Redfield's Theory of Storms. 105 



96. Having said so much against the whirlwind theory of 

 storms, it may be expected that I should, on this occasion, say 

 something respecting the opinions which I entertain of their 

 origin. To a certain extent this will be found in my com- 

 munications published in Silliman's Journal, vol. xxxii. p. 153, 

 vol. xl. p. 137, also in my Essay on the Gales of the United 

 States. I still believe our north-eastern gales were correctly 

 represented in the last-mentioned essay as arising from an ex- 

 change of position made between the air of the Gulf of Mexico 

 and that of the territory of the United States which lies to the 

 north-east of that great estuary; and that the heat given out 

 during the conversion of aqueous vapour into rain, by imparting 

 to the atmosphere as much caloric as could be yielded by 

 twice its weight of red-hot sand, is a great instrument in the 

 production of the phenomena; also, that the cold resulting 

 from rarefaction is a cause of the condensation of that vapour, 

 and of course of clouds. On this last idea, derived from 

 Dalton, Mr. Espy has founded his ingenious theory of storms; 

 alleging, erroneously, as I think, the buoyancy, resulting from 

 the heat thus evolved, to be the grand cause of rain, also of 

 tornadoes, hurricanes, and other electrical storms. In the 

 essay above mentioned, I erred in ascribing too much to vari- 

 ations of density arising from changes of elevation, and twenty 

 years' additional experience as an experimenter in electricity, 

 has taught me to ascribe vastly more to this agent than I did 

 formerly. 



97. In November last, I verified a conjecture of my friend 

 Dr. J. K. Mitchell, that moist, foggy or cloudy air is not a 

 conductor of electricity, its influence, in paralyzing the efficacy 

 of electrical apparatus, arising from moisture deposited on 

 adjoining solid surfaces. 



98. A red-hot iron cylinder, upon which evidently no 

 moisture could be deposited, suspended from the excited con- 

 ductor of an electrical machine, was found to yield sparks 

 within a receiver replete with aqueous vapour, arising from a 

 capsule of boiling water. 



99. Hence it appears that bodies of air, whether cloudy or 

 clear, may be oppositely electrified from each other or from 

 the earth. This would explain the gyration on a horizontal 

 axis which seems to be attendant on thunder gusts, and may 

 account for the ascent of the south-easter and descent of the 

 north-wester in the great storm of December 1836, described 

 by Professor Loom is. 



100. Such gyration may be a form of convective discharge, 

 in which electrical reaction is assisted by calorific circulation 

 and the evolution of latent heat, agreeably to Dalton and Espy. 



