Theory of the Velocity of Chemical Reaction, 673 



The radiation density in the dark at temperature T is 

 given hv 



Stt/ii/ 3 1 



„ AT 



1 



so that the ratio of the radiation density due to sunlight to 

 that in the dark is given by 



u v 



v 4 hv 



In the above instance it has been shown that for T = 303°, 



T =46, so that putting the sun's effective temperature 

 fc JL 



T =6000° and its apparent semi-diameter a- 16' = 4*05 . 10" 3 , 

 one finds 



— =5*42. lO" 6 |__i=5-8.10 18 . 



In other words, the energy density of the radiation which is 

 supposed to determine the reaction velocity, namely that 

 of wave-length 1'046/i, is some 10 13 times greater in 

 sunlight than in the dark. Yet the reaction proceeds at 

 appreciably the same rate whether it is exposed to sunlight 

 or not. 



The obvious conclusion would appear to be that the rate 

 of reaction is not affected by the radiation density. There 

 are, of course, various ways in which one may attempt to 

 escape this conclusion, but a moment's consideration shows 

 them to be untenable, and it is therefore scarcely worth 

 while to enumerate and disprove them here. But until 

 and unless the above difficulty can be disposed of, it would 

 seem to constitute a grave objection to Professor Lewis's 

 theory. 



Clarendon Laboratorv, Oxford, 

 Sept. 19th, 1920. 



