Parlour Magic

by Unknown

TO MAKE A PRISM.

Fig. 1.

Provide two small pieces of window-glass and a lump of wax. Soften and mould the wax, stick the two pieces of glass upon it, so that they meet, as in the cut, where w is the wax, g and g the glasses stuck to it, (Fig. 1.) The end view (Fig. 2) will show the angle, a, at which the pieces of glass meet; into which angle put a drop of water.

To use the instrument thus made, make a small hole, or a narrow horizontal slit, so that you can see the sky through it, when you stand at some distance from it in the room. Or a piece of pasteboard placed in the upper part of the window-sash, with a slit cut in it, will serve the purpose of the hole in the shutter. The slit should be about one-tenth of an inch wide, and an inch or two long, with even edges. Then hold the prism in your hand, place it close to your eye, and look through the drop of water, when you will see a beautiful train of colours, called a spectrum; at one end red, at the other violet, and in the middle yellowish green.

Fig. 3.

The annexed figure will better explain the direction in which to look: here, e, is the eye of the spectator, p, is the prism, h, the hole in the shutter or pasteboard, s, the spectrum. By a little practice, you will soon become accustomed to look in the right direction, and will see the colours very bright and distinct.

By means of this simple contrivance, white light may be analysed and proved to consist of coloured rays, and several of its properties be beautifully illustrated.