386 Remarks on the Dynamical Theory of Heat. 



work referred to, he gave a series of numbers, and that his stre- 

 nuous supporter in putting his claims above those of Mr. Joule, 

 afterwards pointed out that they contained "implicitly" the 

 mechanical equivalent of heat. I was aware that in 1847 he 

 had reduced these numbers so as to express the mechanical 

 equivalent of heat in the usual form, his determinations vary- 

 ing from 395 to 529 grammes raised to a height of 1 metre. 

 (That of Mayer, according to the precise calculations of M. Reg- 

 nault, is 426.) I thought, moreover, that M. Seguin had ope- 

 rated upon steam, and that steam, as he used it, could not give 

 a correct result. I further knew that the intimate friend of 

 M. Seguin, Mr. Grove, had stated, in a lecture given at the 

 Royal Institution on Friday, 25th January 1856, that "since 

 the accurate and elaborate experiments of M. Regnault, M. Se- 

 guin has necessarily varied his estimate, as by those experiments 

 it appears that, within certain limits, for elevating the tempera- 

 ture of compressed vapour by one degree, no more than about 

 -j^-ths of a degree of total heat is required ; consequently the 

 equivalent multiplied in this ratio would be 1666 grammes 

 instead of 500." This would be nearly four times Mayer's equi- 

 valent. Perhaps Prof. Thomson has access to sources of infor- 

 mation which are unknown to me, and therefore I do not presume 

 to deny his statement that M. Seguin obtained " the same nume- 

 rical result" as Mayer, three years before him. Prof. Thomson 

 will no doubt produce his authority. 



But I must here say distinctly that I would not for an instant 

 allow my estimate of Mayer to depend upon his determination 

 of the mechanical equivalent of heat. It is the insight which 

 he had obtained, in advance of all other men, regarding the rela- 

 tionship of the general energies of the universe, as illustrated 

 in the whole of his writings, that gives him his claim to my 

 esteem and admiration*. In 1842, when he published his first 



* I am far from saying that Mayer had mastered the entire details and 

 developments of the conservation of force, or that he is free from error; 

 but he it was who first clearly grasped the philosophy of the subject ; and 

 what was done previous to 1842 is to what Mayer did as twilight is to the 

 light of day. His equals — possibly his superiors — have since appeared 

 upon the field ; but the generous-minded among them, instead of looking 

 down upon the man, will acknowledge him as a successful pioneer into a 

 region which promises possessions ri< her than any hitherto granted to the 

 intellect of man. On one point in particular, Mayer, I think, allowed his 

 caution to cripple his philosophy. He evidently feared having anything 

 to do with atoms or their motions, and hence could hardly be said to have 

 realized the complete physk-al conception of the dynamical theory of heat. 

 Probably, however, many share his caution, and adhere to the external facts 

 without seeking to penetrate the molecular actions which underlie them. 

 It must also be remembered that Mayer's education was that of a doctor 

 of medicine, the power of original genius alone enabling him to break 

 through the limitations which his culture tended to impose. 



