_Measures of Capacity derived from Arabic Linear Measures_
Al-Mamūn’s cubit cubed became the medieval standard of grain measure on the Mediterranean coasts—
21·28 in. cubed = 9639 c.i. = 347·314 lb. water,
which is equal to 34·73 gallons or 4·34 bushels.
This measure subsists in Egypt as the Rebekeh = 4·32 bushels. It passed to Marseilles as the Cargo, and to Paris as the Setier.
These developments of the Arabic cubit and foot will be more fully explained in the chapters on foreign systems. They are sketched in order to show how the Eastern caliphate took up the system begun by the great monarchies of many centuries before, and elaborated by Greece and Rome. Thus, from Moslem Egypt as from Pharaonic Egypt have come virtually all the weights and measures of the Western world.
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THE INVOLUTION OF LINEAR MEASURES FROM WEIGHTS
THE SOURCES OF THE ENGLISH AND OF THE RHINELAND FOOT
Commerce is the great conservator of standards. These may become altered by the ill-advised action of rulers, by municipal or parochial carelessness, even by the desire of profit on short measure, or occasionally, as seen to a slight extent in our old Bushel, by the faulty dimensions of a standard; but wholesale trade, supported, in weights at least, by the goldsmith and the apothecary, preserved the integrity of many standards during the Middle Ages and up to modern times. Commerce conveyed to the West the standards that had developed in the great Oriental Kingdoms, sometimes with the modifications due to Roman influence. Masons and architects also preserved the standards of length and, allowing for variations inevitable under the feudal system, the principal linear measures can generally be traced to their sources as surely as weights. But there are two, yea three, striking exceptions among the linear standards of the West: the English foot, and the Rhineland foot, and also the Pán of Marseilles. These are quite unconnected with any ancient measures, and there is no record of their origin. The only clue to it is found in the simple relation of each to the corresponding weights and measures of capacity, the origin of which can be satisfactorily traced. This leads to the hypothesis that these linear measures were ‘involved,’ that is produced by a method of involution the inverse of that which had evolved the measures of weight and capacity.