ZOETROPE, OR " WHEEL OF LIFE " An open cylinder with vertical slits round its sides, and below them a series of motion pictures which were viewed through the slits as the cylinder revolved on its stand, the result being a kinematograph effect. It embodies in cylindrical form the principle of an earlier disc device—the phenakistoscope (which see), and was invented by Desvignes in 186o. In 1867, a patent for the same device was granted in the United States of America to William E. Lincoln, of Providence, who was the first to call it the zoetrope. But this type of slotted machine had its origin at a date far anterior to those quoted above ; in fact, only a little more than a twelve month elapsed between the invention of the phenakistoscope (1833) and the publication by W. G. Horner in The Philosophical Magazine of a description of a device strongly resembling the zoetrope. The apparatus in its modern form is shown at A. A band of pictures having been placed inside the cylinder, the whole is rotated, when the figures are seen in motion.
A great variety of zoetropic instruments have been devised, one of the most interesting being the stereoscopic zoetrope shown at B. Anschiitz used this form to produce the appearance of motion from a series of animal movements photo graphically recorded. The series of phases was taken in stereoscopic sets, and, as is shown, the cylinder was turned on its side, and the slits were long enough to permit of both eyes gaining a view of their respective series ; the blending of the two series was brought about by suitable prisms or other optical device.
ZoLLNER'S PROCESS An iodide of starch printing process, invented in 1863 by Dr. F. Milner, of Berlin, and used for reproducing plans, drawings, etc. Thin, smooth paper is sized with starch, and sensitised by floating for from thirty to sixty seconds on a solution of ferric chloride and ferric oxalate. The exposure varies from two or three minutes in the sun to fifteen or thirty minutes in diffused light, the image being at first invisible. The exposed prints should not be left longer than twelve hours before developing. The image appears of an intense blue colour on brushing on a solution of potassium iodide in dilute albumen. The developer should be washed off the print before it has time to dry, and the washed prints dried in the open air. To prepare the developing solu tion, the whites of two eggs of average size are well beaten and left for several hours, after which the liquid albumen is decanted from the bottom of the vessel and diluted with one-third its quantity of distilled water, 78 grs. of potassium iodide being then added and dissolved.