3 40 
PROCEEDINGS OF 
[Jan. 
Corresponding Secretary . 
Francis Markoe, Jr. 
Recording Secretary . 
Garret R. Barry. 
Treasurer . 
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 National 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¬ 
ment, which, on being opened, would let the air which had been forced in escape. 
At the moment of escape, there would 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 obtained that he was enabled to frame his theory of storms, 
and other atmospheric phenomena. Mr. Espy stated that he 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 tem¬ 
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 iii which the cloud is formed. This expansion he had found to be about 
eight thousand cubic feet for every cubic foot of water generated in a cloud by the 
