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, than 

 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.f The 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 



* See Vol. IV, p. 142. 



t The hygrometers were constructed by means of the beard of the A vena sen- 

 sitiva or wild oat, also called animated oat. 



