ON THE LAWS OF NATURE. IOJ 



h to be confidered. He confines it to this, to know, 

 whether the laws of equilibrium and of motion which 

 gire obfervable in nature, are different from thole which, 

 matter left to itfelf will follow ? 



According to the judgement of that great geometer, 

 it is of the higheft evidence, that, if we merely fup- 

 pofe the exigence of matter and motion, from this 

 twofold exiftence, certain effects rnufr. neceffarily remit. 

 A body, that is fet in motion by fome caufe, mufl: 

 either flop after running fome time, or mufl always 

 continue to move. A body, which, while it moves, 

 is endeavouring to follow the two fides of a parallelo- 

 gram, mufl neceffarily defcribe either the diagonal or 

 fome other line. If feveral bodies be in motion and 

 llrike againfl each other; then, in confequence of 

 their reciprocal impenetrability, fome alteration in the 

 lituation of all thefe bodies rnufr. neceffarily enfue; 

 or, at leaft, in the lituation of fome of them. Now, 

 among the various poflible effects, whether in the mo- 

 tion of an infulated body, or in the motion of feveral 

 bodies acting on each other, there is neceffarily one 

 which mufl: infallibly take place as a confequence of 

 the bare exiilence of matter, without regard to any 

 other principle. 



• According to d'Alembert's rule, the philofopher 

 fliould ffcrive to find out by reafoning, in which of the 

 laws of ftatics and mechanics matter left to itfelf would 

 be. 



He mufl next difcover, by obfervation, what laws 

 are actually met with in the world. If thofe which his 

 reafoning fupplies him with be different from thofe 



which 



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