TEE POPULAR SCIENCE MONTHLY. 



THE HISTORY OF A DOCTRINE.* 



By Peof. S. p. LANGLEY. 

 I. 



IN these days, when a man can take but a very little portion of 

 knowledge to be his province, it has become customary that 

 your president's address shall deal with some limited topic, with 

 which his own labors have made him familiar ; and accordingly I 

 have selected as my theme the history of our present views about 

 radiant energy, not only because of the intrinsic importance of 

 the subject, but because the study of this energy in the form of 

 radiant heat is one to which I have given special attention. 



Just as the observing youth, who leaves his own household to 

 look abroad for himself, comes back with the report that the 

 world, after all, is very like his own family, so may the specialist, 

 when he looks out from his own department, be surprised to find 

 that, after all, the history of the narrowest specialty is amazingly 

 like that of scientific doctrine in general, and contains the same 

 lessons for us. To find some of the most useful ones, it is impor- 

 tant, however, to look with our own eyes at the very words of the 

 masters themselves, and to take down the dusty copy of Newton, 

 or Boyle, or Leslie, instead of a modern abstract ; for, strange as 

 it may seem, there is something of great moment in the original 

 that has never yet been incorporated into any encyclopaedia, 

 something really essential in the words of the man himself which 

 has not been indexed in any text-book, and never will be. 



It is not for us, then, here to-day, to try — 



" How index-learning turns no student pale, 

 Yet holds the eel of science by the tail " ; 



but, on the contrary, to remark that from this index-learning, 

 from these histories of science and summaries of its progress, we 

 are apt to get wrong ideas of the very conditions on which this 

 progress depends. We often hear it, for instance, likened to the 

 march of an army toward some definite end ; but this, it has 

 seemed to me, is not the way science usually does move, but only 

 the way it seems to move in the retrospective view of the com- 

 piler, who probably knows almost nothing of the real confusion, 

 diversity, and retrograde motion of the individuals comprising 

 the body, and only shows us such parts of it as he, looking back- 

 ward from his x>resent standpoint, now sees to have been in the 

 right direction. 



I believe this comparison of the progress of science to that of 



* President's address before the American Association for the Advancement of Science, 

 at Cleveland, Ohio, August 15, 1888. Reprinted from "Science." 



