BLOWING BUBBLES. 



269 



the nterference. The effects of this interference are mani- 

 fested in many very remarkable and very curious phenom.' 

 ena. John said that he should like to see some of them. 

 Lawrence replied that it was easy to see them, but not so 

 easy to understand how they were produced. 



"They appear in various colored fringes," said Law- 

 rence, " in almost all transparent substances which are 

 made extremely thin so thin that the light, in being re- 

 flected back and forth from one surface to the other, is 

 caused to ' interfere.' We can make a thin film of air 

 which will show them by pressing two plates of glass to- 

 gether which have surfaces that are not exactly parallel. 

 We see them in very thin plates of mica, and in a thin film 

 of oil or other such substance, floating upon water; and, 



[SLOWING IIUJtm.K8. 



