Optical Toys

Many nineteenth-century optical toys delighted spectators by creating the illusion of motion from static images. This illusion depends on the exploitation of the optical phenomenon known as persistence of vision, a characteristic of human perception first theorized by the English physician Peter Mark Roget (1779-1869) in 1824. Roget explained that the eye and brain retain an image on the retina for a fraction of a second after the image has been removed from the field of vision. Hence when a series of images are perceived in rapid succession, the eye will ''fill in'' any gap between them. Put differently, the human eye fails to see the gap that separates images presented in rapid succession, simply because the retina retains an impression of each image for a brief moment even after it has disappeared, thereby allowing one image to blend into the next. The exploitation of the persistence of vision is the foundation of all philosophical toys and optical devices that create the illusion of continuous motion.

In London in 1825 John Paris (1785-1856), a doctor, popularized a philosophical toy called the thauma-trope (''magical turner'' or ''wonder turner''), which demonstrates the eye's fusion of two static images into a single image when shown in rapid succession. The thau-matrope was a simple device made of a paper disk illustrated on both sides. Strings attached opposite one another on the perimeter of the disk on either side of the illustration allowed the disk to be twirled between the viewer's finger and thumb. The illustrations themselves tended to be separated elements of a single picture—for example, a horse depicted on one side and its rider on the other, a bird painted opposite its cage, or a bald man separated from his wig. Twirling the thaumatrope creates the illusion that the two images have fused into a single ''complete'' picture: a man riding a horse, a bird inside a cage, or a man with ample hair.

After 1830 more complex toys using multiple images created the illusion of movement by relying on the use of a shutter mechanism. In the early 1830s the Belgian scientist Joseph Plateau (1801-1883) constructed his ''phenakisto-cope'' (''deceptive view'') to demonstrate the findings of his research into optics, the afterimage, and the persistence of vision. The earliest phenakistoscope consisted of a single disk mounted on a handle, much like a pinwheel. The disk itself was divided evenly into eight or sixteen segments, each of which contained an illustration depicting a single phase of some dynamic action (e.g., a figure jumping rope or juggling, a bird flapping its wings in flight, a galloping horse) alongside a small slot cut into the disc. The phena-kistoscope created the illusion of motion when the illustrated side of the disc was held facing toward a mirror and spun. As the viewer looked through each of the passing slots, its accompanying image was briefly visible in the mirror. When spun rapidly, the phenakistoscope caused the successively viewed images to create the illusion of continuous motion out of the static images, thanks to the persistence of vision. Commercial versions of the

The Zoetrope was a popular toy in the second half of the 19th century. © hulton-deutsch collection/corbis.

phenakistoscope (the Phantasmascope and later the Fantascope) were available by 1833. Like the thaumatrope, the phenakistoscope was a popular parlor toy that educated as it entertained.

Shortly thereafter, in 1834, George Horner (17861837) created a device that he called the daedalum, which was to be known commercially as the Zoetrope (''live turning''). This device operated according to the same principles as the phenakistoscope but had the added advantage of allowing multiple viewers to enjoy the toy simultaneously without the aid of a mirror. Viewers gathered around an open-topped revolving drum illuminated from above. Illustrated strips of paper (again depicting individual phases of a single motion) lined the inside of the drum. These images were visible through evenly spaced, narrow slots placed between them, and the individual images appeared to merge into a single continuous motion when the device was spun. The illustrated strips of paper were changeable, allowing viewers to enjoy a range of animated images. The daedalum was renamed the Zoetrope in 1867 by William F. Lincoln, an American who patented the device and made it available for popular consumption.

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