In No. 6, he tells us, "that all this is likewise certain when taken the contrary way, viz. _from motion to rest_; for the body _a_ moving with a certain velocity, as _c_, requires a certain degree of force or resistance to stop that motion, &c. &c." that is, in other words, equal force is necessary to destroy force. It may be so. But how does that discover a vis inertiæ? would not the effect be the same _if there were no such thing_? A force 1 _f_ strikes a body 1 _a_, and moves it with the celerity 1 _c_, i. e. with the force 1 _f_: It requires, even according to our author, only an opposing 1 _f_ to stop it. But ought it not (if there were a vis inertiæ) to have not only the force 1 _f_, but an additional force equal to the force of vis inertiæ, that _obstinate power by which a body endeavours with_ all its might _to continue in its present state, whether of motion or rest_? I say, ought there not to be an opposing force equal to the sum of these?--The truth however is, that there is no body, how large soever, moving with any velocity, how great soever, but may be stopped by any opposing force, how small soever, continually applied. At least all our modern philosophers agree to tell us so.
Let me turn the thing in what light I please, I cannot discover the vis inertiæ, nor any effect of it. It is allowed by all, that a body 1 _a_ moving with a velocity 1 _c_, and a force 1 _f_ _striking another_ body 1 _a_ at rest, they will afterwards _move on together_, each with ½ _c_ and ½ _f_; which, as I said before, is equal in the whole to 1 _c_ and 1 _f_. If vis inertiæ, as in this case, neither abates the force nor the velocity of bodies, what does it, or how does it discover itself?
I imagine I may venture to conclude my observations on this piece, almost in the words of the author; that if the doctrines of the immateriality of the soul and the existence of God and of divine providence are demonstrable from no plainer principles, the _deist_ [i.e. _theist_] has a desperate cause in hand. I oppose _my theist_ to his atheist, because I think they are diametrically opposite; and not near of kin, as Mr. Whitfield seems to suppose; where (in his journal) he tells us, "_M. B. was a deist, I had almost said an atheist_;" that is, _chalk_, I had almost said _charcoal_.