ON THE LAWS OP NATURE. IO? 



It is eafy to fee, that, whenever a poffible and ne- 

 ceffary cafe of equilibrium is allowed, no other cafe 

 can exift. Elfe, as d'Alembert very well obferves, will 

 the laws of the collifion of bodies, which are neceffarily 

 reducible to equilibrium, be indeterminate. This, 

 however, cannot be, becaufe, if a body ftrike againft 

 another, one fole effect muft neceffarily be the remit, 

 which is the inevitable confequence of the exiftence 

 and impenetrability of this body. • 



Befides, d'Alembert has as good as demonftrated the 

 unity of the law of equilibrium, which involves necef- 

 fity, by a mathematical deduction, in his mafterly 

 Traite de Dynamique. 



From what has been faid, it follows, that the laws of 

 ltatics and mechanics known by experience are the 

 very fame with thole which arife of themfelves from 

 the exiftence of matter and motion. For obfervation 

 mews us thefe laws in the bodies which furround us. 

 Therefore the laws of equilibrium and of motion are 

 neceffary truths. 



Some philofophers have employed the principle of 

 final caufes in the demonflrations they have given of 

 the laws of motion, by endeavouring to deduce thofe 

 laws from ^he views the Author of nature may have 

 propofed to himfelf in the fixation of thofe rules. 

 Bofcovich, d'Alembert, and Buffon, reject this way 

 of reafoning, and, as it feems to me, on good grounds. 

 To afk after the hardnefs of the attractive and repel- 

 lent power, and the fimple but indifpenfable rules by 

 which that power operates, is doubtlefs juft as abfurd, 

 as if a man were to afk for the ultimate aim of exten- 

 sion, of impenetrability, he. The laws by which mat- 

 ter 



