Trans. N. V. Ac. Set. 4 Oct. 8, 



derstand how the force at the centre could exceed the pressure of a 

 vacuum. 



Prof. W. P. Trowbridge repUed 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. Aerial 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 tuindfalls, 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 oft" 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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