99 



WHIRLWINDS 



By Otto Tepper, Corresponding Member. 



[Read July 16, 1878.] 



By whirlwinds are understood local disturbances in the atmosphere, 

 of limited diameter, and moving in a spirally-ascending direction, at the 

 aame time shifting laterally. 



They are during the summer months of such frequent occurrence in 

 Australia and elsewhere that many people do not deign to take much 

 notice of them unless their attention is enforced by some specially de- 

 structive whirlwind. Yet the causes of these phenomena appear so 

 much enveloped in mystery that the careful observation and study of 

 them may well repay for the pains taken, as perhaps through these 

 phenomena the origin of the far grander waterspout and cyclone may be 

 elucidated. 



A. v. Humboldt considers them as effects of opposing currents ; 

 but how currents moving: in straight lines with moderate velocity can 

 produce spiral ones endowed with great swiftness it is hard to compre- 

 hend, even leaving out of question the fact that whirlwinds only take 

 placeduring almost absilute calms. — (Belt,"the Naturalist in Nicaragua.") 



Maury, again, ascribing them also to the meeting of currents, in- 

 vokes the aid of electricity, citing an experiment with a metallic ball, by 

 means of which, when highly charged with electricity, a small water- 

 spout was raised ("G-dOgr. of the Sea"). The objection to lateral currents 

 being the cause having been stated, electricity as such is equally doubt- 

 ful, it being hardly conceivable, in the absence of such powerful concen- 

 trating agent as a metallic ball how thousands of tons of water could be 

 raised for hundreds of feet by any knoivn natural agent. Besides this, it 

 seems that whirlwinds occur as frequently as not in nearly dry atmos- 

 phere, with little indication of electric tension and before any thunder* 



