The magician with a fine flow of language could dwell at length upon the coming to life of the head of an ancient statue which he had in the box in his hand. Walking to the table he could place the box over a trap-door and by the time he had unlatched the door of the box, the assistant kneeling under the table could have his head thrust upward through the trap-door of the table-top into the box. After a few impressive words, supposed to be Hindoo but in reality were Hoodoo, presto! and the Sphinx was revealed. It conversed after a period of silence extending back to the days of Rameses when a wrathful god condemned an unfortunate king to imprisonment in the stone statue. The original trick awed audiences for many nights and defied explanation until one night a keen observer noted finger-prints on what proved to be a mirror. Doubtless a careless accomplice lost his job, but the damage had been done, for the trick was revealed. This "illusion" is so effective that it, or variations of it, are still in use. [Illustration: Fig. 91.--Another example of "mirror magic."] Another simple case is illustrated in Fig. 91. A large plate-glass mirror _M_ was placed at an angle of approximately 45 degrees from the floor. Through a hole in it an assistant's head and shoulders projected and the edge of the opening was covered with a draped cloth. The audience saw the image of the ceiling _C_ of the alcove reflected by the mirror but being ignorant of the presence of the mirror, assumed this image to be the rear wall. This trick was effective for many years. Obviously the mirrors must be spotlessly clean and the illuminations of the walls, ceiling, and in some cases, the floor must be very uniform. Furthermore, no large conspicuous pattern could be used for lining the box-like recess. The foregoing examples illustrate the principles involved in the appearance of ghosts on the stage and of a skeleton or other gruesome object in place of a human being. The possibilities of mirrors in such fields are endless and they can be studied on a small scale by anyone interested. The pseudoscope which produces effects opposite to those of the stereoscope is an interesting device. The foregoing is the faintest glimpse of the use of the mirror, but it does not appear advisable to dwell further upon its use, for after all the results are not visual illusions in the sense of the term as usually employed throughout this book. XV CAMOUFLAGE