| 释义 |
helicoid, a. and n.|ˈhɛlɪkɔɪd|
Also 7 -oeid.
[mod. ad. Gr. ἑλικοειδής of winding or spiral form, f. ἕλιξ helix + εἶδος shape: see -oid. Cf. F. hélicoïde (1704 in Hatz.-Darm.).]
A. adj.
1. Having the form of a helix; screw-shaped; spiral. Chiefly in Zool. of shells, and in Bot. of forms of inflorescence, etc. helicoid parabola, in Geom. a spiral curve formed by twisting the common parabola so that its axis becomes a circle, the ordinates still remaining perpendicular to the axis and in the same plane with it.
1704J. Harris Lex. Techn., Helicoid Parabola, or the Parabolick Spiral, is a Curve which arises from the Supposition of the Axis of the common Apollonian Parabola's being bent round into the Periphery of a Circle. 1796Hutton Math. Dict., Helicoid Parabola, or the Parabolic Spiral. 1835Lindley Introd. Bot. (1848) I. 324 The cyme..is helicoid or scorpioid. 1849Dana Geol. App. i. (1850) 721 The fusiform helicoid cavity. 1875Bennett & Dyer Sachs' Bot. 521 The Unilateral Helicoid Cyme is a sympodial cyme in which the median plane of each of the successive axes..is always situated on the same side.
2. Zool. Belonging to or resembling the Helicidæ, gastropodous molluscs including the snail.
1876tr. Beneden's Anim. Parasites 37 Molluscs..with a helicoid shell, similar to that of a small natica.
B. n.
1. Something of a helicoid or spiral form.
1699Garth Dispens. 80 Shells, Some Helicoeids, some Conical appear, These Miters emulate, Those, Turbans are. 1959New Scientist 5 Mar. 515/2 Inside the silencer cylinders there are two helicoids which have the effect of mincing the air flow passing through the cylinder.
2. Geom.
†a. = Helicoid parabola: see A. 1. Obs.
b. A warped surface generated by a moving straight line which always passes through or touches a fixed helix.
1842Brande Dict. Sc., etc. 547/1 [This] spiral curve..is the helicoid. 1855Davies & Peck Math. Dict., Helicoid, a warped surface, which may be generated by a straight line moving in such a manner that each point of it shall have a uniform motion in the direction of a fixed straight line, and at the same time a uniform angular motion about it. |