144 IIELMHOLTZ ON THE CONSERVATION OP FORCE. 



never be generated, but electric tensions only. These tensions, 

 however, are not equivalent to a certain quantity of force like 

 those heretofore considered, which implied a disturbance of the 

 electric equilibrium ; galvanic tensions are, on the contrary, con- 

 sequent upon the establishing of the electric equilibrium ; no 

 motion of the electricity can be generated by them further than 

 a change of distribution of the electricity consequent upon 

 a change of position. Let us suppose all the metals of the 

 earth brought into connexion with each other, and the corre- 

 sponding distribution of electricity established; by no other 

 combination of the same metals can any one of them suffer an 

 alteration of its tension until contact is established with a con- 

 ductor of the second class. The idea of the force of contact, the 

 force which is active at the place where two different metals 

 touch each other, and w hich developes and sustains the different 

 electric tensions of the latter, has not hitherto been rendered 

 more determinate than it is here, because the attempt to em- 

 brace the phaenomena resulting from the contact of conductors 

 of the first and second classes was made at a time when the 

 constant and distinguishing feature of the phaenomena, namely 

 the chemical process, was not yet properly recognized. From 

 this indefinite mode of regarding the subject, it would certainly 

 appear that the force of contact is such that by means of 

 it infinite quantities of free electricity, and hence mechanical 

 force, might be generated, if a conductor of the second class 

 could be found which was not electrolysed during the con- 

 duction. It was precisely this circumstance which excited such 

 a resistance to the contact theory, notwithstanding the simplicity 

 and precision of the explanations which it furnished*. The 

 principle which we have thus far advocated contradicts the idea 

 of such a force directly, if it do not recognise also the necessity 

 of the chemical processes. If this how^ever be admitted, if it be 

 assumed that the conductors of the second class do not follow 

 the law of the tension series, just because they conduct by elec- 

 trolysis, then the idea of the force of contact is capable of great sim- 

 plification, and may at once be referred to attractive and repul- 

 sive forces. All phaenomena exhibited by conductors of the first 



* Faraday's Experimental Researches in Electricity, 17th Series; Phil. 

 Trans. 1840, p. 1, No. 2071 ; and Pogg. Jnn. vol. liii. p. 568. 



