THE SMITHSONIAN INSTITUTION. 313 



on one of the metals. It has been shown that a galvanic current can 

 be produced by the action of two licjuids without metallic contact, 

 and therei'ore the theory of contact requires to be so modified as to 

 extend the idea of contact to that of the liquids as well as the solids 

 of the galvanic combination. On tlie other hand, it has never been 

 lully proved that the contact of two metals does not in itself produce 

 a disturbance of the electrical equilibrium, though tliis effect does not 

 appear sufficient to account for the great amount of electricity evolved 

 in the action of the battery. The two theories, properly modified, 

 approximate each other, and each, perhaps, involves elements of truth. 



The hypothesis, that the development of electricity is only the con- 

 sequence of chemical action — that without chemical decomposition of 

 the electrolyte no electricity can appear in the circuit, is that against 

 which the attacks of the advocates of the contact theory were directed ; 

 and it is, indeed, opposed to a great number of facts. The chemical 

 theory, in this form, ignores completely the fundamental experiment 

 of Volta ; it does not explain how the tension of electricity of the open 

 ])ile increases with the number of plates. But what is most incon- 

 sistent with the maintenance of this theory, is the circumstance that 

 a number of galvanic circuits can be constructed in which, when 

 open, not a trace of chemical decomposition takes place, but which, 

 nevertheless, give rise to currents when they are closed. 



Schonbein, in a memoir "On the cause of the hydro-electric current," 

 in his " Beitragen zur Fhydcalischen Chcmie — (Basel, 1844,") has re- 

 ferred to several such circuits. A solution of perfectly neutral sulphate 

 of zinc does not attack zinc; yet a combination of zinc and copper in 

 this solution produces a current. 



Another weighty objection to the form of the chemical theory_, 

 which attributes the formation of the current to a preceding chemical 

 attack upon one of the metals of the circuit, is, that the electro- 

 motive force of a circuit is not at all proportional to the violence of 

 the attack. If the copper of a Daniells' battery be placed in a solu- 

 tion of sulphate of copper, the electro-motive force of the apparatus is 

 almost wholly unchanged, whether the zinc is placed in water, dilute 

 sulphuric acid, or in a neutral solution of sulphate of zinc. This has 

 been proved by Svanberg, among others, by accurate measurements. 

 {Pogg. Ann. , LXXIII, 290.) If the current had its origin in chemical 

 action, the electro-motive force should be far greater upon application 

 of dilute acid than of water and sulphate of zinc. 



It is a fact, that the current of the water-battery (hydro-kette) 

 cannot circulate without decomposition of the liquid. The decompo- 

 sition appears essentially connected with the passage of the electricity 

 through the liquid, and the contact theory has lully acknowledged 

 the important part which chemical decomposition in the cells plays in 

 the formation of the current. A dispute as to whether decomposi- 

 tion is the cause of the electrical current_, or whether the chemical 

 decomposition in the battery is preceded by a state of electric tension, 

 the source of which we need not at present ask, is the same as though 

 there should be a controversy as to whether the motion of a water- 

 wheel is owing to the fall of water or the weight of water. The 

 weight occasions the fall^ and the fall the revolution of the wheel, just 



