vbl. sb. Also centring. [f. center, CENTRE v. + -ING1; the spelling on the analogy of settle, etc., would be centring, but as the word is of 3 syllables, centering (more rarely centreing) is generally used, esp. in technical senses.]
1. See CENTRING.
2. A placing in the center or making central; the bringing of two or more centers into coincidence; spec. the setting of lenses so that their axes are in the same straight line.
1768. E. Buys, Dict. Terms of Art, Centering of an Optick-glass, is the grinding it so that the thickest part is exactly in the Middle.
1831. Brewster, Optics, xliii. 358. The … risk of imperfect centering, or of the axes of the three lenses not being in the same straight line.
1881. Edin. Rev., Oct., 537. Mr. Carter recommends that people should look to the centreing of their spectacles for themselves.
1883. Daily News, 10 Sept., 6/1. When the ring rotates at high speed, any slight error of centring tends to injure the ring.
3. Arch. ‘The temporary woodwork or framing, whereon any vaulted work is constructed’ (Gwilt).
a. 1766. Parentalia, in Entick, London (1766), IV. 206. Both centering and scaffolding.
1861. Smiles, Engineers, II. 182. The centering upon which the arches of the bridge were built.
1879. Sir G. Scott, Lect. Archit., II. 194. The use of continuous timber centering.
1885. Ruskin, Præterita, iii. Well-made centreings … made this model … attractive.
4. attrib. and Comb., as centering motion, punch (sense 2), stone (sense 3).
1855. I. Taylor, Restor. Belief, 138. A centering-stone of that structure which in the age of the Antonines had arched over the Roman world.
1883. Knowledge, 27 April. i, Secondary stage with centering motion [in a microscope].
1884. F. J. Britten, Watch & Clockm., 148. Another spring … carrying a fine centreing punch.
