ENERGY IN GENERAL. 77 



A body which has been raised to a certain 

 height will, if it be let fall, perform work which 

 can be exactly measured in kilogrammetres by the 

 product of its weight into the height it falls. Such 

 work may be utilized in many ways. In this way, 

 for instance, public clocks are worked. Now, as long 

 as the clock-weight is raised and not let go, and 

 as long as it 'is motionless, the physics of early 

 days would say that there is nothing to discuss; 

 the phenomenon is the fall ; it is going to take 

 place, but at the present moment there has been 

 no fall. 



In energetics we do not reason in this way. We 

 say that the body possesses a capacity for work which 

 will be manifested when the opportunity arises, a 

 storage of energy, a virtual or potential energy^ or 

 again, an energy of position, which will be transformed 

 into actual energy or real work as soon as the body 

 falls. 



Let us ask whence this energy arises. It proceeds 

 from the previous operation which has raised the 

 weight from the surface of the soil to the position it 

 occupies. For example, if it is a question of the 

 weights of a public clock, which, by its fall, will develop 

 in 15 days the work that is necessary to turn the 

 wheels, to strike the bell, and to turn the hands, 

 this work ought to bring to our minds the exactly equal 

 and opposite work done by the clockmaker, who has 

 to carry the clock-weight and to lift it up from the 

 ground to its point of departure. The work of the 

 fall is the faithful counterpart of the work of elevation. 

 The phenomenon has therefore in reality two phases. 

 We find in the second exactly what was put into the 

 first, the same quantity of energy — ?>., the same work, 



