180 THE WORLD-ENERGY 



A phase of force drawing bodies together is thus seen 

 to develop into a phase of force driving the constituent 

 portions of those bodies asunder. Nay, the bodies them- 

 selves, so far as they are elastic, rebound; and the expan- 

 sion of the body as a whole is but the increased intensity 

 of rebound of the molecules of the body, estimated in 

 the increased extension or volume of the body as a whole. 



But whether the impact and rebound be between large 

 bodies (moles), or between small bodies (molecules), in 

 either case precisely the same principle applies ; and the 

 thing to especially notice just at this point is that the 

 manifestation of force is perpetually dual. Concentra- 

 tion, we are accustomed to say, is due to attraction, while 

 expansion is due to repulsion. But we must repeat that, 

 as here shown in brief, and as proven more extendedly in 

 preceding chapters, the tendency toward concentration 

 itself involves the tendency toward expansion, just as the 

 tendency toward expansion involves the tendency toward 

 concentration. Attraction and repulsion are reciprocal 

 phases of every manifestation of force ; and their interre- 

 lation, as exhibited in the particles of any given mass, 

 great or small, is precisely what we are accustomed to call 

 the " elasticity" of that mass. That is, elasticity is a 

 molecular property of bodies ; and it should not be for- 

 gotten that this property is nothing else than an essential 

 relation or interplay between attraction and repulsion, as 

 the two necessary, and mutually inclusive, properties of 

 all matter. 



Finally, since the same principles determine motion, 

 whether molar or molecular the difference between 

 these two classes of motion being, as just seen, arbi- 

 trarily assumed rather than actually existent and, since 



