128 



SCIENTIFIC THOUGHT. 



24. 

 The two 

 laws of 

 thermo- 

 dynamics. 



quainted with Carnot's ideas and with Joule's work, 

 increasingly felt the necessity of reconciling both views 

 in one consistent view. So did Clansius independently 

 at Ziirich. The result was the doctrine of the " con- 

 servation of energy," — not of heat, as Carnot had it, — 

 and the embodiment of the two correct ideas contained 

 independently in Carnot's and Joule's work in the two 

 well-known laws of thermo-dynamics ^ — viz., the con- 

 servation, equivalence, and convertibihty of energy, as 



mation or destruction of heat as an 

 equivalent for the destruction or 

 formation of other agencies, such as 

 mechanical work " ( ' Math, and 

 Phys. Papers,' vol. i. p. 161, note). 

 The acceptance of the doctrine of 

 the convertibility of heat and 

 mechanical work — implying the 

 conservation of energy in place of 

 the conservation of heat, as Carnot 

 had it — seems to have taken place 

 in Lord Kelvin's mind immediately 

 after his paper referred to ahove in 

 consequence of a paper by Rankine 

 " On the Mechanical Action of 

 Heat " (Roy. Soc. Edinburgh, Feb. 

 1850), as is shown by his letter to 

 Joule, dated October 1850 {loc. cit., 

 vol. i. p. 170). He there refers also 

 to a memoir by Clausius in Poggen- 

 dorf's ' Annalen ' of April and May 

 of the same year as adopting 

 " Joule's axiom instead of Carnot's " 

 (ibid., p. 173). 



^ The reconciliation of Joule's 

 dynamical theorj' of heat with Car- 

 not's doctrine, and the necessary 

 modification of the latter, is con- 

 tained in Lord Kelvin's classical 

 memoir, " On the Dynamical 

 Theory of Heat," in the ' Trans, of 

 the Roy. Soc. of Edinburgh,' March 

 1851 ('Math, and Phys. Papers,' 

 vol. i. p. 173 sqq.) In the intro- 

 duction, Davy, Mayer, Joule, and 

 notably Liebig, are mentioned as 

 earlier supporters of the doctrine of 



the convertibility of heat into me- 

 chanical effect, Rankine and Clau- 

 sius as the latest contributors (p. 

 176). The first and celebrated 

 enunciation of the second law by 

 Thomson is given at the very be- 

 ginning (p. 179), and in the sequel 

 the denial of it is shown to mean 

 the possibility of a perpetual mo- 

 tion. A little farther on Thomson 

 refers to Clausius in the words : 

 " The merit of first establislung the 

 proposition upon correct principles 

 is entirely due to Clausius, who 

 published his demonstration of it 

 in the month of May last year " 

 (1850). It has on the other side 

 been admitted by Clausius (' Die 

 mechanische Wiirmetheorie,' 2te 

 Aufl., 1876, vol. i. p. 358) that 

 Thomson's independent develop- 

 ment of the second law, though 

 published later, is conducted from 

 a more general point of view, 

 whereas his own treatment was 

 purely mathematical and confined 

 to special cases. The most general 

 and philosophical expression of the 

 new principle was given by Thom- 

 son in his celebrated communication 

 to the Roval Society of Edinburgh, 

 April 19," 1852, "On a Universal 

 Tendency in Nature to the Dissipa- 

 tion of Mechanical Energy " (re- 

 printed in ' Math, and Phys. 

 Papers,' vol. i. p. 511). 



