LIGHT. 



143 



The accompanying figure represents a chromatrope 

 with an arrange- 

 ment for quickly 

 replacing one 

 disk by another 

 of different pat- 

 tern. Rotation 

 is given by fric- 

 tion pulleys. 

 With this form 

 there is a disk 

 with the so-called 

 seven primary 

 colors to illus- 

 trate Newton's 

 theory of colors, 

 one to illustrate Brewster's theory, two to illustrate 

 Young's theory, and a chameleon top, designed by 

 President Morton, of Stevens Institute, Hoboken. 



The effects with all the forms of chromatropes are 

 due to persistence of vision. 



Interesting subjective effects may be observed by 

 projecting in the ordinary way bits of colored glass an 

 inch or two square, so as to have upon the screen a large 

 patch of color with a boundary of white light. The eyes 

 must be fixed attentively upon the colored patch for 

 about half a minute, when the colored piece must be 

 quickly removed, the eyes to be kept meanwhile upon 

 the screen. To prevent the eyes from unconsciously 

 wandering while looking, it will be found advisable to 

 pin a large black button or a piece of black paper to 

 the screen in the middle of the disk. This is to be 

 kept in the centre of vision. The effects observed will 

 of course depend upon the color upon the screen, and 



