Math. [L. = side.] Used in the following terms in Conic sections: latus rectum, a straight line drawn through the focus of a conic at right angles to the transverse diameter, the parameter; latus primarium (see quot. 1706); † latus transversum, the transverse diameter.
1702. Ralphson, Math. Dict. App. Conic Sections 11. In a Parabola the Rectangle of the Diameter, and Latus Rectum, is equal to the Rectangle of the Segments of the double Ordinate.
1706. Phillips (ed. Kersey), Latus primarium,… a Right-line drawn thro’ the Vertex, or Top of the Section, parallel to the Base of the Triangular Section of the Cone, and within it. Ibid., Latus Transversum, (in an Hyperbola) is a Right-line lying between the Vertex’s of the two opposite Sections.
1734. J. Ward, Introd. Math., IV. i. (ed. 6), 367. The Diameter of a Circle being that Right-line which passes thro’ its Centre or Focus … may … be properly call’d the Circle’s Latus Rectum: And altho’ it loses the Name of Diameter when the Circle degenerates into an Ellipsis, yet it retains the Name of Latus Rectum.
1859. Parkinson, Optics (1866), 256. A luminous point is placed at one of the foci of a semi-elliptic arc bounded by the axis major: prove that the whole illumination of the arc varies inversely as the latus rectum.
