THE COPLEY MEDALIST OF 1871. 437 



5,000 years. He shows the difficulties attending the 

 assumption that the sun is a cooling body; for, sup- 

 posing it to possess even the high specific heat of water, 

 its temperature would fall 15,000 in 5,000 years. He 

 finally concludes that the light and heat of the sun are 

 maintained by the constant impact of meteoric matter. 

 I never ventured an opinion as to 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 me- 

 chanical 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 demonstra- 

 tion 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 high- 

 est honour. 



Comparing this brief history with that of the Cop- 

 ley Medalist of 1870, the differentiaffng influence of 

 * 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 Withdrawn from mechanical appliances, Mayer fell 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 sagac- 

 ity, from existing physical data, the single result on 

 which could be founded a calculation of the mechan- 

 ical 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 fol- 



