CONCEPTS OF PHYSICAL SCIENCE. 65 



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

 medium may be made to serve not only for the numerous phenomena 

 of optics, but, without ascribing to it any characteristics incompatible 

 with a luminiferous ether, 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 speculation ; 

 but it should not be forgotten that a system, entirely imaginary, 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 mathe- 

 matical laws and which are entirely independent of all theories of the 

 ultimate nature of matter and those which deal with the latter ques- 

 tions 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 opening pass- 

 ages of his recent ' Treatise on Physics,' Chwolson* has employed. 



For every one there exist two worlds, an inner and an outer, and our senses 

 are the medium of communication between the two. The outer world has the 

 property of acting upon our senses, to bring about certain changes, or, as we say, 

 to exert certain stimuli. 



The inner world, for any individual, consists of all those phenomena which 

 are absolutely inaccessible (so far as direct observation goes) to other indi- 

 viduals. The stimulus from the outer world produces in our inner world a sub- 

 jective perception which is dependent upon our consciousness. The subjective 

 perception is made objective, viz., is assigned time and place in the outer world 

 and given a name. The investigation of the processes by which this objectivica- 

 tion is performed is a function of philosophy. 



Some such confession of faith is good for the man of science; lest 

 he forget; but once it is made he is free to turn his face to the light 

 once more, thankful that the investigation of objcctivkation is, indeed, 

 a function of philosophy and that the only speculations in which he, as 

 a physicist, is entitled to engage are those which are amenable at every 

 step to mathematics and to the equally definite axioms and laws of 

 mechanics. 



* Chwolson, ' Physik,' Vol. I., Introduction. 

 vol. lxvi. — 5. 



