Also 7–8 æquator. [a. late L. æquātor one who makes equal, hence in late L. (circulus) æquator diei et noctis ‘the equalizer of day and night’ (cf. equinoctial), f. æquāre to make equal, f. æquus equal.]
1. Astr. A great circle of the celestial sphere, whose plane is perpendicular to the axis of the earth. (When the sun is in the equator, day and night are equal in length: hence the name.) Commonly called the EQUINOCTIAL.
c. 1391. Chaucer, Astrol., I. § 17. The middel cercle … is cleped also the weyere, equator of the day.
1594. J. Davis, Seamans Secr., II. (1607), H 2 b. When the Sunne commeth vpon the Equator, then the daies and nights are of one length through the whole worlde.
1682. Sir T. Browne, Chr. Mor. (1716), 121. The time might come when Capella, a noble Northern Star, would have its motion in the Æquator.
1726. trans. Gregory’s Astron., I. II. 295. The beginning of the Equator, from whence the Right Ascension of the Stars is reckoned, is where it intersects the Ecliptic.
1837. Whewell, Hist. Induct. Sc., III. i. § 8. I. 144. The circle which divided the sphere [of the heavens] exactly midway between these poles was called the equator.
2. Geog. A great circle of the earth, in the plane of the celestial equator, and equidistant from the two poles.
1612. Brerewood, Lang. & Relig., xiv. 149. That the Earth on the South side of the Æquator, should be of a more ponderous disposition then on the North.
1646. Sir T. Browne, Pseud. Ep., II. ii. 61. The Northern pole of the Loadstone attracteth a greater weight then the Southerne on this side the Equator.
1727. Thomson, Summer, 647. Mountains big with mines, That on the high equator ridgy rise.
1774. Goldsm., Nat. Hist. (1776), I. 11. A polar prospect, and a landscape at the equator, are as opposite in their appearances as in their situation.
1856. Emerson, Eng. Traits, Voy. Eng., Wks. (Bohn), II. 12. The sea-fire shines in her wake…. Near the equator, you can read small print by it.
fig. a. 1631. Donne, Select. (1840), 105. A Christian hath no solstice…; much less hath he any equator, where days and nights are equal, that is, a liberty to spend as much time ill, as well.
a. 1661. Fuller, Worthies, I. 39. It [the Reformation] is as it were the Æquator, or that remarkable Line, dividing between Eminent Prelates, Learned Writers, and Benefactors to the Publick, who lived Before or After it.
3. transf. A similarly situated circle on any heavenly (or, occasionally, any spherical) body.
1746. J. Parsons, Hum. Physiognomy, i. 14. Because Santorini, in his Figure of the Face, makes the Eye-lids meet upon the very Equator of the Eye-ball.
1834. Nat. Philos., Astron., iii. 83. (Usef. Knowl. Soc.). The great circle perpendicular to the axis of the moon, is called for a similar reason the equator of the moon.
1839. G. Bird, Nat. Philos., 351. In a sphere of quartz … at the equator.
1868. Lockyer, trans. Guillemin’s Heavens (ed. 3), 37. The rapidity of this movement varies regularly with their [Sun-spots’] distance from the solar equator.
b. Magnetic equator, an irregular line, passing round the earth in the neighborhood of the equator, on which the magnet has no dip; = Aclinic line (see ACLINIC).
1832. Nat. Philos., Magnetism, iii. § 98 (Usef. Knowl. Soc.). The magnetic equator.
1849. Mrs. Somerville, Connex. Phys. Sc., xxx. 342. A line encircling the earth, called the magnetic equator.
c. Equator of the magnet (see quots.).
1635. N. Carpenter, Geog. Del., I. iii. 60. The Magnet … is separated or diuided by a middle line or Æquator.
1837. Brewster, Magnet., 251. It is obvious … that the magnetic intensity increases from the equator to the poles.
1871. Tyndall, Fragm. Sc. (ed. 6), I. xv. 416. Hold the needle over the equator of the magnet.
1885. S. Thompson, Electr. & Magn., ii. § 78. The portion of the magnet which lies between the two poles is apparently less magnetic…. This region Gilbert called the equator of the magnet.
4. attrib. and Comb., as equator-sun; equatorwards adv., towards the equator.
1735. Thomson, Liberty, IV. 413. Those [paths of the sea] that, profuse Drunk by Equator-Suns, severely shine.
1875. Croll, Climate & T., x. 187. The pressure … impels the bottom-water equatorwards.
1884. Daily News, 2 Aug., 5/4. To continue the voyage equatorwards, you must sail up the White or Western Nile.
