17!) 



investigation, have been found to entirely conform to the theory or to 

 require only minor modifications, that we hesitate to accept such a sweep- 

 ing statement as that contained in Shinn's paper. The facts cited do not 

 necessarily conflict with the theory — indeed, they would seem to point to 

 the truth of the theory. What is needed is more experimental evidence 

 covering these points. 

 Purdue University, 

 Lafayette. Ind. 



