| 单词 | focal axis |
| 释义 | > as lemmasfocal axis focal axis n. (a) Geometry the line passing through the focus or foci of a conic section, perpendicular to the directrix; (b) Optics the line which passes through the focal point (or points) of a curved mirror or lens and its centre; the line which passes through the centre of each lens in a compound lens, telescope, microscope, or other optical instrument; cf. axis n.1 9a. ΘΚΠ the world > relative properties > number > geometry > geometric space > [noun] > division or marking of > axis > passing through foci principal axis1704 transverse axis1704 transverse1743 longitudinal axis1744 focal axis1794 major axis1840 1794 G. Walker Treat. Conic Sections i. 58 Let A then be a point in the plane of a conic section, whose focus is F, directrix XX, and semi-parameter of the focal axis Z. 1828 C. Rumker in Mem. Astron. Soc. London (1829) 3 ii. 278 A telescope placed at the distance of six feet, so that its focal axis, produced, touched the screen and passed through the wire and cross when at rest. 1838 C. Tomlinson Stud. Man. Nat. Philos. ix. 416 The refracted rays..congregate, and produce upon the eye of the observer, placed in the focal axis, a greatly increased impression. 1885 C. Leudesdorf tr. L. Cremona Elements Projective Geom. 255 The point in which a directrix cuts the focal axis. 1905 Canad. Patent Office Rec. 2451/1 An arc lamp having its carbons disposed at an angle with the focal axis of the reflector. 1948 Amer. Math. Monthly 55 156 Our purpose is to examine the possibility of exhibiting the ellipse as the locus of a point on a rotating circle with a center moving on the focal axis. 2003 Physiol. & Biochem. Zool. 76 362/2 The middle web of each foot..was the web most consistently held perpendicular to the focal axis of the camera by the birds. 2011 Math. Mag. 84 91 The second focal circle now becomes a line perpendicular to the focal axis, which we call a floating focal line. < as lemmas |
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