102- THE MA&iTtf89*.6& MODERN SCIENCE 



dition, or reach a possible initial condition, in which 

 there was present a sufficient amount of energy to 

 account for the present distribution of energy among 

 the component parts. 



Although in this chapter we shall state the funda- 

 mental ideas as to energy in connection with visible 

 and tangible bodies, e.g. stones or a> baseball, this 

 should not mislead as to the relative importance of 

 the energy associated with groups of molecules as 

 compared to that of the molecules themselves or their 

 component parts. The energy which is most important 

 in nature is not that of bodies like trains and bullets, 

 hammers and fists, but the interatomic and molecular 

 energy. The interatomic energy of the sun, trans- 

 mitted to the earth, is recognized as heat and light, 

 and is the cause of the chemical synthesis in growing 

 plants. It is interatomic energy which causes the 

 heat evolved by some chemical changes, as that of com- 

 bustion. (The heat itself we shall find to be molecu- 

 lar energy of the body which is heated.) The energy 

 of organic life is the result of innumerable small contri- 

 butions of interatomic energy and to some extent of 

 molecular energy. The rise of sap in plants is a phe- 

 nomenon of molecular energy. 



As has been indicated above, energy may be asso- 

 ciated with the component parts of the atom, with the 

 molecules and atoms themselves, or with bodies of more 

 than molecular size. Of the kinds of energy we dis- 

 tinguish, however, only two, namely "potential" and 

 "kinetic," the latter due to motion and the former 

 existing only in possibility. Whenever a body is 

 given the ability to do work as a result of the motion 



