124 Philosophy of Storms. 
the dew point would fall about 20°, but the temperature would 
fall less than 20°, and estes no vapor would be condensed by 
such ascent. 
When a cloud begins to form from an ascending column of air, 
it will be seen to swell out at the top while its base continues on 
the same level, for the air has to rise to the same height before it 
becomes cold enough by diminished pressure to begin to condense 
its vapor into water ; this will cause the base to be flat, even after 
_ the cloud has acquired great perpendicular height, and assumed 
the form of a sugar loaf. Other clouds also for many miles 
around, formed by other ascending columns, will assume similar 
appearances, and will moreover have their bases all on the same 
or nearly the same horizontal level; and the height of these bases 
from the surface of the earth will be the greatest about three 
o’clock, when the dew point and temperature of the air is 6 
_ greatest distance apart. 
The outspreading of the air in the upper parts of an ascending 
column will form an annulus all round the cloud, under which 
the barometer will stand above the mean; of course the air will 
descend in the annulus, and increase the salactiy of the wind at 
the surface of the earth towards the centre of the ascending col- 
umn, while all round on the outside of the annulus there will be 
a gentle wind outwards. Any general currents of air which may 
exist at the time, will of course modify these motions from the 
‘oblique forces they would occasion. — 
The up-moving current of air must of course =s entirely sup- 
plied by the air within the annulus, and that which descends i in 
the annulus itself. 
The rapid disturbance of equilibrium, which is produced by 
one ascending column, will tend to form others in its neighbor- 
hood ; for the air being pressed outwards from the annulus, or at 
least retarded on the windward side, will form other ascending 
columns, and these will form other annuli, and so the process will 
be continued. 
These ascending columns will have a tendency to approach, 
and finally unite; for the air between them must descend, and 
in descending the temperature of the whole column will increase, 
for it is known that the air, at great elevation, contains more ca- 
os tema atime the air near the surface of the earth, be- 
pp gions that receive the caloric of elasticity 
