CHAPTEE XII. 



THE LAWS OF MOTION.* 



IT has been seen that a single, isolated body in space 

 could not be said to be either at rest or in motion. 

 Motion can only be of one body with reference to 

 another body. It is, to repeat, a change of relation 

 between bodies in space, and can no more be said to 

 belong to the one than to the other. It is simply an 

 approach or a recession an increase or a diminution 

 of the distance between them and is thus essentially 

 mutual. 



But since motion can only take place on the part of 

 bodies with reference to each other, it must be occa- 

 sioned by some fundamental connection between the 

 bodies themselves ; and this connection, or concrete re- 

 lation, we have already seen developed in the discussion 

 of the fundamental nature of matter, or the extended, 

 of which " bodies" are but the local aggregations. 



Force or energy being the substance of the extended 

 world, its modes of manifestation, or phases of dif- 

 ferentiation, give rise to infinitely multiple relations of 

 force, some of which, in turn, appear under the form 

 of " bodies" in space. And these bodies, thus consti- 

 tuted, must, in the nature of the case, be fundamentally 

 related, each to every other. 



Each body is, in fact, itself a force-center, involv- 

 ing necessarily both phases of force attraction and 



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