468 Mr. Lubbock on the Heat of Vapours 



This expression can be integrated, and I find, supposing z 0, 

 after a proper determination of the constants, 





If the variation of the force of gravity be neglected, the pressures 

 p, p' may be represented by the heights of the barometer 7z, h'. 

 If M be the modulus or the quantity by which Naperian logarithms 

 must be multiplied to give common logarithms, Laplace makes 



k 



-~^i= 18337 m< 46. log M = 9-6377843. 

 gM 



In order to give an example of the use of this expression, I take 

 the 21st observation of Gay Lussac, 



k -76568 6 = 30-75 



k'= -3339 0'= 7-00 



log 18337-46 =4-2633392 



log(l + ad) =0-0474015 



i + ) 



= 8-7762776 



3-3566882 

 9-5176049 



3-8390833 

 = 6903-7 



log a == 6-804 1 ! 63 in metres. 

 2'= 6921-7 metres. 



