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—AËrial images—Images on smoke—Combination 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 lantern—Improvements upon it—Phantasmagoric exhibitions of Philipstall and others—Dr. Young’s arrangement of lenses, &c., for the Phantasmagoria—Improvements suggested—Catadioptrical phantasmagoria for producing the pictures from living objects—Method of cutting off parts of the figures—Kircher’s mysterious hand-writing on the wall—His hollow cylindrical mirror for aËrial images—Cylindrical mirror for re-forming 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 exercise 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 superstition. 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 government which was in perfect accordance with their religious belief: but it will scarcely be believed that the same delusions were practised after the establishment of Christianity, and that even the Catholic sanctuary was often the seat of these unhallowed 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 magician’s wand over the diadem 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 intellectual darkness, and it is entirely in consequence of its wide diffusion that we live in times when sovereigns 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 engine 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 practised by means of plane and concave mirrors. It has been clearly shown by various writers that the ancients made use of mirrors of steel, silver, and a composition of copper and tin, like those now used for 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 presented to them was illuminated in a very high degree, 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, mentioned 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 another place, recovered their property of reflection.7 M. Salverte is of opinion that, in quoting Varro, Aulus Gellius was not sufficiently acquainted with the subject, and erred in supposing that the phenomenon depended on the place instead of the position of the mirror; but this criticism is obviously made with the view of supporting an opinion of his own—that the property in question may be analogous 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 nicely 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 thoroughly acquainted with the modern discovery of the polarisation of light by reflexion. Without seeking for so profound an explanation of the phenomenon, we may readily understand how a silver mirror may instantly lose its reflecting power in a damp atmosphere, in consequence of the precipitation of moisture upon its surface, and may immediately recover it when transported into drier air.

One of the simplest instruments of optical deception is the plane mirror, and when two are combined for this purpose it has been called the magician’s mirror. An observer in front of a plane mirror sees a distinct image of himself; but if two persons take up a mirror, and if the one person is as much to one side of a line perpendicular to the middle of it as the other is to the other side, they will see each other, but not themselves. If we now suppose MC, CD, NC, CD to be the partitions of two adjacent apartments let square openings be made in the partitions at A and B, above 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 himself, 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 seeing himself transformed into another person, or into 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 moveable mirror, would be still more astonished when he afterwards perceived in the same place a face different from his own. By drawing the moveable mirror 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 F and the apartment NCD are not absolutely necessary for carrying on this deception; for the very same effects will be produced if the person at B is stationed at 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 CN, 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 combined, 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 almost supernatural.

The method of exhibiting the effect of concave mirrors most advantageously is shown in Fig. 4, 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 surrounded with a picture-frame, and a painting which exactly filled it might be so connected with a pulley that it could be either slipped aside, or raised so as to leave the frame empty. A large concave mirror MN is then placed in another apartment, so that when any object is placed at A, a distinct image of it may be formed in the centre of the opening EF. Let us suppose this object to be a plaster cast of 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 reaching the opening EF. When this is done, a spectator placed at O will see an erect image of the statue 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 distance 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 below, the image will appear in the middle of the smoke depicted upon it as upon a ground, and capable of being seen by those spectators who could not see the image of the air. The rays of light, in place of proceeding without obstruction to an eye 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 invisible 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 himself of so admirable a resource; but this difficulty may be removed by employing a second concave mirror. The second mirror may 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 inverted image will then be formed at B, either suspended in the air, or depicted upon a wreath of smoke. This aËrial 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 unsubstantial fabric.

A deception of an alarming kind, called the Mysterious dagger, has been long a favourite exhibition. If a person with a drawn and highly polished dagger, illuminated by a strong light, stands a little farther from a concave mirror than its principal focus, he will perceive in the air between himself and 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 mirrors concavity, the two daggers will meet point to point, and, by pushing it still farther from him towards the mirror, the imaginary dagger will strike at his heart. In this case it is necessary that the direction of the real dagger coincides with a diameter of the sphere of which the mirror is a part; but if its direction is on one side of that diameter, the direction of the imaginary dagger will be as far on the other side of the diameter, 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 therefore placed behind a screen, or otherwise concealed from the view of the spectator, who is made to approach 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 experiment 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 mirrors, indeed, this defect might be remedied, and the spectator would witness an exact image of the assassin 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 aËrial image of the fruit is formed in the focus of the mirror. The spectator, having been desired to take some fruit from the basket, approaches 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 spectator.

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 background 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 aËrial image is to that of the real object as their distances from the mirror, we may, by varying 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 luminous spot to a gigantic size, and again passing through all intermediate magnitudes, till it vanishes in a cloud of light.

Those who have studied the effects of concave mirrors of a small size, and without the precautions necessary to ensure deception, cannot form any idea of the magical effect produced by this class of optical apparitions. When the instruments of illusion 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 representation on ignorant minds is altogether overpowering; while even those who know the deception, 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 apartment, to the same picture exhibited under all the imposing accompaniments of a dioramic representation.

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 celebrated as the place where the goddesses exhibited themselves to mortals. Iamblichus actually informs 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 incense, he was obviously dealing with the image of a living object dressed in the costume of the sorceress.

The character of these exhibitions in the ancient temples is so admirably depicted in the following passage of Damascius, quoted by M. Salverte, that we recognise all the optical effects which have been already described. “In a manifestation,” says he, “which ought not to be revealed ... there appeared on the wall of the temple a mass of light, which at first seemed to be very remote; it transformed itself, in coming nearer, into a face evidently divine and supernatural, of a severe aspect, but mixed with gentleness, and extremely beautiful. According to the institutions of a mysterious religion, 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 ecclesiastical 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 disappeared. 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 discovered and denounced, even if we could explain how the son could be so instantaneously disentangled from his father’s embrace. The emperor, in short, saw the aËrial 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 instrument of government, must have brought into requisition not merely the scientific skill of the age, but a variety of subsidiary contrivances calculated to astonish the beholder, to confound his judgment, to dazzle his senses, and to give a predominant 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, supplied by an account of a modern necromancy, which has been left us by the celebrated Benvenuto 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 Sicilian priest, who was a man of genius, and well versed in the Latin and Greek authors. Happening one day to have some conversation with him when the subject turned upon the art of necromancy, I, who had a great desire to know something of the matter, told him, that I had all my life felt a curiosity to be acquainted with the mysteries of this art.

“The priest made answer, ‘that the man must be of a resolute and steady temper who enters upon that study.’ I replied, ‘that I had fortitude and resolution 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 satisfaction you can desire.’ Thus we agreed to enter upon 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 cultivated 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 imaginable: he likewise brought hither asafoetida, several precious perfumes, and fire, with some compositions 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, ordered the other necromancer, his partner, to throw the perfumes into the fire at a proper time, entrusting the care of the fire and perfumes to the rest; and thus he began his incantations. This ceremony lasted above an hour and a half, when there appeared several legions of devils, insomuch that the amphitheatre was quite filled with them. I was busy about the perfumes, when the priest, perceiving there was a considerable number of infernal spirits, turned to me and said, ‘Benvenuto, ask them something.’ I answered, ‘Let them bring me into the company of my Sicilian mistress Angelica.’ That night he obtained no answer of any sort; but I had received great satisfaction in having my curiosity so far indulged. The necromancer 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 companion the first time, and one Agnolino Gaddi, an intimate acquaintance, whom I likewise prevailed on to assist at the ceremony. When we came to the place appointed, the priest having made his preparations as before, with the same and even more striking ceremonies, placed us within the circle, which he had likewise drawn with a more wonderful 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 Vincenzio, 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 filled with demons more numerous than at the former conjuration. Vincenzio Romoli was busied in 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 enormous stature were endeavouring to break into our circle. During this time, whilst the necromancer, trembling with fear, endeavoured by mild and gentle methods to dismiss them in the best way he could, Vincenzio Romoli, who quivered like an aspen 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 contributed 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, ‘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 sooner did he look up than he cried out, ‘The whole amphitheatre is burning, and the fire is just falling upon us.’ So covering his eyes with his hands, he again exclaimed, ‘that destruction was inevitable, and desired to see no more.’ The necromancer entreated me to have a good heart, and take care to burn proper 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 assistance, so come directly and put on some more of these.’ The effects of poor Agnolino’s fear were overpowering. The boy, hearing a crepitation, ventured 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 rang 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 performed 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, especially 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 running upon the roofs of the houses, and sometimes 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, ‘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 intrepidity 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 description without being satisfied that the legions of devils were not produced by any influence upon the imaginations of the spectators, but were actual optical phantasms, or the images of pictures or objects 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 images, 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 placed that the persons within the circle could not see the aËrial image of the objects by the rays deeply reflected from the mirror, the work of deception was ready to begin. The attendance of the magician upon his mirror was by no means necessary. He took his place along with the spectators within the magic circle. The images of the devils were all distinctly formed in the air immediately 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 spectators, 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 spectators, and what parts of it were imagined by themselves. 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 declares that four armed giants, of an enormous stature, were threatening to break into the circle, he gives an accurate description of the effect that would be produced by pushing the figures nearer the mirror, and then magnifying their images, and causing them to advance towards the circle. Although Cellini declares 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 shadow.”

Mr. Roscoe, from whose Life of Cellini the preceding description is taken, draws a similar conclusion from the consolatory words addressed to the boy, and states that they “confirm him in the belief, that the whole of these appearances, like a phantasmagoria, were merely the effects of a magic 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 necromancer either had a regular magic lantern, or that he had fitted up his concave mirror in a box containing the figures of his devils, and that this box 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 we had seen at the amphitheatre went on before us leaping and skipping, sometimes running 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 appear 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 difficult on ordinary occasions to command; but the magic lantern, containing in a small compass its lamp, its lenses, and its sliding figures, was peculiarly fitted for the itinerant conjuror, who had neither the means of providing a less portable and more extensive apparatus, nor the power of transporting and erecting it.

The magic lantern shown in the annexed figure consists of a dark lantern, AB, containing a lamp G, and a concave metallic mirror, MN, 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, CD, 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 CE, there is joined a groove EF, in which the sliders containing the painted objects are placed, and through which they can be moved. Each slider contains a series of figures or pictures painted on glass with highly transparent colours. The direct light of the lamp G, and the light reflected from the mirror MN, falling upon the illuminating 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 formed on a white wall or white cloth placed at PQ. If the lens D is brought nearer to EF, 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 EF.

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 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 EF, 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 inverted in reference to the position of the painted objects; but in order to render them really erect, we have only to invert the sliders. The representations of the magic lantern never fail to excite a high degree of interest, even when exhibited with the ordinary apparatus; but by using double sliders, 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 introduction 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 motion is communicated.

The magic lantern is susceptible of great improvement 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 magnified 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 expense of exceedingly minute and spirited drawings could not be afforded; but I have no doubt that if such drawings were executed, a great part of the expense might be saved by engraving them on wood, and transferring their outline to the glass sliders.

A series of curious representations might be effected, 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 introduced at EF, 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 transparent fluid, the picture at PQ will be seen with the same distinctness as if the figure had been introduced by itself into the groove EF; 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 PQ will undergo singular changes. If spirits of wine, or any ardent spirit, are mixed with the water, so as to produce throughout its mass partial variations of density, the figure at PQ, 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 density 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 substances, soluble in water, are laid at the bottom of the trough, the density will diminish upwards, and the figure will undergo the most curious elongations and contractions. Analogous effects may be produced by the application of heat to the surface or sides of the trough, so that we may effect at the same time both an increase and a diminution 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 phenomena 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 taffeta which receives the images, while the spectators are placed on the other side, and by making 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 produce a much greater effect with the same degree of illumination. An exhibition depending on these principles was brought out by M. Philipstall in 1802, under the name of the Phantasmagoria, and when it was shown in London and Edinburgh, it produced the most impressive effects upon the spectators. 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 skeletons and other terrific figures in relief upon its walls. The flickering light was then drawn up beneath its shroud, and the spectators in total darkness found themselves in the middle of thunder and lightning. A thin transparent screen had, unknown to the spectators, been let down after the disappearance of the light, and upon it the flashes of lightning and all the subsequent appearances were represented. 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 aËrial pictures. The thunder and lightning were followed by the figures of ghosts, skeletons, and known individuals, whose eyes and mouth were made to move by the shifting of combined sliders. After the first figure 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 attained its perfect development. 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 skeletons returned in the drapery of flesh and blood.

The exhibition of these transmutations was followed by spectres, skeletons, and terrific figures, which, instead of receding and vanishing as before, suddenly 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 surprised but agitated, and many of them were of opinion that they could have touched the figures. M. Robertson, at Paris, introduced along with his pictures the direct shadows of living objects, which imitated 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 AB, 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 EF. When the lantern approached to PQ, the circle of light PQ, or the section of the cone of rays PDQ, 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 into the new one. Although the figure was always at the same distance from the spectators, yet, owing to its gradual diminution in size, it necessarily appeared to be retiring to a distance. When the magic lantern was withdrawn from PQ, and the lens D at the same time brought nearer to EF, the image in PQ gradually increased in size, and therefore seemed in the same proportion to be approaching the spectators.

Superior as this exhibition was to any representation that had been previously made by the magic lantern, it still laboured under several imperfections. The figures were poorly drawn, and in other respects not well executed, and no attempt whatever was made to remove the optical incongruity of the figures becoming more luminous when they retired from the observer, and more obscure when they approached to him. The variation of the distance of the lens D from the sliders in EF was not exactly adapted to the motion of the lantern to and 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.

The magic lantern is mounted on a small car H, which runs on wheels WW. The direct light of the lamp G, and that reflected from the mirror M, is condensed by the illuminating lenses CC, upon the transparent figures in the opaque sliders at E, and the image of these figures is formed at PQ, by the object lens D. When the car H is drawn back on its wheels, the rod IK brings down the point K, and by means of the rod KL, pushes the lens D nearer to the sliders in EF, and when the car advances to PQ, the point K is raised, and the rod KL 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 KN must be equal in length to IK, and the point I must be twice the focal length of the lens D before the object, L being immediately under 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 satisfied, 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 EF, and throw less light upon the figures when D is removed from EF, and to make C recede from EF when D approaches 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 being removed from the slider EF, when a greater intensity of light is required for the images when they are rendered gigantic, and of being brought close to EF 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 EF 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 pulling 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, however, clumsy in itself, and the connexion of the levers with the screen, and their interposition between it and the lantern, must interfere with the operations of the exhibitor. It is, besides, suited 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 KL, KI, KT, would bend by the least strain, and become 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 greatest distance from EF by a slender spring, and should be pressed to its proper distance by the action of a spiral cam suited to the optical relation between the two conjugate focal distances of the lens.

Superior as the representations of the phantasmagoria 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, mimicking humanity by the most absurd gesticulations, we shall have phantasms of the most perfect delineation, clothed in real drapery, and displaying all the movements of life. The apparatus by which such objects may be used, may be called the catadioptrical 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 AB is a living figure placed before a large concave mirror MN, by means of which a diminished and inverted image of it is formed at ab. If PQ is the transparent screen upon which the image is to be shown to the spectators on the right hand of it, a large lens LL must be so placed before the image ab, as to form a distinct and erect picture of it at A´B´ upon the screen. When the image A´B´ is required to be the exact size of AB, the lens LL must magnify the small image ab as much as the mirror MN diminishes the figure AB. The living object AB, the mirror MN, and the lens LL, 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 LL, 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 AB will require to be illuminated in the strongest 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 stretched at some distance behind them. Many interesting effects might also be produced by introducing at AB 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 ab, Fig. 7, and the lens LL, the part of the figure immediately opposite to the prism will be as it were detached from the figure, and will be exhibited separately on the screen PQ. Let us suppose that this part is the head of the figure. It may be detached 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 ab is the inverted image formed by a concave mirror, ABC a prism with a small refracting angle BCA, placed between ab and the lens LL, s a small opaque screen, and AB 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 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 replaced upon the figure. If the head A of the living object AB, 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 AB by the refraction of a prism.

When the figure ab, Fig. 8, is of very small dimensions, as in the magic lantern, a small prism of glass would answer the purpose required of it; but in public exhibitions, where the image ab must be of a considerable size, if formed by a concave mirror, a very large prism would be necessary. This, however, 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 window would make a prism capable of doubling the whole of the bust of a living person placed as an object at AB, Fig. 7, so that two perfectly similar phantasms might be exhibited. In those cases where the images before the lens LL are small, they may be doubled and even tripled by interposing 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.8

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 parallel, 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 hand-writing on the wall of an apartment, from which the magician and his apparatus were excluded. The annexed figure represents this apparatus as given by Schottus. The apartment in which the spectators are placed is between LL and GH, and there is an open window in the

side next LL, GH being the inside of the wall opposite to the window. Upon the face of the plane speculum EF are written the words to be introduced, and when a lens LL is placed 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 GH. The letters on the speculum are of course inverted, as seen at EF, 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 experiment, 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 daytime 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 produce a singular effect upon his mind. The words might be magnified, diminished, multiplied, coloured, 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 aËrial representations was a great desideratum among the opticians of the 17th century. Vitellio and others had made many unsuccessful 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, therefore, 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 water, 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 indeed. 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 upon 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 AB, he placed a figure CD, which we presume must have been highly illuminated from below, and to the spectators 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 had attempted to handle them, that they were not real substances. Although Kircher does not mention 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 proportions. We doubt, indeed, if the representation or the figure was ever exhibited. It is entirely incompatible with the laws of reflexion.

Among the ingenious and beautiful deceptions of the 17th century, we must enumerate that of the re-formation of distorted pictures by reflexion from cylindrical and conical mirrors. In these representations, the original image from which a perfect picture is produced is often so completely distorted, that the eye cannot trace in it the resemblance to any regular figure, and the greatest degree 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. 11 a simple and practical method of executing them. Let MN be an accurate cylinder made of tin-plate or of thick pasteboard. Out of the farther side of it cut a small aperture abcd; and out of the nearer side cut a larger one ABCD, the size of the picture to be distorted. Having perforated the outline of the picture with small holes, place it on the opening ABCD, so that its surface may be cylindrical. Let a candle or a bright luminous object, the smaller the better, be placed at S, as far behind the picture ABCD 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 substitute a polished cylindrical mirror of the same size in place of MN, then the distorted picture, when laid horizontally at A´B´C´D´, will be restored to its original state when seen by reflexion at ABCD in the polished mirror. It would be an improvement on this method to place at ABCD a thin and flexible plate of transparent mica, having 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 accurately 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 variable curvature like ABC, Fig. 13, we obtain an instrument for producing an endless variety of caricatures, all of which are characterised by their resemblance to the original. If a figure MN is placed before such a mirror, it will of course appear distorted and caricatured; but even if the figure takes different distances and positions, the variations which the image undergoes are neither sufficiently numerous nor remarkable to afford much amusement. But if the figure MN 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 forwards 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 contracted at pleasure. By stretching out the arms before the body they become like those of an ourang-outang, and by drawing them back they dwindle into half their regular size. All these effects, which depend chiefly 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 produced, adds greatly to the interest of the exhibition; and we have seen individuals so annoyed at recognising 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 of a statue, the effect is very curious, as the swelling and contracting of the parts and the sudden change of expression give a sort of appearance of vitality to the image. The inflexibility of such a figure, however, is unfavourable to its transformation 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 aËrial representation of the caricatured figures. This may be done by means of the apparatus shown in Fig. 7,9 where we may suppose AB to be the reduced image seen in the reflecting surface ABC, Fig. 13.10 By bringing this image nearer the mirror MM, Fig. 7, a magnified and inverted image of it may be formed at ab, of such a magnitude as to give the last image in PQ 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.

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