CHAP, in.] ELECTRICITY AND MAGNETISM. 



125 



by a moist conductor. Such a pile, if composed of 

 a number of such pairs of discs, will produce electricity 

 enough to give quite a perceptible shock, if the top and 

 bottom discs, or wires connected with 

 them, be touched simultaneously with 

 the moist fingers. When a single pair 

 of metals are placed in contact, one 

 becomes + ly electrical to a certain small 

 extent, and the other ly electrical, or in 

 other words there is a certain difference 

 of electric potential (see p. 40) between 

 them. But when a number are thus set 

 in series with moist conductors between 

 the successive pairs, the difference of 

 potential between the first zinc and the 

 last copper disc is increased in propor- 

 tion to the number of pairs ; for now 

 all the successive small differences of potential are added 

 together. 



151. The Crown of Cups. Another combination 

 devised by Volta was his Couronne de Tasses or Crown 

 of Cups. It consisted of a number of cups (Fig. 70), 



Fig. 69. 



Fig. 70. 



filled either with brine or dilute acid, into which dipped 

 a number of compound strips, half zinc half copper, 

 the zinc portion of one strip dipping into one cup, while 



