| 释义 |
trigonal, a. (n.)|ˈtrɪgənəl|
[ad. L. trigōnāl-is, f. trigōn-um: see prec. and -al1.]
A. adj.
1. a. Of, pertaining or relating to, a trigon or triangle; of the form of a triangle, having three angles, triangular. (In quot. 1570 = triangular 2 b.)
trigonal co-ordinates (Geom.), a system of co-ordinates related in a particular way to trilinear co-ordinates, invented by S. Levi in 1876.
1570Billingsley Euclid vii. def. x. 186, 6 in diuers respectes is a lineall number..and also a trigonall or trianguler number. 1571Digges Pantom. iv. def. viii. T j b, When any equiangle triangle..is..described within a circle..[its] sides are called the trigonal..Cordes of that circle. 1849Freeman Archit. ii. v. 170 A fine lofty pile, with..three trigonalapses. 1891Cent. Dict. s.v., A linear equation in trigonal coördinates of the first class represents a cubic [curve].
b. Geom. and Cryst. Applied to a solid figure with triangular faces, or having some other relation to a triangle. Also, Having a relation to three angles: as trigonal quoin, a solid angle contained by three plane angles; trigonal symmetry, the symmetry of a figure or body which coincides with its original position after rotation about an axis through an angle of 120° or 240°.
1878Gurney Crystallogr. 38 If three symmetral planes and no more intersect in the same straight line, it is called an axis of trigonal symmetry. 1891Cent. Dict. s.v. Trisoctahedron, The trigonal trisoctahedron has each face an isosceles triangle. 1895Story-Maskelyne Crystallogr. iv. §79. 98 A plane figure may..be symmetrical with regard to a point within it as a pole of symmetry... Where n = 2, or = 3, 4, or 6, the symmetry may be defined as being diagonal, trigonal, tetragonal, or hexagonal. Ibid. vii. §180. 211 The trigonal dodecahedron,..a tetrahedron with a three-faced pyramid on each of its faces. Ibid. §257. 302 The trigonal trapezohedron..has trapezoids for its faces, which meet in two trigonal quoins.
c. Chem. Characterized by three orbitals lying in a plane and directed to the corners of an equilateral triangle.
1939L. Pauling Nature Chem. Bond 429/2 (Index), Trigonal bond orbitals. 1961A. Streitwieser Molecular Orbital Theory i. 20 Linear combinations of s- and two of the p-orbitals result in three trigonal sp2-orbitals. 1979B. M. Gimarc Molecular Struct. & Bonding iv. 79 These complexes are mainly trigonal bipyramidal..in structure with the bonds to the axial ligands..being slightly longer than those to the equatorial ligands.
2. Triangular in section, triquetrous: now esp. in Zool. and Bot.
1571Digges Pantom. iv. xi. Y iij b, The solide of Tetraedron may..be parted into 4 equal Trigonal Pyramides. a1728Woodward Nat. Hist. Fossils (1729) i. 158 Spar of a yellow Hue, shot into numerous trigonal pointed Shoots. 1753Chambers Cycl. Supp. s.v. Leaf, Trigonal Leaf, one much like the triquetrous, only that..the several faces are each hollowed in form of channels. Ibid., Lilium, the lilly..The pistil..finally becomes an oblong and trigonal fruit. 1854Woodward Mollusca ii. 225 Shell impunctate, oblong, or trigonal. 1895W. M. Macpherson Monymusk v. 76 A plain roundheaded door with a trigonal hood.
3. Astrol. Relating to, or of the nature of, a trigon (in either sense): see prec. 2.
1603Sir C. Heydon Jud. Astrol. xxi. 470 All trigonall aspects doe accord. 1635Swan Spec. M. v. §2 (1643) 105 The Trigonall revolution..of the Planets [cf. trigon 2 quot. 1704].
†4. Of or pertaining to a trigon (trigon 3 a). Also as n., short for trigonal instrument. Obs. rare.
1593T. Fale Dialling 39 Your Diall being made, and the Stile placed therein: take your Trigonall Instrument, and set it upon the Stile, so that the whole Diameter thereof may stand plaine upon the edge or upper part, the centre A, of your Instrument... Then fasten a thread at the uppermost end of your Trigonall in every line of the signes so yt you may direct downeward by the centre A, to the plat of your Diall: and..then moving the Trigonall on the right hand, so that the thread may be stretched on the left hand, make there likewise a prick upon the plat.
B. n.
1. See A. 4.
2. Anat. = trigone, trigonum 2 (Cent. Dict.).
Hence ˈtrigonally adv., (a) triangularly (rare—0); (b) Chem., in a trigonal manner.
1891Cent. Dict. 1962P. J. & B. Durrant Introd. Adv. Inorganic Chem. xviii. 590 (heading) Compounds in which the carbon atom is trigonally hybridised. 1982Nature 25 Feb. 658/1 The borates, where trigonally and tetrahedrally bonded atoms may occur. |