SECOND EDITION. Vll 



science ; just as in a history of a present war, those 

 military operations of which the aim and effect are 

 yet unknown, cannot be rightly narrated. 



From this cause, it can hardly happen but 

 that such a work as this must fail to give to some 

 distinguished contemporary labourers in the field 

 of science the pre-eminence and lustre which their 

 activity and intelligence merit ; because their labour 

 is not yet crowned by its result. For such cases, 

 my office is like writing the story of Columbus while 

 he was still sailing westwards. So far as I have 

 ventured to deal with lines of scientific research at 

 present incomplete, what I have to offer is rather a 

 discussion of principles than a narrative of facts ; 

 and accordingly, such discussions, on several points 

 now in question, will be found in the Philosophy of 

 the Inductive Sciences ; sufficient, I hope, to show 

 that I have stopped where I have, out of no want 

 of sympathy with the ulterior progress of know- 

 ledge. 



In correcting the errours of the work, I have 

 availed myself of all the critiques of the former 

 edition which have come under my notice, without 

 regard to the spirit in which they were written, 

 whether hostile or friendly. I have not noticed 

 such criticism in any other way than by thus using 



