on and all that you got by it is deſtroyed, and goes out together. And this is univerſally true, be the Subjectt what it will, throughout all the Branches of humane Knowledge; in any other of which, I believe. Men would hardly admit ſuch a reaſoning as this, which in Mathematics is accepted for Demonſtration.
XVII. It may not be amiſs to obſerve, that the Method for finding the Fluxion of a Rectangle of two flowing Quantities, as it is ſet forth in the Treatiſe of Quadratures, differs from the abovementioned taken from the ſecond Book of the Principles, and is in effect the ſame with that uſed in the calculus differentialis[1]. For the ſuppoſing a Quantity infinitely diminiſhied and therefore rejecting it, is in effect the rejecting an Infiniteſimal; and indeed it requires a marvellous ſharpneſs of Diſcernment, to be able to diſtinguiſh between evaneſcent Increments and infiniteſimal Differences. It may perhaps be ſaid that the Quantity being infinitely diminished becomes nothing, and ſo nothing is rejected. But according to the
- ↑ Analyſe des infiniment petits, part. 1. prop. 2.
