Through the characters of his “novel,” Paris then commented on the illusion of the persistence of vision which makes the Thaumatrope (and the motion picture) a reality. He discussed the whirling flame which appeared to make a circle; Homer’s reference to “long shadowed” spear; and the tail of a rocket. Paris also described an improved model of the Thaumatrope. In this card device a center disk is allowed to change from one position to another as the whole revolves. In one illustration a jockey was on one side and a horse on the other. By tightening the strings as the card revolved the jockey appeared to be falling over the neck of the horse. In another an Indian juggler was represented as using two, then three and finally four balls. Other illusions indicated were a sailor rowing a boat, “a dandy making a bow.” Through the words of the vicar, Paris then warned, “I hope that, amidst all your improvements (in the Thaumatrope), you will still keep in view your first and most laudable design, that of rendering it subservient to classical illustration.” It is certain that Paris developed the Thaumatrope, first, for scientific illustration of the persistence of vision, perhaps to better explain the phenomenon to one of his patients or students. But being a clever man, he immediately realized its commercial value and arranged to have sets of the cards made up and sold in London. Doubtless the chapter in his book on the Thaumatrope did much to increase the sale of the toys. David Brewster (1781–1868), Scottish scientist whose work on the polarization of light led him to invent, around 1815, the Kaleidoscope--an optical instrument which creates and exhibits by reflection a variety of beautiful symmetrical designs in varied colors--was the first to comment in print on the Thaumatrope of Paris, the year before the latter’s book appeared. In the fourth volume of his _Edinburgh Journal_ Brewster wrote, under the description of the Thaumatrope, “a very ingenious philosophical toy, invented, we believe, by Dr. Paris.” Brewster remarked that the circular disks should be 2½ inches in diameter and that the cord should be of silk. Brewster described the following Thaumatrope cards: Rose-tree and garden-pot, horse and man, a branch with and without leaves, woman in one dress and then another, body of a Turk and his head, watchman’s box and the watchman, Harlequin and Columbine, comic head and wig, a man asleep and awake, and the use of the cards for cipher writing. According to Brewster, “the principle of the thaumatrope may be extended to many other devices.” He also commented on the imperfections of the toy arising from the hobbling effect of irregular rotation. He suggested that a “solid axis of rotation is decidedly preferable and will produce much more pleasing combinations.”