PREFACE TO THE SECOND 



EDITION 



The need for a reprint of this book, coming as 

 it does within a few weeks of publication, must 

 be set down in part to the exceptional interest in 

 the problems with which it deals that has been 

 aroused by Mr Balfour's Presidential Address to 

 the British Association. 



For, when attention has been drawn to the 

 new theory of matter — to "the most far-reach- 

 ing speculation about the physical universe which 

 has ever claimed experimental support " — a state 

 of mind is created that, in thoughtful men, will 

 not rest satisfied without some effort to under- 

 stand the basis of the speculation, and to weigh 

 the evidence which can be arraigned in its favour. 

 Truly, the new theory is concerned, not '* about 

 things remote or abstract, things transcendental 

 or divine, but about what men see and handle, 

 about those * plain matters of fact ' among which 

 common-sense daily moves with its most confident 

 step and most self-satisfied smile." 



The importance of the position now gained 

 for the survey of the material universe lies in the 

 unity of conception it discloses and the resulting 

 simplification of detail. Either instinctively, or 

 as the unconscious result of experience, the mind 

 of man naturally grasps at any plan thus to reduce 



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