2 S. P. LangJey — The History of a Doctrine. 



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 towards 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 compiler, 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 backward from his present standpoint, now sees to 

 have been in the right direction. 



I believe this comparison of the progress of science to that 

 of an army, which obeys an impulse from one head, has more 

 error than truth in it ; and, though all similes are more or less 

 misleading, I would prefer to ask you to think rather of a 

 moving crowd, where the direction of the whole comes some- 

 how from the independent impulses of its individual members ; 

 not wholly unlike a pack of hounds, which, in the long-run, 

 perhaps catches its game, but where, nevertheless, when at 

 fault, each individual goes his own way, by scent not by sight, 

 some running back and some forward ; where the louder- 

 voiced bring many to follow them, nearly as often in a wrong 

 path as in a right one ; where the entire pack even has been 

 known to move off bodily on a false scent ; for this, if a less 

 dignified illustration, would be one which had the merit of 

 having a truth in it, left out of sight by the writers of text- 

 books. 



At any rate, the actual movement has been tortuous, or often 

 even retrograde, to a degree of which you will get no idea from 

 the account in the text-book or encyclopedia, where, in the 

 main, only the resultant of all these vacillating motions is 

 given. With rare exceptions, the backward steps — that is, the 

 errors and mistakes, which count in reality for nearly half, and 

 sometimes for more than half, the whole — are left out of scien- 

 tific history ; and the reader, while he knows that mistakes 

 have been made, has no just idea how intimately error and 



