| 释义 |
octad|ˈɒktæd|
[ad. L. octas, octad-, a. Gr. ὀκτάς, -άδα a group of eight: see -ad 1 a.]
1. A group or series of eight; spec. in ancient systems of arithmetical notation: A group or series of eight characters corresponding to successive powers of ten (analogous to the groups of six figures marking millions, billions, etc. now used).
1883Sir E. C. Bayley Geneal. Mod. Numerals ii. in Jrnl. R. Asiat. Soc. XV. 48 [The Greeks] had, however, a system of ‘octads’ and ‘tetrads’ for expressing numbers of very high value. Ibid. 49 By collecting the alphabetical signs in groups of eight or ‘octads’, decimally arranged.
2. Math.
a. Mod. Geom. The set of eight intersections of three quadric surfaces.
1889Cayley in Messenger XVIII. 149 The eight points of intersection of any three quadric surfaces are an octad.
†b. pl. A system of eight imaginaries analogous to quaternions, also called octaves. Obs.
1845J. T. Graves in Phil. Mag. XXVI. 315–20. 18.. Cayley Collected Papers I. 586.
3. Chem. An element or radical that has the combining power of eight units, i.e. of eight atoms of hydrogen.
1877Watts Fownes' Chem. I. 268 Ru[bidium] and Os[mium] form tetroxides (analogous to octochlorides), and may therefore be regarded as octads.
Hence octadic |ɒkˈtædɪk| a., of or pertaining to an octad. octadic surface (Mod. Geom.), a quartic surface, eight of whose nodes form an octad.
1870Cayley in Proc. Lond. Math. Soc. III. 20. |