Philosophy of Storms. 129 
It is indeed probable that in all violent thunder storms in which 
hail falls, the upmoving current is so violent as to carry drops of 
rain to a great height, when they freeze and become hail. It is 
- difficult if not impossible to conceive any other way in which 
hail can be formed in the summer, or in the torrid zone. 
In those countries in which an upper current of air prevails in 
a particular direction, the tornadoes and water spouts will gene- 
rally move in the same direction ; because the upmoving column 
of air in this meteor rises far into this upper current, and of course 
its upper part will be passed in this direction, as the great tornado 
cloud moves on in the direction of the upper current, the air at 
the surface of the earth will be pressed up into it by the superior 
weight of the surrounding air. It is for this reason the tornado 
in Pennsylvania generally moves towards the eastward. 
If a tornado should stop its motion for a few seconds, as it 
might do, on meeting with a mountain, it would be likely to pour 
' down an immense flood of water or ice, in a very small space ; 
for the drops which would be carried up by the ascending current 
would soon accumulate to such a degree, as to force their way 
back, and this they could not do, without collecting into one 
united stream of immense length and weight, and of course on 
reaching the side of the mountain, this stream, whether it con- 
sisted of water or hail, would cut down into the side of the moun- 
tain a deep hole, and make a gully all the way to the bottom of 
the mountain from the place where it first struck. 
As the air spreads out more rapidly above than it runs in be- 
low, there will be a tendency in storms to increase in diameter, 
and also to become oblong from the influence of the upper current 
in carrying the top of the cloud in its own direction. 
At the equator, or at least those parts of it where the trade 
winds are constant from east to west, it is probable tornadoes 
travel from east to west. For as the air in the torrid zone is 
about 80° in temperature at a mean, and the air in the frigid zone 
is about eer, the air in the torrid zone is constantly expanded by 
heat about ;%", of its whole bulk in the frigid zone. This will 
cause the air ys the equator to stand more than seven miles higher 
from the surface of the earth to the top of the atmosphere than 
at the north pole. The air therefore will roll off from the torrid 
zone both ways towards the poles, causing the barometer to fall 
in low latitudes and rise above the mean in high latitudes. This 
Vol. xxxix, No. 1,—April-June, 1840. 17 
