278 Dr. 0. J. Lodge on a Systematic Classification 



or to an authoritative statement which shall conduce to a better 

 understanding of the matter than is at present general. 

 I am, Gentlemen, 



Your obedient Servant, 



Oliver J. Lodge. 



1. Every action which takes place between two bodies* is 

 of the nature of a stress. A stress consists of two equal op- 

 posite forces (called action and reaction, or force and anti- 

 force), one of them exerted by the one body, and the other by 

 the other ; and it is impossible for one force to be exerted 

 without the other. 



2. Whenever a body exerting a force moves in the sense 

 of the force it exerts, it is said to do work\\ and whenever a 

 body exerting a force moves in the sense opposite to that of 

 the force it exerts, it is said to have work done upon it, or to 

 do anti-work, the quantity of the work being measured in each 

 case by the product of the force into the distance moved 

 through in its own direction. 



3. Whenever two bodies exert a stress on each other, they 

 are in contact ; and if they move, they move together over 

 the same distance J: hence, since the force equals the anti- 

 force, the work done by the one in any movement is equal to 

 the anti-work done by the other. 



4. The working-power § of a body is measured by the average 

 force it can exert, multiplied by the range or distance through 

 which it can exert it. The working-power of a body may be 

 increased or diminished by increasing or diminishing either 

 the force, or its range, or both ; and it must remain dormant 

 so long as external circumstances do not allow it to exert a 

 force through a distance. 



5. Whenever work is done upon a body, an effect is pro- 

 duced in it which is found to increase the working-power of 



* The term body is here used in its most general sense, viz. as standing 

 for a piece of matter in general, without regard to size. It may mean a 

 planet or an atom; and it may even apply to such extra-material things 

 as the sether and the hypothetical ultra-mundane corpuscles, or to any 

 thing else which is sufficiently like ordinary matter to he capable of pos- 

 sessing energy and of doing work therewith. 



t It seems preferable to speak of the work as being done by the body 

 rather than by the force', though the latter expression is undoubtedly 

 convenient sometimes. 



X This step is rendered necessary by the preceding one of considering 

 the work as done by the body. If it is the force which does the work, it 

 is unnecessary. 



§ Or power of doing work. But either term is objectionable, because 

 power means rate of doing work. The term entropy has been used, but I 

 believe that the accepted connotation of this word is now different. 



