430 



SCIENCE. 



[N. S. Vol. XIV. No. 351. 



mere friction of metals produced heat in 

 unlimited quantity, and argued that heat 

 was therefore a mode of motion, he formed 

 a clear mental picture of what he believed 

 to be occurring. But his experiments may 

 be quoted as proving only that energy 

 can be supplied to a body in indefinite 

 quantity, and when supplied by doing work 

 against friction it appears in the form of 

 heat. 



By using this phraseology we exchange a 

 vivid conception of moving atoms for a col- 

 orless statement as to heat energy, the 

 real nature of which we do not attempt to 

 define ; and methods which thus evade the 

 problem of the nature of the things which 

 the symbols in our equations represent have 

 been prosecuted with striking success, at all 

 events within the range of a limited class of 

 phenomena. A great school of chemists, 

 building upon the thermodynamics of Wil- 

 lard Gibbs and the intuition of Van't 

 Hofi", have shown with wonderful skill 

 that, if a sufficient number of the data of 

 experiment are assumed, it is possible, by 

 the aid of thermodynamics, to trace the 

 form of the relations between many phys- 

 ical and chemical phenomena without the 

 help of the atomic theory. 



But this method deals only with matter 

 as our coarse senses know it ; it does not 

 pretend to penetrate beneath the surface. 



It is therefore with the greatest respect 

 for its authors, and with a full recognition 

 of the enormous power of the weapons em- 

 ployed, that I venture to assert that the 

 exposition of such a system of tactics can- 

 not be regarded as the last word of science 

 in the struggle for the truth. 



Whether we grapple with them, or 

 whether we shirk them ; however much or 

 however little we can accomplish without 

 answering them, the questions still force 

 themselves upon us : Is matter what it 

 seems to be? Is interplanetary space full 

 or empty? Can we argue back from the 



direct impressions of our senses to things 

 which we cannot directly perceive; from 

 the phenomena displayed by matter to the 

 constitution of matter itself? 



It is these questions which we are dis- 

 cussing to-night, and we may therefore, as 

 far as the present address is concerned, put 

 aside, once for all, methods of scientific 

 exposition in which an attempt to form a 

 mental picture of the constitution of matter 

 is practically abandoned, and devote our- 

 selves to the inquiries whether the effort 

 to form such a picture is legitimate, and 

 whether we have any reason to believe that 

 the sketch which science has already drawn 

 is to some extent a copy, and not a mere 

 diagram, of the truth. 



SUCCESSIVE STEPS IN THE ANALYSIS OF 

 MATTER. 



In dealing, then, with the question of 

 the constitution of matter and the possi- 

 bility of representing it accurately, we may 

 grant at once that the ultimate nature of 

 things is, and must remain, unknown ; 

 but it does not follow that immediately 

 below the complexities of the superficial 

 phenomena which affect our senses there 

 may not be a simpler machinery of the ex- 

 istence of which we can obtain evidence, 

 indirect indeed but conclusive. 



The fact that the apparent unity which 

 we call the atmosphere can be resolved into 

 a number of different gases is admitted ; 

 though the ultimate nature of oxygen, ni- 

 trogen, argon, carbonic acid and water 

 vapor is as unintelligible as that of air as 

 a whole, so that the analysis of air may be 

 said to have substituted many incompre- 

 hensibles for one. 



Nobody, however, looks at the question 

 from this point of view. It is recognized 

 that an investigation into the proximate 

 constitution of things may be useful and 

 successful, even if their ultimate nature is 

 beyond our ken. 



