LIGHT. 141 



5. If a small wheel but two or three or four inches 

 in diameter, and toothed like a cog-wheel in a clock, be 

 placed within a foot or two of the disk, and so that its 

 shadow will fall upon the screen, its shadow will not 

 only be much magnified, but the motions of the wheel 

 will appear as with the larger one, number i. 



6. Let large disks three or four feet in diameter be 

 made, having various symmetrical figures painted upon 

 them. When the disks are revolved, many curious 

 motions may be simulated : as of a girl jumping rope, 

 a man sawing or chopping wood, boys playing leap- 

 frog, a man opening and shutting his eyes and mouth, 

 wind-mill with sails turning, etc. Such designs gen- 

 erally come with the toy called the thaumatrope, 

 made to look through into a mirror while turning. 

 These may be copied upon large sheets of pasteboard 

 and rotated in any convenient way. The turning-table 

 may be made to answer for this. 



7. Another good and very pretty application of 

 this is to have a large star with five or six points made, 

 and the alternate points colored with different tints, 

 as red and blue. When such a disk is revolved in this 

 intermittent light it may appear to stand very still, or 

 to slowly revolve forward or backward, while its points 

 may be doubled or tripled or quadrupled, and its colors 

 will apparently overlap and give the tints proper to the 

 mixture. 



8. Such pictures as are sold with the thaumatrope 

 may be fastened to the front of the disk containing 

 the holes through which the light passes, as is repre- 

 sented in Fig. 107, and after the light has passed through 

 the disk, it may be reflected upon its face by a small 

 mirror, m (Fig. 108), and can thus be seen very well if 

 the light be strong. When used in this way the disk 



