of Air and the Gases, and the Velocity of Sound. 7 



equal to h. A portion of the air was now extracted from the 

 vessel, and, allowing the loss of temperatin-e caused by the 

 rarefaction to be restored, the pressure within the vessel was 

 observed equal to h'. A communication was next opened be- 

 tween the confined air and the atmosphere ; and the barome- 

 tric pressure in the vessel having increased in a very short 

 moment of time to the height h the same as on the outside, 

 the communication with the external air was instantly shut- 

 Lastly, the heat of the condensation caused by the rushing in 

 of the external air being entirely dissipated, the barometric 

 height within the vessel was again observed equal to h". It 

 is essential that the temperature and barometric pressure of 

 the atmosphere remain unchanged during the time of this ex- 

 periment. 



We shall most readily understand the conclusions to be 

 deduced from the experiment, if we note separately the cir- 

 cumstances occurring at the different epochs during the course 

 of it. 



1st. The initial pressure, density, and temperature, may 

 be thus marked, viz. 



P, S, T + z -H &. 



2dly. A portion of the air being extracted, and the pressure 

 and density having decreased ; 



p -Ip, f - Sf, T + i + L 



3rdly. The communication with the external air being 

 opened, and shut as soon as the pressure was observed equal 

 to the first quantity p ; 



/?» ? — 8 f 4- 8' f , T + z + fl 4- 8' i, 

 £'f being the increase of density, and S'f the latent heat dis- 

 engaged by the condensation. 



4thly. The heat of condensation S' / being entirely dissi- 

 pated, and the pressure having decreased a little, 



P - 8>, f - 8? -f- 5'?, T + ?■ + 6. 

 Now, at three of these epochs, namely, the 1st, 2d, and 4th, 

 the temperature is the same : wherefore, the elasticities being 

 as the densities, we get, 



Again 



