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44 Proceedings of the American Philosophical Society. 
Dr. Hare made some observations on the effect of the rarefaction of 
“air, on its desiccation and refrigeration, and on other phenomena con- 
- nected with the presence of aqueous vapor in the atmosphere. He also 
detailed some experiments, showing that the phenomena of air, heated 
by re-entering a receiver partially exhausted, ‘were more consistent, in 
some respects, with the idea that a vacuum has a capacity for heat, tha 
that it is destitute of any appropriate portion of caloric. 
Dr. Hare adverted to the fact, that in an essay published in this Journal 
in 1822,* he had, agreeably to the authority of Dalton and Davy, stated, 
that the cold consequent on the rarefaction of air in its ascent towards 
the upper strata of the atmosphere, was one of the causes of the forma- 
tion of clouds; and in his text-books he had soon after published an en- 
graving of an apparatus, by means of which he was accustomed to illus- 
trate, before his pupils, the transient cloud which arises from a diminution 
of pressure in air containing aqueous vapor. 
In the essay above mentioned, Dr. Hare had alleged, that as much ca- 
loric was given out by aqueous vapor during its conversion into snow, as 
would be yielded by twice the weight of red hot powdered glass. But 
Mr. Espy, he considered, had the merit of being the first to suggest, that 
the heat, thus evolved, might be an important instrument in causing a 
buoyancy tending to accelerate any upward current of warm moist air. 
Dr. Hare had been willing to admit, that this transfer of heat might 
co-operate with other causes in the production of storms, but could not 
concur with Mr. Espy in considering it competent to give rise to thunder 
gusts, tornadoes, or hurricanes. ‘These he had considered, and still con- 
siders, to be mainly owing to electrical discharges between the earth and 
the sky, or between one mass of clouds and another. 
With a view to a more accurate estimate of the comparative influence 
of rarefaction and condensation, in causing evolution of heat in dry air, 
and in air replete with aqueous vapor, Dr. Hare had performed a number 
of experiments, of which he proceeded to give a description. 
Large globes, each containing about a cubic foot of space, furnished 
with thermometers and hygrometers, were made to communicate, respec- 
tively with reservoirs of perfectly dry air, and of air replete with aqueous 
vapor.t e cold, ultimately acquired by any degree of rarefaction, ap- 
peared to be the same, whether the air was in the one state or the other, 
provided that the air replete with aqueous vapor, was not in contact with 
liquid water in the vessel subjected to exhaustion. When water was pre- 
sent, in consequence of the formation of additional vapor, and a conse- 
quent absorption of caloric, the cold produced was nearly twice as great 
; eA eh a OMe I a 
* See Vol. 1v, p. 142. 
{ The hygrometers were constructed by means of the beard of the Avena sen 
sitiva or wild oat, also called animated oat. “ = 
~ 
