CHEMICAL ACTION. 



225 



Each metal in the list is arranged so that it is electro-positive to any one 

 below, and electro-negative to any one above it. 



There is another curious fact which should be mentioned. In associ- 

 ating these metals it has been found that when two are brought into contact 

 the electro-motive force becomes greater the more distant they are in the 

 series given above ; in other words, the force between any two is equal to 

 the sum of the forces between those intervening between those two. So 

 when zinc is used with copper its force is not so great as when used with 

 platinum. 



It was Herr G. S. Ohm who laid down the law that the strength of 

 the electric current is equal to the electro-motive force divided by the 

 resistance, for he proved that the "resistance was inversely proportional to 

 the strength of a current." 



There are two other laws respecting currents, viz., 



(i.) Parallel currents in the same direction attract each other. 



(2.) Parallel currents in opposite directions repel each other. 



Upon these two hang all the varied phenomena of electro-dynamics. 



Fig. 228. Chemical action of electricity. Fig. 229. 



That chemical action develops electricity we can perceive with the aid of the 

 two cuts (figs. 228 and 229). If the wires be attached to the collecting-plate 

 of a condenser of electricity and the metal plate of a cell, as shown in the 

 figure (fig. 228), the electricity on the plate will be negative. If the operation 

 be reversed, and the plate be put in connection with the acid, and the metal 

 with the earth, the instrument will be charged with positive electricity. In 

 the other case, when two cups are used, united by a magnet so that the 

 solutions (one acid and the other alkaline) can by capillary attraction unite 

 upon the binding of the magnet, and we place the wires as in fig. 229, 

 the charge on the plate will be positive if it be in connection with the 

 acid, and negative if in communication with the alkaline solution. Every 

 time there is chemical action between two bodies in contact electricity is 

 produced positive on one negative on the other, and that is the funda- 

 mental principle of the voltaic pile. 



