445 
with the wettened bulb in these experiments; and that the 
values which they give for the elastic force of vapour, for 
these temperatures, are too low. 
(Additional Note by Dr. Apjohn.) 
«‘M. Kupffer has recently been engaged in discussing the 
value of m, the coefficient in the hygrometric formula. Ina 
note read by him at the Petersburgh Academy, on the 22nd 
of last January, and published in the Bulletin Scientifique, 
No. 132, after a detailed examination of the experiments 
of August, Gay-Lussac, Erman, Bohnenberger, and 
Kimtz, he comes to the conclusion, that the theoretic value 
of m, or ud A agrees sufficiently well with that deduced 
from the most trust-worthy comparative observations on 
the dew-point. The formula which he definitively adopts, is 
f' =f — ‘267 ¢ —#); 
f’ and f” being expressed in tenths of an English inch, and 
t and ¢’ in degrees of Reaumur’s thermometer. But this, ex- 
pressing f’ and f” in inches, and ¢ and ¢’ in degrees of Fah- 
renheit’s scale, becomes 
Sf’ =f — 01142 ¢ —?¢); 
an expression in which the coefficient is almost identical with 
that which has been deduced above from the three series 
of experiments to which I have so often referred. This for- 
mula, however, M. Kupffer observes, gives results in ac- 
cordance with direct observation, only when the table of the 
elastic force of vapour drawn up by Kamtz is employed; 
from which he infers, that i¢ alone represents with accuracy 
the relation between the tension and the temperature of 
steam—an opinion from which, notwithstanding the high 
authority of M. Kupffer, I am compelled to differ, on the 
grounds already stated by Professor Lloyd. 
‘‘ There is another statement of less importance made by, 
