486 On the Tension and the Latent Heat of different Vapours, 



tion is observed which it is impossible to regard as accidental. 

 We will therefore for the present assume the law to be correct, 

 and thus make use of it for further deductions. 



In the first place, it is clear that if tlie law be true for the 

 boiling-points of all fluids, it must also be true for every other 

 system of corresponding temperatures; for the boiling-points 

 depend merely upon the accidental pressure of the atmosphere, 

 and hence the law can be immediately expanded thus : the latent 

 heat calculated for the volume is for all fluids the same function of 

 the tension. Let r be the latent heat of a unit of weight of va- 

 pour at the temperature /, the volume of the unit of weight for 

 the same temperature being =5, the latent heat of a unit of vo- 

 lume will then be expressed by the fraction - j let jo be the cor- 



s 



responding tension ; the law will then be. expressed by the 

 equation 



^-=fip)> (I) 



in which / is the symbol of a function which is the same for all 



fluids. 



7* 

 Let this function be substituted for - in the equation (Va.) of 



s 



my memoir '^On the Moving Force of Heat*,^' by neglecting 



therein the volume cr of a unit of weight of water as compared 



with that of vapour, we thus obtain 



/(p)=A(a + <)|, 



where A and a are two constants, the latter denoting the number 

 273, so that a -H / is the temperature of the vapour reckoned from 

 —273° downwards. If, for the sake of brevity, we call this 

 quantity T, we have 



d^_kdp 



' T -fipY 



and from this we obtain by integration 



c.T=F(p), 



in which F is the symbol of another function, which is likewise 

 the same for all fluids, and c an arbitrary constant which must 

 be determined for each fluid. Let us suppose this equation 

 solved for ^, it will assume the form 



P=<i>{c.T), (II) 



♦ Pogg. Ann. vol. Ixxix. p. 508; and Phil. Mag. p. 10/ of the present 

 volume. 



