484 MAGNETISM AND ELECTRICITY 



Serviceable Electrical Energy. In Experiments 152 to 

 156, muscular energy was transformed into electrical energy. 

 In none of these cases, however, could the electrical energy 

 have been made of practical service to man. Methods 

 of producing electrical energy under different conditions had 

 to be found before this form of energy could be made to do 

 work. Within recent years man has done this and has thus 

 added electricity to the forms of energy he is able to con- 

 trol for his service. 



Current Electricity. In Experiment 155 it was found 

 that it was impossible to charge the pith ball when it was 

 suspended by the copper wire. The electricity passed off, 

 was conducted away, through the wire. 

 We had here a current of electricity 

 through the wire, but it was only for 

 an instant. At the opening of the 

 nineteenth century, an Italian by the 

 name of Volta discovered how a con- 

 tinuous electric current could be pro- 

 duced. If a strip of zinc and a strip of 

 copper or carbon are placed in dilute 

 sulphuric acid and connected with a wire (Figure 154), a 

 current of electricity will flow through the wire from the 

 copper or carbon to the zinc. The current is due to the 

 chemical action of the sulphuric acid on the zinc. Chemical 

 energy has been transformed into electrical energy. 



An arrangement such as that shown in Figure 154 is 

 called a voltaic cell, after its discoverer. In a cell of this kind, 

 hydrogen bubbles formed by the action of the acid on the 

 zinc (see Experiment 56) soon collect on the copper strip, 

 and the current weakens and finally stops. The cell is 



