M*. GREGORY ON MECHANIC FOWER. Q 



error, for the things to which the terms were appropriated 

 would exhibit fuch fpecific differences as would almoft entirely 

 preclude the chance of confounding one with ano;her; and 

 leave no room to tear, that when the terms were applied to 

 inanimate beings, they would be concluded to exert ilrength, 

 or to potfefs power, as animals did ; any more than we fliould 

 now tear being mifunderftood when we fpeak of the force of 

 arguments, the attractions of benevolence, the fafcinations of 

 beauty, or the repulfive tendency of envy. Thus, from 

 contemplating the procefs of this gradual refinement, (a re- 

 finement produced not by barren fpeculators, but by the 

 neceflary demands occationed by the progrefs of civilization,) 

 we fee that the words power and force, primarily ufed to 

 denote animal energy, are now, by a natural extenfion 

 grounded upon an obvious analogy, employed to exprefs 

 efficiency in general. It will hence be eafy to affign the proper 

 philotophical acceptation of thefe terms, when ufed in the 



fcience of mechanics. Force or power, in a mechanical lerij'e, ^ cfimtion of th& 

 . a/i , ., ,., ' , . , ■'< _ ' *i terms force ani 



is that, whatever it be ntucU caufes a change in the jiate of a po Wer . 



body, whether that Jiate be rejl or motion. This definition does 



not requiie our entering into any metaphyseal difquifitions 



relative to the nature of caules, or the connection of caufe 



and effect: that every event is brought about by fome caufe, 



that is, by fome agency, or fomeihing which precedes in the 



order of occurrence, is a truth which I think none will be 



difpofed to deny ; but what is the agency, or where it actually 



relides, we can feldom know, except perhaps in the cafe of 



our own voluntary actions. It is not then the butinefs of the Forces only 



mechanic, ftri&ly ipeaking, to enquire into the modus operandi; ^ e ° W "ff°#s 



we learn from univerfal experience, that the mufcular energy thence meafure- 



of animals, the operation of gravity, electricity, impact, able * 



pretfure, &c. are fources x of motion, or of modifications of 



motion ; and hence, without pretending to know any thing 



of the effence of either of thefe, we do not hefitate to call 



them mechanical forces; becaufe it is incontrovertible that 



bodies expofed to the free aclion of either, are put into motion, 



or have the flate of their motion changed. Forces therefore, 



being only known to us by their effects, can only be meafured 



by the effects they produce in like circumftances, whether 



thofe effects be creating, accelerating, retarding, deflecting, 



or preventing motions : and it is by comparing thefe effects, 



or 



