下文引自"Visual Complex Analysis, Oxford University Press,Tristan Needham"的前言

It is fairly well known that Newton's original 1665 version of the calculus was different from the one we learn today: its essence was the manipulation of power series, which Newton likened to the manipulation of decimal expansions in arithmetic. The symbolic calculus - the one in every standard textbook, and the one now associated with the name of Leibniz - was also perfectly familiar to Newton, but apparently it was of only incidental interest to him. After all, armed with his power series, Newton could evaluate an integral like ∫e(-x2)dx just as easily as ∫sinxdx. Let Leibniz try that!
It is less well known that around 1680 Newton became disenchanted with both these approaches, whereupon he proceeded to develop a third version of calculus, based on geometry. This "geometric calculus" is the mathematical engine that propels the brilliant physics of Newton's Principia.

然后举了一个带图的微分例子.

Only gradully did I come to realize how naturally this mode of thought could be appplied-almost exactly 300 years later! - to the geometry of the complex plane.