Trans. N. Y. Ac. Sct. 4 Oct. 8, 
derstand how the force at the centre could exceed the pressure of a 
vacuum. 
Prof. W. P. TROWBRIDGE replied that in a cyclone the motion, 
which in the Northern Hemisphere proceeds from right to left, comes 
from the motion of the earth. In whatever direction a body may be 
moving along the surface of the earth, a tendency to deflect it to the 
right is caused by the earth’s motion. Aérial currents flowing toward 
a central point thus become deflected, and a rotary motion ensues. 
In a cyclone, therefore, the currents of heated air rushing from oppo- 
site directions result in an ascending current, surrounded by a rotating 
column, both of extreme velocity. 
The PRESIDENT remarked that he had been much in the arid regions 
of the West, as in Arizona and Nevada, where the sun’s rays produce 
intense heat, with violent currents of wind and numerous eddies or 
“‘ whirlwinds.” This action was often observed in running water, as 
shown by the whirlpools, which possess far higher velocity than that 
of the main eddy. So in this arid region frequent contrasts of currents 
of air occurred, generating at the points of junction local whirlpools of 
great velocity. 
He regarded the statistics that had been published, in relation to 
the occurrence and number of tornadoes, as likely to mislead. The 
atmospheric conditions were much alike in most of the States of the 
Mississippi valley, and it is probable that if observations on the occur- 
rence of tornadoes should be carried on for a long time, perhaps for 
some centuries, closely agreeing results would be obtained. 
He described the phenomena of a tornado in Ohio in 1847, by which 
not only fences and houses were destroyed, but half-buried logs were 
torn up out of the ground, a plow carried along by the wind left a spiral 
furrow, and chickens were almost completely stripped of their feathers. 
In the forest-covered region east of the Mississippi, winds are more 
obstructed and less violent, and tornadoes are probably less common 
than on the prairies, but are not unknown. Many have been recorded 
since the country was occupied by the whites, and many more are self- 
registered in the tracks they have left in the forest. These tracks are 
known as windfalls, and every woodsman is familiar with them. They 
are passes opened by whirlwinds, which, for a longer or shorter dis- 
tance, and greater or less breadth, have prostrated or twisted off the 
trees. In Ohio and Michigan hardly a township is without them, 
some recent and some very old, for such a record would hardly be ob- 
literated in a hundred years. Their number proves the frequency of 
the occurrence of wind-storms, and that no part of the country was ex- 
empt from them. As the number of towns, villages, and farmhouses 
increases, storms attract more attention, as they cause destruction of 
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