FORCE, A SPACE RATE OF ENERGY 153 



seemed futile, for he stated as a scholium to his third 

 law what we know to-day as the "work principle." 

 What he said may be expressed in our modern terms as 

 follows: "In any machine or combination of machines 

 the work of the acting forces is equal to the work of the 

 resisting forces." If we understand the "work of re- 

 sisting forces" to include not only the useful work but 

 also the work done against fractional forces, we have a 

 statement conforming to our present ideas of energy. 



To-day the goal of the scientist is not an impossible 

 perpetual motion machine but rather the efficient utili- 

 zation of the available energy of the universe and 

 that increase in availability which may follow further 

 knowledge as to the composition of matter. Scientifi- 

 cally the aims are radically different, but socially they 

 are identical, for in both cases the ami is to lift man 

 above the struggle for existence. 



To understand more fully the present limitations 

 which the scientist encounters hi making available for 

 man some of the untouched sources of energy in the 

 universe, we need to consider the energy of molecules 

 and electrons. In so far as the energy they possess 

 is potential we are in ignorance of its very existence 

 except in those cases where we have already learned 

 to release it, as in various chemical or electrical actions. 

 In so far as it is kinetic energy we may measure its 

 amount even in cases where we do not as yet know how 

 to utilize it. On the part of the molecules of a sub- 

 stance such a measurement is possible because the 

 energy is manifested as heat. 



The kinetic energy of translation of any body may 

 be expressed in terms of its velocity and its mass. 



