Page:The American Boy's Handy Book edition 1.djvu/399

If a larger machine be wanted, the illustration here given may be enlarged by the process described on page 250. To use the magic wheel, stand in front of a mirror, as shown in the small illustration; hold the disk before the eyes; look through the slots under the figures, and turn the wheel rapidly. Image missingMaking the Horses Trot. The horses' legs will commence to move as in life, and as each successive position drawn upon the phantasmoscope is the exact one taken by a trotting horse, the horses in the mirror will all appear to be in actual motion, on a fast trot. If the eye is directed over the margin of the paste-board disk, an indistinct blur is all that is seen. The principle is generally well known and easily explained. It pertains to the phenomenon known as the persistence of vision. When the eye is directed through the slot, the figure of a horse is seen for an instant as the opening passes the eye, and the impression is retained after the object is shut off by the intervening portion of the board between the slots until another horse appears through the succeeding opening, when an additional impression is made, the same as the preceding impression, except a slight change in the position of the legs. These impressions follow each other so rapidly that they produce upon the retina of the eye the effect of a continuous image of the horses, in which the limbs, replaced by a succession of positions, present the appearance of a file of horses in actual motion.

The instantaneous photographs taken nowadays of people, horses, and other animals in motion, opens a new field for inves-