Pl. umbræ. [L. umbra shade, shadow, UMBER sb.1 Cf. It. ombra, ombria, F. ombre.]
1. The shade of a deceased person; a phantom or ghost. Also fig.
1599. B. Jonson, Cynthia’s Rev., Induct. The umbræ or ghosts of some three or four playes, departed a dozen yeeres since.
1654. Gayton, Pleas. Notes, III. iii. 78. Such kind of Tones as these the Umbræ use, when they call upon Charon for a Boat.
1654. trans. Scudery’s Curia Pol., Pref. I have not troubled their famous umbra’s, whom an innocent kind of Magick hath so often summoned from their Royal Tombs.
1878. Besant & Rice, Celia’s Arb., xi. The faint and dimly-seen ghost of a possible repentance,… a spectral umbra pointing heavenward.
1883. Sat. Rev., 21 April, 486/1. Had Lord Beaconsfield ever indulged in such rashness, his umbra might point out … the disaster and the disgrace which have followed on their neglect of the warning.
b. (See quot.)
a. 1652. J. Smith, Sel. Disc., v. 176. The spiritual vehicle of the soul,… kind of umbra or aërial mantle in which the soul wraps herself.
2. A mere shadow of something. In quot. fig.
1634. Rainbow, Labour (1635), 33. The pride of those … who are their owne umbra’s, the servants and shadowes of their owne reflected shadowes.
b. An uninvited guest accompanying one who is invited.
1696. S. Sewall, Diary, 7 May. And let my dear Wife and all my children partake in this priviledge, and that not as Umbras, but on their own account.
1724. Moffet, Hesperineso-gr. (1755), 9. Most of the guests their umbra’s brought And sauce that money never bought.
c. 1800. R. Cumberland, John De Lancaster (1809), II. 71. Mr. David Owen and his umbra in the bottle green were missing.
1834. Lytton, Pompeii, I. iii. The sixth banqueter, who was the umbra of Clodius,… muttered also ‘Ædepol.’
3. Shade; shadow.
1638. Sir T. Herbert, Trav. (ed. 2), 5. To all in the temperate Zone, in the Sunnes Meridian their shadowes cast North, having past the Zenith, the shade or umbra becomes contrary.
1856. Ruskin, Mod. Paint., IV. V. v. § 11. If any of these wayward umbræ are faithfully remembered and set down by the painter, they nearly always have an unaccountable look.
4. Astr. a. The shadow cast by the earth or moon as visible in an eclipse; now spec. that portion in which the shadow is complete, as contrasted with the penumbra.
1679. Moxon, Math. Dict., Umbra, a shadow, a word oft used in the obscuration [sic] of Eclipses.
1812. Woodhouse, Astron., xxxv. 344. The cones of the umbra and penumbra … formed by lines drawn from the Sun and touching the Earth’s surface.
1833. Herschel, Astron., vi. 225. Owing to the great size of the earth, the cone of its umbra always projects far beyond the moon.
1868. Lockyer, Elem. Astron., § 237. If the Sun were a point of light merely, the shadow would be all umbra.
b. In sun-spots: (see quots.).
The earlier nucleus and umbra correspond respectively to the modern umbra and penumbra.
1788. Encycl. Brit. (ed. 3), II. 434/2. The increase of a spot is gradual, the breadth of the nucleus and umbra dilating at the same time. Ibid. Small umbræ are often seen without nuclei.
1860. Olmsted, Mech. Heavens, x. 103. A solar spot usually consists of two parts, the nucleus and the umbra…. The umbra is a wide margin, of lighter shade, and is often of greater extent than the nucleus.
1868. Lockyer, Guillemin’s Heavens (ed. 3), 32. The spots consist almost invariably of one or several dark portions called umbræ, which seem black when compared with the luminous parts of the disk.
1878. Newcomb, Pop. Astron., III. ii. 245. The shaded penumbra seems to form the sides of the cavity, while the umbra is the invisible bottom.
5. Algebra. A symbol that requires to be paired with another in order to denote a quantity.
1851. Sylvester, in Lond., etc. Phil. Mag., April, 296. Each quantity is now represented by two letters; the letters themselves, taken separately, being symbols neither of quantity nor of operation, but mere umbræ or ideal elements of quantitative symbols.
1855. Rankine, Misc. Sci. Papers (1881), 139. The tasinomic coefficients for oblique axes may be regarded as compounded of umbræ.
