# The wonders of optics/The magic lantern

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PART III.
NATURAL MAGIC.
THE MAGIC LANTERN.
The illusions of which we have spoken in the first part of this work depended principally on the nature of man's vision, who, we found, was the constant and heed-*less victim of his own powers of sight. We shall now examine a series of illusions that are still more extraordinary, but which have nothing to do with the deceptions practised on us by our visual organs. Instead of being deceived by ourselves, we shall find that we are led astray by others whose knowledge of the laws of optics is greater than our own, enabling them to construct instruments capable of amusing us or imposing on us, according to our ignorance of natural laws. Let us hope, however, that the science of optics has now become so familiar to most educated people, that no such thing as a real imposition can take place, although at the present day there are so many exhibitions of the marvellous that ordinary observers have the greatest ​difficulty in accounting for them. In former ages, when the knowledge of science was confined to a certain class the commonest optical facts of the present day were taken advantage of to delude the ignorant. The deceptions practised by the ancient priests of Egypt, Greece, and Rome were undoubtedly many of them of this description. It is a well known fact that both plane and concave metallic mirrors were used by the ancients, and a passage in Pliny gives an account of certain glass mirrors that were made at Sidon. Aulus Gellius, quoting Varro, speaks of the reflecting properties of hollow mirrors, and we shall see, as we go on, what a number of illusions may be practised by means of a series of plane mirrors arranged in a particular way. But we will first devote a short time to the curious historical facts connected with the principle of the magic lantern which took place long before the modern invention of this instrument by Father Kircher.
Brewster says, when treating of this subject, that there can be little doubt that the concave mirror was the principal instrument used in connexion with the pretended apparitions of the gods and goddesses in the ancient temples. In the meagre history of these apparitions that has come down to us, we can easily perceive the traces of an optical illusion. In the ancient temple of Hercules at Tyre, there existed a certain seat made of consecrated stone, out of which the gods rose, apparently at the will of the priests. Æsculapius appeared frequently to his worshippers in his temple in Tarsus, and the temple of Eugenium was famous for the number of gods and goddesses which were constantly visiting its sacred precincts. Iamblicus tells us that the priests showed the gods to the people in the midst of smoke; and when the great magician Marinus terrified his auditory by suddenly showing them the statue of Hercules in the midst of a cloud of ​incense, it was undoubtedly a woman who performed the part, dressed up in man's robes for the occasion.
The character of these spectacles in the ancient temples is admirably described by Damasius, and there is no difficulty in seeing that optical illusions were the means employed to delude the audience. He describes the apparition on the wall of a large spot of white, which at first appeared at a distance, but gradually came nearer and nearer until at last it assumed the form of a divine or supernatural being, of severe yet mild aspect and of great personal beauty. This being the Alexandrians immediately honoured as Osiris or Adonis.
Amongst more modern examples of this illusion may be mentioned that of the Emperor Basil of Macedonia. Inconsolable at the loss of his son, this potentate had recourse to the prayers of the Pontiff Theodore Lantabaren, who was celebrated for his power of working miracles. The conjurer showed the Emperor the image of his dead son magnificently attired and mounted on a splendid war-horse. The young man dismounted, and, going up to his father, threw himself into his arms and disappeared. Salvertius, in speaking of this story, observes judiciously, that the deception could only take place through the agency of some person who closely resembled the Emperor's son, and that the trick would have been easily discovered when the person embraced the Emperor. A better explanation of the affair is, however, afforded by supposing that the Emperor saw an aërial image of a person resembling his son, and that when he rushed forward to embrace him it disappeared.
The accounts of the operations of the ancient magicians are too meagre to give us any idea of the splendour of some of these ancient ceremonies. A system of deception such as this, employed as a means of ​government, must have brought into requisition not only the talents of all the learned men of the day, but a crowd of accessories calculated to astonish and confound the judgment, fascinate the senses, and facilitate imposture.
An account of an instance of modern necromancy has been left us by Benvenuto Cellini, who played a prominent part in a case of this sort.
He accidentally made the acquaintance of a Sicilian priest, a man of great genius and acquirements, and well versed in Greek and Latin classical lore. One day the conversation turned on necromancy, and the great goldsmith told him that he had the greatest desire to know something about this wonderful art, and that he had felt all his life a great curiosity to penetrate its mysteries.
The priest replied, that a man ought to have a very resolute and fearless character to study this art; but Benvenuto answered he had both resolution and courage. The priest went on to say, that if he had the heart to try, he would be the means of obtaining the fulfilment of his wishes. They consequently agreed upon a plan of necromantic study. One evening, Benvenuto invited one of his companions, Vincenzio Romoli, to take part in some experiments that were to be made amongst the ruins of the Coliseum. They there met the Sicilian priest, who after the manner of the ancients began to describe a number of circles in the air in the most imposing manner. He had brought with him various gums and perfumes, and had made a fire, into which his assistant necromancer was to throw them at the proper time. He commenced his conjurations, the ceremony continuing about an hour, when there appeared legions of demons, in such numbers that the whole of the ruins seemed filled with them. Benvenuto was nearly fainting with the perfumes, when the priest roused him by ​telling him to ask for something. He replied, that he wished to be transported to the side of his Sicilian mistress; but the demons were evidently unpropitious, for nothing came of it. His instructor, however, told him that they must repeat their experiments a second time, and that Benvenuto must bring with him a child that had never committed sin. The next time Benvenuto took with him a boy of twelve years old whom he had in his service, and his friends Romoli and Guddi. When they arrived at the place of meeting, they found the priest had made the same preparations as before. This time, however, he used more powerful conjurations, calling on a number of demons by their names, in Hebrew, Greek, and Latin; so that the ruin was filled with a still greater mass of them than on the other occasion. The fire and perfumes were put under the charge of Guddi and Romoli, and he gave Benvenuto a magic picture to hold in a certain direction, the boy being placed underneath it. The priest told him again to wish to be in the company of his lady love, but on his expressing the wish, the magician told him that the demons still refused to do his bidding in this way, but that he should visit her once more in a month's time. The poor boy underneath the magic picture was seized with a terrible fright, and exclaimed, that he saw millions of ferocious spirits and four giants, all endeavouring to break through the magic circle the priest had formed. All there were evidently in a most abject state of terror, and remained in the place until the church bells began to ring for morning prayers, when they returned home, the boy declaring that two of the demons preceded them, dancing and gambolling before them, and sometimes running along the housetops.
The priest then advised him to try another spiritual séance, and endeavour to induce the demons to point out sundry pots of buried gold, so that they all might ​become rich, but it does not appear that the priest's advice was followed.
It is impossible to read the foregoing description of what happened, without being convinced that the whole affair was an optical illusion, and not the mere result of the imagination of those who took part in it. The smoke was evidently caused in order to afford a field for the exhibition of painted images reflected by concave mirrors, and the circle was formed in order that those within it might be within range of the images formed on the smoke. The mirrors reflecting the images of the demons had undoubtedly already been arranged so that they would fall just above the fire, and become visible when the gums began to burn with a smoky flame. The perfumes were simply to help to stupify the spectators, and aid in working on their imaginations for those occurrences which were beyond the reach of optics, for the poor unfortunate boy saw things that his companions did not, even to a couple of demons dancing through the streets in broad daylight. In fact, it is somewhat difficult to draw the line between reality and imagination in this case. No doubt the story is considerably exaggerated by Cellini, who was a fervid Italian, and prone to believe in wonders, as is instanced by his wish to study the black art. The priest, too, whom he describes as a man of genius, no doubt had a great influence over the famous artist, and made him see a great deal more than was really there.
The introduction of the magic lantern provided the magicians of the seventeenth century with a very powerful instrument with which to continue their deceptions. The use of the concave mirror, which does not appear to have had any accessories worth speaking of, required a separate apartment, or at least a hiding-place of some sort that was difficult to discover under ordinary circumstances; but the magic lantern, inclosing as it did the ​lamp, the optical apparatus, and the figures in a comparatively small space, was particularly appropriate to the wants of the Homes and Davenports of the day, who until then had never possessed anything so convenient and portable.
The magic lantern shown in figures 50 and 51 consists of a dark box, containing a lamp and a concave metallic mirror, constructed in such a way that the Fig. 50.—Section of the Magic Lantern. whole of the rays proceeding from the lamp are reflected through the aperture holding the optical portion of the apparatus. In front of the box is fixed a double tube C D, one-half of which (D) slides in the other. A large plano-convex lens c is fixed at the inner extremity of the double tube, and a small one at its outer end. To the fixed tube C E is attached a groove b b, which serves to hold the painted glass. These glasses, or slides as they are generally called, are painted with strong transparent colours.
The direct light of the lamp G, as well as that reflected by the mirror and passing through the lens c, is ​so concentrated as to project a brilliant beam of light through the painted slide, which being in the conjugate focus of the large plano-convex lens d, the pictures on the glass are refracted in a magnified form on the white cloth P Q.
The magic lantern, therefore, consists of a box to hold the lamp, a concave mirror, and a convex lens to concentrate the light on the slide, and a second convex lens to throw the image on the screen. ​
Fig. 51.—Magic Lantern.