and the Laws regarding the Nature of Heat, 119 



corresponding to the adjacent temperatures,, a series of numbers 



are obtained for -r> all of which lie between 416 and 462. 



It has been mentioned above, that the specific weight of the 

 vapour of water at its maximum density given by Gay-Lussac is 

 probably a little too small, and the same may be said of the 



specific weights of vapours generally. Hence the value of -r- 



derived from these must be considered a little too large. If the 

 number 0*645 given in Table V. for the vapour of water, and 

 from which we find s = l"638, be assumed, we obtain 



which value is perhaps still too great, though probably not 

 much. As this result is preferable to that obtained from the 

 atmospheric air, we may conclude that the equivalent of work for 

 the unit of heat is the raising of something over 400 kits, to a 

 height of 1 metre. 



With this theoretic result, we can compare those obtained by 

 Joule from direct observation. From the heat produced by 

 magneto-electricity he found 



Ova \o in ]- =460*. 



From the quantity of heat absorbed by atmospheric air during 

 its expansion, 



J=438t; 



ana as mean of a great number of experiments in which the heat 

 developed by the friction of water, of mercury, and of cast iron 

 was observed. 



The coincidence of these three numbers with each other, not- 

 withstanding the difiiculty of the experiments, dispels all doubt 

 as to the correctness of the principle which asserts the equivalence 

 of heat and work; and the agreement of the same with the num- 

 ber 421 corroborates in like manner the truth of Carnot^s prin- 

 ciple in the form which it assumes when combined with our 

 original maxim. 



* Phil. Mag., vol. xxiii. p. 441. The English measure has been reduced 

 to the French standard. 



t Ibid. vol. xxvi. p. 381. J Ibid. vol. xxxv. p. 534. -^K' 



K2 



