MECHANICAL ENEKGY AND HEAT 185 



209. Transformations of energy. There are other forms of 

 energy besides heat and mechanical energy, but we shall not 

 discuss these at any great length. Both electricity and light 

 are forms of energy, and potential or kinetic energy may be 

 transformed into heat, light, or electric energy. The steam 

 engine, together with some of the machinery that it may drive, 

 furnishes a good illustration of the many possible transforma- 

 tions of energy. Let us suppose that our engine is driving a 

 dynamo, and that the electric current which the dynamo gen- 

 erates is employed in operating a number of lights. In that 

 case we may start with energy in the form of heat contained 

 in the steam. In the engine cylinder a portion of the energy 

 is imparted to the moving piston, and this energy no longer 

 appears in the form of heat. This energy in the moving piston 

 is transmitted to the dynamo, and there it is transformed into 

 a current of electricity. We therefore speak of an electric 

 current as a form of energy. The current is passed through 

 a lamp in which it gives off its energy in the form of light 

 and heat. This energy passes off into the surrounding space 

 and is usually lost to us. 



210. Loss of energy. The amount of heat and light energy 

 that is secured from the lights which may be operated by the 

 dynamo is not at all equal to the amount of heat energy that 

 was produced by the coal burned in the furnace. It may be 

 no more than 5 per cent of the total produced by the coal. 

 Plainly there has been a very great loss somewhere in the 

 route that the energy has traveled in passing from the fur- 

 nace to the light. This is not difficult to find. A great deal 

 of heat goes up the chimney, some radiates from the boiler 

 and engine into the air, and some passes off in the exhaust 

 steam. In these and other ways the steam engine wastes pos- 

 sibly 85 per cent or more of the energy produced by the coal. 

 Of the energy actually utilized by the engine some is lost by 

 friction in the engine and dynamo, showing itself in the form 

 of heated bearings, and some is lost through the heating of 



