472 Mr. Lubbock on the Heat of Vapours 



z 1 



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, 



6 being the temperature at the lower station, 3' at the upper, and 

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



1 + 0' = 1 + (0 A a/), 

 and if the variation of the force of gravity be neglected 



d . d z' 



k { 1 + (0 A z') } 



ka.A 



JV |>V I 

 \ L \) J 



p 



ri+ xQ~Az' 

 =. n 



' 



I 1 + 



// being the pressure at the upper station^ and p at the lower. 

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



&c. 



