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

WEIGHTS AND MEASURES.

As the method of enumerating by tens was originally derived from
the fingers of the human hand, so also in the same manner were the
primary units of measures of length derived and named from the
members of the human body, and from the spaces included in their
ordinary motions. The primitive names of these measures in the languages of all nations prove the identity of their origin. Thus of
the former are the lengths of the human foot, the nail, the fingerbreadth, the hand-breadth or palm, and the cubit; and of the latter,
the span, the step, the pace, and the fathom, employed as ordinary
measures of length. The palm was reckoned the breadth of four
fingers; the nail was the length from the end of the nail of the
longest finger to the first joint; the inch, the length from the end of
the thumb to its first joint, was adopted as an unit measure of length.
This unit repeated four times was considered equal to the palm or the
hand-breadth, and the hand-breadth taken three times gave the
measure of the foot. The greatest expansion of the hand between the
ends of the thumb and the middle finger gave the span; the distance
from the end of the longest finger to the elbow, the cubit; the entire
length of the arm, the yard; and the distance to which a man's two
hands can be extended across the shoulders, the fathom. As the foot
was too small an unit for estimating long distances with convenience, the step was reckoned equal to three feet; and the pace (passus),
the interval between two steps, and equivalent to six feet, was also
assumed as a measure; and a mile, as the word imports, consisted of
one thousand paces (mille passus). Other measures of length have been
derived and named from other considerations; as, for instance, the
furlong (furrow long), taken to express the eighth part of a mile; the
league (lugen, to see), a measure of three miles, supposed to express the
distance the eye of a man, when standing upright, can see on a level
plain; and the bow-shot, an ordinary measure of length formerly used
in England and among other people who used the bow as a weapon.
It will be evident that these measures, however sufficient they might
be for the ordinary wants and conveniences of life in the early
condition of human society, would be found to require more strict
and exact definition as knowledge advanced, with the requirements of
science and commerce.
The earliest lineal measures of which any certain knowledge has
descended to modern times, are those of the Hebrews and Egyptians,
the Greeks and the Romans. The most ancient writings of the
Hebrews supply facts in evidence that Egypt in very early times was
a country under a regular form of kingly government, its people
civilised and trading with the people of other countries in the fruits
and productions of those lands.
The oldest lineal measure named in these writings is the cubit, a
measure used in describing the dimensions of the Ark (Gen. vi.)