no THE ART OF PROJECTING. 



focus of the lens, and then the light will appear as a 

 brilliant white spot. Interpose a piece of colored 



glass, and the spot will 

 at once change its color. 

 3d. By reflection from 

 a concave mirror. The 

 colored rays will be con- 

 86. verged as white light 



would be, and appear upon a small screen placed at the 

 focus as a spot of white light 

 4th. By reflection from a 

 series of small mirrors. Let 

 the spectrum fall upon the 

 small mirrors, and so incline 

 them that they will reflect F *ff* 97. 



the light to the same place upon the screen or the wall. 

 5th. By rotating colored disks. 

 Disks painted with the colors of the spectrum are 

 sold in the market under the name of Newton's disks. 

 They are made by pasting sections of colored tissue 

 paper upon a large, stiff pasteboard disk. 



These colors should have the following angular 

 value : 



Red, 60, Blue, 55, 



Orange, 35, Indigo, 35, 



Yellow, 55, Violet, 60. 



Green, 60, 



This disk may be rotated upon the whirling table, 

 or, what is much better, a zoetrope rotator, and it will 

 appear a dusky white. It will be better to have a strong 

 light thrown upon it while it is turning. 



Another good way is to cut disks of properly-colored 

 papers and make a radial slit in them. When put 



