748 



terest, and the inextricable complications to which these theories led 

 have been almost forgotten. This quiescence has been recently dis- 

 turbed by the experiments of M. Cr6mieu, which have contradicted, 

 or at least have seemed to contradict, the results formerly obtained 

 by Eowland. Numerous investigators have endeavored to solve the 

 question, and fresh experiments have been undertaken. What result 

 will they give ? I shall take care not to risk a prophecy which might 

 be falsified between the day this treatise is ready for the press and the 

 day on which it is placed before the public. 



