304 NATURE^ TEACHINGS. 



Upon its surface are fixed little pins, with polished globular 

 steel heads, and, when the handle is turned, these heads form 

 the most beautiful and intricate figures with exact accuracy. 



Another toy, called the Thaumatrope, or Wonder-turner, is 

 equally ingenious and beautiful, and is sufficiently simple to be 

 made by any one with a slight knowledge of drawing. A disc 

 of white cardboard is cut, and upon each side of it is portrayed 

 some object. If the disc be caused to revolve rapidly, these 

 two subjects will be seen at the same time, the image of each 

 being held on the retina long enough to allow the other to take 

 its place. 



Some very beautiful combinations may be made by means of 

 this instrument. For example, a horse may be on one side, and 

 a man on the other, and, by spinning the disc, the man will be 

 seen mounted on the horse. Then we may have a boat on one 

 side, and a rower with his oars on the other. Similarly a mouse 

 can be put into a trap, or a bird into a cage. 



The reader must remember that these subjects must be 

 drawn as if they were upside down with regard to each other, 

 so that the man who is to ride the horse is drawn as if he were 

 standing on his head, and the mouse which is to enter the trap 

 looks as if it were lying on its back. 



The most simple manner of spinning the disc is by means of 

 two threads, each being inserted near the edge of the disc, and 

 exactly opposite each other. 



A very ingenious modification of the Thaumatrope is made 

 by inserting at one side of the disc two strings, of which one is 

 elastic. It is evident, then, that by lengthening or shortening 

 the elastic string, the axis can be changed, and the objects on 

 the opposite sides placed in positions relatively different from each 

 other. Thus the jockey may be made to jump on and off his 

 horse, the bird to go in and out of its cage, the mouse to enter 

 the trap, and so on. This simple invention allows of infinite 

 combinations, so that a tree may be made to sprout, a man to 

 move his limbs, and a bird to flap its wings. It was invented, 

 I believe, by Dr. Paris, author of " Philosophy in Sport made 

 Science in Earnest.' ' 



On the right hand of the illustration are seen three figures, 

 each representing a means of obtaining an ocular delusion 

 through the principle of which we are now treating. 



