ON ELECTRICITY IST MOTION. 



679 



at least counteracting, the natural tendency of the electric fluid to pass from 

 the water to the zinc, and from modifications of this counteraction he explains 

 the effects of galvanic combinations in all cases. Thus, in a circle composed 

 of copper, sulfurct, and iron, the fluid tends to pass from the iron towards 

 the sulfuret, and from the copper to the iron, in one direction, and in the 

 opposite direction from the copper to the sulfuret, with a force which must be 

 equal to both the others, since there would otherwise be a continual motion 

 without any mechanical cause, and without any chemical change; but the 

 action of the sulfuret on the copper tends to destroy its electromotive, or rather 

 electrophoric, power, of directing the current towards the sulfuret, and its 

 combination with the sulfur makes it either positively electrical, or negatively 

 electrical in a less considerable degree; consequently the fluid passes, accord- 

 ing to its natural tendency, from the copper to the iron, and from the iroa "REEsfT^ 

 to the sulfuret. In a third case, when copper, an acid, and water, forra 

 a circle, the natural tendency is from the acid to the copper on one side, s^.'*'<j//.'. '' 

 and from the acid to the water, and from the water to the copper on the other; ^"<<^ ' 

 here we must suppose the first force to be only a little weakened by the che- 

 mical action, while the third is destroyed, so that the first overcomes the sc 

 cond, and the circulation is determined, although very feebly, in such a direc- 

 tion, that the fluid passes from the acid to the copper. When, in the fourth 

 place, the combination consists of copper, sulfuret, and water, the tendencies 

 are, first, from the copper to the sulfuret, and from the water to the copperi 

 and secondly, from the water to the sulfuret : in this instance a chemical ac- 

 tion must be supposed between the oxygen of the water and the sulfuret, 

 which lessens the electromotive tendency, more than the action that takes 

 place between the sulfuret and the copper, so that the fluid passes from the 

 copper to the sulfuret; and the current has even force enough to prevent 

 any chemical action between tlie water and the copper, which would tend to 

 counteract that force, if it took place. 



Mr. Davy has observed that the decomposition of the substances, employed 

 in the battery of Volta, is of much more consequence to their activity than 

 cither their conducting power, or their simple action on the other elements of the 

 series: thus, the sulfuric acid, which conducts electricity better, and dissolves 

 the metals more readily, than a neutral solution, is, notwithstanding, less 

 active in the batt-ery, because it is not easily decomposed. Mr. Davy lias also 



