MECHANICAL EQUIVALENT OF PRESSURE MARGULES 525 



and for the vertical change of pressure under static equilibrium 



RT dp 

 p dz 



whence this second step requires that 



d _Q = c ( dl ' + I 



dz v \ dz C. 



But in addition to the quantity of heat C p (T 2 — T\) addel at 

 P, there is still to be added 



C,(„-T, + l-k 



along the path P 2 p 2 ; and as before there is to be subtracted 

 at p l the quantity 



C P ( r 2 - 0, 



the quantity converted into work is 



q = C p (r 2 - T[ +~~h+ z t - r' 2 ) 



= C p (T t - T[ + r 2 - r^ 



(IV) 



But this expression, which is of the same form and meaning as in 

 the process for dry air (see iv of §7), has now a different numerical 

 value. If Pj P 2 7\ T 2 and h remain the same in the two cases but 

 the column P 2 p 2 is warmer now than before, then will p 2 be larger, 

 but p t remains unchanged and a larger value of r 2 — r' 2 corre- 

 sponds to the larger difference p 2 — p v In the se?ond case more 

 heat is converted into work than in the first case; this increase will 

 be used to maintain the greater difference of pressure that now 

 exists in the upper layer. 



The following numerical data are made the basis of an example 

 of this second method : 



