1908] on the Scientific Work of Lord Kelvin. 200 



point. He seems to have had access then only to Clapevron's account 

 of Carnot, of date 184o, from which, howevei-, he expounds the 

 argument succinctly and correctly. He admits the probability of 

 the truth of Clapeyron's deductions for gases, but falls back on the 

 suggestion that they may also be obtainable otherwise on more cer- 

 tain principles ; while he characterises as very unlikely the (correct) 

 inference that compression of water between its point of maximum 

 density and the freezing-point would absorb heat. Thus Helmholtz,* 

 contrary to Thomson, saves the conservation of total energy by 

 abandoning and ignoring the ideas belonging to the principle of 

 Carnot. 



The brilliant and suggestive writings of J. R. Mayer on the con- 

 servation of total energy were at that time unknown to Helmholtz : 

 they seem to have been first brought to general notice j by Joule 

 himself in the classical memoir on the Mechanical Equivalent of Heat 

 presented by Faraday to the Royal Society in 1849. The sketch 

 above given will have shown how little such theoretical considera- 

 tions as those of flayer, however illuminating and acute within their 

 own range, were calculated to remove the profounder perplexities of 

 Thomson, so long as there remained the apparently essential contra- 

 diction on Avhich these doubts had their foundation. His insistence 

 in class lectures on the absolute necessity for Joule's experimental 

 work is still recalled by his students. 



The credit of being the first to resolve these difficulties belongs 

 to Clausius. In his memoir ' On the Motive Power of Heat and the 

 Laws of Heat which may be deduced therefrom,' communicated to 

 the Berlin Academy in February 18.50, he quotes the title of Carnot's 

 tract (Paris, 1824) in a footnote at the beginning { of the paper, which 

 proceeds as follows : " I ha^e not been able to procure a copy of 

 this work : I know it solely through the writings of Clapeyron and 

 Thomson, from which latter are taken the passages hereafter cited." 

 Then, in the introductory section, after referring to the difficulties 

 above discussed, and the work of Holtzmann, Mayer and Joule, he 

 continues : — 



" The difference between the two ways of regarding the subject 

 has been seized with much greater clearness by W. Thomson, who 

 has applied the recent investigations of Regnault, on the tension and 

 latent heat of steam, to the completing of the memoir of Carnot.§ 

 Thomson mentions distinctly the obstacles which lie in the way of 

 an unconditional acceptance of Carnot's theory, referring particularly 

 to the investigations of Joule, and dwelling on one principal objection 

 to which the theory is liable. If it be even granted that the produc- 



* Wissenscliaftliclie Abhandlungen, 1. p. 38. 



t Osborne Reynolds, Life of J. P. Joule (Manchester Memoirs, vi.),p. 133. 

 % The quotations are here printed from Hirst's translation, in which this 

 memoir occupies pp. 14-68, 



§ Trans. R. S. Edinburgh, xvi. 



Vol. XIX. (Xo. 102) p 



