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V. Or the Aj)plication of Thermodynamics to the Study of the 

 Variations of Fotential Energy of Liquid Surfaces. By G. 

 Van der Mensbrugghe, Correspondent of the Royal Aca- 

 demy of Belgium* . Second Preliminai'y Communication. 



IN my first communication t I proposed to determine the 

 quantity of heat dQ, gained or lost by a Hquid mass of 

 which the surface S receives an increment c/S. Representing 

 by T the potential energy of the unit of surface at the absolute 

 temperature t, and neglecting every other cause of variation in 

 the energy of the body, I found the equation 



«S)^ w 



and having applied it successively to various particular cases, 

 I then deduced from it the transformed equation 



dQl = A.td( 



ich 



which gives the intensity i of the current corresponding to the 

 quantity of heat c/Q by which the surface S is traversed in the 

 time dr, x being the difference of electric level. 



As I have already said, the surface S may represent either 

 the free surface of a liquid, or the surface of separation of two 

 liquids which do not mix, or the surface of contact of a solid 

 and a liquid. 



On the present occasion I will suppose that we give to the 

 temperature t of the unit of weight of a liquid an increment 

 dt, which will necessarily produce an increase JS of the sur- 

 face. Since this augmentation d^ develops a variation of heat 

 c?Q (expressed above), I shall be able to write, designating by 

 K the specific heat as given by experiment at the temperature 

 t, and by k the specific heat as it would be at this temperature 

 if the surface had no potential energy. 



(4) (') 



Y.dt = Mt—A.td{^ 



According to this equation, the specific heat K would be a 

 function not only of the temperature t, but also of the surface 

 S of the liquid and of the potential energy T of this surface. 



* Translated from a separate impression, communicated bytlie Antlior, 

 from the Bulletins de VAcademie Royale de Belgique, 2^ s6rie, tome xli. 

 No. 7, Jnly 1876. 



t Bulletins de VAcademie Rot/ale de Belqi(pie, 2e serie, t. xli. p. 769 ; 

 Phil. Mag. [V.] vol. ii. p. 450, December 1876. 



