THE CONQUEST OF NATURE 



any more than in the case of the dynamo, as to why the 

 electrons rush off in a particular direction and thus 

 establish an electrical current. Perhaps we should re- 

 call that the very existence of this current has at times 

 been doubted. Quite recently, indeed, it has been held 

 that the seeming current consists merely of a condi- 

 tion of strain or displacement of the ether. But we are 

 here chiefly concerned with the electron theory, ac- 

 cording to which, as we have all along noted, the seem- 

 ing current is an actual current; the ether strain, if 

 such exists, being due to the passage of the electrons. 



PRACTICAL USES OF ELECTRICITY 



Various effects of the current of electrons have been 

 hinted at above. Considered in detail, the possible ways 

 in which these currents may be utilized are multifarious. 

 Yet, they may be all roughly classified into three 

 divisions as -follows: 



First, cases in which the current of electricity is used 

 to transmit energy from one place to another, and re- 

 produce it in the form of molar motion. The dynamo, 

 in its endless applications, illustrates one phase of such 

 transportation of energy; and the call-bell, the telegraph, 

 and the telephone represent another phase. In one 

 case a relatively large quantity of electricity is necessary, 

 in the other case a small quantity; but the principle in- 

 volved that of electric and magnetic induction is the 

 same in each. 



The second method is that in which the current, 

 generated by either a dynamo or a battery of voltaic 



[168] 



