( 133 ) 



lias decreased, tliat of the figure below AB lias increased in conse- 

 quence of the modification. The line A' B' must therefore be traced 

 noticeably lo\ver in order to get again equal areas. ^' will of course 

 lie on the right of J3, and we may also expect that A' will lie on 

 the left of A. 



We have, ho^vever, [)ut the question in too general terms ; for 

 our purpose it should have been put as follows : what modification 

 in the quantities (t and h makes the vapour pressure at a temperature 

 which is an equal fraction of Tk, decrease below the amount which 

 we find for it, keeping a and b constant — and it would even be 

 still more accurate not to speak of the absolute value of the pres- 



P 



sure, but of the fraction 



The modifications in a and b should 



2^k 



then be such, — if we base our considerations on the preceding 



figure — that in ccmsequence of the modifications themselves the 



values of Tk and p/, either do not change at all or very slightly. 



Tf we make a a function of the temperature we have to compare 



the following two equations : 



RT a 

 P 



and 



V — b 

 RT 



aTi, 



P = 



V — b Tv"^ 



1 a 



id pic = — — 1. e. the same 



values for 7^• and ^y^. if (/ and b have the same \'alues in both 



Both equations yield R2\ z= ~^-- 



