| 单词 |
pyramidion |
| 释义 |
‖ pyramidion|pɪrəˈmɪdɪɒn|
Pl. -ia, -ions.
[mod.L., a. Gr. type *πῡραµίδιον, dim. of πῡραµίς pyramid. Cf. F. pyramidion (Littré).]
A small pyramid; spec. in Arch., the pointed pyramidal portion forming the apex of an obelisk.
1840Bonomi in Trans. Roy. Soc. Lit. (1843) Ser. ii. I. 161 The height of the pyramidion should be about a tenth of the whole length. 1850J. Leitch tr. C. O. Müller's Anc. Art §224 Four-sided pillars on a low base, which diminish upwards and end in a pyramidion, usually of granite. 1877W. R. Cooper Egypt. Obelisks i. (1878) 2 Its apex is abruptly terminated by a small pyramidion, whose faces are inclined at about an angle of sixty degrees.
b. Cryst. Used by Story-Maskelyne in naming figures formed from other solid figures by constructing a small pyramid upon each face of the original.
1895Story-Maskelyne Crystallogr. §167 Holo-symmetrical forms of this [the cubic] system:..2. The triakis⁓octahedron or the octahedrid pyramidion...4. The tetrakis⁓hexahedron or the cube-pyramidion..: the term pyramidion being employed in the case of forms in which a pyramidion or small pyramid composed of similar isosceles triangles surmounts every face of a simpler figure..: such a figure is then an isoscelohedron. Ibid. §172 The figure presents the aspect of a cube each face of which is surmounted by an obtuse pyramid, and it may, on this account, be termed the cube pyramidion. |
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