PREFACE 



OBSERVERS of Nature generally belong to 

 one of two classes the scientific and the 

 imaginative. If scientists, they refuse to consider 

 any thesis not founded on a vast array of facts ; 

 and if poets, they may readily initiate a theory 

 on too few data. These two classes are always 

 in conflict with each other. The scientist despises 

 the poet as a visionary ; and is himself regarded 

 by the adversary as a narrow-minded person. 



The accurate classifier is of course highly com- 

 mendable ; but the propounder of mere theories is 

 not to be despised, for he is drawing visionary 

 maps of lines of thought along which the scientist 

 may find it convenient to travel ; he is like a 



