February 22, 1907] 



SCIENCE 



301 



alysis of things there is nothing in the uni- 

 verse which is not hypothetical to any par- 

 ticular individual except the fact of his own 

 consciousness. But the ordinary reader will 

 scarcely understand that in the above state- 

 ments the author is merely denying the exist- 

 ence of matter in the broad, metaphysical 

 sense in which the philosopher denies the ex- 

 istence of any external world whatever. He 

 will rather understand him to be using lan- 

 guage in the sense in which it is commonly 

 used in books on physical subjects, and to be 

 tacitly assuming the existence of an external 

 world and yet denying the existence of matter 

 as a constituent of that world ; and indeed this 

 is certainly what he does do, since in the next 

 sentence we find him asserting the reality of 

 energy. 



Such assertions seem to me to be particu- 

 larly fruitful of confusion of thought in the 

 minds of the untrained, while to the trained 

 they are devoid of all meaning. For matter 

 ' as we ordinarily understand the term ' does 

 not involve any particular hypothesis as to the 

 inner nature of the atom. As commonly un- 

 derstood, matter is merely that something 

 which possesses the properties of weight and 

 inertia. Its existence is, therefore, just as 

 real as the existence of these properties. As 

 investigation goes on the more properties 

 which we find ourselves agreed in associating 

 with weight and inertia the more definite does 

 our idea of matter become. Thus there is 

 now practical unanimity in regarding matter 

 as composed of discrete particles, and recently 

 some evidence has appeared which makes it 

 plausible at least to endow the discrete par- 

 ticles with an electrical property as well as 

 with weight and inertia, and it has also been 

 suggested that the inertia property may be 

 entirely wrapped up in the electrical property. 

 If further experimenting should justify this 

 hypothesis the term matter would lose none 

 of its present significance, but would rather 

 gain additional meaning, just as the term 

 ' light ' gained rather than lost in significance 

 when Maxwell and Hertz discovered a relation 

 between light and electricity. The assertion 

 that light ' is a pure hypothesis, that there is 

 not the least evidence for its existence,' would 



be in every respect as warrantable as the sim- 

 ilar assertion regarding matter. Either asser- 

 tion, I take it, is completely misleading in 

 popular writing, even though there may be 

 some technical justification for it. 



But I can see no sort of justification, tech- 

 nical or otherwise, in denying the existence 

 of matter and in the same breath asserting 

 that ' energy is the only reality ' ; for, since 

 energy is defined only in terms of matter and 

 motion, it is obviously absurd to consider it 

 any more real than matter. It is merely a 

 case of the recrudescence of the confusion of 

 ideas which Boltzmann and Planck eliminated 

 to so large an extent from German thinking 

 by their masterly articles on ' Energetik ' 

 which appeared in Wiedemann's Annalen in 

 the winter of 1906. Of course, no one will 

 deny that it might, perhaps, be possible to 

 describe natural phenomena from some other 

 view-point than that which has been adopted 

 by the master minds of science from Galileo 

 and Newton down to J. J. Thomson, and to 

 start with a fundamental something which 

 might be called energy instead of with the 

 something which we now call matter, but this 

 possibility, if it be a possibility, has certainly 

 not yet been realized, and the attempts which 

 have thus far been made in this direction have 

 resulted only in a confused mass of logical 

 contradictions, so that, in point of fact, energy, 

 as the term is now used in scientific literature, 

 is still defined in terms of matter, space and 

 time. In view of the gross abuse which the 

 word energy commonly receives at the hands 

 of the unthinking, an abuse which is well 

 illustrated by the effort which is sometimes 

 made by high school teachers to ' get at every- 

 thing,' as they say, from the standpoint of 

 energy, even before their pupils have been 

 taught enough mechanics to make a concise 

 conception of the meaning of energy possible, 

 in view, I say, of this popular abuse of the 

 term it is particularly desirable that men of 

 science do not add to the confusion by using 

 it in a loose and indefinite sense. 



E. A. MiLLIKAN 



University of Chicago, 

 January 28, 1907 



