CHAP. V. 

 OF MOTION AND REST. 



Newtonian Theory of Motion and Reft. Vis inertia. Laws of 

 Motion. 



E S I D E S the principles of gravitation and re- 

 pulfion, there are other laws to which all matter 

 in certain circumftances appears to be fubjed ; thefe 

 are termed by modern philofophers the laws of motion, 

 fince they relate to that change of place or fitualiori 

 of bodies which is denominated motion, to the force 

 which is neceffary to this effect, and the velocity which 

 is given to moving bodies by the application of this 

 force or power. 



An attentive and judicious obfervation of the ufual 

 courfe of nature, enabled Sir Ifaac Newton to reduce 

 the general principles or Jaws of motion to the three 

 following axioms. There appears little neceffity to 

 illuftrate them by particular inftances, fince they are 

 confirmed by conftant and univerfal experience ; and 

 however the application of thefe principles to the mo- 

 tions of the heavenly bodies, or to thofe departments 

 of nature which are out of the reach of our obferva- 

 tion, may be contefted, their truth and utility, with 

 refpect at lead to thofe bodies with which we are beft 

 acquainted and have the moil intimate connexion, will 

 fcarcely admit of difpute. 



I. All bodies are perfectly indifferent to motion and 

 reft. In other words, a body, if once at reft, will na- 

 turally 



