While looking at the goat, the plane glass is substituted for the prism, and the man reappears; another movement of the prism, and he changes into a sheep, a figure of a sheep having in the meantime replaced that of the goat. Of course it is necessary not merely to have the walls, floors, and chairs precisely alike, but they must each occupy the same relation to each other. If it is desirable only to change the head, it is simply necessary to have a lay figure with a moveable head, dressed precisely in the same manner as the living operator, in the upper portion of the chamber. At the end, by the substitution of the empty chair, the individual may be made to disappear entirely. There may often be seen in the streets of London, a man showing a wonderful instrument, consisting of a telescope cut in two, the two portions being separated from each other by an interval of three or four inches. On looking through the instrument, the spectator of course sees the object at which it is pointed; but what is his astonishment to find, that when the showman places a brick between the two halves of the instrument he sees just as well as before. The showman generally informs him that the instrument in question has such powerful lenses, that it will not only see through a brick, but even through a policeman’s head if it happened to be in the way; and the spectator, having paid his penny, goes away perfectly mystified, until, like the young lady who believed that all machinery was worked “by a screw, somehow,” he comforts himself with the idea that the trick is performed “by a mirror, somehow.” The following figure will, however, soon clear up the mystery. [Illustration: FIG. 58.—The Goat Trick. ] Let F M, L G be an ordinary telescope tube, to be separated in the middle by an interval large enough to insert a brick, the hand, or some other opaque object. The whole is fixed on a stand, consisting of a square tube with a couple of elbows to it. Between G and L a mirror (A) is placed diagonally, which receives the image of the objects to be looked at. This mirror sends the image downwards to another placed diagonally at C, a third being placed at D, and a fourth at B. The horizontal ray, meeting the mirror at A, is consequently bent downwards to C, then travels horizontally to D, when it is reflected upwards to B, in which it is seen by the eye. Of course a simple tube without any lenses at all would serve the same purpose, but the fact of its being a telescope serves to distract the attention of the too curious observer. [Illustration: FIG. 59.—How to see through a Brick. ]