Elementary arithmetic, with brief notices of its history... by Robert Potts.

WEIGHTS AND MEASURES.

5

Galen discovered, by comparing the measures and the scale weights,
that the horn used for measuring oil at Rome held one-sixth part less
than the weight of the libra. The metrical horn was divided into twelve
parts or ounces, like the libra; and each of these divisions was commonly supposed to be equal to an ounce scale weight, and passed for
such in estimation. Galen, as a physician, thought it requisite to
interpose some caution; that, in prescribing oil, they ought to
distinguish by what ounces they prescribed, whether the scale ounce
or the metrical ounce: as the scale pound determinecl the weight of
bodies, but the metrical only the contents, or the quantity of space
they filled.
The pound of 100 denarii or 100 drachmme was merely nominal,
and employed for the purpose of trade. Both the denarius and the
drachma, during the Consular and part of the Imperial Government,
were only seven to the ounce. They began to lessen under Nero.
WVhat Pliny writes of the aurei is equally true of the silver coins,
" Paullatim principes imminuere pondus." They probably did not coin
8 in the ounce till the time of Galen. about a century after Nero. A
drachma has ever since been reckoned the eighth part of the ounce,
and probably was so some time before. Thus the drachma reckoned
at 6 to the ounce, gives 72 in the pound; at 7, gives 84; and at 8,
96 in the pound.
The congius of Vespasian supplies a method of discovering the
true weight of the Roman pound. This congius was made A.D. 75,
according to the standard of measure preserved in the Capitol, and
contains ten pounds, as the inscription upon it testifies: "IMP.
C(ESAE VI. T. CmES. AUG. F. IIII. Cos. BMENTSUR EXACT2E IN CAPITOLIO.
P.X." It is commonly called the Farnese Congius, and is now preserved at Dresden. In 1824 Dr. Hase had it filled with distilled
water and carefully weighed, and the weight of the water was found
to be equal to 52037-69 grains Troy weight, giving 5203-769, or
nearly 5204 grains to the Roman pound.
It has been remarked by Dr. Hussey (Essay on Ancient Weights)
that " the ancient metallic weights in themselves are too unequal and
inconsistent with each other to give any certain result." He regards
more favourably the two obtained from the excavations at Herculaneum-the only two large specimens which are perfect-one of
50 and the other of 100 Roman pounds. Of these, the former
weighing 256564 grains Troy, gives a pound of 5131-28 grains; the
latter, weighing 518364 Pgrains, gives a pound of 5183-64 grains,
which is between 20 and 21 grains less than that given by the
congius of Vespasian. If the experiment with the congius had been
made with water not distilled, the result would have shown a less
difference. And so small a difference in the two calculations is no
matter of surprise, when much greater differences are found between
the old Roman weights themselves. The modern Roman pound
contains 5236 grains Troy, and exceeds the old Roman pound, as
given by the congius, by only 32 grains. This fact affords a strong
presumption that the ancient and modern weights were identical, and
that the difference is not greater than was likely to be found in the
lapse of so many centuries.
The Roman pound libra, called also as, was divided into twelve
equal parts, called uncie (ounces); and for every number of ounces
under 12, the Latin language has a distinct name.