The illusion was obtained by means of a simple mirror which starting from the upper part of the back of the stage descended obliquely to the front. In the center of this there was an opening which was concealed by the satin collar and through this the young girl passed her head. The inclination of the mirror was, in fact, indicated by a gold rod designed to hide the junction of the mirror and the side. The arrangement will be better understood by reference to the annexed [diagram], which belongs to the same illusion, only the clown is substituted for the girl’s head.
Now, by virtue of the optical law that “an object reflected from a mirror appears to be behind the latter at a distance equal to that which separates it from it,” every point of the line, M l, reflected from the mirror, P M, will appear to be situated upon the line, M L.
So, to the spectator located at O, the point, c, reflected at C′ will appear to be the point, C; the distance, c C′ equaling C C′. The point, l, reflected at L′, will appear to be L. And it will be the same for all the intermediate points. The spectator, then, will believe that he sees the line, M L, when in reality he sees only the reflection of M l. Now, as we have just said, he will believe that he sees the back of the stage, when, in fact, he sees nothing but a reflection of the ceiling in the mirror. In the same way, the reflection from the front of the ceiling will produce the illusion of the stage floor. This fact still further contributes to increase the illusion, for the spectators are not aware of the difference that exists between the arrangement of the place where the bust appears and of that of the place where the showman is walking.
DIAGRAM EXPLANATORY OF THE PHENOMENON.
In the illusion of “Stella” the aperture through which the table was seen was in reality at the top. The table was vertical and the candle which was firmly fixed to it was horizontal. The farce of blowing out the candle and carrying it behind the scenes was only designed to make the spectators believe it was the same candle that was seen at the rear of the stage, when in reality it was only a duplicate.