MAGNETIC EFFECTS OF ELECTRIC CURRENTS 241 



meter is then inserted in the circuit, and the electricity is 

 finally available in the rooms of the residence, as shown in 

 figure 121. 



246. Electrical industries. It has been estimated that about 

 70 per cent of the whole population that is, over 70,000,000 

 people use electricity in some way every day. The follow- 

 ing table of estimates indicates the extent to which these 

 industries constitute a source of national wealth as compared 

 with other industries: 



The values for the various branches of the electrical in- 

 dustry for the year 1917 are approximately as follows: 



Electric railways 

 Electric manufacturing 

 Power plants . 

 Telephony . . . 

 Telegraphy . . . 

 Miscellaneous 

 Total . 



$800,000,000 

 600,000,000 

 550,000,000 

 425,000,000 

 175,000,000 

 275,000,000 

 $2,825,000,000 



Electrical industries produce thousands of articles, but 

 the chief ones are dynamos, transformers, switchboards, 

 motors, storage and other batteries, arc lights, searchlights, 

 incandescent lamps (fig. 122), lighting fixtures, telegraph 

 apparatus, telephones, insulated wire, annunciators, electric 

 clocks, fuses, rheostats, heating and cooking apparatus, meas- 

 uring instruments, magneto and automobile apparatus. 



1 Timbie, W. H., Elements of Electricity. 



