438 
Mr. Lubbock on the Heat of Vapours 
CONTENTS. 
General Expressions. — On the Pressure of Steam. — On the Steam 
Engine. — On the Vapours of .<®ther. Alcohol, Petroleum, and Oil of 
Turpentine. — On the Conditions of the Atmosphere and on the Calcula- 
tion of Heights by the Barometer. — On Astronomical Refractions. 
GENERAL EXPRESSIONS. 
Let V be the quantity of absolute heat, considered as a function 
of the sensible heat or temperature 0, 
dV d Fd g ^ ^ 
d0 dgd0~^d^ d0 
p z=. k q (1 -f a 0). 
q being the density, p the pressure, k and « constants, 
d ^ CC q 
d 0 1 + a 0 
dp ctp 
d 0 1 -p a 0 
if 
dV a q dV a p 
d q [I + OL^) dp (1 + a 0) 
dV dF ^ 
If y be considered as a constant quantity the integral of this 
partial differential equation is 
= funcP^. F*. 
The simplest form which can be assigned to this function of V\ 
such that 1 
F= ^ 4 -B — 
? 
A and B being constants. 
IS 
* So far the reasoning is identical with that contained in the Mecanique of M. Poisson; 
but M. Poisson proceeds further upon the limited supposition of V being constant. 
