174 A MODEL OF NATURE. 



the laws by language and symbols which lead to results that are true, 

 whatever be our view as to the real nature of the objects with which 

 we deal. From this point of view the atomic theory becomes not so 

 much false as imnecessary. It may be regarded as an attempt to give 

 an luniatural precision to ideas which are and must be vague. 



Thus, when Rumford found that the mere friction of metals pro- 

 duced heat in unlimited (piantity, smd 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 he quoted as proving only 

 that energy can be supplied to a body in indefinite quantity, and when 

 supplied l)y doing work against friction it appears in the form of heat. 



By using this phraseology we exchange a vivid conception of mov- 

 ing atoms for a colorless statement as to heat energ}^, the real nature 

 of which we do not attempt to detine; 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 Willard 

 Gibl)s 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, ])y 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 onl}^ 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 recogjiition of the enormous power of the weapons employed, 

 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 can not 

 directly perceive — from the ph(>nomena displayed by matter to the 

 constitution of matter itself? 



It is these (luestions 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 al)andoned, 

 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. 



