8112. STANDARD (Measures), Method of obtaining.—
To obtain uniformity in
measures, weights and coins, it is necessary to
find some measure of invariable length, with
which, as a standard, they may be compared.
There exists not in nature, as far as has been
hitherto observed, a single subject or species
of subject, accessible to man, which presents
one constant and uniform dimension. The
globe of the earth itself, indeed, might be considered
as invariable in all its dimensions, and
that its circumference would furnish an invariable
measure; but no one of its circles,
great or small, is accessible to admeasurement
through all its parts, and the various trials to
measure definite portions of them, have been of
such various result as to show there is no dependence
on that operation for certainty. Matter,
then, by its mere extension, furnishing
nothing invariable, its motion is the only remaining
resource. The motion of the earth
round its axis, though not absolutely uniform
and invariable, may be considered as such for
every human purpose. It is measured obviously,
but unequally, by the departure of a
given meridian from the sun, and its returning
to it, constituting a solar day. Throwing together
the inequalities of solar days, a mean
interval, or day, has been found, and divided,
by very general consent, into 86,400 equal parts.
A pendulum, vibrating freely, in small and equal
arcs, may be so adjusted in its length, as, by
its vibrations, to make this division of the
earth's motion into 86,400 equal parts, called
seconds of mean time. Such a pendulum, then,
becomes itself a measure of determinate length,
to which all others may be referred to as to a
standard. But even a pendulum is not without
its uncertainties.—
Coinage, Weights and Measures Report. Washington ed. vii, 473.
(July. 1790)
