ON THE PHYSICAL VIEW OF NATURE. 137 



to glance summarily at these revolutions in the domain 

 of scientific thought which the physical view, by re- 

 garding nature as the playground of the transformations 

 of energy, has brought about. What I have just in- 27. 



. . Revolutions 



dicated will suffice to bring some order into the account brought 



about by 



I propose to give. There are four distinct directions in 

 which we have to look. Firstly, there is the clearer 

 definition of the new ideas laid down in the new vocab- 

 ulary of scientific and popular language during the 

 second half of the century. Secondly, there is the 

 revision and recasting of the whole body of physical 

 and chemical knowledge in the light of the new insight 

 which had been attained. Thirdly, there is the criticism 

 of existing theories from the new points of view ; and 

 lastly, there are the fresh departures which these novel 

 ideas have suggested. 



The first definite use of the new conceptions of power 

 and work, and of a scale of mechanical value, were con- 

 tained in the writings of Poncelet and Sadi Carnot in 

 France during the first quarter of the century. The 

 first philosophical generalisations were given by Mohr 

 and Mayer ; the first mathematical treatment was given 

 by Helmholtz ; the first satisfactory experimental verifica- 

 tion by Joule, during the second quarter of the century. 

 The practical elaboration of the whole system following 

 upon Joule's and Eegnault's experiments belongs, through 

 Thomson and Eankine in this country, and through 

 Clausius in Germany, to the third quarter of the century. 

 Students in our age entering on the study of mechanical, 

 physical, chemical, and even physiological processes, reap 

 the benefit of these labours by at once grasping the 



