136 FIRST YEAR COURSE IN GENERAL SCIENCE 



Electric lights are of two kinds, incandescent and arc 

 lights. In the incandescent light a thread-like conductor, 

 called the filament, is heated white-hot by its resistance to 

 the electric current passing through, it. This filament is 

 enclosed in a bulb, which is either a partial vacuum or is 

 filled with nitrogen. The filament would be burned if the 

 bulb contained air. Arc lights are caused by a powerful 

 electric current passing between two carbon rods slightly 



separated from each other. 

 This separation causes a re- 

 sistance which heats the ends 

 of the carbons white-hot. 

 These white-hot carbon ends 

 give the brilliant light. The 

 hot carbon vapor, which fills 

 the space between the ends, 

 conducts the current. 



146. Transformation of 

 Energy. Whenever an 

 electric motor is used, it 

 must be run by power 

 furnished by a dynamo, 

 which in turn is run by water 



FIG. 70. AN ELECTRIC GENER- 

 ATOR OR DYNAMO 



Such a machine as this is a 



dynamo. It consists of a revolving power Or by steam. In the 



former case, the force of 



magnets set up currents of electricity, gravity gives energy to the 



core of electro-magnets within a 

 great permanent magnet. The 



first in one direction and then in the foil watpr- in the rase of 

 opposite direction, so rapidly that. * 

 they seem continuous. The currents 

 pass off by wires connected at the 

 axle. The revolution of the core is 



steam, 

 duced 



the energy is pro- 

 >y the chemical action 



caused by power transmitted by a between fuel and the Oxygen 



belt over the axle at the side. What 

 power might be used? 



of the air. 



There are several steps in 

 the transformation of chemical energy into electrical energy. 

 Chemical energy from oxidation of coal becomes heat energy; 

 heat causes the expansion of steam which produces energy 



