45() M. G. Van der Mensbrugge on the 



Before reporting the verification-experiments, I will men- 

 tion that equation (2) is identical with that obtained by M. 

 Lippmann * for the quantity of electricity which passes through 

 the surface of contact of mercury and acidulated water, of 

 which surface T is the superficial tension (that is, the potential 

 energy of the unit of surface), x the difference of electric 

 level when the surface of contact S receives an increment dS. 



The new interpretation which I have just given to equation 

 (1), and which has permitted me to deduce very simply from it 

 the formula (2) already obtained by M. Lippmann for a par- 

 ticular case, leads me to believe that the elegant experiments 

 of that physicist, and those, of the same kind, published by M. 

 Quincke f, are decidedly in favour of the theory of thermo- 

 electric currents. If this assertion, rendered so probable by 

 the preceding considerations, and supported besides by all the 

 details of those experiments, should be confirmed by my sub- 

 sequent researches, we shall perhaps recognize the true 

 relations between thermal, electric, and capillary phenomena. 



M. Lippmann has proved the existence of two very im- 

 portant laws, of which the following is the expression : — 



1st. The capillary constant at the surface of separation of 

 mercury and dilute sulphuric acid is a function of the electric 

 difference which takes place at that surface. 



2nd. When a liquid surface is deformed by mechanical 

 means, the electrical difference of that surface varies in a 

 direction such that the superficial tension developed opposes 

 the continuance of the movement. 



The preceding demonstration enables us to see that these 

 two laws amount to the two following, at the same time clearer 

 and more general ; for they apply to all liquids, whether they 

 have surfaces of contact with air, with other liquids, or with 

 solids : — 



1 . The capillary constant at the free surface of any liquid, 

 at the surface of separation of two liquids which do not mix, 

 or at the surface of contact of a liquid with a solid, is a 

 function of the absolute temperature of the surface. (This 

 law, known long since, involves, pursuant to the first propo- 

 sition of M. Clausius (see above), that of M. Lippmann, 

 generalizing this latter.) 



2. When, by mechanical means, a liquid surface is deformed, 

 the temperature of this surface varies in a direction such that 



* Relations entre les phenombnes electriques et capillaires, 1873, Paris, 

 chez Gauthier-Villars. 



t " Ueber elaktrische Strome "bei ungleichzeitigem Eintanchen zweier 

 Quecksilber-Electroden in verschiedene Fliissigkeiten/' Pogg\ Ann, vol. 

 cliii. p. ]61. 



