262 



EIGHTEENTH CENTURY. 



Volta found not only that it was necessary to have 

 moisture between the two metals, but that some acid put in 

 the water greatly increased the strength of the electricity. 

 Fig. 44 shows the first electric battery which he made, and 

 which is the one now commonly used for simple experi- 

 ments. In this battery each piece of zinc is joined to one 

 of copper, and where the two are not united they are in the 

 same cup, so that the liquid acts as a link to them. We 

 know now what Volta did not know, that a chemical change 

 is going on between the zinc and the acid water, which sets 

 the action going, but we do not yet know exactly what the 

 electricity itself is. The movement in Fig. 44 begins on the 



Fig. 44. 

 -,— 3 



Volta's Crown of Cups (Fownes). 



z, Zinc, c, Copper, a a, b. Connecting wires. The arrows show the course of 

 the positive currents. 



left-hand side at z. Here the current' is set up by the 

 action of the acid and water upon the zinc, and is passed on 

 to the copper, c ; then along the wire a, to the next z, and so 

 on till it reaches the last cup, when it is carried by the wire 

 b back to the first piece of zinc, and so the round is com- 

 pleted. 



* There are always two currents passing along the wire— the /^JtV/z/^r 

 current, starting from the copper to the zinc, and the negative current, 

 going the opposite way from the zinc to the copper ; but to avoid con- 

 fusion, the positive current is always called the current^ and no notice 

 is taken of the other. 



