522 On Heat & Cold produced by Mechanical 
EXPERIMENTS 8 & g. 
In a cold morning last winter when the air 
was clear and the thermometer without stood at 
zo’, I took the receiver and condenser into the 
open air, and let them stand for 15 minutes to ac- 
quire its temperature ; then repeatedly condens- 
ed the air to a double density, and suddenly hibe- 
rated it again. On a medium of 5 trials the 
mercury fell 3°.3 on opening the cock. —The 
vapour precipitated was whiter than usual and 
not nearly so dense. 
Again, took the receiver and condenser into. 
a dyer’s stove where the temperature was about 
100°, and the air abounded with vapour in a 
transparent state: after some time, condensed the 
air and liberated it as before, when on a me- 
dium of 5 trials the mercury sunk only 3°, and 
a very copious mist was precipitated, so dense 
that one could but just distinguish the degree of 
the thermometer through it, 
These experiments shew that the greater the 
quantity of vapour condensed the less is the 
change of temperature; and that consequently, 
if air was entirely free from vapour, the change 
of temperature would be a maximum. Indeed 
this is clearly consistent with the known law, 
that when vapour is condensed, heat is given 
