PREFACE TO THE ENGLISH EDITION 



My father's life was one of so many interests, and his 

 work was at all times so diversified, that to follow each 

 thread separately, as if he had been engaged on that alone 

 for a time, would be to give a false impression of his activity 

 and the peculiar character of his labours. All through his 

 active career he was equally busy with research into nature, 

 with studies in philosophy, with teaching and administra- 

 tive work. The real measure of his energy can only be 

 found when all these are considered together. Without 

 this there can be no conception of the limitations imposed 

 upon him in his chosen life's work. The mere amount of 

 his research is greatly magnified by the smallness of the 

 time allowed for it. 



But great as was the impression left by these researches 

 in purely scientific circles, it is not by them alone that he 

 made his impression upon the mass of his contemporaries. 

 They were chiefly moved by something over and above 

 his wide knowledge in so many fields — by his passionate 

 sincerity, his interest not only in pure knowledge, but in 

 human life, by his belief that the interpretation of the book 

 of nature was not to be kept apart fron'. the ultimate prob- 

 lems of existence ; by the love of truth, in short, both 

 theoretical and practical, which gave the key to the char- 

 acter of the man himself. 



Accordingly, I have not discussed with any fulness the 

 value of his technical contributions to natural science ; I 

 have not drawn up a compendium of his philosophical 

 views. One is a work for specialists ; the other can be 

 gathered from his published works. I have endeavoured 

 rather to give the public a picture, so far as I can, of the 

 man himself, of his aims in the many struggles in which 



