Newton's Method of Fluxions was formally published posthumously, but following Leibniz's publication of the calculus a bitter rivalry erupted between the two mathematicians over who had developed the calculus first and so Newton no longer hid his knowledge of fluxions.
^The Method of Fluxions and Infinite Series: With Its Application to the Geometry of Curve-lines. By Sir Isaac Newton, Translated from the Author's Latin Original Not Yet Made Publick. To which is Subjoin'd, a Perpetual Comment Upon the Whole Work, By John Colson, Sir Isaac Newton. Henry Woodfall; and sold by John Nourse, 1736.