PHYSICAL AND LITERARY. 99 



deed. Upon the fuppofition of perfea 

 inaaivity, the quantity of motion muft 

 remain unchanged : And we here abftrad 

 entirely from elafticity, whofe eflfeds pro- 

 ceed from a real aaivity, and have no re- 

 lation to what is called the vis inertk.To 

 find the length of the fpace defcribed by 

 the impinging body, we divide the fpace 

 by the quantity of matter, which is as it 

 were the bafc. And, to have the length 

 of the fecond fpace defcribed by the two 

 bodies conjointly, we muft divide the 

 fame fpace by the mafs of matter in both. 

 As the divifor increafes, the quotient muft 

 jiiminifli in the fame proportion. 



Were we indeed to examine very mi- 

 nutely the gradual communication of mo- 

 tion from one body to another, vve fhall 

 find a real aaivity concerned in the ope- 

 ration ; but then it is not of that fort a- 

 gainft which we are now contending. It 

 is that aaive force known by the name 

 of the attra^ion of cohefton, which there 

 takes place. When any part of a body 

 is pulled or ftruck upon by any moving 

 power, it would neceffarily be feparated 



from 



