UN THE PHY.SH'AL NIKW i)l- NATl'KK. l'J9 



forced to consider anew tlie ultimate principles of all 

 physical reasoning, notaljly the scope and validity of the 

 Newtonian laws of motion and of the conceptions of 

 force and action, of absolute and relative motion, as 

 defined or implied in the mechanical scheme which is 

 l)ased upon them. Also with their increasiui; com- «». 



" Artllicul 



plexity modern dynamical exidanations have undoubt- e'^rarur of 

 edly, to every impartial observer, acquired a certain llxpuia"'' 

 character of artificiality which su^^gests the question to """"■ 

 what extent all such mechanical schemes are an expres- 

 sion of actual truths or merely useful illustrations. For 

 the pursuit of scientific research this question is perhaps 

 of little importance : a method is a correct one if it 

 leads to correct results verified by oltservation. Philo- 

 sophically, as bearing upon the processes, powers, and 

 limits of human reasoning, the question is all-important. 

 We are thus led beyond the province of scientific into m. 



'' ^ Tlie philo- 



that of philosophic thought. In future chapters we shall j^p'''^ p">*>- 

 frequently ha\e occasion to note this tendency of the 

 jiurely scientific thought of the century to lead uj* to 

 philosophical problems. Wherever this is the case a 

 history of scientific thought may legitimately close one 

 of its chapters. 



and physical theory is really the of iitature as the two conditions 

 mechanically available energy. ... whicli make generalisations pos- 



This energy is definite, but is not, 

 like matter itself, an entity that is 

 conserved in unchanging amount. 

 ... It may and usually does di- 

 minish, in the course of gradual 

 physical changes." 



' The three volumes of the 

 'Rapports,' ka., mentioned above, 

 have been significantly prefaced by 

 a discourse of M. Poincard on the 

 relations of exi>eriiiiental and ma- 

 thematical physics, in wliiuh he in- 

 sists ujion tiic unity and simplicity 



sible and useful. With special ref- 

 erence to modern electrical theories, 

 such as those of Lorentz and Ijarmor, 

 which he had aliejuly criticised in 

 his course on ' Electricit«5 ct Op- 

 tique' (2nd ed., 1901, p. lul. &c. ), 

 he discusses the i)i)ssibility <»f ulti- 

 mate mechanical explanations. Of 

 these, according to his view, an 

 " infinity " is always possible. He 

 asks what is the aim we are follow- 

 ing — " Ce n'est pas le mo<'anisme, 

 le vrai, le seul but, c'cit lunito." 



