102 Dr. Hare on the Lax<o of Storms. 



The momentum by which any body is kept in motion, is as 

 its weight multiplied by its velocity, while the expenditure of 

 momentum is cceteris paribus as its surface. On this account, 

 a globe of which the content in proportion to its superficies is 

 pre-eminently great, will, in a resisting medium like the air, 

 retain a rotatory motion longer than an equal weight, of the 

 matter forming it, in any other shape. The flat cylinder, in 

 diameter about 200 times its thickness, of which the existence 

 would be necessary to an extensive whirlwind, is a form of 

 which the surface would be very great in proportion to the 

 quantity of matter which it contains. No observer ever noticed 

 any whirl produced as above described, to have a diameter 

 many times greater than its height, or to endure many minutes. 

 Such pigmy whirls appear to be the consequence of eddies re- 

 sulting from the conflict with each other, or with various im- 

 pediments, of puffs or flaws of wind. No doubt in this way a 

 deficit of local density is easily caused in a fluid so elastic as 

 the air, and consequently by gravity as well as its elastic re- 

 action, a centripetal motion is induced in the surrounding aerial 

 particles. From the confluence and conflict of the air thus 

 put into motion, a whirl may arise. The manner in which 

 light bodies are gathered towards the axis of these whirls, 

 shows that they are accompanied by a centripetal tendency. 

 It is only when the wind blows briskly that such whirls are 

 ever seen to take place; but tornadoes, agreeably to universal 

 observation, occur when there is little or no wind externally 

 (see par. 93). 



131. According to the evidence adduced by the advocates 

 of the whirlwind theory, there is in this respect perfect simi- 

 larity in the phaenomena of tornadoes and hurricanes. Be- 

 yond the sphere of the alleged gyration, there is but little if 

 any atmospheric commotion, and certainly none competent to 

 be the cause of a great whirlwind. It follows that pigmy 

 whirlwinds and hurricanes can have no analogy. The former 

 are never produced without a proportionable external activity 

 in the wind, while comparative external quiescence seems to 

 accompany the latter. 



132. I will conclude by applying to Prof. Dove the stricture 

 which I applied on a former occasion to Espy and to Red- 

 field. He has, I think, committed a great oversight in neg- 

 lecting to take into consideration the agency of electricity in 

 the generation of storms. 



[The memoir of Prof. Dove, to which this communication of Dr. Hare 

 relates, will be found in Taylor's Scientific Memoirs, vol. iii. p. 197. In 

 Dr. Hare's quotation from it, supra, p. 96, lines 9 and 10, some words are 

 omitted : instead of " at the so-called region of calms," it should have been, 

 "at the limit of the so-called region of calms;" and in the last line of the 

 quotation, for "violence" read "velocity." — Edit.] 



