Ee PS 7 AP

150 THE YARD

was a rod having two raised “cheeks,” the space

between which was exactly a yard, and between
which any bar to be tested should exactly fit. This
was to be kept at the Exchequer as the working
standard. Another committee in the following year
proposed that a replica of the sacred bar should be
made and deposited in some public office, to be
referred to on special occasions. This was done,
and thus there were formed two British standards
ef a yard length. Bills were taken into Parliament
to legalize these measures, in 1765, but before they
eould be carried through, there was a dissolution,
and no legislation whatever took place then, nor,
as we shall presently see, for more than half a cen-
tary after.

In the meantime the question of an invariable
znd universal unit of linear measure was largely
discussed—some measure not like barleycorns or
men’s limbs, subject to alteration according to
climate or other accident of development. A
century before, that is about 1670, it had been
proposed, by Sir Christopher Wren and another,
that the length of the pendulum vibrating seconds
ef time in a certain latitude would be the perfection
of a linear standard, for it would never vary while
the earth preserved its form and dimensions. And
at about the same time another philosopher, Mouton
by name, proposed that a definite portion of the
earth’s surface—whose proportion to the circum-
ference of the globe could be ascertained by astro-
nomical observation—should furnish a great scale
of which some convenient aliquot part should be
the unit of linear measure. This second idea was
eventually carried out in France, whose métre
professes to be the ten-millionth part of a meri-
dian are between Dunkirk, on the French North
eoast, and Formentera, off the South of Spain.
English metrologists seem generally to have in-
elined their preference 1o the pendulum as a more
zecessible unit, and Wren’s idea was revived about
the year 1774. We are told that prizes were
offered for the ascertainment of a universal type
of linear measure ; but nothing was then achieved
im this direction beyond directing public attention
to the necessity of securing and preserving correct
standards. In the year 1790 a Government com-
mittee was appointed to consider the matter, but
it did practically nothing. Another committee,
in 1814, was equally ineffectual. But in 1818, a
third body similarly appointed worked with better
effect, as their report shows. They remarked that
there was no practical advantage in having as a
wait any linear measure commensurable to an
original quantity existing or imagined to exist in
nature (such as the pendulum length) ; so they exa-
mined and compared what standards they could
discover, and recommended the adoption, as the
foundation of all legal measures and weights, of that

MEASURE.

one made by Bird in 1760, partly on account of the
care with which it had been made, and also because |
comparisons between it and other bars had been cir-
culated throughout Europe. But in order to fix the
exact length of this yard in terms of a pendulum’s
length, they recommended that the pendulum vibrat-
ing seconds of mean solar time, in London, but at the
level of the sea, should be 39 73929, inches equal
in length to those of which the yard contained
exactly 36. Thus was the British standard yard
referred to or defined as a proportion of the seconds
pendulum.

In 1824 these recommendations became. law.
Bird’s yard of 1760 was a brass rod more than a
yard long, with gold studs let in near its ends.
On each of these studs was a dot, and it was the
distance between the centres of these dots, with
the rod at a temperature of 62° Fahrenheit, that
the Act declared to be the Imperial standard
yard. And the same Act provided that if this
standard should be at any time lost or destroyed,
it should be recovered by reference to the seconds
pendulum, that is by making a bar or setting off
a linear measure whose length should be to that of
the pendulum as is 36 to 89°13929. Eighty-four
years of legislative apathy had passed between the
time of Bird making his standard and the law
establishing it. Now that it was legalized, it was
preserved with scrupulous care in the House of
Commons, but was of course allowed to be used
for the formation of high class copies.

Alas! it did not long maintain its high estate.
In October, 1834, fire laid waste the Parliament
Houses, and the standard yard became worthless
as a bar of old brass. It was not utterly destroyed,
but it was battered, and one of the gold studs
bearing the defining point was melted out, effec-
tually annihilating the measure. Its restoration
became an obvious necessity, and a commission
of highly scientific men was appointed in 1838 to
consider and report on the course best to be
followed. We should expect them to have pro-
posed the restoration by means of the pendulum in
accordance with the Act; but they actually pro-
posed that all that part of the law relating to this
process of restoration should be repealed! A
body of less scientific men would probably have
followed the law as it stood; but the committee
found that there were elements in the reduction of
the pendulum observations (upon which that pro-
portion above given was based) which were doubtful
and erroneous, and that therefore the prescribed
course for restoring the standard would not neces-
sarily reproduce the original yard. On the other
hand, there were in existence several bar-measures
which had been most accurately compared with
that original before it perished, and by means of
these the committee were fully persuaded they