140 PROCEEDINGS OF [Jail. 



Corresponding Sea-etary . 

 Francis Maukoe, Jr. 



Recording Secretary. 

 Garret R. Barry. 



Deasurer. 

 William J. Stone. 



''! The Corresponding Secretary announced the arrival of Mr. Cas- 

 telnau's entomological collection. 



Whereupon, it was 



Resolved, That a committee be appointed to open and examine 

 the collection, and to report upon it previous to its being deposited 

 in the Cabinet of the INational Institution ; and, that a copy of the 

 report, giving the number and contents of the cases, and the condi- 

 tion in which they may be found, be furnished to Mr. Castelnau's 

 attorney. 



Mr. James P. Espy, of Philadelphia, exhibited his nephelescope, 

 and briefly explained its powers and uses, and gave an outline of the 

 elements of his theory or philosophy of storms. 



The nephelescope of Mr. Espy is a glass vessel, containing about a gallon, fur- 

 nished with a condensing pump and barometer gauge, with an attached scale. With 

 the condensing pump, air could be forced into the vessel, and with the gauge, the 

 quantity forced in could be measured. A stop.cock was also attached to the instru. 

 tnent, which, on being opened, would let the air which had been forced in escape. 

 At the moment of escape, there v^ ould be an expansion, and the chief object of the 

 instrument is to measure the exact degree of cold produced by any expansion, 

 whether the air employed is dry, or whether it is saturated with aqueous vapor. This, 

 he stated, it was most important to know, from its connection with meteorology ; and 

 it was from the result obtaim^d thai lie w.is enabled to frame his theory of storms, 

 and other r>tmospheric phenomena. Mr. Espy stated that ho had performed many 

 hundred experiments with this instrument, employing sometimes dry and sometimes 

 moist air; and he found that when moist air was used at the temperature of about 

 71° of Fahr. the reduction of temperature for a given expansion was only about half 

 as great as in dry air. If the temperature was lower, more than half; and if the tern- 

 perature was higher, less than half; and in general the higher the temperature the 

 less was the reduction in moist air, and the greater the reduction in dry air. In 

 this way Mr. Espy was enabled to measure with great accuracy the expansion 

 which the evolution of latent caloric during the formation of cloud produces on 

 the air in which the cloud is formed. This cxpansiion he had found to be about 

 eight thousand cubic feet for every cubic foot of water generated in a cloud by the 



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