Tractatus de Methodis Serierum et Fluxionum

The Tractatus de Methodis Serierum et Fluxionum, written by Isaac Newton around 1671, is a foundational work in the development of calculus. In this treatise, Newton introduced his concept of "fluxions," which is the original term for the derivative in mathematics.123

Newton described a "fluent" as a varying quantity and its "fluxion" as its instantaneous rate of change. The work outlines two primary problems of calculus: finding the fluxion of a fluent (now known as finding the derivative of a function) and finding a fluent given its fluxion (now known as integration). Newton's terminology and notation for fluxions were eventually superseded by those developed by G.W. Leibniz. The "method of fluxions" is essentially synonymous with differential calculus.34