Regulate its distance from the eye so that each side will refract the various parts of the drawing on the border so as to form one figure, and the centre object be entirely unreflected.
The ace of clubs is, therefore, drawn mechanically on the circle of refraction at six different parts of the border, and blended in with it. So with the other drawings.
THE MAGIC CUBE-BOX.
An illusion is often practised at fancy fairs and bazaars, when a spectator, looking into what he supposes to be an ordinary looking-glass, sees his companion instead of himself. Of course the exhibitor endeavours to show the illusion to two persons at once; and if they are strangers to each other, and of opposite sex, a great deal of fun is made out of the trick. Showmen at the fairs have made immense harvests by showing two such mirrors, one to all the young girls who wished to see their future husbands, and the other to all the young men who wished to see their future wives.
Explanation.—Make a cube-box, fifteen inches, say, each way, and stand it on a pedestal to bring it to the height of the eye. In each side of this box let there be an opening of an oval form, ten inches high and seven wide. In this box place two mirrors with their backs against each other. Let them cross the box in a diagonal line, and in a vertical position. Decorate the openings in the side of this box with four oval frames and transparent glasses, and cover each with a curtain so contrived that all draw up together.
Place four persons (in the case first mentioned two are confederates) in front of the four sides, and at equal distances from the box, and then draw them up that they may see themselves in the mirrors, when each of them, instead of his own figure, will see that of the person next to him, but who will appear to him to be placed on the opposite side. Their confusion will be the greater, as it will be very difficult, if not impossible, for them to discover the mirrors concealed in the box. The reason is that though the rays of light may be turned aside by a mirror, yet they always appear to proceed in right lines.
Fig. 123.
YELLOW AND BLUE DO NOT MAKE GREEN.
With an electric or lime-light throw a disc of blue light and of yellow light upon a screen, and cause them to overlap each other. Where they overlap the space on the screen will be, not green, but a pure white. If you then place a rod or pencil near the two sources of light, so that two shadows of it shall fall on the white space where the discs overlap, one shadow will be of brilliant blue colour, and the other deep yellow. Mixed blue and yellow lights, therefore, do not make green. Mixed blue and yellow paints make green, because between them they absorb nearly all the rays of the spectrum except green, so green is the only colour which escapes from the mixture.