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 zero, the air in the torrid zone is constantly expanded by 

 heat about ^W of its whole bulk in the frigid zone. This will 

 cause the air at 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 



