190 ELEMENTS OF GENERAL SCIENCE 



The moving piston may be connected to machinery which 

 is to be operated. The work which i done by the piston 

 upon the machinery is derived from the steam as it expands 

 in the cylinder. The steam which leaves the exhaust outlet, 

 having parted with some of its energy to the piston, is no 

 longer as hot as it was when it entered the cylinder. 



205. 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 sources of energy, and potential or kinetic energy may be 

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

 engine, together with some of the machinery that it may 

 drive, furnishes a good illustration of the many possible 

 transformations of energy. Let us suppose that our engine 

 is driving a dynamo and that the e T ectric current which 

 the dynamo generates 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. The 

 energy in the moving piston is transmitted to the dynamo 

 and is there 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. 



206. 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 

 furnace to the light. This loss is not difficult to find. A great 

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



