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T. IV, Vol. 2
p5 Radius

Article by Georges Lafaye in

Daremberg & Saglio,
Dictionnaire des Antiquités Grecques et Romaines,
Librairie Hachette et Cie., Paris, 1877‑1919.

translation and © William P. Thayer

RADIUS.​1 — Stick, wand, spoke.

1. A branch of a stake in an entrenchment. This meaning is based on a passage of Livy known from a single manuscript, the reading of which has seemed suspect, perhaps wrongly so. Radii may well have been the proper designation for the sharp entangled branches, the spikes that bristled on the stipites and the valli in the palisades of Roman camps [vallum].2

2. The wand or pointer used by professors to bring a point, a line, or a drawing to the attention of their students (fig. 5217). It was especially useful to astronomers in the study of the celestial sphere; it thus was made one of their chief attributes, as is attested by a painting from Pompeii depicting the muse Urania (fig. 5912).​3 The radius was used by astronomers, geographers, mathematicians, geometricians to draw their numbers and figures on the surface of the sand that filled the abacus [abacus, I],​4 so that "sand and pointer, pulvis et radius" are for Cicero the very insignia of their profession. When the ancients brought to mind a Conon, a Euclid or an Archimedes, they always saw them radius in hand.5

[A woodcut of a woman in a long robe, seated on an armless and almost backless chair, holding in her left hand a sphere, about the size of a volleyball, and pointing to it with a small, thin, tapering wand in her right. She is the muse of astronomy, Urania; the woodcut is meant to illustrate the Graeco-Roman 'radius' or pointer.]

Fig. 5912. — Pointer.

3. A shuttle (κερκίς), a small sharp stick around which the weaver winds the thread of the weft to pass it thru the warp [textrinum].6

4. The spoke (ἀκτίς) of a radiate crown [figs. 646, 651, 653, 655, etc.].7

5. The spoke (ἀκτίς, κνήμη, ῥάδις)​8 of a wheel [currus, plaustrum, etc.].

The Author's Notes:

1 Perhaps derived from Greek ῥάβδος, which has about the same range of meanings; Bréal and Bailly, Dict. étym. lat. s.v.; synonym virga in Serv. ad Virg. Ecl. III.40.

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2 Acuti aliusque per alium immissi radii, Liv. XXXIII.5.11; the radii of codex Bambergensis (B) has been emended to rami by Madvig, Emend. Livianae2 (1877), an emendation followed ad loc. by Weissenborn.

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3 Pitt. d'Ercol. II, 8, p53; Millin, Gal. Myth. 23, 75; Müller-Wieseler, Denkm. d. alt. Kunst, II, 58, 740; Helbig, Wangem. Campan, n889, Pythagoras pointing to a sphere with a radius; imperial coins of Samos, Barclay Head, Catal. of the Greek Coins in the Brit. Museum, Ionia, Samos, n237, 257, 351, 364, pl. XXXVII, 14.

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4 Or on the sand of the palaestrae [educatio, pp472, 473]. See also the mosaic given the name of "Plato's Academy" (fig. 2541).

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5 Cic. Tusc. V.23, where it is not a compass [circinus]; Virg. Ecl. III.40 and Serv. ad loc.; Aen. VI.850; Boeth. Geom. Eucl. II, p1352 Migne; Martian. Capell. IV.337; VI.580; VII.728.

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6 Lucr. V.1352; Virg. Aen. IX.476; Ov. Fast. III.819; Met. IV.275; VI.56, 132.

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7 Flor. IV.2.91.

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8 Varr. R. R. III.5.15; Virg. Georg. II.444; Aen. VI.616; Ov. Met. II.318; Val. Flacc. VI.414. Κνήμη, Poll. I.144, X.157; Eustath. p598, 4; Hesych. s.v. There is no reason to suppose with Rich, Dict. of Ant., that κνήμη was reserved for a particular shape of spoke. Ῥάδις, Edict. Diocl. XV.5.

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