660 REGNAULT’S HYGROMETRICAL RESEARCHES. 
perature ¢; the value 610 — #, which I have given above, has 
been admitted, after numerous experiments which I have made 
on the latent heat of aqueous vapour under different pressures, 
and which I shall soon publish. But in these experiments I 
have never operated under pressures of vapour weaker than jth 
of an atmosphere, and these are still much greater than the ten- 
sions which we find in atmospheric vapour. 
It will be desirable also to make new experiments in very ele- 
vated localities, to ascertain whether the second term corrects 
properly the formula for the variations of h. 
The developments which I have just given will suffice to prove 
that the theory of the psychrometer is not so simple as is gene- 
rally admitted, and that, to render this instrument really useful 
for meteorology and physical science, a great number of direct 
experiments must be instituted, under very various circum- 
stances, to ascertain whether it is possib/e to determine a single 
formula for the psychrometer, and to obtain the necessary ele- 
ments to calculate the coefficients. 
It is to be wished that scientific men who are interested in 
the progress of meteorology would engage in these experiments 
in different climates ; and I hope that the discussion in which I 
have engaged, and the methods which I have put forward in this 
memoir, may be of some use to them in their researches. 
