THE ORIGIN OF MOTIVE POWER. 427 



energy and most kinetic energy in January, when 

 they are at their least distance, and when their 

 relative motion is most rapid. The gain of kinetic 

 energy from one time to the other is equal to the 

 loss of potential energy. 



Potential energy of gravitation is possessed by 

 every two pieces of matter at a distance from one 

 another ; but there is also potential energy in the 

 mutual action of contiguous particles in a spring 

 when bent, or in an elastic cord when stretched. 



There is potential energy of electric force in any 

 distribution of electricity, or among any group of 

 electrified bodies. There is potential energy of 

 magnetic force between the different parts of a 

 steel magnet, or between different steel magnets, 

 or between a magnet and a body of any substance 

 of either paramagnetic or diamagnetic inductive 

 capacity. There is potential energy of chemical 

 force between any two substances which have what 

 is called affinity for one another, for instance, 

 between fuel and oxygen, between food and oxygen; 

 between zinc in a galvanic battery and oxygen. 

 There is potential energy of chemical force 



