The similarity between the zoetrope, despite the fact that it did not make use of photography, and the modern motion picture, lies in the scientific principle responsible for the illusion of moving figures. In viewing a particular object there is the briefest delay in conveying the impression from the eye to the brain, so that the latter has the conception of seeing the object after it has actually passed from the field of vision. If, during this fractional part of a second, another picture of the object, in a slightly different position, is presented to the eye, the brain’s sensation will be that of having seen the object move. Were a series of such pictures moved before the eye in rapid succession, the impression registered would seem more like a streak than an object in motion, so that there must be some way of cutting off the vision until the second picture has been moved into the exact position held by the first, and so on. The spaces between the slots in the zoetrope served this purpose, and so rapid was the revolution of the cylinder that the spectator was not aware of having had his vision interrupted, and only received the impression that on a direct line with the eye there was an object which seemed to be moving. To understand the application of this principle to modern motion pictures let us take a strip of film a foot in length as an example. There are sixteen separate pictures on this piece of film. The screen of the motion-picture theater serves as the fixed point at which the spectator is gazing. One second is required to show this foot of film on the screen, and the spectator is of the opinion that pictures have been shown throughout that entire second. In reality, the shutter of the projection-machine threw each separate picture on the screen for about one thirty-second of a second, and there was an interval of about the same duration while the next picture was being moved into place. The zoetrope had many successors, as new devices of improvement were discovered. It never became much more than a toy, however, interesting solely because the simple objects shown appeared to move. The next important chapter in motion-picture history concerns the experiments of Edward Muybridge, an Englishman, in 1871-2. Photography had by this time advanced so that it was possible to take pictures with an exposure of less than one-twentieth of a second. Muybridge conceived the plan of using several cameras to photograph an object in motion. Governor Leland Stanford, of California, offered to finance an experiment by which pictures were to be taken of his race-horse, Occident.