8. P. Langley — The History of a Doctrine. 15 



At this time, however fairly we seem embarked on the 

 paths of study which are followed to-day, and while the move- 

 ment of the main body of workers is in the right direction, it 

 is yet instructive to observe how eminent men are still spend- 

 ing great and conscientious labor, their object in which is to 

 advance the cause, while the effect of it is to undo the little 

 which has been rightly done, and to mislead those who have 

 begun to go right. 



As an instance both of this and of the superiority of mod- 

 ern apparatus, we may remark, — after having noticed that the 

 ability of obscure heat to pass through glass, if completely 

 established, would be a strong argument in favor of its kin- 

 ship to light, and that De la Roche and others had indicated 

 that it would do so (in which we now know they were right), — 

 that at this stage, or about 1816, Sir David Brewster, the 

 eminent physicist, made a series of experiments which showed 

 that it would not so pass. Ten years later, in view of the im- 

 portance of the theoretical conclusion, Baden Powell repeated 

 his observations with great care, and confirmed them, an- 

 nouncing that the earlier experimenters were wrong, and that 

 Brewster was right ; so that here all these years of conscien- 

 tious work resulted in establishing, so far as it could be estab- 

 lished, a wholly wrong conclusion in place of a right one 

 already gained. 



It may be added, that with our present apparatus, the pas- 

 sage of obscure radiant heat through glass could be made 

 convincingly evident in an experiment which need not last 

 a single second. 



We are now arrived at a time when the modern era begins ; 

 and in looking back over one hundred and fifty years, from 

 the point of view of the experimenter himself with his own state- 

 ment of the truth as he saw it, we find that the comparison of the 

 progress of science to that of an army, which moves, perhaps 

 with the loss of occasional men, but on the whole victoriously 

 and in one direction, is singularly misleading ; and I state this 

 more confidently here, because there are many in this audience 

 who did not get their knowledge of nature from books only, 

 but who have searched for the truth themselves ; and, speak- 

 ing to them, may I not say that those who have so searched know 

 that the most honest purpose and the most patient striving 

 have not been guaranties against mistakes, — mistakes which 

 were probably hailed at the time as successes % It was some 

 one of the fraternity of seekers, I am sure, who said, " Show 

 me the investigator who has never made a mistake, and I will 

 show you one who has never made a discovery." 



We have seen the whole scientific body, as regards this par- 

 ticular science of radiant energy, moving in a mass, in a wrong 



