| 释义 |
nutation|njuːˈteɪʃən|
[ad. L. nūtātiōn-em, noun of action f. nūtāre to nod. So F. nutation, It. nutazione, Sp. nutacion.]
1. The action of nodding the head; an instance of this. Also transf.
1612Cotta Disc. Dang. Pract. Phys. i. v. 42 The nutation and staggering of nature doth make warie proceeding. 1656Blount Glossogr., Nutation, nodding, as one doth when he sits sleeping. 1728Pope Dunc. ii. 409 So from the mid-most the nutation spreads Round, and more round, o'er all the sea of heads. 1859J. G. Saxe Poems, Richard of Gloster, Ugly relations Who'll be very apt to disturb your nutations By unpleasant allusions, and rude observations! 1897Allbutt's Syst. Med. III. 78 The cervical vertebræ are usually attacked first; a difficulty is felt in rotation and nutation.
2. a. Astr. A slight oscillation of the earth's axis; now spec. that by which the pole of the equator would describe a small ellipse in about 19 years, and which actually renders its motion round the pole of the ecliptic (see precession) wavy instead of purely circular.
1715tr. Gregory's Astron. (1726) I. 502 Another Nutation arising from another Cause may produce all this diversity in the distance of the Pole-Star from the Pole. 1748Bradley in Phil. Trans. XLV. 13 This apparent Motion, in both those Stars, might proceed from a Nutation in the Earth's Axis. Ibid. 15 The Changes which I had observed, both in the annual Precession and Nutation. 1789E. Darwin Bot. Gard. ii. (1791) 63 Marking her solar and sidereal day, Her slow nutation, and her varying clime. 1842Penny Cycl. XXII. 448/1 A large number of stars..have a slight apparent motion not attributable either to precession or nutation. 1882R. Proctor in Knowledge 220 A more perfect method of illustrating the precession of the equinoxes or the earth's reeling, and also the nutation (or nodding, still to be described).
b. The oscillation of a top in spinning.
1879Thomson & Tait Nat. Phil. I. i. §107 If a Troughton's top be placed on its pivot in any inclined position, and then spun off with very great angular velocity about its axis of figure, the nutation will be insensible.
c. Movement (as of a beam or aerial) by which an axis is made to describe a cone. (Analogous to the precession of a spinning top rather than its nutation.)
1947Bell Syst. Techn. Jrnl. XXVI. 307 The axis of the beam was rotated in an orbit by ‘nutation’ about the mechanical axis of the antenna. 1966McGraw-Hill Encycl. Sci. & Technol. XI. 204/2 Either the feed or the reflector whirls rapidly in a manner that causes the beam axis to describe a circular cone; this motion of the beam axis is called nutation.
3. Curvature in the stem of a growing plant.
1789E. Darwin Bot. Gard. ii. (1791) 19 The sun flower follows the course of the sun by nutation, not by twisting its stem. 1816Keith Phys. Bot. II. 447 Such flowers are designated by the appellation of Heliotropes, on account of their following the course of the sun; and the movement they thus exhibit is denominated their nutation. 1880C. & F. Darwin Movem. Pl. 1 The stem of a climbing plant, which bends successively to all points of the compass, so that the tip revolves. This movement has been called by Sachs ‘revolving nutation’. |