324 MR. E. H. GRIFFITHS ON THE LATENT 
Assuming Scorr and RAYLEIGH’s values we get— 
Molecular weight of water-vapour = 17°862. 
Lord RAYLEIGH in 1888-9* pointed out that Reanavut’s conclusions as to the 
weights of unit volumes of hydrogen and air required correction, as REGNAULT had 
not allowed for the change in volume of the bulb consequent on changes in pressure. 
Crartst has applied this correction, and finds the resulting comparative densities of 
air and hydrogen to be as follows :— . 

| REGNAULT’S value. | Corrected value. 

Dre Oe bh | 1 1 
Hydrogen. . | (06927 06949 (p. 1664, ibid.) 

OstWALp} deduces from these numbers the weights of 1 litre at 0° and 76 
centims., as 
Air, 1°29349 grams. Hydrogen, ‘08988 gram. 
Hence we get 
“Theoretical Density ” of water-vapour = ‘6206 (air = 1). 
I will now proceed to deduce the density at various temperatures by means of the 
thermodynamic equation 
dp 
T Qe = 
te Ac — 8) op? 
and I assume the values of the various quantities to be as follows :— 
J = 4199 X 107. (My value after ScHusTER’s correction for the specific heat 
of the displaced air, see p. 314, swp7a). 
L = 596°73 — 60100. . . formula G, (supra). 
T= 2730: 
The values of dp/dT are taken from Brocu’s reduction of ReGNAULT’s experimental 
results,§ and are as follows :— 
* €Proc. Roy. Soc.,’ vols. 43 and 45. 
+ ‘Comptes Rendus,’ vol. 106, pp. 1662-4, 1888. 
tf 2nd ed., vol. 1, p. 181. 
§ ‘Trav. et Mém. du Bur. Intern. des Poids et Mes.,’ 1, A, 1881. 
