ADDRESS. 9 



within the range of a limited class of phenomena. A great school of 

 chemists, building upon the thermodynamics of Willard Gibbs and the 

 intuition of Van 't Hoff, 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 physical 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 employed, that I 

 venture to assert that the exposition of such a system of tactics cannot 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 per- 

 ceive ; from the phenomena displayed by matter to the constitution of 

 matter itself ? 



It is these questions which we are discussing 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 

 ourselves 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 Stej^s in the Analysis of Hatter. 



In dealing, then, with the question of the constitution of matter and 

 the possibility 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 existence of which we can obtain evidence, indirect indeed but 

 conclusive. 



The fact that the appai^ent unity which we call the atmosphere can be 

 resolved into a number of different gases is admitted ; though the ultimate 

 nature of oxygen, nitrogen, argon, carbonic acid, and water vapour is as 

 unintelligible as that of air as a whole, so that the analysis of air, taken 

 by itself, may be said to have substituted many incomprehensibles for one. 



Nobody, however, looks at the question from this point of view. It 

 is recognised that an investigation into the proximate constitution of 

 things may be useful and successful, even if their i;ltimate nature is 

 beyond our ken, 



