the Roman land surveyors elaborated their system of mensuration, they found that the simplest method of expressing the fractional parts of the jugerum was to employ the old duodecimal method of the as. Nor is this without a parallel elsewhere. As the yard was the common English unit of linear measure, it was applied to the most common unit of land, the quarter of the hide, which was accordingly termed a yard of land, or a virgate (virga terrae). The English analogy is even still more complete, for as the as or foot-rod became the unit of weight, so in Cambridge the yard of butter is identical with the pound of butter[1].
Our next step will be to trace the process by which the as or rod became the general weight-unit, the pound (libra). The term libra is not the oldest Latin name for weight, for pondus or its cognate verb pendeo, which literally means to hang, is the true claimant for that position. Libra seems properly to mean the balance, as is seen from the legal formula (employed in Mancipatio) per aes et libram, by means of copper and the balance. From the fact that its chief use was to weigh asses of copper, the mass of an as came to be termed the weight par excellence, just as the most usual amount weighed in the Greek talanta (scales) became the talanton par excellence. This process can be illustrated by modern examples. Thus in the south of Ireland potatoes are sold by the unit of 21 lbs., which consequently is termed a weight, and instead of speaking of so many stones or hundredweights, everyone speaks of a weight of potatoes. But, as already remarked, it was only at a comparatively late epoch that the bars of copper were weighed. It would be only with the growth of greater exactitude in commercial dealings that the art of weighing, which was employed for all dealings in gold and silver, would be applied to copper. Just as the Malays and Tibetans have been gradually taught by the careful Chinese to employ weights commercially, so the Italian tribes may have been led to do so under the influence of the astute Greek traders from Magna Graecia and Sicily.
- ↑ So the word mark means not only a weight but is also used as a linear measure = 48 alen, and also as a measure of area, as in the term arable mark etc. See Appendix.
