On Electric Phenomena. 13 



second plate will be decomposed, the positive and negative 

 accumulate in different parts of the glass plate, from whence 

 they are taken up by imbibers and conducted to the inside 

 and outside coating of a Leyden-jar, through the discharge 

 of which we can obtain all the before mentioned effects in the 

 most violent manner. 



Friction is not the only means by which the natural 

 electricity of bodies can be decomposed, contact alone can 

 operate in the same manner. It is particularly the contact 

 of metals and fluids, which produces a decomposition of elec- 

 tricities. If we immerse two different metals, for example, a 

 plate of zinc and one of copper into a glass, which is filled 

 with diluted sulphuric acid, the positive electricity goes from 

 the zinc through the sulphuric acid to the copper, the nega- 

 tive from the copper through the sulphuric acid to the zinc. 

 Free positive electricity collects in the protuberating end of 

 the copper, and free negative electricity accumulates in the 

 projecting end of the zinc. Such an apparatus as this is 

 called a galvanic element or a galvanic chain according to the 

 Italian anatomist Galvani, whom we have to thank for the 

 first knowledge of this fact, although the most correct expla- 

 nation was not given by him, but by his renownd countryman 

 Alessandro Volta. 



The prominent metaUic ends of the chain are called its 

 poles, and indeed the copper end is designated the positive 

 pole or positive electrode, and the zinc end the negative pole 

 \or the negative electrode. If we join the poles by a wire, 

 the opposite electricities are united. But, as the cause of the 

 decomposition of the natural electricities continues in opera- 

 tion, viz; the contact of the two metals with the fluid; the 



(135) 



