The foundation principle upon which these moving pictures exist is that of persistence of vision. If a succession of views of the same object in motion is made, with the moving object in each consecutive figure changed just a little, and progressively so in a constantly advancing attitude in a definite movement, and those different positions are rapidly presented in sequence to the eye in detached views, the figures appear to constantly move through the changing position. The theory of the duration of visible impressions was taught by Leonardo da Vinci in the fifteenth century, and practical advantage has been taken of the same in a variety of old-fashioned toys, known as the phenakistoscope, thaumatrope, zoetrope, stroboscope, rotascope, etc. The phenakistoscope was invented by Dr. Roget, and improved by Plateau in 1829, and also by Faraday. A circular disk, bearing a circular series of figures is mounted on a handle to revolve. The figures following each other show consecutively a gradual progression, or change in position. The disk has radial slits around its periphery, and is held with its figured face before a looking glass. When the reflection is viewed in the looking glass through the slits, the figures rapidly passing in succession before the slits appear to have the movements of life. The thaumatrope, which originated with Sir John Herschel, consists of a thin disc, bearing on opposite sides two associated objects, such as a bird and a cage, or a horse and a man. This, when rotated about its diameter, to bring alternately the bird and cage into view, appears to bring the bird into the cage, or to put the rider on the horse’s back, as the case may be. The zoetrope, described in the _Philosophical Magazine_, January, 1834, employs the general principle of the phenakistoscope, except that, instead of a disc before a looking glass, an upright rotating drum or cylinder is employed, and has its figures on the inside, and is viewed, when rotating, through a succession of vertical slits in the drum. The earliest patents found in this art are the British patent to Shaw, No. 1,260, May 22, 1860; United States patents, Sellers, No. 31,357, February 5, 1861, and Lincoln, No. 64,117, April 23, 1867. In Brown’s patent, No. 93,594, August 10, 1869, the magic lantern was applied to the moving pictures, and Muybridge’s photos of trotting horses in 1872, followed by instantaneous photography, which enabled a great number of views to be taken of moving objects in rapid succession, laid the foundation for the modern art. [Illustration: SHOOTING GLASS BALLS. FIRING DISAPPEARING GUN. FIG. 200.]