LIGHT. 107 



COLORS OF THIN FILMS. 



Let a soap bubble be held in the beam of diverging 

 rays, near the focus of the lens (Fig. 74), and in such 

 a position that some of the light will be reflected from 

 its upper surface. 



As soon as the bubble becomes thin enough, brilliant 

 colors will appear upon it, which will be reflected to 

 the walls and ceiling, as they will spread over a 

 large surface. If the bubble is held quiet long enough, 

 each of the prismatic tints will appear in turn upon the 

 walls, and sometimes the series will be repeated. 



If the bubble is projected in the way mentioned 

 upon page 44, three or four of these series may be seen 

 at the same time. 



Instead of blowing a bubble with a pipe, as shown 

 in that figure, blow a mass of them in the dish con- 

 taining the solution. Very large masses may be made 

 and the colors reflected from them in the same way as 

 above, or with the lantern. 



The tension of the bubble film may be shown by 

 leaving the tube open after the bubble is blown, when 

 the latter will contract as if it were being drawn into 

 the bowl of the pipe ; or the bubble may be blown upon 

 the end of a glass tube 

 bent twice at right an- 

 gles, after which the 

 open end may be put 

 an inch or two under 

 the surface of water in 

 the chemical tank and ^"^""^^^^^^^^ 

 projected. The water in the tube will stand below the 

 level of the water in the tank indicating pressure. 



When these colors from thin films appear upon the 



