8. P. Langley — The History of a Doctrine. 21 



see whether this were the lot of other and greater men, I have 

 found that it was, and that, though no one was altogether for- 

 saken of the truth he sought, or, on the whole review of his 

 life as a seeker, but might believe he had advanced her cause, 

 yet there was no absolute criterion by which it could be told 

 at the time, whether, when after long waiting, there came in 

 view what seemed once more her beautiful face, it might not 

 possibly prove, after all, the mockery of error ; and, doubtless, 

 appeal might be made to the experience of many investigators 

 here with the question, " Is it not so ?" 



What then ? Shall we admit that truth is only to be surely 

 found under the guidance of an infallible church ? If there be 

 such a church, yes ! Let us, however, remember that the 

 church of science is not such a one, and be ready to face all 

 the consequences of the knowledge that her truths are put for- 

 ward by her as provisional only, and that her most faithful 

 children are welcome to disprove them. 



What then, again ? Shall we say that the knowledge of 

 truth is not advancing ? It is advancing, and never so fast as 

 to-day ; but the steps of its advance are set on past errors, and 

 the new truths become such stepping-stones in turn. 



To say that what are truths to one generation are errors to 

 the next, or that truth and error are but different aspects of 

 the same thing to our poor human nature, may be to utter tru- 

 isms ; but truisms which one has verified for one's self out of a 

 personal experience are apt to have a special value to the 

 owner ; and these lead, at any rate, to the natural question, 

 " Where is, then, the evidence that we are advancing in reality, 

 and not in our own imagination ?" 



There are many here who will no doubt heartily subscribe to 

 the belief that there is no absolute criterion of truth for the 

 individual, and admit that there is no positive guaranty that 

 we, with this whole generation of scientific men, may not, like 

 our predecessors, at times go the wrong way in a body, yet 

 who believe as certainly that science as a whole, and this 

 branch of it in particular, is actually advancing with hitherto 

 unknown rapidity. In asking to be included in this number, 

 let me add that to me the criterion of this advance is not in 

 any ratiocination, not in any a priori truth, still less in the 

 dictum of an}? authority, but in the undoubted observation 

 that our doctrine of radiant energy is reaching out in every 

 direction, and proving itself by the equally undoubted fact 

 that through its aid nature obeys us more and more ; proving 

 itself by such material evidence as is found in the electric 

 lights in our streets, and. in a thousand such ways which I need 

 not pause to enumerate. 



