326 MR. H. H. GRIFFITHS ON THE LATENT 
I have previously pointed out that the values of L given by my experiments are 
independent of errors in the electrical standards used during my determination of J. 
This, however, is not the case when the density is obtained from the thermo-dynamic 
equation, as the results then depend upon the absolute value assigned to the 
mechanical equivalent. Now my corrected value of J exceeds Professor SCHUSTER 
and Mr. Gannon’s by about 1 in 1000, hence the values of d in Col. IV., Table XIX., 
would, according to ScuusTER, have to be increased by ‘0006, whereas if we use 
RowLaAnv’s value (4190) the increase would be about °0012. 
I have given the above determination of the relative densities of water-vapour and 
air, because it was the method of calculation adopted by WINKELMANN, and therefore 
enables a comparison to be made between his conclusions and those arrived at by the 
use of formula G, (supra). It appears to me to be an unsatisfactory method, as it 
involves unnecessary data regarding air. A more direct way of obtaining some 
information concerning the density of water-vapour, is that of finding PV, z.e., the 
“volume energy.” Now PV= RIT, and the value of R for a true gas is 0°0815,* 
when P is pressure in atmospheres, and V the volume in litres occupied by the 
molecular weight in grams, Assuming as before the molecular weight of water to be 
17°862, and obtaining the values of V and P from Col. II., Table XIX., and Col. IV., 
Table XVIII, we get :— 



Temperature. = = R. 
| 0 | 0827 
9 “NR95 
5 ee as compared with 
60 | 0813, ‘0826 in the case 
| OS of hydrogen. 
80 | O811 
100 0812 



and here again we find that at temperatures near 0° water-vapour resembles a 
true gas. 
* This value of R depends on the assumptions that 1 litre of hydrogen at 0° and 76 centims. weighs 
008988 gram. (supra), and that the coefficient of expansion of hydrogen = -0036613 (the value 
obtained by CaLLENDAR and myself in 1893). Dr. Suietps, however, assigns to R the value 0:0819 
(see ‘Science Progress,’ December, 1894). 
