46 Proceedings of the American Philosophical Society. 



6.29X 4 = 25. 1 6, or nearly 25° F. As air at 32° F. expands ^| o for each 

 additional degree, the difference of bulk, arising from the heat received, 

 as above calculated, would be ^Yoj or j\ nearly. 



When air replete with aqueous vapor was admitted into a receiver par- 

 tially exhausted, and containing liquid water, a copious precipitation of 

 moisture ensued, and a rise of temperature greater than when perfectly 

 dry air was allowed to enter a vessel containing rarefied air in the same 

 state. In the instance first mentioned, a portion of vapor rises into the 

 place of that which is withdrawn during the partial exhaustion. Hence, 

 when the air, containing its full proportion of vapor, enters, there is an 

 excess of vapor which must precipitate, causing a cloud, and an evolution 

 of latent heat from the aqueous particles previously in the aeriform state. 

 Dr. Hare conceives that as the enlargement of the space occupied by a 

 sponge, allows proportionably a larger quantity of any liquid to enter its 

 cells, so any rarefaction of the air when in contact with water, conse- 

 quent on increase of heat or diminution of pressure, permits a proportion- 

 ably larger volume of vapor to associate itself with a given weight of the 

 air. When, subsequently, by the afflux of wind replete with aqueous 

 vapor, the density of the aggregate is increased, a portion of the vapor 

 equivalent to the condensation must be condensed, giving out latent heat, 

 excepting so far as the heat thus evolved, being retained by the air, raises 

 the dew point. 



Hence, whenever a diminution of density of the air inland causes an 

 influx of sea air to restore the equilibrium, there may result a condensa- 

 tion of aqueous vapor, and evolution of heat, tending to promote an as- 

 cending current. This process being followed by that which Mr. Espy 

 has pointed out, of the transfer of heat from vapor to air, during its ascent 

 to the region of the clouds, and consequent precipitation of moisture, 

 might. Dr. Hare thought, be among the efficient causes of those wow- 

 electrical rain storms, during which the water of the Gulf of Mexico, or 

 of the Atlantic, is transferred to the soil of the United States. 



Dr. Hare proceeded to mention some additional experiments which he 

 had made respecting the increase of temperature resulting from the ad- 

 mission of dry air into an exhausted receiver. When the receiver was 

 exhausted so as to reduce the interior pressure to one fourth of that of 

 the atmosphere, and one fourth was suddenly admhted, so as to reduce a 

 gage from about 221 inches to 15 inches, heat was produced ; and how- 

 ever the ratio of the entering air to the residual portion was varied, still 

 there was a similar result. 



When the cavity of the receiver was supplied with the vapor of ether 

 or with that of water, so as to form, according to the Dakonian hypothe- 

 sis, a vacuum for the admitted air, still heat was produced by the latter, 

 however small might be the quantity or rapid the readmission. When the 

 receiver was exhausted, until the tension was less than that of aqueous 



