The first establishment of a uniform standard appears to have been made
in 1101 by Henry I., who is said to have fixed the ulna (now the yard)
at the length of his arm; but nothing definite was done till 1736, when
the Royal Society took steps toward securing a general standard, and
in 1742 they had a standard yard made by Graham from a comparison of
various yards and ells of Henry VII. and Elizabeth, that were kept in the
Exchequer.
Two copies of the Royal Society standard yard were made by Bird in
1758 for a committee of Parliament, one of which was marked “standard
of 1758,” and the other 1760. But no exact legal standard was yet
established, as shown by comparisons in 1802 of the various standard
measures in use which Pictet, of Geneva, made with an accurate scale by
Troughton, using means exact to the ten thousandth part of an inch, with
the following results at the temperature of 62° F.:
Troughton Scale 36·00000 inches.
Parliamentary Standard (1758, Bird) 36·00023 “
Royal Society “ (1760, “ ) 35·99955 “
“ “ (Graham) 36·00130 “
Exchequer “ 35·99330 “
Tower “ 36·00400 “
Gen. Roy “ (Trig. Survey) 36·00036 “
Parliament finally undertook to reform the measures of England, and
appointed a commission in 1818, under whose authority Capt. Kater
compared the standard yards then in use with the following results, as
referred to the Indian Survey standard:
Col. Lambton Standard (Indian Survey) 36·000000 inches.
Bird’s Standard (1760) 36·000659 “
Sir Geo. Schuckburgh’s Standard 36·000642 “
Ramsden’s Bar. Ordnance Survey 36·003147 “
Gen. Roy’s Scale 36·001537 “
Royal Society Standard 36·002007 “
The commission reported in favor of adopting Bird’s standard of 1760, as
it differed so slightly from Sir George Schuckburgh’s standard (which
had been used in deducing the value of the French mètre) that those
values could be assumed as correct. They also established the length of
the seconds pendulum at level of sea in London and in vacuo as 39·13929
inches. The seconds pendulum had been previously fixed by Wollaston and
Playfair in 1814 as 39·13047 inches.
On this report, an Act of Parliament in 1823 declared the only standard
measure of length for the United Kingdom to be the yard as given by the
distance at 32° F. between two points in gold studs on the brass bar,
made by Bird, and marked “Standard of 1760,” and in the keeping of the
Clerk of the House of Commons; also it referred this standard yard to the
natural standard of a pendulum vibrating seconds of mean solar time at
the level of the sea, in vacuo at London and temperature of 32° F., as
in the proportion of 36 to 39·13929; so that a pendulum 36 inches long
ought to make 90088·42 vibrations in 24 hours.
The Royal Society had a copy of the legal standard made by Bailey in
1834; and in the same year the Parliamentary standard was destroyed by
fire at the burning of the Houses of Parliament, leaving the kingdom
again without a legal standard.
All attempts made by a commission consisting of Airy, Bailey, Herschel,
Lubbock, and Sheepshanks, to restore the standard by means of the seconds
pendulum failed in exactness, on account of the many conditions of a
vibrating pendulum, and recourse was had to the Royal Society standard,
which had been carefully compared by Captain Kater in 1818, and from this
in 1838 Bailey and Sheepshanks made six bronze bars, one inch square, and
38 inches long, which in 1855 were legalized by Act of Parliament, and
the English standard of length defined as follows:
“That the straight line on distance between the centres of the transverse
lines in the two gold plugs on the bronze bar deposited in the Exchequer
shall be the genuine standard yard at the temperature of 62° Fahrenheit;
and if lost, it shall be replaced by means of its copies.”
The French metrical system was made legal permissively in 1864, at the
length established by Captain Kater, referred to in Act of Parliament of
1823, of 1 mètre equal to 39·37079 inches, or 3·28089916 feet.
These are the standards now in use in the United Kingdom.