70 On the Whirling Action of the 



The whirling motion, however, has not been recognized by 

 Prof. Bache, Mr. Espy,* or Prof. Walter R. Johnson,f in their 

 several accounts of the New Brunswick tornado ; these writers 

 having been led to adopt or favor a theory of ascending columns 

 in the atmosphere, founded on the supposed influence of calorific 

 expansion accompanying the condensation of vapor. 



It is remarkable that previous to this period the evidences of 

 the rotation or other characteristic action of tornadoes appear not 

 to have been duly examined and recorded, nor even to have re- 

 ceived the distinct consideration of scientific observers. We are 

 therefore left to seek out the peculiarities of their action, by ex- 

 amining the direction of the prostrations and other effects of the 

 wind ; and from a careful induction from the effects which are 

 thus registered as by the finger of the tornado, we may hope to 

 arrive at satisfactory conclusions. 



If the numerous prostrations of trees and other objects, which 

 may be observed in the path of a tornado, be the effects of a vio- 

 lent whirlwind, it appears most reasonable to infer that this whirl 

 had the common properties which may be observed in all narrow 

 and violent vortices, viz. a spirally descending and involuted mo- 

 tion of the exterior and lower portions of the vortex, rapidly 

 quickened in its gyrations as it approaches toward the centre or 

 axis of the whirl, and thence continued (in the case of the whirl- 

 wind) spirally upward, but gradually expanding in its spiral 

 course by an evolute motion in ascending towards the extreme 

 height of the revolving mass. 



If we now contemplate the action of this whirling body, while 

 in a state of rapid progression, on the several objects found in dis- 

 tinct portions of its path, we may expect to witness effects of 

 much complexity, particularly as regards direction ; and, also, 

 that amid this apparent complexity, some clue may be obtained 

 that will serve to indicate or establish the true character of its 

 action. Some of the effects which may be expected or observed, 

 will be here considered. 



1. We may expect to find, in the path of the whirlwind, strong 

 evidence of the inward or vorticular course of the wind at the 

 earth's surface ; the violence of which inward motion is clearly 



* Trans, Amer. Phil. Society, vol. v, New Series. 



t Journ. Academy Nat. Sciences of Philadelphia,, vol. vii, part ii. 



