FUNDAMENTAL CONCEPTS OF PHYSICAL SCIENCE 27 



transmutation of elements, variation of mass, or even the complete 

 disappearance or creation of matter. The absence of such phe- 

 nomena in our experience has been the real difficulty, and if the 

 views of students of radioactivity concerning the transformations 

 undergone by uranium, thorium, and radium are substantiated, the 

 doctrines of the conservation of mass and matter which lie at 

 the foundation of the science of chemistry will have to be modified. 

 There has been talk of late of violations of the principle of the con- 

 servation of energy in connection with the phenomena of radio- 

 activity, but the conservation of matter is far more likely to lose its 

 place among our fundamental conceptions. 



The development of physics on the speculative side has led, then, 

 to the idea, gradually become more definite and fixed, of a universal 

 medium, the existence of which is a matter of inference. To this 

 medium properties have been assigned which are such as to enable 

 us to form an intelligible, consistent conception of the mechanism by 

 means of which phenomena, the mechanics of which is not capable of 

 direct observation, may be logically considered to be produced. The 

 great step in this speculation has been the discovery that a single 

 medium may be made to serve for the numerous phenomena of optics, 

 and that, without ascribing to it any characteristics incompatible 

 with a luminiferous ether, it is equally available for the description 

 and explanation of electric and magnetic fields, and finally may be 

 made the basis for intelligible theories of the structure of matter. 



To many minds this seemingly universal adaptability of the ether 

 to the needs of physics almost removes it from the field of specu- 

 lation; but it should not be forgotten that a system, entirely imagin- 

 ary, may be devised, which fits all the known phenomena and appears 

 to offer the only satisfactory explanation of the facts, and which 

 subsequently is abandoned in favor of other views. The history of 

 physics is full of instances where a theory is for a time regarded 

 as final on account of its seeming completeness, only to give way to 

 something entirely different. 



In this consideration of the fundamental concepts I have attempted 

 to distinguish between those which have the positive character of 

 mathematical laws and which are entirely independent of all theories 

 of the ultimate nature of matter, and those which deal with the latter 

 questions and which are essentially speculative. I have purposely 

 refrained from taking that further step which plunges us from the 

 heights of physics into the depths of philosophy. 



With the statement that science in the ultimate analysis is nothing 

 more than an attempt to classify and correlate our sensations the 

 physicist has no quarrel. It is, indeed, a wholesome discipline for 

 him to formulate for himself his own relations to his science in terms 

 such as those which, to paraphrase and translate very freely the 



