56 Whirlwinds excited by Fires. 



appears to have formed part of a more extended notice of that re- 

 gion of country ; and the occurrence of this calamitous fire, is a 

 fact well remembered. 



Remarks on the foregoing Cases. 



Among the many considerations suggested by these interesting 

 phenomena, I shall notice in a cursory manner, the following : 



1. The rarefactio7i lohich is ordinarily produced hy fires, even 

 if they are of an extensive and violent character, is not attended 

 with these effects. Common observation and experience are suffi- 

 cient to determine this point ; and to show that rarefaction alone, 

 is entirely inadequate to the production of such results. The 

 strongest degree of heat which has ever been created in the at- 

 mosphere by fires, has never produced an ascending current of 

 sufficient power to prostrate or carry forward any contiguous body 

 possessed of tolerable stability or weight, much less to carry any 

 such body into the air. 



2. The foregoing results can he accounted for, only hy a violent 

 vortical action, steadily maintained. This appears too plain to 

 need illustration. 



3. The origin of the rotative action and its continuance for 

 a considerable period, in the circuit of conflagration, appear to he 

 chiefly owing to the circular outline of the several fires, and to the 

 absence of a disturbing horizontal current. When, however, the 

 principal seat of the vortical action is found in the body of an 

 elevated current of atmosphere, we then find that the progressive 

 action of the foot of the whirling column upon the earth's surface, 

 and the resistance which is also offered to its progress by an in- 

 ferior cross current, are not sufficient to break up, or sensibly im- 

 pede, the regular action and progress of a powerful vortex. This 

 was strikingly manifested in the tornado which passed through 

 the city of New Brunswick, in New Jersey, in June, 1835. 



4. The ascending power of the vortical column or whirhoind is, 

 in these cases, strongly exhibited. We observe, that the heated 

 air from large fires, or even from the most powerful furnaces, ejec- 

 ted in a column at the heat of melted iron, will ascend only to a 

 comparatively short distance from the earth ; the ascending force 

 being lost in counter movements and convolutions with the adja- 

 cent colder air, and the combined product soon spreads off" in a 



