Sentence:  And let him ſuppoſe, that if a Man in the beginning of the World, or four or five hundred Years ago, had laid a little round Marble upon a Table, and to put the ſame in Motion, had given it a <WSD>Fillip</WSD> with his Finger; the ſaid Marble, according to the abovemention'd Law of Nature, would (if no other Force had oppos'd its Motion) have moved to this very Minute with the ſame Velocity in a Right-Line, and without ceaſing, would have continued to run in the ſame Line ſuch a Length, as no Man could determine the end of. 
Meaning of the word marked with <WSD> tags:  The action of holding the tip of a finger against the thumb and then releasing it with a snap; a flick.