A. R. MOORE • 169 



not in contact with a surface. It is also clear from the figures in the 

 table that the length of exposure is inversely proportional to the 

 light intensity since the product of intensity by time equals a con- 

 stant. This shows that a certain quantity of light is required to 

 bring about the reaction, which is but another way of saying that the 

 Bunsen-Roscoe law holds here as it does in other photochemical 

 reactions.^'^ 



^Loeb, J., Forced movements, tropisms, and animal conduct, Philadelphia and 

 London, 1918, 83. 



