506 Meteorology. 
atmosphere exists ina state of combination 
with heat, but without any chemical, union 
with the elements of the atmosphere; only 
‘it is subject to be wafted along mechanically 
by the great body of the atmosphere, in its 
ordinary currents. This opinion was founded 
and supported on the authority of the late 
M. Saussure in part; he having determined 
by. direct’ experiment, that a cubic foot. of 
dry air of the temperature 66° would im- 
bibe 12 grains of water’ for its saturation. 
Now, from experiments on the boiling of 
water in yacuo, I was persuaded. that this 
quantity of vapour was nearly what would 
fill a cubic foot of empty space, in the 
temperature of 66°; and by analogy, I con- 
cluded ,that the quantity of steam necessary 
to saturate any giyen volume of air, at any 
temperature, was the same that would be re- 
quisite to fill an equal void space at the same 
température. ‘This reasoning was of course 
hypothetical at that time, and unsupported 
by any direct experiment. 
In 1801 a series of essays of mine were 
read before the society, and ' subsequently 
published in the 5th Vol. of; Memoirs 3 one 
object of experimental enquiry, was, whe- 
ther steam of any kind was the same in quan- 
tity in air and in a vacuum, all other circum- 
