APPLICATIONS OF ELECTRICITY 89 



connection on part of the hammer, and the latter flies back 

 only to connect the electricity and be attracted again. This 

 continues as long as the supply of electricity lasts. 



The electric motor consists of two magnets, one stationary 

 and the other free to move on an axis. The unlike poles at- 

 tract each other, but the electricity is shut off, or turned into 

 other coils of the moving magnet, just before it comes into a 

 position of equilibrium, and the motion continues. 



The telegraph is nothing but an electromagnet and a mov- 

 able piece of iron, which is attracted when the current passes, 

 and is pulled away from the magnet by a spring, when the 

 current ceases to flow. 



If a coil of wire is revolved in a place where there is magnetism, 

 electricity is produced. This is made use of for the production 

 of electricity in large quantities. The more electricity produced, 

 the harder it is to move the coil of wire. A machine for this 

 purpose is called a dynamo, and resembles an electric motor. 



The telephone is a very useful application of electricity, and 

 the student should consult the references for a fuller consid- 

 eration of it, as well as for details concerning all of the appli- 

 cations of electricity. 



References : 



1. 1803 : 312-342. The Dynamo, Motor, and Magnetic In- 

 duction. 



a. 1801 : 391-392. The Dynamo-Electric Machine. 

 6. 1804 : 595-606. The Telegraph and the Telephone. 



c. 1805:401-404. Electric Bell and the Telegraph. 



d. 1807 : 365-369. Electric Bell and Telegraph. 



e. 1808 : 353-363. Electric Bell, Telegraph, and Telephone. 

 /. 1809:436-445. Electric Bell, Telegraph, and Telephone. 

 g. 1810:288-300. The Telegraph and Electromagnetic In- 

 duction. 



h. 1811 : 280-291. The Electromagnet, Telegraph, and Bell. 



