Electricity 



207 



the zinc the negative. 

 Although we now know 

 that the electrons flow 

 from the zinc to the car- 

 bon, it is much more con- 

 venient to use the old 

 way of speaking, as was 

 explained on page 199. 

 Practically, it makes no 

 difference which way the 

 electrons are going as 

 long as a current of elec- 

 tricity is flowing through 

 the wire from one pole 

 of the battery to the 

 other pole. So every 

 one speaks of electricity 

 as flowing from the posi- 

 tive pole of a battery 

 (usually the carbon or 

 copper) to the negative 

 pole (usually the zinc), although the electrons actually 

 move in the other direction. 



Batteries make enough electricity flow to do a good 

 deal of work. But they are rather expensive, and it 

 takes a great many to give a flow of electricity sufficient 

 for really heavy work, such as running street cars or 

 lighting a city. Fortunately there is another way of 

 getting large amounts of electricity to flow. This is 

 by means of dynamos. 



How a dynamo makes a current flow. To under- 



FIG. 113. A storage battery. 



