Philosophy of Storms. — 125 
given out in the condensation of vapor into clouds. © There: 
when the air has descended some time in the middle, between 
two ascending columns, the barometer will fall a little, or at least 
not stand so high above the mean as it does on the outside of 
the two clouds, and so the columns will be pressed towards each 
other. 
{f one of two neighboring columns should be greatly higher 
than the other, its annulus may overlap the smaller one, and of 
course the current under the smaller cloud will be inverted, and 
the cloud which may have been formed over the column thus 
forced to descend, will soon disappear ; for as it is forced down- 
wards by the overlapping annulus of the more lofty column, it 
will come under greater pressure, and its temperature will be thus 
increased, and it is manifest that as soon as its top descends as 
low as its base, it will have entirely disappeared, and in the mean 
time the larger cloud will have greatly increased. 
As the air above the cloud formed by an ascending column is 
forced upwards, if it contains much aqueous vapor, a thin film of 
cloud will be formed in it by the cold of diminished pressure, 
entirely distinct from the great dense cumulus below ; but:as the 
cumulus rises faster than the air above it (for some of the air will 
roll off) the thin film and the top of the cumulus will come in 
contact ; and sometimes a second film or cap may be formed in 
the same way, and perhaps a third and fourth. When these caps 
form, there will probably be rain, as their formation indicates a 
high degree of saturation in the upper air. 
When the complement of the dew point is very great, (20° and 
more,) clouds can searcely form; for up- - columns will 
generally either come to an equilibrium with surrounding air, or 
be dispersed before they rise twenty hundred ‘yards, which they 
must do in this ease, before they form clouds. Sometimes, how- 
ever, masses of air will rise high enough to form clouds, but they 
are generally detached from any up-moving column underneath, 
and of course cannot then form cumuli with flat bases; such 
clouds will be seen to dissolve as soon as they form, and even 
while forming they will generally appear ragged, thin and ir- 
regular. 
Moreover, if the ground should be colder during the day, than 
the air in contact with it, as it sometimes happens after a very 
cold spell of weather, then ascending columns cannot exist, and 
