and tJie Laws regarding the Nature of HeaM Wft 



A.ps 7=A.R«. 



a-i-t 



where instead of s we can, with a near approach to accuracy, set 

 the quantity s^a. By a comparison with its true vahies calcu- 

 lated from the foi-mula at the right-hand side of (22.), this equa- 

 tion becomes peculiarly suited to exhibit every divergence from 

 the law of M. and G. I have carried out this calculation for a 

 series of temperatures, using for r and p the numbers given by 

 Regnault*. 



With regard to the latent heat, moreover, according to Reg- 

 naultf the quantity of heat X necessary to raise a unit of weight 

 of water from 0° to t°, and then to evaporate it at this tempera- 

 ture, may be represented with tolerable accuracy by the following 

 formula : 



\=606-5 + 0-305^ (23.) 



In accordance, however, with the meaning of \, we have 



cdt (23«.) 



^ 



For the quantity c, which is here introduced to express the spe- 

 cific heat of the water, Regnault J has given in another investiga- 

 tion the following formula : 



c=l + 0-00004. if-f 0-0000009. ^2/ ^ ^2Sb.) 



By means of these two equations we obtain from (23.) the fol- 

 lowing expression for the latent heat : 



/• = 606-5-0-695. ^-000002. /2_0-000000./3^. . (24.) 



Further, with regard to the pressure, Regnault has had recourse 

 to a diagram to obtain the most probable value out of his nume- 



* 3Iem. de VAcad. de VInst. de France, vol. xxi. (1847). 



t Ibid. Mem. IX. ; also Pogg. Ann., vol. Isxviii. 



X Mem. de VAcad. de VInst. de France, Mem. X. 



§ In the greater number of his experiments Regnault has observed, not 

 so much the heat which becomes latent during evaporation, as that which 

 becomes sensible by the precipitation of the vapour. Since, therefore, it 

 has been shown, that if the maxim regarding the equivalence of heat and 

 work be correct, the heat developed by the precipitation of a quantity of 

 vapour is not necessarily equal to that which it had absorbed during evapo- 

 ration, the question may occur whether such differences may not have 

 occurred in Regnault's experiments also, the given formula for r being thus 

 rendered useless. I believe, however, that a negative may be returned to 

 this question ; the matter being so arranged by Regnault, that the precipi- 

 tation of the vapour took place at the same pressm-e as its development, 

 that is, nearly under the pressure corresponding to the maximum density 

 of the vapour at the observed temperature ; and in this case the same quan- 

 tity of heat must be produced during condensation as was absorbed by 

 evaporation. 



