OP ARTS AND SCIENCES. 427 



Since 



Suppose we have a vertical glass tube, the lower half containing 

 mercury and the upper half dilute sulphuric acid. Suppose the -(- 

 pole of a battery, the electromotive force of which does not exceed 

 0.9 Dauiell, is connected with the acid, and the — pole with the 

 mercury. The superficial tension is increased and there is a contrac- 

 tion of the surface. From equation (c) a quantity of heat Q is 

 evolved : 



If the poles of the battery are reversed there will be an absorption 

 of heat of the same amount. If the difference of potential exceeds 

 0.9 Daniell the effects will be reversed. 



This is completely analogous to the Peltier phenomenon ou earh 

 side of a neutral point. 



If the surface of separation between mercury at constant potential 

 and dilute sulphuric acid at constant higher potential is increased by 

 the action of any force, work is done against superficial tension, and 

 the energy of electrical separation appears. Positive electricity is 

 separated across the surface from mercury to acid ; and the tendency 

 of the electrical action is to oppose the force. Conversely if the 

 energy of electrical separation disappears by the passage of positive 

 electricity from the acid to the mercury, mechanical work is done 

 against superficial tension by dilatation of the surface. 



Suppose we have a bent glass tube of nniform bore, containing dilute 

 sulphuric acid in the bent part, and a column of mercury in each arm 

 A and B. Let the temperature of the meniscus at A be T, and that 

 of the meniscus at B be 7' — d T. Let the potential of the sulphuric 

 acid be maintained constant, by any means, and equal to V. 



Let the mercury at ^be put in contact with a conductor of constant 

 potential Kj, and infinite capacity. Let the mercury at A be 2^ut in 

 contact with a similar conductor at potential F^. 



Let these potentials be so arranged that the change in the difference 

 of potential at B is equal and opposite to that at A. 



K the difference of potential at B is increased an electrical separa- 

 tion takes place so as to produce a contraction of the surface. At A 



