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ABSCISSA, in Conies, a Part of the Diameter, or transverse Axis of a Conic Section, intercepted between the Vertex or Tome other fix'd Point, and a Semiordinate. See CONIC Section.

Such are the Lines AP, AP, &c. (Tab. Conics, Fig. 20.) intercepted between the Vertex A and the Semiordinates PM, PM, &c.

They are called Abscisses of the Latin Absindo, I cut off ; as being Parts cut off from the Axis. Others call 'em Sagittæ, Arrows. See SAGITTA.

In the Parabola, the Absciss is a third Proportional to the Parameter and Semiordinate ; and the Parameter a third Proportional to the Absciss and Semiordinate. See Paraboia, Semiordinate, &c.

In the Ellipsis, the Square of the Semiordinate is equal to the Rectangle of the Parameter into the Abscisse, subtracting another Rectangle of the same Abscisse, into a fourth Proportional to the Axis, Parameter, and Abscisse. See ELLIPSIS.

In the Hyperbola, the Squares of the Semiordinates are to each other as the Rectangles of the Abscisse into another Line, compos'd of the Abscisse and the transverse Axis. See HYPERBOLA.