Prof. Daniell on the Constant Voltaic Battery. 301 



maintain a current equivalent to 20 cubic inches of the mixed 

 gases in the same time. It is scarcely necessary to obsei've, 

 that the difficulty of maintaining constancy of action is, of 

 course, proportioned to the energy of the action. 



It is this almost unlimited command of steady force which 

 renders its application, either in the electrolytic or magnetic 

 direction, possible to mechanical or manufacturing ])urposes : 

 magnetic locomotive engines never could have been dreamt 

 of without the solution of this preliminary problem. 



M. E. Becquerel proceeds to say, " M. Daniell, iVapres les 

 principes exposes precedeinment, a construit une pile dont nous 

 allons donner la description, et qui est a present generalement 

 employee." (P. 442.) 



Now I not only most emphatically deny that I was in any 

 degree guided by these principles, but I assert that they were 

 incapable of leading me to any such conclusion ; as they, in 

 fact, failed to lead M. Becquerel to the same. 



In proof of this, I will briefly recapitulate the real principles 

 of "the constant battery;" the different steps of the investiga- 

 tion which preceded its invention being all clearly stated in 

 my papers in the Philosophical Transactions. 



1. In the first place, I traced the origin of the decline and 

 ultimate annihilation of the current in the common voltaic 

 battery not to the evolution of acid and alkaline matter at the 

 opposite plates, and the consequent establishment of a coun- 

 ter current by their mutual reaction, but to the deposition 

 upon the conducting plate of a substantial coatingof pure me- 

 tallic zinc, the weight of which upon a platinum plate of three 

 inches by one I have stated to be nearly 29 grains. In con- 

 sequence of this, zinc becomes opposed to zinc in the cii'cuit, 

 and all current is stopped. 



2. To prevent this deposition of active metal upon the con- 

 ducting metal, it occurred to me, — 1st, to divide the portion of 

 the electrolyte in contact with the generating plate from that 

 in contact with the conducting plate by a porous diaphragrn, 

 by which the solution of zinc is prevented from reacliing the 

 copper or platinum; and 2ndly, to provide for the perpetual 

 renewal of the surface of the conducting plate by the deposi- 

 tion of fresh inactive metal upon it, transferred by the pro- 

 cess of electrolysis from the solution of a salt selected for the 

 purpose and placed in the partition next to it, or precipitated 

 by the secondary action of the hydrogen evolved upon it. By 

 this contrivance, not only is the surface of the conducting 

 plate perpetually renewed, but the opposing influence of the 

 hydrogen during its evolution is removed, and the battery is 

 at once rendered constant and its power greatly exalted. 



