472 Mr. Lubbock on the Heat of Vapours 



a 



= aiu. 



The day on which M. Gay Lussac made his ascent was very 

 warm, and the values of y and //determined from his observations 

 may differ slightly from those mean values which will be obtained 

 hereafter from more complete data. The preceding theory supposes 

 implicitly that a given temperature at the earth's surface always cor- 

 responds in any given place to a given pressure ; this, owing to the 

 currents, the winds, and to other causes, is not the case; for the 

 atmosphere is never in a state of repose, and its temperature and 

 density are in a continual state of oscillation about their mean 

 values. The constants y and E may also be subject to variations 

 from fluctuations in the quantity of aqueous vapour diffused through 

 the atmosphere. 



If the decrements of temperature are the same for equal incre- 

 ments of altitude, which observation shows is nearly the case at 

 small elevations, 



$ -Z' = Az f , 



being the temperature at the lower station, V at the upper, and 

 z f as before, the altitude of the latter reckoned from the former, 



1 + « 0' = 1 + & (0 — A jfy 



and if the variation of the force of gravity be neglected 



d p ! _ ^ds' 



~p r ~ k {1 + a(9 _ Az')} 



^{-(f)'} 



f l+ u(b-A z')~\k*A 



8 1 



p 1 being the pressure at the upper station, and p at the lower 

 Mr. Ivory assumes, Phil. Trans., 1838, p. 192, 





&c. 



