[f. as prec. + -ITY.] The state or quality of being ECCENTRIC, q.v.
1. The quality of being abnormally centered; of not being concentric; of not having the axis in the center. † Orig. of planetary orbits: The fact of having the earth at a distance from the center (Obs. exc. Hist.). In mod. astronomy of a circle or arc in the celestial sphere: The fact of not being concentric with the sphere.
1551. Recorde, Cast. Knowl. (1556), 247. Sith the centre of the greater circle is by A, and the centre of the lesser circle is by B, the distaunce betweene A and B is the quantitie of their eccentricitye.
1594. J. Davis, Seamans Secr. (1607), B 3. All which differences are caused by the excentricity of her Orbe wherein she moueth.
1646. Sir T. Browne, Pseud. Ep., VI. x. 325. Yet by reason of his Excentricity, his [the Sun’s] motion is unequall.
1839. R. S. Robinson, Naut. Steam Eng., 107. o r, being the whole motion caused by the eccentricity … a portion of o r must be cut off by the eccentric pulley.
1849. Sir J. Herschel, Outlines Astron., iii. § 141 (1858), 83. The effect of excentricity is … to increase the arc representing the angle in question on one side of the circle.
† 2. The condition of not being centrally situated; distance from the center. Obs.
1825. T. Jefferson, Autobiog., Wks. 1859, I. 48. Its local eccentricity … lessened the general inclination towards it.
1836–7. Sir W. Hamilton, Metaph., xxxii. (1870), II. 241. The agitation of one place of a sheet of water expands itself, in wider and wider circles … although, in proportion to its eccentricity, it is always becoming fainter.
3. Of a curve: Deviation from circular form.
1696. Whiston, The. Earth, I. (1722), 18. All degrees of Eccentricity make Ellipses of all species.
1868. Lockyer, Guillemin’s Heavens (ed. 3), 72. The orbit of Mercury is very elongated, or, in astronomical language, its excentricity is considerable.
b. as a measurable quantity.
The eccentricity of an ellipse was formerly defined as the distance between the center and one of the foci; it is now represented as an abstract number, e.g., as the ratio of the focal distance of the center to the semi-major-axis. The more modern expression, however, for the eccentricity of all conic sections is the ratio of the focal distance (of any point in the curve) to the distance from the directrix. In the case of the ellipse this is numerically identical with the ratio previously mentioned.
1726. trans. Gregory’s Astron., I. 71. The right Line AP, connecting the Apsides … the Line of the Apsides; the Part CS of it, the Excentricity.
1787. Bonnycastle, Astron., vi. (ed. 4), 90. The distance between the centre of the ellipse O, and one of its foci F, is called its eccentricity.
1854. Moseley, Astron., lxxiii. (ed. 4), 209–10. Ellipses whose foci … are near one another … are called ellipses of small eccentricity.
1881. C. Taylor, Geom. Conics, 164. Having given four points and the eccentricity of a hyperbola … shew how to construct the curve.
4. The quality or habit of deviating from what is usual or regular; irregularity, oddity, whimsicality.
1794. R. J. Sulivan, View Nat., V. 187. An excursion, for the eccentricity of which I shall most probably be condemned.
1859. Mill, Liberty, iii. (1865), 39/2. Eccentricity has always abounded when and where strength of character has abounded.
1886. L. Forbes Winslow, in Pall Mall Gaz., 29 April, 4/1. What in some persons is called eccentricity, in others would be called insanity.
b. concr. An instance of deviation from what is usual, an extravagance. Also pl.
1657. Colvil, Whigs Supplic. (1751), 49. The like uncertainty he sees In change of Excentricities.
1818. Mrs. Shelley, Frankenst., i. (1865), 10. To render their seeming eccentricities consistent for ever.
1856. Emerson, Eng. Traits, vi. Manners, Wks. (Bohn), II. 47. I know not where any personal eccentricity is so freely allowed.
1870. Hawthorne, Eng. Note-bks. (1879), II. 196. Miscellaneous eccentricities of sculpture.
