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 p706  Article by Philip Smith, B.A., of the University of London
on p706 of

William Smith, D.C.L., LL.D.:
A Dictionary of Greek and Roman Antiquities, John Murray, London, 1875.

LIBRA or AS, a pound, the unit of weight among the Romans and Italians. Many ancient specimens of this weight, its parts and multiples, have come down to us; but of these some are imperfect, and the rest differ so much in weight that no satisfactory conclusion can be drawn from them. The difference between some of these specimens is as much as two ounces. An account of some of the most remarkable of them is given by Hussey (Ancient Weights, &c. IX §3), and Böckh (Metrolog. Untersuch. p170). This variety is to be accounted for partly by the well-known carelessness of the Romans in keeping to their standards of weight, and partly by the fact that many of the extant weights are from provincial towns, in which this carelessness was notoriously greater than in the metropolis.

The computation of the weight of the libra has been attempted in two ways, which are more fully discussed under Pondera. The method which has been followed by most writers is that of deducing it from the weights of the silver coins — a process which gives, according to Hussey, 5040 grains, and according to Wurm and Böckh, a little more than 5054. The other plan is that of weighing the quantity of water held by the Congius of Vespasian, which originally contained 10 Roman pounds, which gives a result of about 5200 grains. According to the former computation, it was somewhat less than 11½, according to the latter, somewhat more than 11¾ ounces avoirdupois; and, according to either, its value may be roughly stated as a little less than ¾th of a pound avoirdupois.

The uncial division, which has been noticed in speaking of the coin As, was also applied to the weight (see the Tables). The divisions of the ounce are given under Uncia. Where the word pondo, or its abbreviations P. or POND., occur with a simple number, the weight understood is the libra.

The name libra was also given to a measure of horn divided into twelve equal parts (unciae) by lines marked on it, and used for measuring oil (Suet. Caes. c38; Galen, de Comp. Med. Gen. I.17, VI.8; Horat. Sat. II.2.59‑61).

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