504 SIR DAVID BREWSTER ON THE COLOURS OF THE SOAP-BUBBLE. 



In protecting the colouring matter upon films from currents of air, I at first 

 employed watch-glasses and plates of parallel glass, but the protection was not 

 complete ; and the phenomena were obscured by the vapour deposited upon 

 them, and by the light reflected from their surfaces. When I discovered the 

 method of forming films beneath bubbles, and by the union of bubbles of different 

 sizes, I was able to protect the colouring matter completely from currents of air, 

 and at the same time to get rid of the aqueous vapour and the reflected light. 



In examining films produced upon wine-glasses or other bright substances, 

 the brilliancy of the colours is greatly impaired by the light which these sub- 

 stances reflect ; but if we cover the inside of the glasses with black varnish, or 

 blacken it with smoke, we remove entirely the reflected light, and give great dis- 

 tinctness and brilliancy to the phenomena. 



