directrix
(dɪˈrɛktrɪks)
Pl. -ices.
[a. med. or mod.L. dīrectrix, fem. of *dīrector director.]
1. = directress.
| 1622 H. Sydenham Serm. Sol. Occ. ii. (1637) 112 As if the same pen had beene as well the directrix of the languages, as the truth. 1656 Artif. Handsom. (1662) 31 The Regent and directrix of the whole bodies culture, motion, and welfare. 1678 Cudworth Intell. Syst. i. iii. §37. 164 The several parts..acting alone..without any common directrix. 1843 H. Rogers Ess. (1860) III. 40 An unfailing directrix in all difficulties. 1892 J. Rickaby Aquinas Ethicus I. 224 Reason is the directrix of human acts. |
2. Geom. † a. = dirigent n. 3; (see quot. 1753). Obs. b. A fixed line used in describing a curve or surface; spec. the straight line the distance from which of any point on a conic bears a constant ratio to the distance of the same point from the focus.
| 1702 Ralphson Math. Dict., Directrix of the Conchoid. Ibid. App., The two Conchoids, whereof the line CD will be the common Asymptote, which is also called the Directrix. 1753 Chambers Cycl. Supp., Directrix, in geometry, the line of motion, along which the describing line, or surface, is carried in the Genesis of any plane or solid figure. 1758 Monthly Rev. 403 A certain circle on the same surface, which is, as it were, the conical directrix. 1807 Hutton Course Math. II. 117 If, through the point G, the line GH be drawn perpendicular to the axis, it is called the directrix of the parabola. 1840 Lardner Geom. xx. 269 Lines drawn perpendicular to the transverse axis, through the points D,D', are called directrices of the ellipse. |
3. directrix of electrodynamic action (of a given circuit): the magnetic force due to the circuit.
| 1881 Maxwell Electr. & Magn. II. 157 Their resultant is called by Ampère the directrix of the electrodynamic action. Ibid. 158 We shall henceforth speak of the directrix as the magnetic force due to the circuit. |