"Scientific writings may he divided into three 

 groups: technical works intended for scientific 

 men, popular compilations for general use, 

 and works which contribute to literature and 

 science at the same time. Of the first two 

 there is no lack, hut our third division is so 

 poorly represented as to have led to the say- 

 ing that those who can write on scientific 

 subjects have no original ideas, while those 

 who have ideas cannot write. It is even true 

 that popular works hy eminent investigators 

 are usually to he described as critical compi- 

 lations, taking no high rank as science or 

 literature." 



