426 SCIENCE PROGRESS. 



were thus required of the ether could not possibly be stable, 

 and, as a necessary consequence, can have no physical 

 existence. Doubtless the idea of sparing the now generally 

 received electro-magnetic theory of light a similar fate 

 prompted the immortal Hertz, to whom this theory owes 

 so much, when he expressly declined to see in it anything 

 beyond a system of six differential equations. That the 

 evolution of the theory should end in this point is a far 

 more convincing argument than any I could adduce against 

 the permanent value of the theoretical methods previously 

 followed on mechanical lines. 



But you may urge the fruitfulness of these theories. 

 Yes, they were fruitful in so far as they contained correct 

 elements, just as they were harmful on account of the false 

 ones. Which were the right and which were the wrong 

 elements, however, was only revealed after long and dearly 

 bought experience. 



The result of our remarks up to the present is in the first 

 place purely negative ; we have learned how not to proceed, 

 and it may appear of little use to bring forward such 

 negative results. However we may already note one gain 

 here which many of you will not consider worthless. In this 

 way we discover the possibility of critically correcting a 

 view which in its own time created no small sensation, 

 and caused many of those interested great trouble. I 

 refer to the widely known views first expounded twenty- 

 three years ago by the celebrated Berlin Professor of 

 Physiology, Emil du Bois-Reymond, at the Leipzig meeting 

 of the German Association of Natural Philosophers, and 

 later in some other much-read papers ; views dealing with 

 the prospects of our future knowledge of nature and 

 culminating in the much-discussed irnorabimus. In the 

 long controversy which this speech gave rise to du Bois- 

 Reymond has, so far as I can see, victoriously withstood 

 all attacks, and naturally so, since all his opponents have 

 proceeded from the same premises which led him to his 

 ignorabimits, and his conclusions stand as firm as the 

 basis upon which he built them. This basis, which mean- 

 while had been called in question by no one, is the me- 



