‖ tractrix Geom.
(ˈtræktrɪks)
Pl. ˈtractrices (-ɪsiːz).
[mod.L. (Huygens) fem. of tractor: see tractor, and cf. directrix.]
A curve such that the intercept on the tangent between its point of contact and a fixed straight line is constant; so called as being traced by the centre of gyration of a rigid rod of which one end is moved along the fixed straight line, or as being the form assumed by an inextensible string which is first laid straight upon a plane surface, and one end of it then drawn in a direction at right angles to that in which the string was laid. Also, one of a class of curves similarly traced, e.g. by movement along a fixed curve.
| 1727–41 Chambers Cycl., Tractrix, in geometry, a curve line, called also catenaria. [Error: the tractrix is the involute of the catenary, not the catenary itself.] 1843 Penny Cycl. XXV. 109/2 Tractrix, or Tractory, the name given to a curve described by a heavy point attached to a string, the other end of which is moved along a given straight line or curve. 1852 Salmon Higher Plane Curves vii. (1879) 289 The involute of the catenary is therefore a curve such that the intercept SN, on its tangent between the point of contact and a fixed right line, is constant. Such a curve is called the tractrix. 1877 B. Williamson Int. Calc. (ed. 2) vii. Ex. 9. |