Meteorology, 507 
stances being the same. The result was de- 
cidedly for the affirmative. 
Another object was to ascertain the true 
force of steam in all atmospheric tempera- 
tures. This was clearly proved to be pro- 
gressively increasing with the temperature, as 
Dr. Hutton had rightly conjectured. Indeed, 
with a slight modification of the thermome- 
trical scale, the temperature.is an arithmetical 
progression, and the force of steam a geo- 
metrical one. Hence the curve shewing the 
force of steam, is what mathematicians call 
the Logarithmic, one remarkably convex to 
its axis. 
~The cause of rain, therefore, is now, I 
consider, no longer an object of doubt. If 
two masses of air of unequal temperatures, 
by the ordinary currents of the winds, are 
intermixed, when saturated with vapour, a 
precipitation ensues. If the masses are un- 
der saturation, then less precipitation takes 
place, or none at all, according to the de- 
gree. Also the warmer the air, the greater 
is the quantity of vapour precipitated in like 
circumstances, as is evident to any one, on 
‘inspecting the logarithmic curve, or on con- 
sidering that the increments of a geometrical 
‘progression, are in proportion to the terms. 
Hence the reason why rains are heavier in 
