THE SOURCE AND NATURE OF VITAL ENERGY 297 



energy in the coal in the furnace is converted into heat ; the heat 

 is converted by the engine into motion; the motion of the fly- 

 wheel, by being attached to a dynamo, may be converted into 

 electricity; the electricity, passing over the wires, may run 

 into an electric lamp, where it is converted into light, or it 

 may go into an electric stove to be converted into heat. The 

 motion of water over a waterfall may easily be converted into 

 the motion of a wheel by the means of a water-wheel, this into 

 electricity, and this in turn into light, heat, motion, or any other 

 form of energy that we wish to obtain. 



Some of the types of transformation of energy are more easy to 

 bring about than others. It is much easier to convert motion 

 into heat than to convert heat into motion. Any form of mo- 

 tion is sure to take the form of heat eventually, whether we 

 are turning a grindstone or putting a brake on a railroad train, 

 or whether a cannon ball is stopped by a stone cliff. Heat, 

 indeed, seems to be the type which all forms of energy have a 

 tendency to assume in the end; it is then radiated into the atmos- 

 phere and into space, where it is beyond the reach of this earth 

 and is called radiant heat. It is true that we have some devices 

 by which heat may be reconverted into motion, but always with 

 considerable loss as radiant heat. We put into our steam en- 

 gines five times as much stored energy in the form of coal as 

 we receive in return in the form of motion, not because the 

 energy is destroyed, but because four-fifths of the energy of 

 the coal is wasted in heating the machinery and the air, and 

 then passes away as radiant heat, only a small part being con- 

 verted into motion. 



Definition of a Machine. A machine is any device which 

 converts one form of energy into another. The locomotive is 

 a machine for converting heat into motion; the electric bulb 

 is a machine for converting electricity into light; the motor 

 converts electricity into motion. Even the gas burner is a 

 machine for converting the chemical energy of the gas into 

 light. A clock is a machine which converts the potential 



