CHAPTER XXV 

 HOW ELECTRICITY IS OBTAINED ON A LARGE SCALE 



One source. We have learned that cells furnish current 

 as a result of chemical action, and that the substance usually 

 consumed within the cell is zinc. Just as coal by combus- 

 tion furnishes heat, so zinc within the cell furnishes elec- 

 tricity. But zinc is a much more expensive fuel than coal 

 or oil or gas, and to run a large motor by electricity produced 

 in this way would be very much more expensive than to run 

 the motor by water or steam. For weak and infrequent cur- 

 rents such as are used in the electric bell, only small quantities 

 of zinc are needed and the expense is small. But for the 

 production of such powerful currents as are needed to drive 

 trolley cars, elevators, and huge machinery, enormous quantities 

 of zinc would be necessary and the cost would be prohibitive. 

 It is safe to say that electricity would never have been used on 

 a large scale if some less expensive and more convenient source 

 than zinc had not been found. 



A new source of electricity. It came to most of us as a sur- 

 prise that an electric current has magnetic properties and trans- 

 forms a coil into a veritable magnet. Perhaps it will not sur- 

 prise us now to learn that a magnet in motion has electric 

 properties, and is able to produce a current within a wire. 

 This can be proved as follows : 



Attach a closely wound coil to a current detector or galvanom- 

 eter (Fig. 106) ; naturally there is no deflection of the galvanom- 

 eter needle, because there is no current in the wire. Now 



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