Ill 



ON THE ROTARY ACTION OF STORMS 



BY CHARLES TRACY 1 



The investigations of Mr. Redfield and Colonel Reid have accumu- 

 lated a vast amount of evidence in favor of the propositions they 

 maintain. The tendency of this evidence is to demonstrate, 

 that in the large storms which affect extensive districts, and also 

 in the violent tornadoes which devastate a brief path, there are 

 two motions, the rotary and the progressive; and that the rotary 

 is by far the most violent, and has an uniform direction of revolu- 

 tion, being from right to left if the storm is in the northern hemi- 

 sphere, and the reverse if it is in the southern hemisphere. That 

 is to say, on our side of the equator the rotation is about the cen- 

 ter through the points of the compass, in the order of N. W. S. E., 

 or contrary to the movement of the hands of a watch lying on 

 its back; and south of the equator the rotation is through the 

 points in the order of N. E. S. W., or conformable to that of the 

 hands of a watch. 



These propositions, although authorized by induction, have en- 

 countered doubts or gained a feeble faith in many minds, for the 

 want of a good cause to assign for the production of the alleged 

 phenomena. Hence the occurrence of rotary storms, and the uni- 

 formity of direction of revolution, have been too readily attributed 

 to mere accident; and the notion that a whirlwind, once started 

 by mere chance, contains the elements of growth and stability of 

 motion, has been too easily admitted. An active whirlwind, 

 great or small, undergoes a constant change of substance. As the 

 central portions waste into the ascending column, supplies from 

 the adjacent tranquil air must be drawn into the vortex and set 

 in motion; and if the fresh air is neutral to the circular movement 

 and must acquire velocity from the whirling mass itself, then 

 since "action and reaction are equal and in opposite directions," 



1 Reprinted from the American Journal of Science and Arts, Vol. XLV, 

 October, 1843, pp. 65-72. Read before the Utica Natural History Society. 

 (Dated Utica, N. Y., February 27, 1843.) 



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