Now, as stated before, the phenomenon of the persistence of vision is the fundamental physiological fact upon which the whole possibility of seeing screen pictures rests. One of the first devices made that depended upon it, and that very simply demonstrated this faculty of the retina for holding a visional image for a time, was an optical toy called the thaumatrope. It dates from about 1826. It was a cardboard disk with two holes close to the edge at opposite points. Strings were passed through these holes and fastened and the dangling ends held and rolled between the thumbs and fingers so that the disk was made to twirl rapidly. Each side of the disk had a picture printed or drawn upon it. These two pictures when viewed together while the disk was twirled appeared as one complete picture. A favorite design for depiction was an empty bird-cage on one side and a bird on the other. The designs were placed with respect to each other in the same way as the marks and insignia of the two sides of most coins. (The coins of Great Britain are an exception, on them the designs are placed differently. In reading their marks or looking at the images of the two sides, we turn the coin over like the page of a book.)
THE THAUMATROPE.
Above: How the designs of the two sides are placed with respect to each other.
Below: The combined image when the thaumatrope is twirled.
The thaumatrope illustrates the persistence of vision in a very elementary way. Simply explained, the face of one side of the disk with its design is before the eye, the design impresses its true image upon the retina, the disk turns away and the picture disappears, but its after-image remains on the retina. The disk having turned, brings the other picture into view. Its true image is impressed upon the retina to blend with the after-image of the first picture. In rapid sequence this turning continues and the two images commingle to give the fantasy of a perfect design.
A limited number of subjects only were suitable for demonstration by a toy of this character. Two other subjects were those showing designs to give the effect of a rider on a horse and a tight-rope dancer balanced on a rope.
1837 FARADAY'S WHEEL 1841
TWO INSTRUMENTS USED IN EARLY INVESTIGATIONS OF OPTICAL PHENOMENA.
From The Saturday Magazine of 1837 and 1841.