MAGNETISM AND ELECTRICITY. 157 
by an arc, one half zine, the other copper. When the two metals are 
brought into contact, the legs assume the position shown by the dots in the 
figure. A proof of the correctness of Volta’s theory of the phenomenon just 
mentioned, is furnished by an experiment with the condenser (p/. 20, jig. 26). 
lf the upper plate be touched with the finger, and the lower with a piece 
of zinc, lead, tin, iron, &c., and the upper plate then removed, the gold 
leaves will diverge, and thus indicate an electricity developed by the 
metallic contact. The following experiment, also suggested by Volta, is 
still more satisfactory: Solder two different metals, as zine and copper, 
together, as shown in pl. 20, fig. 48 (ss’ being the place of junction), and 
taking the zinc in the hand, touch the lower plate of the condenser with 
the copper, applying the finger at the same time to the upper plate, and a 
divergence of the leaves will immediately ensue. When zinc and copper 
are in contact, the former becomes positively, the latter negatively 
electrified ; and generally, if any two different metals are in contact, one 
will be positively electrified, and the other negatively. This may even be 
the case with the same metal in different states, as cast and rolled zinc. 
Metals and other bodies becoming electric by contact, form, in this respect, 
a series, called the scale of electric tension. This scale is as follows: 
manganese, carbon, platinum, gold, mercury, silver, copper, iron, tin, lead, 
zinc, &c. Any one of these will become electrified, negatively by contact 
with one following it in the series, and positively by contact with one 
preceding it. The electricity developed is more sensible as the two 
substances stand further apart in the scale. When three or more metals 
are laid one above the other, the electric tension of the terminal plates is 
the same as if the intervening ones were altogether absent. 
2. Of the Galvanic Circuit. 
When two different metals are connected by a liquid conductor, as salt 
or acidulated water, a galvanic or electric current will be established in the 
liquid. From one metal there passes a positive current, and from the other 
a negative, both meeting in the liquid. A combination of several series of 
elements succeeding each other in the same relative order, is called a 
compound galvanic series or battery. The arrangement recommended by 
Volta for generating galvanic electricity, and called the Voltaic pile, is as 
follows: a square or round plate of zinc is to be soldered to one similarly 
shaped of copper, a sufficient number of these pairs being provided to make 
the pile of the proper height. These are to be placed one above the 
other, the zinc element having the same relative position in all the pairs, 
and each pair being separated from the next by a disk of flannel soaked in 
acidulated or salt water. The order will then be copper, zinc, cloth, copper, 
zinc, cloth, &c. ( pl. 22, fig. 69). Pl. 20, fig. 49, represents a pile of twenty 
pairs of plates, which are held in place by a frame of glass or wooden rods. 
That end of the pile towards which the zinc element of each pair is turned, 
is termed the positive pole, and the other the negative. When both poles are 
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