592 APPLIED MATHEMATICS 



logically from unified principles and firmly established theories. 

 Natural science seems to him a primary science only in so far as 

 it rests on a mathematical basis. Thus, he does not reckon the chem- 

 istry of his day among the sciences, because it rests merely upon 

 an empirical basis and lacks a unified, regulative principle. 



From this point of view theoretical physics is preferred to ex- 

 perimental physics, and occupies, in a sense, a higher rank. Experi- 

 mental physics was merely to gather the material, but it remained 

 for the theoretical physics to form the structure. 



But the succession in the order of rank becomes reversed when 

 we take into account the acquisitions of the last decades as well as 

 the progress which is to be expected in the immediate future. The 

 chain of experimental discoveries of the last century received a 

 fitting completion with the discovery of the Rontgen rays. Con- 

 nected with these there appear in the present century a multitude 

 of new rays, with the most enigmatical properties, which have the 

 profoundest effects upon our conceptions of nature. The more 

 enigmatical these newly discovered facts are, and the more they 

 seem at first to contradict our present conceptions, the greater the 

 successes which they promise for the future. But this is not the occa- 

 sion for the discussion of these experimental triumphs. I must leave 

 to the representatives of experimental physics at this Congress the 

 prolific problem of portraying all of the fruits which have hitherto 

 been gathered in this domain, one might almost say, daily, and 

 those which are to be expected. 



The representative of theoretical physics scarcely finds himself in 

 an equally fortunate position. Great activity does indeed prevail 

 in this domain. One could almost say that it is in process of revolu- 

 tion. Only how much less tangible are the results here attained in 

 comparison with those in experimental physics! It appears here 

 that in a certain sense experimentation deserves precedence over 

 all theory. An immediate fact is at once comprehensible. Its fruits 

 may become evident in the shortest time, such as the various appli- 

 cations of the Rontgen rays and the utilization of the Hertz waves 

 in wireless telegraphy. The battle which the theories have to fight 

 is, however, an infinitely wearisome one; indeed, it seems as if cer- 

 tain disputed questions which existed from the beginning will live 

 as long as the science. 



Every firmly established fact remains forever unchangeable; at 

 most, it may be generalized, completed, additions may be made, 

 but it cannot be completely upset. Thus it is explained why the 

 development of experimental physics is continuously progressive, 

 never making a sudden jump, and never visited by great tremblings 

 and revolutions. It occurs only in rare instances that something 

 which was regarded as a fact turns out afterwards to have been an 



