26 REPOKT — 1901. 



tentative nature of some of our theories, in spite of many outstanding 

 difficulties, the atomic theory unifies so many facts, simplifies so much 

 that is complicated, that we have a right to insist— at all events till an 

 equally intelligible rival hypothesis is produced— that the main structure 

 of our theory is true ; that atoms are not merely helps to puzzled mathe- 

 maticians, but physical realities. 



