74 LIFE AND DEATH. 



we call energy; and if we agree to give it this name, 

 we may say that the conservation of energy is 

 invariable throughout all mechanical transforma- 

 tions. 



Distinction between Work and Force, and between 

 Energy and Work. The history of mechanics shows 

 us what trouble has been taken and what efforts have 

 been made to distinguish work (now mechanical 

 energy) from force. 



It is worth while insisting on this distinction. It 

 could be easily shown that force has no objective ex- 

 istence. It has no duration, no permanence. It does 

 not survive its effect, motion. There is no conserva- 

 tion of force. It passes instantly from infinity to 

 zero. It is a vectorial magnitude that is to say, it 

 involves the idea of direction. Work, on the other 

 hand, is the real element; it is a scalar magnitude 

 involving the idea of opposite directions, indicated by 

 the signs + and - . Work and force are hetero- 

 geneous magnitudes. Energy, and this is the only 

 characteristic by which it is distinguished from work, 

 is an absolute magnitude to which we may not even 

 give opposite signs. 



An example may perhaps throw these characteristics 

 into relief namely, the hydraulic press. We have on 

 the platform exactly the work which has been done 

 on the other side. The machine has only made it 

 change its form. On the contrary, the force has been 

 infinitely multiplied. We may, in fact, consider an 

 infinite number of surfaces equal to that of a small 

 piston, placed and orientated at will within the liquid ; 

 each, according to Pascal's principle, will support a 

 pressure equal to that which is exercised. As soon as 

 we cease to support it, this infinity falls at once to zero. 



