Mr Joseph J. Murphy on Revolving Storms. 235 
of vapour, we take gths of the quotient, as watery vapour 
has only ths of the specific gravity of air. Supposing con- 
densation to take place at 80°, the heating effect will be 
5 1178—80 . 
5 gay = 2877 
In other words, the condensation of any given volume of 
vapour will liberate as much heat as, if concentrated, would 
raise the temperature of an equal volume of air by 2877" 
Fahr. : 
This heat will expand the air. The addition of a degree 
Fahr. of temperature expands air at 32° by a 492d of its 
volume, and at 80° by a 540th. Consequently the expanding 
effect at 80° will be, after deducting the destroyed volume 
of the condensed vapour, 
2877 
eae 1=4:35 
In other words, for every cubic foot of vapour condensed, 
4°35 cubic feet will be added to the volume of the air. This 
expansion will increase the ascending force of the column, 
and produce an outward flow of air at its top, a fall of the 
barometer at its base, and an inward flow fowards its base 
to fill up the void. 
The foregoing reasoning is identical with that of ‘‘ Espy’s 
Philosophy of Storms.” In order, however, to estimate the 
force of indraft at the base of such an ascending column, it 
would be necessary to know not only the temperature at 
every height in the column itself, which is a matter of cal- 
culation when that at its base is known, but also the tem- 
perature of the surrounding air at every height, a subject 
on which very little is known for any given time and place ; 
for the ascending force of one mass of fluid im another de- 
pends on the difference of specific gravity, and this with 
air depends almost entirely on the temperature. 
It has been stated by Professor Thomson of Glasgow, in 
a paper lately read at the Manchester Philosophical Society, 
that the temperature of air satwrated with moisture, when 
in astate of convective equilibrium (as an ascending current 
of such air must necessarily be), will diminish at the rate of 
