THE PRESIDENTIAL ADDRESS. 19 



which I employed a few years ago in addressing a University audience 

 familiar with lecture time-tables, on Mondays, Wednesdays and Fridays 

 we adopt the one hypothesis, on Tuesdays, Thursdays and Saturdays the 

 other. We know that we cannot be seeing clearly and fully in either 

 case, but are perfectly content to work and wait for the complete under 

 standing. 



And when we look back over the two centuries or so during which 

 scientific men have tried systematically to solve the riddle of light, or 

 even go further back to the surmisings of philosophers of still older time, 

 we see that every conscientious attempt has made some approach to the 

 goal. The theories of one time are supplanted by those of a succeeding 

 time, and those again yield to something more like the first. But it is 

 no idle series of changes, no vagaries of whimsical fashion ; it is growth- 

 The older never becomes invalid, and the new respects the old because 

 that is the case. 



Surely it is the same in regard to less material affairs. The scientific 

 worker is the last man in the world to throw away hastily an old faith or 

 convention or to think that discovery must bring contempt on tradition. 



There is a curious parallelism here to a relation between science and 

 industry of which I have already spoken. Just as any particular case of 

 mass production can be regarded as a temporary condition which the 

 growth of knowledge brings about, and in the end supersedes, so also it 

 may be said of any law or rule or convention or definition that knowledge 

 is both the parent and eventually the destroyer. Time devours his own 

 children. Even if a statement retains its outward form, its contents 

 change with the meanings attached to its terms : and change moreover 

 in different directions when used by different people, so that constant 

 re-definition is necessary. How much more is this the case when the 

 contents themselves have to be added to. The distinction between truth 

 itself and attempts to embody it in words is so constantly forced upon the 

 student of science as to give his statements on all matters a characteristic 

 form and expression. And this is, I think, one of the reasons why men 

 are often needlessly alarmed by the new announcements of science and 

 think they are subversive of that which has been proved by time. 



To this consideration I may add yet one more, which may be illustrated 

 by the same analogy. Scientific research in the laboratory is based on 

 simple relations between cause and effect in the natural world. These 

 have at times been adopted, many of us would say wrongly, as the main 

 principle of a mechanistic theory of the universe; That relation holds in 



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