14 Instinct and Intelligence 



marble which it might strike ; it therefore pos- 

 sesses kinetic or free energy in virtue of its 

 motion or active condition. 



Potential energy, on the other hand, is asso- 

 ciated with a body in virtue of its position. 

 Thus, when a stone is lifted above the ground, 

 the energy expended and the work done in lift- 

 ing it are measurable quantities of energy stored 

 up or rendered passive in some way, and this 

 energy can be recovered or set free in a measur- 

 able form. Coal represents an accumulation of 

 light and heat energy derived by plants in by- 

 gone ages from the sun, which has been trans- 

 formed by means of the living basic substance 

 of these plants into chemical energy. In order 

 to liberate this potential or latent energy another 

 chemical substance in the shape of oxygen is 

 required, which acts on the molecular structure 

 of the coal and sets its latent energy free in the 

 form of heat, light, etc. 



We have given an example (p. 10) of a 

 change in the arrangement of the atoms in an 

 organic substance which completely alters the 

 character of the work it performs ; the same rule 

 holds good for inorganic matter. For instance, 



