At the end of the last century and the beginning of the present, a very curious experiment, and one which was looked upon as marvelous by the credulous, was wonderfully popular at Paris. The representation took place at the old Capuchin convent. The spectator entered a well lighted hall in which, in part of a window, there was a box suspended by four brass chains attached by bows of ribbon. The box, which was surrounded by a grating, was provided with two panes of glass that permitted of seeing that it was absolutely empty. To one of the extremities was fixed a speaking trumpet. When a visitor spoke in the latter, he was answered by a hollow voice; and when he placed his face near the box, he even felt upon it the action of a mysterious breath. When he presented any object whatever in front of the mouthpiece, and asked the voice to name it, an answer immediately came from the speaking tube. The box was suspended freely from the ceiling, and it could be made to swing at the extremity of the chains; it was empty and isolated in space. People were lost in conjecture as to the secret of the experiment. Among the unlikely theories that were put forth was that of the invisibility of a person obtained by unknown processes.
As usual in these kinds of impostures, there was here merely an ingenious application of a scientific principle. A physicist, E. J. Ingennato, revealed the mystery in a pamphlet published in 1800 under the title of “The Invisible Woman and Her Secret Unveiled.” This tract, now rare, had for a frontispiece the [engraving] which we reproduce herewith and which explains the whole experiment. The invisible woman of the Capuchin convent was named Frances, and the following is the explanatory legend appended to the original engraving:
“Questioner: ‘Frances, what is this that I have in my hand?’
“Frances (after looking through the little peep-hole, D): ‘A stick with a crooked handle.’
“The entire assembly at once: ‘It is incomprehensible!’”
Ingennato, in his pamphlet, explains that above the ceiling there was a low, darkish chamber, in which Frances was concealed, and that she looked at the object presented to her through a small aperture, D, which was skillfully hidden by a hanging lamp, and then answered through the speaking tube, B B B, hidden in the wall. The sound traversed a space of about six inches, that separated the speaking tube from the speaking trumpet.
MAGIC HARPS.
The experiment which we are about to describe, while it is thoroughly scientific, was taken up under the name of “Æolian Harps” by Robert-Houdin, who introduced several modifications of it. When the experiment was performed by Wheatstone in 1855, four harps were arranged in a semi-circle on the stage of the Polytechnic Institution. These harps, at the pleasure of the experimentor, vibrated as if they were made to resound by invisible hands. This effect was produced by fixing to the sounding board of each of them vertical rods of fir-wood which passed through the floor of the stage and ceilings, into the cellar of the Institution, where one of them was fixed upon a sounding board of a piano, another upon the sounding board of a violoncello, and two others upon the sounding boards of violins. In order to render it possible to interrupt the vibrations between the instruments and the harps, the rods supporting the latter were divided at two inches above the floor. Each harp could be cut off from communication with the instrument below by turning it around upon its axis. When Robert-Houdin introduced the illusion, he used a stage elevated in the very midst of the spectators. This stage was traversed by two fir-wood rods which, after passing through the floor, rested upon harps placed in the hands of skillful players. At the command of the prestidigitateur two other harps supported upon the upper extremity of the rods executed a concert which was very successful, thanks to the careful preparations and the elegant mise en scène. Of course the harps were supposed to operate through the intervention of mediumistic spirits.