been accompanied, as is usual, with their va- cuities, the interposed fluid would have remained immoveable between the two equal and opposite expansions ; but owing- to the accidental circum- stance of these vacuities having passed over into the other branch A of the cavity, the fluid yield- ed to the difference of the expansive forces between which it lay, and thus exhibited its fluid character to the eye. When we examine these cavities narrowly, we find that they are actually little laboratories, in Fig. 79. which chemical operations are constantly going- on, and beautiful optical phenomena continually dis- FLUIDS IN MINERALS. 337 playing themselves. Let ABDC, for example, be the summit of a crystallized cavity in topaz, S S re- presenting- the dense, N N the expansible fluid, bound- ed by a circular line abed, and V V the vacuity in the new fluid, bounded by the circle ef g h. If the face A B D C is placed under a compound micro- scope, so that light may be reflected at an angle less than that of total reflexion, and if the observer now looks through the microscope, the temperature of the room being 50°, he will see the second fluid S S shining with a very feeble reflected light, the dense fluid N N with a light perceptibly brighter, and the vacuity V V, with a light of considerable brilliancy. The boundaries abed, efgh are marked by a well-defined outline, and also by the concentric coloured rings of thin plates produced by the extreme thinness of each of the fluids at their edges. If the temperature of the room is raised slowly to 58°, a brown spot will appear at x in the centre of the vacuity V V. This spot indicates the com- mencement of evaporation from the expansible fluid below, and arises from the partial precipitation of the vapour in the roof of the cavity. As the heat increases, the brown spot enlarges and becomes very dark. It is then succeeded by a white spot, and one or more coloured rings rise in the centre of the vacuity. The vapour then seems to form a drop, and all the rings disappear by retiring to the centre, but only to reappear with new lustre. During the application of heat, the circle efgh contracts and dilates like the pupil of the eye. When the vaporization is so feeble as to produce only a single ring of one or two tints of the second 338 LETTERS ON NATURAL MAGIC. order, they vanish instantly by breathing upon the crystal, but when the slight heat of the breath reaches the fluid, it throws off fresh vapour, and the rings again appear. If a drop of ether is put upon the crystal when the rings are in a state of .rapid play, the cold pro- duced by its evaporation causes them to disappear, till the temperature again rises. When the tem- perature is perfectly uniform, the rings are station- ary, as shewn between V and V in Fig. 79 ; and it is interesting to observe the first ring produced by the vapour swelling out to meet the first ring at the margin of the fluid, and sometimes coming so near it that the darkest parts of both form a broad black band. As the heat increases, the vacuity V V diminishes and disappears at 79°, exhibiting many curious phenomena, which we have not room to describe. Having fallen upon a method of opening the cavi- ties, and looking at the fluids, I was able to examine their properties with more attention. When the expansible fluid first rises from the cavity upon the surface of the topaz, it neither remains still like the fixed oils, nor disappears like evaporable fluids. Under the influence, no doubt, of heat and moisture it is in a state of constant motion, now spreading itself on a thin plate over a large surface, and now contracting itself into a deeper and much less ex- tended drop. These contractions and extensions are marked by very beautiful optical phenomena. When the fluid has stretched itself out into a thin plate, it ceases to reflect light like the thinest part of the soap-bubble, and when it is again accumulated NEW FLUIDS IN MINERALS. 339 into a thicker drop, it is covered with the coloured ring-s of thin plates. After performing these motions, which sometimes last for ten minutes, the fluid suddenly disappears, and leaves behind it a sort of granular residue. When examining this with a single microscope, it again started into a fluid state, and extended and contracted itself as before. This was owing to the humidity of the hand which held the microscope, and I have been able to restore by moisture the fluidity of these grains twenty days after they were formed from the fluid. This portion was shewn to the Reverend Dr Fleming, who remarked, that, had he observed it accidentally, he would have ascribed its apparent vitality to the movements of some of the animals of the genus Planaria. After the cavity has remained open for a day or two, the dense fluid comes out and quickly hardens into a transparent and yellowish resinous-looking substance, which absorbs moisture, though with less avidity than the other. It is not volatilized by heat, and is insoluble in water and alcohol. It readily dissolves, however, with effervescence in the sul- phuric, nitric, and muriatic acids. The residue of the expansible fluid is volatilized by heat, and is dis- solved, but without effervescence, in the above- mentioned acids. The refractive power of the dense fluid is about 1.295, and of the expansible one 1.131. The particles of the dense fluid have a very powerful attraction for each other and for the mine- ral which contains them, while those of the expan- sible fluid have a very slight attraction for one another, and also for the substance of the mine- 340 LETTERS ON NATURAL MAGIC. ral. Hence the two fluids never mix, the dense fluid being- attracted to the angles of angular cavi- ties, or filling- the narrow necks by which two cavi- ties communicate. The expansible fluid, on the other hand, fills the wide parts of the cavities, and in deep and round cavities it lies above the dense fluid. , When the dense fluid occupies the necks which join two cavities, it performs the singular function of a fluid valve, opening- and shutting- itself accord- ing- to the expansions or contractions of the other fluid. The fluid valves thus exhibited in ac- tion may sug-gest some useful hints to the mecha- nic and the philosopher, while they afford ground of curious speculation in reference to the func- tions of animal and vegetable bodies. In the larger organizations of ordinary animals, where gravity must in general overpower, or at least modify, the influence of capillary attraction, such a mechanism is neither necessary nor appropriate ; but, in the lesser functions of the same animals, and in almost all the microscopic structures of the lower world, where the force of gravity is entirely subjected to the more powerful energy of capillary forces, it is extremely probable that the mechanism of immis- cible fluids and fluid valves is generally adopted. In several cavities in minerals I have found crys- tallised and other bodies, sometimes transparent crystals, sometimes black spicular crystals, and sometimes black spheres, all of which are moveable within the cavity. In some cavities the two new fluids occur in an indurated state, and others I have found to be lined with a powdery matter. This last class of cavities occurred in topaz, and they 4 CHANGE OF COLOUR IN CLOTHES. 341 were distinguished from all others by the extraor- dinary beauty and symmetry of their form. One of these cavities represented a finely ornamented scep- tre, and, what is still more singular, the different parts of which it is composed lay in different planes. When the gem which contains the highly ex- pansive fluid is strong, and the cavity not near the surface, heat may be applied to it without danger, but in the course of my experiments on this sub- ject, the mineral has often burst with a tremendous explosion, and in one case wounded me on the brow. An accident of the same kind occurred to a gentleman, who put a crystal into his mouth for the purpose of expanding the fluid. The specimen burst with great force and cut his mouth, and the fluid which was discharged from the cavity had a very disagreeable taste. In the gems which are peculiarly appropriated for female ornaments, cavities containing the ex- pansible fluid frequently occur, and if these cavities should happen to be very near the surface or the edge of the stone, the fever heat of the body might be sufficient to burst them with an alarming and even dangerous explosion. I have never heard of any such accident having occurred ; but if it has, or if it ever shall occur, and if its naturally marvel- lous character shall be heightened by any calamitous results, the phenomena described in the preceding pages will strip it of its wonder. There are no facts in chemistry more interesting than those which relate to the changes of colour, which are produced by the mixture of fluids, and to the creation of brilliant colours by the combination of bodies in which no colouring matter is visible. 342 LETTERS ON NATURAL MAGIC. Feats of this kind are too common and too general- ly known to require to be noticed in a work like this. The art of producing such changes was known to some of the early impostors, who endea- voured to obtain a miraculous sanction to their parti- cular dogmas. Marcos, the head of one of the sects that wished to engraft paganism upon Christianity, is said to have filled three transparent glasses with white wine, and while he prayed, the wine in one of the glasses became red like blood, that in another became purple, and that in the third sky-blue. Such transformations present no difficulty to the chemist. There are several fluids, such as some of the coloured juices of plants, which change their co- lour rapidly and without any additional ingredient ; and in other cases, there would be no difficulty in making additions to fluids, which should produce a change of colour at any required instant. A very remarkable experiment of an analogous nature has been publicly exhibited in modern times. Professor Beyruss, who lived at the court of the Duke of Brunswick, one day pronounced to his highness that the dress which he wore should during dinner become red ; and the change actually took place to the astonishment of the prince and the rest of his guests. M. Vogel, who has record- ed this curious fact, has not divulged the secret of the German chemist ; but he observes, that, if we pour lime-water into the juice of beet root, we shall ob- tain a colourless liquid ; and that a piece of white cloth dipped in this liquid and dried rapidly will in a few hours become red by the mere contact of air. M. Vogel is also of opinion that this singular effect would be accelerated in an apartment where EFFECTS OF INTOXICATING GAS. 348 champagne or other fluids charged with carbonic acid are poured out in abundance. Among the wonders of chemistry we must num- ber the remarkable effects produced upon the hu- man frame by the inhalation of paradise or intoxi- cating gas, as it has been called. This gas is known to chemists by the name of the nitrous oxide, or the gaseous oxide of azote, or the protoxide of nitrogen. It differs from atmospheric air only in the proportion of its ingredients, atmospheric air be- ing composed of twenty-seven parts of oxygen and seventy-three of nitrogen, while the nitrous oxide consists of thirty-seven parts of oxygen, and sixty- seven of nitrogen. The most convenient way of procuring the gas is to expose nitrate of ammonia in a tubulated glass retort to the heat of an argand's lamp between 400° and 500° of Fahrenheit. The salt first melts ; bubbles of gas begin to rise from the mass, and in a short time a brisk effervescence takes place, which continues till all the salt has dis- appeared. The products of this operation are the nitrous oxide and water, the watery vapour being condensed in the neck of the retort while the gas is received over water. The gas thus obtained is generally white, and hence, when it is to be used for the purposes of respiration, it should remain at least an hour over water, which will absorb the small quantity of acid and of nitrate of ammonia which adhere to it. A pound of the nitrate of ammonia will in this way yield five cubic feet of gas fit for the purpose of inhalation. It was discovered by Sir Humphry Davy, that this gas could be safely taken into the lungs, and that it was capable of supporting respiration for a 344 LETTERS ON NATURAL MAGIC. few minutes. In making this experiment he was surprised to find that it produced a singular species of intoxication, which he thus describes : " I breath- ed/' says he, " three quarts of oxide from and into a silk bag for more than half a minute without pre- viously closing my nose or exhausting my lungs. The first inspiration caused a slight degree of gid- diness. This was succeeded by an uncommon sense of fulness in the head, accompanied with loss of distinct sensation and voluntary power, a feeling analogous to that produced in the first stage of in- toxication, but unattended by pleasurable sensa- tions.'' In describing the effects of another expe- riment, he says, " Having previously closed my nos- trils and exhausted my lungs, I breathed four quarts of nitrous oxide from and into a silk bag. The first feelings were similar to those produced in the last experiment, but in less than half a minute, the respiration being continued, they diminished gradually, and were succeeded by a highly pleasur- able thrilling, particularly in the chest and the ex- tremities. The objects around me became dazzling, and my hearing more acute. Towards the last respiration the thrilling increased, the sense of muscular power became greater, and at last an ir- resistible propensity to action was indulged in. I recollect but indistinctly what followed ; I knew that my motions were varied and violent. These effects very rarely ceased after respiration. In ten minutes I had recovered my natural state of mind. The thrilling in the extremities continued longer than the other sensations. This experiment was made in the morning ; no languor or exhaustion was consequent, my feelings through the day were EFFECTS OF INTOXICATING GAS. 345 as^ usual, and I passed the night in undisturbed re- pose." In giving an account of another experiment with this gas, Sir Humphry thus describes his feelings : " Immediately after my return from a long journey, being fatigued, I respired nine quarts of nitrous oxide, having been precisely thirty-three days with- out breathing any. The feelings were different from those I had experienced on former experi- ments. After the first six or seven respirations, I gradually began to lose the perception of external things, and a vivid and intense recollection of some former experiments passed through my mind, so that I called out, 6 what an annoying concatenation of ideas.' " Another experiment made by the same distinguish- ed chemist was attended by still more remarkable results. He was shut up in an air-tight breathing box, having a capacity of about nine and a-half cubic feet, and he allowed himself to be habituated to the excitement of the gas, which was gradually intro- duced. After having undergone this operation for an hour and a quarter, during which eighty quarts of gas were thrown in, he came out of the box and began to respire twenty quarts of unmingled nitrous oxide. " A thrilling," says he, " extending from the chest to the extremities, was almost immediately produced. I felt a sense of tangible extension, highly pleasurable in every kind, my visible im- pressions were dazzling, and apparently magnified. I heard distinctly every sound in the room, and was perfectly aware of my situation. By degrees, as the pleasurable sensation increased, I lost all connection with external things ; trains of vivid 346 LETTERS ON NATURAL MAGIC. visible images rapidy passed through my mind, and were connected with words in such a manner as to produce perceptions perfectly novel. I existed in a world of newly connected and newly modified ideas. When I was awakened from this same de- lirious trance by Dr Kinglake, who took the bag from my mouth, indignation and pride were the first feelings produced by the sight of the persons about me. My emotions were enthusiastic and sublime, and for a moment I walked round the room, perfectly regardless of what was said to me. As I recovered my former state of mind, I felt an inclination to communicate the discoveries I had made during the experiment. I endeavoured to recal the ideas ; they were feeble and indistinct. One recollection of terms, however, presented itself, and with the most intense belief and prophetic manner I exclaimed to Dr Kinglake, 6 nothing ex- ists but thoughts ; the universe is composed of im- pressions, ideas, pleasures, and pains.' " These remarkable properties induced several per- sons to repeat the experiment of breathing this ex- hilarating medicine. Its effects were, as might have been expected, various in different individuals ; but its general effect was to produce in the gravest and most phlegmatic the highest degree of exhilaration and happiness, unaccompanied with languor or de- pression. In some it created an irresistible disposi- tion to laugh, and in others a propensity to muscular exertion. In some it impaired the intellectual functions, and in several it had no sensible effect, even when it was breathed in the purest state and in considerable quantities. It would be an inquiry of no slight interest to ascertain the influence of this EFFECTS OF INHALING NITROUS OXIDE. 347 gas over persons of various bodily temperaments, and upon minds varying in their intellectual and moral character. Although Sir Humphry Davy experienced no unpleasant effects from the inhalation of the ni- trous oxide, yet such effects are undoubtedly pro- duced ; and there is reason to believe that even per- manent changes in the constitution may be indu- ced by the operation of this remarkable stimulant. Two very interesting cases of this kind presented themselves to Professor Silliman of Yale College, when the nitrous oxide was administered to some of his pupils. The students had been in the habit for several years of preparing this gas and admini- stering it to one another, and these two cases were the only remarkable ones which deserved to be re- corded. We shall describe them in Professor Sil- liman's own words : — " A gentleman about nineteen years of age, of a sanguine temperament, and cheerful temper, and in the most perfect health, inhaled the usual quan- tity of the nitrous oxide when prepared in the or- dinary manner. Immediately his feelings were uncommonly elevated, so that, as he expressed it, he could not refrain from dancing and shouting. Indeed to such a degree was he excited, that he was thrown into a frightful fit of delirium, and his exertions became so violent, that after a while he sunk to the earth exhausted, and there remained, until having by quiet in some degree recovered his strength, he again arose only to renew the most convulsive muscular efforts, and the most piercing screams and cries ; within a few moments, over- powered by the intensity of the paroxysm, he again 348 LETTERS ON NATURAL MAGIC. fell to the ground apparently senseless and panting vehemently. The long- continuance and violence of the affection alarmed his companions, and they ran for professional assistance. They were, how- ever, encouraged hy the person to whom they ap- plied to hope that he would come out of his trance without injury, hut for the space of two hours these symptoms continued ; he was perfectly unconscious of what he was doing-, and was in every respect like a maniac. He states, however, that his feel- ings vibrated between perfect happiness and the most consummate misery. In the course of the afternoon, and after the first violent effects had sub- sided, he was compelled to lie down two or three times, from excessive fatigue, although he was im- mediately aroused upon any one's entering the room. The effects remained in a degree for three or four days accompanied hy a hoarseness, which he attri- buted to the exertion made while under the imme- diate influence of the gas. This case should pro- duce a degree of caution, especially in persons of a sanguine temperament, whom, much more frequent- ly than others, we have seen painfully and even alarmingly affected." The other case described by Professor Silliman was that of a man of mature age, and of a grave and respectable character. " For nearly two years previous to his taking the gas his health had been very delicate, and his mind frequently gloomy and depressed. This was peculiarly the case for a few days immediately preceding that time, and his ge- neral state of health was such that he was obliged almost entirely to discontinue his studies, and was about to have recourse to medical assistance. In this CONCLUSION. 349 state of bodily and mental debility he inspired about three quarts of nitrous oxide. The consequences were, an astonishing- invigoration of his whole sys- tem, and the most exquisite perceptions of delight. These were manifested by an uncommon disposition for pleasantry and mirth, and by extraordinary mus- cular power. The effects of the gas were felt with- out diminution for at least thirty hours, and in a greater or less degree for more than a week. " But the most remarkable effect was that upon the organs of taste. Antecedently to taking the gas, he exhibited no peculiar choice in the articles of food, but immediately subsequent to that event, he mani- fested a taste for such things only as were sweet, and for several days ate nothing but sweet cake. In- deed this singular taste was carried to such excess, that he used sugar and molasses not only upon his bread and butter and lighter food, but upon his meat and vegetables. This he continues to do even at the present time, and although eight weeks have elapsed since he inspired the gas, he is still found pouring molasses over beef fish, poultry, potatoes, cabbage, or whatever animal or vegetable food is placed before him. " His health and spirits since that time have been uniformly good, and he attributes the restoration of his strength and mental energy to the influence of the nitrous oxide. He is entirely regular in his mind, and now experiences no uncommon ex- hilaration, but is habitually cheerful, while before he was as habitually grave, and even to a degree gloomy.'' Such is a brief and a general account of the prin- 350 LETTERS ON NATURAL MAGIC. cipal phenomena of Nature, and the most remark- able deductions of science, to which the name of Na- tural Magic has been applied. If those who have not hitherto sought for instruction and amusement in the study of the material world shall have found a portion of either in the preceding pages, they will not fail to extend their inquiries to other po- pular departments of science, even if they are less marked with the attributes of the marvellous. In every region of space, from the infinitely distant recesses of the heavens to the " dark unfathomed caves of ocean," the Almighty has erected monu- ments of miraculous grandeur, which proclaim the power, the wisdom, and the beneficence of their au- thor. The inscriptions which they bear — the hand- writing which shines upon their walls — appeal to the understanding and to the affections, and demand th& admiration and the gratitude of every rational being. To remain willingly ignorant of these reve- lations of the Divine Power is a crime next to that of rejecting the revelation of the Divine will. Know- ledge, indeed, is at once the handmaid and the com- panion of true religion. They mutually adorn and support each other ; and beyond the im- mediate circle of our secular duties, they are the only objects of rational ambition. While the calm deductions of reason regulate the ardour of Christ- ian zeal, the warmth of a holy enthusiasm gives a fixed brightness to the glimmering lights of know- ledge. It is one of the darkest spots in the history of man that these noble gifts have been so seldom com- bined. In the young mind alone can the two kindred seeds be effectually sown ; and among the 3 CONCLUSION. 351 improvements which some of our public institutions require, we yet hope to witness a national system of instruction, in which the volumes of Nature and of Revelation shall be simultaneously perused. D. Brewster. Allerly, April 24th 1832. THE END. EDINBURGH I PRINTED BY JOHN STARK, Old Assembly Clone. If