Sir David Brewster, in his work on natural magic, has the following to say about concave mirrors and the art of phantasmagoria: “Concave mirrors are distinguished by their property of forming in front of them, and in the air, inverted images of erect objects, or erect images of inverted objects, placed at some distance beyond their principal focus. If a fine transparent cloud of blue smoke is raised, by means of a chafing dish, around the focus of a large concave mirror, the image of any highly illuminated object will be depicted in the middle of it, with great beauty. A skull concealed from the observer is sometimes used to surprise the ignorant; and when a dish of fruit has been depicted in a similar manner, a spectator, stretching out his hand to seize it, is met with the image of a drawn dagger which has been quickly substituted for the fruit at the other conjugate focus of the mirror.” {92}
Thoroughly conversant with the science of optics, it is more than probable that Robertson made use of large concave mirrors to project inverted phantoms of living persons in the air, with convex lenses to restore the ghosts to an upright position. If he merely used painted images, which is the more likely, then he had resort to the phantasmagoric magic lantern, rolling upon a small track. Pushing this contrivance backwards and forwards caused the images to lessen or increase, to recede or advance.
Robertson realized quite a snug fortune out of his ghost exhibition and other inventions. His automaton speaking figure, called le phonorganon, uttered two hundred words of the French language. Another interesting piece of mechanism was his Trumpeter. These two machines formed part of a beautiful Cabinet de Physique in his house, the Hotel d’ Yorck, Boulevard Montmartre, No. 12 Paris. He has left some entertaining memoirs, entitled Mémoires récréatifs et anecdotifs (1830–1834), copies of which are exceedingly rare. He was a great aeronaut and invented the parachute which has been wrongly attributed to Garnerin.
Robertson, as Commandant des Aerostiers, served in the French army, and rendered valuable service with his balloons in observing the movements of the enemy in the campaigns in Belgium and Holland, under General Jourdain. In the year 1804 he wrote a treatise on ballooning, entitled, La Minerve, vaisseau Aérien destiné aux découvertes, et proposé, à toutes les Académies de l’Europe, published at Vienna. He died at Batignolles (Paris) in 1837.
In his memoirs, Robertson describes a species of optical toy called the Phantascope, for producing illusions on a small scale. This may give a clue to his spectres of the Capuchin Convent. He also offers an explanation of Nostradamus’ famous feat of conjuring up the likeness of Francis I. in a magic mirror, for the edification of the beautiful Marie de Médici.
II.
We now come to the greatest of all ghost-shows, that of the Polytechnic Institute, London. In the year 1863 letters patent {93} were granted to Professor John Henry Pepper, professor of chemistry in the London Polytechnic Institute, and Henry Dircks, civil engineer, for a device “for projecting images of living persons in the air.” Here were no concave mirrors, no magic lanterns, simply a large sheet of unsilvered glass. The effect is founded on a well-known optical illusion. “In the evening carry a lighted candle to the window and you will see reflected in the pane, not only the image of the candle, but that of your hand and face as well. A sheet of glass, inclined at a certain angle, is placed on a stage between the actors and spectators. Beneath the stage and just in front of the glass, is a person robed in a white shroud, and illuminated by the brilliant rays of the electric or the oxy-hydrogen light. The image of the actor who plays the part of spectre, being reflected by the glass, becomes visible to the spectators, and stands, apparently, just as far behind the glass as its prototype is placed in front of it. This image is only visible to the audience. The actor who is on the stage sees nothing of it, and in order that he may not strike at random in his attacks on the spectre, it is necessary to mark beforehand on the boards the particular spot at which, to the eyes of the audience, the phantom will appear. Care must be taken to have the theatre darkened and the stage very dimly lighted.”
At the Polytechnic Institute the ghost was admirably produced. The stage represented the room of a mediaeval student who was engaged in burning the midnight oil. Looking up from his black-letter tome he beheld the apparition of a skeleton. Resenting the intrusion he arose from his chair, seized a sword which was ready to his hand, and aimed a blow at the figure, which vanished, only to return again and again.
The assistant who manipulated the spectre wore a cover of black velvet. He held the real skeleton in his arms, and made the fleshless bones assume the most grotesque attitudes. He had evidently studied Holbein’s “Dance of Death.” The lower part of the skeleton, from the pelvis downward, was dressed in white linen, presumably a shroud. To the audience the figure seemed to vanish and reappear through the floor. {94}
This ghost-making apparatus has been used with splendid success in the dramatizations of Dickens’ Christmas Carol and Haunted Man; Bulwer’s Strange Story; and Alexander Dumas’ Corsican Brothers.