 But Newton’s exploitation of the kinematic conception went much deeper than had Barrow’s. In De Analysi, for example, Newton introduces a notation for the “momentary increment” (moment)—evidently meant to represent a moment or instant of time—of the abscissa or the area of a curve, with the abscissa itself representing time. This “moment”—effectively the same as the infinitesimal quantities previously introduced by Fermat and Barrow—Newton denotes by \(o\) in the case of the abscissa, and by \(ov\) in the case of the area. From the fact that Newton uses the letter \(v\) for the ordinate, it may be inferred that Newton is thinking of the curve as being a graph of velocity against time. By considering the moving line, or ordinate, as the moment of the area Newton established the generality of and reciprocal relationship between the operations of differentiation and integration, a fact that Barrow had grasped but had not put to systematic use. Before Newton, quadrature or integration had rested ultimately “on some process through which elemental triangles or rectangles were added together” (Baron 1969 [1987: 268]), that is, on the method of indivisibles. Newton’s explicit treatment of integration as inverse differentiation was the key to the integral calculus.