490 FKAGMENTS OF SCIENCE. 



the truth of this theory ; that is a question which 

 may still have to be fought out. But I refer to it as 

 an illustration of the force of genius with which Mayer 

 followed the mechanical theory of heat through all its 

 applications. Whether the meteoric theory be a matter 

 of fact or not, with him abides the honour of proving 

 to demonstration that the light and heat of suns and 

 stars may be originated and maintained by the collisions 

 of cold planetary matter. 



It is the man who with the scantiest data could 

 accomplish all this in six short years, and in the hours 

 snatched from the duties of an arduous profession, that 

 the Royal Society, in 1871, crowned with its highest 

 honour. 



Comparing this brief history with that of the Copley 

 Medalist of 1870, the differentiating influence ef 

 'environment,' on two minds of similar natural cast 

 and endowment, comes out in an instructive manner. 

 Withdrawn from mechanical appliances, Mayer fell back 

 upon reflection, selecting with marvellous sagacity, from 

 existing physical data, the single result on which could 

 be founded a calculation of the mechanical equivalent 

 of heat. In the midst of mechanical appliances, Joule 

 resorted to experiment, and laid the broad and firm 

 foundation which has secured for the mechanical theory 

 the acceptance it now enjoys. A great portion of Joule's 

 time was occupied in actual manipulation; freed from 

 this, Mayer had time to follow the theory into its most 

 abstruse and impressive applications. With their places 

 reversed, however, Joule might have become Mayer, and 

 Mayer might have become Joule. 



It does not lie within the scope of these brief articles 

 to enter upon the developments of the Dynamical 

 Theory accomplished since Joule and Mayer executed 

 their memorable labours. 



