244 CHEMICAL KAYS AND EADIANT HEAT. [MEMOIR XVII. 



of the sensitiveness or non - sensitiveness of the same 

 chemical compound being determined merely by the fact 

 of its thickness or thinness, these, and many other similar 

 results obviously depending upon mechanical principles, 

 it seems to me that very powerful evidence may be 

 drawn against the materiality of light, and its entering 

 into chemical union with ponderable atoms. Those phi- 

 losophers who have adopted the undulatory theory will 

 probably find in studying these subjects evidence in 

 favor of their doctrines. 



