“When the two objects or sets of objects thus successively presented to the view are properly placed and sufficiently alike, the audience will be unaware that any change has been made. In some cases, in place of a single sheet of glass, two or more sheets may be employed.” By consulting Fig. 1, the reader will understand the construction of the illusion, one of the best in the repertoire of the {102} conjurer. The shaded drawing in the left upper part, represents a portion of the mirror, designed to show its graduated opacity. “_a_ is a stage. It may be in a lecture-room or theatre. _bb_, the seats for the audience in front of the stage. _cc_ is a small room—eight or ten feet square and eight high will often be sufficiently large; but it may be of any size. It may advantageously be raised and approached by two or three steps from the stage _a_. “_d_ is a vertical mirror, passing diagonally across the chamber _c_ and dividing it into two parts, which are exact counterparts the one of the other. The mirror _d_ is so mounted that it can be rapidly and noiselessly moved diagonally across the chamber in the path represented by the dotted line _d_^1, and be withdrawn whenever desired. This can conveniently be done by running it in guides and upon rollers to and from a position where it is hidden by a screen, _e_, which limits the view of the audience in this direction. “In consequence of the exact correspondence of the two parts of the chamber _c_, that in front and that behind the mirror, the audience will observe no change in appearance when the mirror is passed across. “The front of the chamber is partially closed at _cx_ by a shield or short partition-wall, either permanently or whenever required. This is done in order to hide from direct view any object which may be at or about the position _c_^1. “The illusions may be performed in various ways—as, for example, an object may, in the sight of the audience, be passed from the stage to the position _c_^2, near the rear short wall or counterpart shield _f_, diagonally opposite to and corresponding with the front corner shield _cx_, and there be changed for some other. This is done by providing beforehand a dummy at _c_^1, closely resembling the object at _c_^2. Then when the object is in its place, the mirror is passed across without causing any apparent change. The object, when hidden, is changed for another object externally resembling the first, the mirror is withdrawn, and the audience may then be shown in any convenient way that the object now before them differs from that which their eyesight would lead them to suppose it to be. {103}