. Condensation & Rarefaction of Air, 521 
EXPERIMENT 7. 
On condensed Air. 
Took a large spherical glass receiver, the capa- 
city of which was something more than twice 
that of the former (above one gallon), and sus- 
pended a thermometer in the centre of it, of a 
larger bulb than that before used; the receiver 
had a brass cap and stop-cock adapted to it: 
Then doubled the density of the air within it 
by a condenser. The thermometer rose 2° or 
more. Let out the air suddenly and the ther- 
mometer immediately sunk each time from 3° 
to 3°. 5; at the same time an exceedingly dense 
mist was produced in the receiver, which soon 
subsided. 
Suspecting that aqueous vapour, which always 
- exists in the atmosphere, and is liable to assume 
the liquid or aérial form according to circum- 
stances, might be the principal agent in the pro- 
duction of heat and cold by condensation and 
rarefaction, I thought that an increase of it might 
produce a greater effect, and that cold air, which 
contains less vapour, might have a less effect. 
The reverse however was the fact, as appears by . 
the following, 
