266 MR. E. H. GRIFFITHS ON THE LATENT 
tions at low temperatures than to those above 65°C. In Table IV. of his paper, 
“Sur les chaleurs latentes de la vapeur aqueuse 4 saturation sous diverses pressions,” 
are given the results of all his experiments below 63°, and in his introductory remarks 
to this table (pp. 712-719) he clearly indicates his comparative want of contidence in 
the results. * 
A searching criticism of ReGNAULT’s work is given by WINKELMANN in ‘ Wied. 
Ann.,’ vol. 9, 1880, and had the limits of this communication permitted it, I should have 
liked to quote several pages of that paper, but I will content myself with giving a 
short summary of his arguments. 
I would first remark that WINKELMANN’s object was to explain the discrepancy 
between what he terms the “theoretical density” of water vapour, and that which 
results from “the mechanical theory of heat.” He assumes the former as 0°6225 ; 
but does not give the data by which he obtains that number (I find that if we take 
the molecular weight of H,O as 17°98, and the density of H as -06924 (air = 1), we 
arrive at the same value). He then (assuming that J = 424) calculates the density 
from the thermodynamic equation L = T/J (s’ — s) dP/dT, by substituting for L— 
(a) the values resulting from Reanautt’s formula for the “ total heat,” viz., 
606°5 + ‘3056, 
(>) the values of L given by the equation 
L = 589°5 — 0'2972¢ ~~ 0:0032147¢? + 0°0000081478. . . . (W), 
the last being a formula constructed by WINKELMANN, but based on REGNAULT’s 
experiments at high temperatures. 
WINKELMANN contends that not only does the use of (W) bring the values 
obtained by the “mechanical theory” into greater harmony with the “ theoretical 
value,” but also that the formula (W) is in closer agreement with RecNnau.t’s 
experiments than is the formula given by REGNAULT himself. 
True, the values obtained by WINKELMANN are always greater than 0°6225, but he 
contends that it is impossible to imagine the real density as less than the “ theo- 
retical,” although it is easy to see that it may be greater. 
* “ Jai cherché a obtenirla chaleur latente de la vapeur d’eau a saturation aux basses températures 
par une autre méthode qui me permettra, j’espére, d’obtenir cette donnée avec beancoup d’exactitude et 
contre laquelle on ne peut pas élever les objections que nous avons faites contre le premier procédé. 
Mais cette méthode, que j’ai décrite 4 la fin de mon Mémoire sur l’hygrométrie (‘ Annales de Chimie et 
de Physique,’ 3° série, tome 15, p. 227), exige la connaissance de plusieurs données sur lesquelles il reste 
encore beaucoup Cincertitude. On a besoin notamment de connaitre la capacité calorifique de l’air et la 
quantité de chaleur que l’air absorbe pendant sa dilatation. II m’a paru nécessaire de déterminer ces 
deux éléments par de nouvelles expériences, et c’est seulement Jorsyue celles-ci seront terminées que je 
pourrai calculer les déterminations de la chaleur latente de Ja vapeur d’eau,” p. 722. 
