240 



with aqueous vapour, the density of the aggregate is increased, a por- 

 tion of the vapour equivalent to the condensation must be con- 

 densed, 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 con- 

 densation of aqueous vapour, and evolution of heat, tending to promote 

 an ascending current. This process being followed by that which 

 Mr. Espy has pointed out, of the transfer of heat from vapour to air, 

 during its ascent to the region of the clouds, and consequent precipi- 

 tation of moisture, might, Dr. H. thought, be among the efficient 

 causes of those non-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 admission of dry air into an exhausted receiver. When the re- 

 ceiver was exhausted so as to reduce the interior pressure to one- 

 fourth of that of the atmosphere, and one-fourth was suddenly ad- 

 mitted, so as to reduce a gage from about 22 5 inches to 15 inches, 

 heat was produced ; and however 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 vapour of 

 ether or with that of water, so as to form, according to the Daltonian 

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

 the latter, however small might be the quantity, or rapid the re- 

 admission. When the receiver was exhausted, until the tension was 

 less than that of aqueous vapour at the existing temperature, so as 

 to cause the water to boil, as in the Cryophorus, or Leslie's experi- 

 ment, still the entrance of j-^q-q of the quantity requisite to fill the 

 receiver caused the thermometer to rise a tenth of a degree. An al- 

 ternate motion of the key of the cock, through one-fourth of a circle, 

 within one-third of a second of time, was adequate to produce the 

 change last mentioned. 



Dr. Hare considered the fact, that heat is produced, when to 

 air, rarefied to one-fourth of the atmospheric density, another fourth 

 is added, irreconcileable with the idea, that this result arises from 

 the compression of the portion of air previously occupying the cavity, 

 since the entering air must be as much expanded as the residual por- 

 tiori is condensed. 



