98 PRACTICAL LESSONS IN SCIENCE. 



chines or dynamos have been constructed by which electricity 

 may be transformed into work. 



The dynamo electric machine, or the dynamo, consists of an 

 iron core wound with long coils of wire constituting the arma- 

 ture, which revolves between the poles or within the field of a 

 powerful electro-magnet, called a field magnet. The armature is 

 rotated by steam, and the currents induced are gathered up for 

 transmission by brushes of copper wire. These machines vary 

 greatly in detail, but all contain the above essentials. The 

 energy generated in the dynamo is transmitted through wires to 

 a similar machine called a motor, which transforms the electrical 

 energy into mechanical work. 



The energy developed in the dynamo may be transmitted to 

 electric lamps where it is transformed into light. If the termi- 

 nals of the wires from a dynamo are connected with pencils of 

 carbon and these brought near each other, their tips are intensely 

 heated, some of the carbon being volatilized. This vapor, a con- 

 ductor of high resistance, attains a very high temperature, 

 emitting intense light. The light of the incandescent lamps is 

 produced by introducing some refractory substance of lower con- 

 ducting power into the circuit, which soon becomes heated to 

 incandescence. The substance commonly used is carbon, inclosed 

 in a glass bulb from which the air has been exhausted. 



The value of the dynamo machines and the conducting wires 

 is not in gain of power, but in the distribution of power. The 

 heat energy which drives a great engine may through the dynamo 

 and conducting wires be distributed to hundreds of motors in 

 different parts of a city, to hundreds of arc lamps or thousands 

 of incandescents. 



The power of falling water, as at Niagara Falls, may be trans- 

 formed through turbine wheels and dynamos into electric energy, 

 which may be transferred through long distances, even as far as 

 Buffalo, and then through motors be transformed to light or 

 mechanical work. In this way water power becomes as available 

 as steam power, and much cheaper. 



The dynamo is also used in charging storage batteries, A 



