428 



PROCEEDINGS OF THE AMERICAN ACADEMY 



the separation takes place so as to produce a dilatation of the surface. 

 The electrical change causes an evolution of heat at B, and an absorp- 

 tion of heat at A. 



For the present it will be assumed that the superficial tension is a 

 function of the temperature. 



The electrical works at A and B are equal and opposite. 



Since, however, the superficial tensions at the two surfaces are dif- 

 ferent, the changes in the areas of these surfaces, though opposite, 

 are not equal. 



Let d Sji equal the increment of area at A. Let d S^ equal the 

 increment of area at B. 



The work done at A is 



k d Sj . 



The work done at B is 



— V — Tit ^ ^) ^^£ ' 



Since these works are equal, 



dS, 



~ [ k dT 



dT 



d On • 



The quantity of heat absorbed during the expansion d Sj^ is 



Qa — — ^-ppd S^ , 



= — T 



dk 



It 



1-1^ ^r"^ 



d Sji . 



The quantity of heat given out during the contraction d Sb is 



Q^={T-dT) 



(I l' 

 11' 



d Sq , 



= T -jyj, dSji — dT j^ d S^ 



dk 



iim^r-.Tiii 



d Sj} . 



As long as y" is minus, the right-hand member of this equation is 



essentially minus, and there is consequently more heat absorbed than 

 evolved. 



