224- DISCOURSE ON THE STUDY 



mena are to be explained, or effects calculated. 

 Hence, they include every question that can arise 

 respecting the motions and rest of the smallest par- 

 ticles of matter, as weir as of the largest masses. 

 But the mode of reasoning from these general prin- 

 ciples differs materially, whether we consider them 

 as applied to masses of matter of a sensible size, or 

 to those excessively minute, and perhaps indivisible, 

 molecules of which such masses are composed. 

 The investigations which relate to the latter subject 

 are extremely intricate, as they necessarily involve 

 the consideration of the hypotheses we may form 

 respecting the intimate constitution of the several 

 sorts of bodies above enumerated. 



(237.) On the other hand, those which respect the 

 equilibrium and motions of sensible masses of matter 

 are happily capable of being so managed as to render 

 unnecessary the adoption of any particular hypothesis 

 of structure. Thus, in reasoning respecting the ap- 

 plication of forces to a solid mass, we suppose its parts 

 indissolubly and unalterably connected ; it matters 

 not by what tie, provided this condition be satisfied, 

 that one point of it cannot be moved without setting 

 all the rest in motion, so that the relative situation 

 of the parts one among another be not changed. 

 This is the abstract notion of a solid which the me- 

 chanician employs in his reasonings. And their con- 

 clusions will apply to natural bodies, of course, only 

 so far as they conform to such a definition. In strict- 

 ness of speaking, however, there are no bodies which 

 absolutely conform to it. No substance is known 

 whose parts are absolutely incapable of yielding one 

 among another ; but the amount by which they do 





