THE NEW NATIONAL STANDARD OF LENGTH, AND ITS PRINCIPAL COPIES. G20 
touched each other ; the other by microscopic vieAV of the edges, alternately with white 
ground and black ground beneath them. The thermometric expansion of the pendulum- 
bar was ascertained. The determination of the vibrations of the pendulum was made in 
Mr. Browne’s house, Portland Place, in the atmospheric air ; the correction applied, to 
obtain the number of vibrations which would have been made at the level of the sea, 
was computed by increasing the number of vibrations in the proportion of the terrestrial 
radius at the sea to the terrestrial radius at the station ; and the correction, to obtain 
the number of vibrations which would have been made m vacuo, was computed by 
assuming that the only etfect of the air Avas to diminish the attraction of the pendulum 
in the proportion of the specific gravity of the air to that of the pendulum. 
Philosophical Transactions, 1818, page 103, &c. Kater on the length of the French 
Metre, as compared with Shuckburgh’s scale, 0 — 39‘4. The optical comparison Avith 
the Metre a traits is simple ; that of the Metre a bouts Avas effected in the same manner 
as the measure of the pendulum, by the use of supplementary blocks bearing lines. 
Philosophical Transactions, 1821, page 75, &c. Kater, Comparison of various British 
Standards. The standards compared are, the Eoyal Society’s standard (ToAver Yard), 
General Boy’s, Shuckburgh’s (0 — 36 or 0 — 40), Bird’s standard of 1760, a standard 
supposed to represent Colonel Lambton’s, and a 40-inch bar, supposed to represent 
Ramsdex’s, It appears that the comparing-apparatus Avas attached to a bar of maho- 
gany, AA’hich AA’as to be placed upon the standard to be obseiwed ; the standard, appa- 
rently, being laid upon a table. In this paper is stated the reason for recommending 
Bird’s standard of 1760 for the Imperial Standard; namely, because Bird’s standard of 
1760 agrees closely AAnth Shuckburgii’s scale (0 — 36), Avith Avhich the pendulum and the 
metre had been compared, and of Avhich a facsimile Avas knoAvn to exist at Geneva. 
A general Aiew of the relations betAveen the different standards mentioned above Avill 
be found in a “ Statement ” by Mr. Sheepshanks, given in a subsequent part of this 
paper. 
The Bill for giving legal authority to the late Imperial Standards, for providing for 
theii’ restoration in case of loss or injury, and for settling various other points relating 
to standards, received the Royal Assent 1824, June 17. It is intituled, “Anno Quinto 
Georgii IV. Regis, cap. lxxit.. An Act for ascertaining and establishing Uniformity of 
Weights and Measures.” The folloAving Excerpts contain all that relates to the defi- 
nition and preseiwation of the Standard of Length : — 
Section I. “ ... Be it enacted . . . that from and after the first day of May, One thou- 
sand eight hundred and tAventy-five, the Straight Line or Distance betAveen the Centres 
of the Tavo Points in the Gold Studs in the Straight Brass Rod, noAv in the Custody of 
the Clerk of the House of Commons, Avhereon the Words and Figures ‘ Standard Yard, 
1760,’ are engraA'ed, shall be and the same is hereby declared to be the original and 
genuine Standard of that Measure of Length or lineal Extension called a Yard ; and that 
the same Straight Line or Distance betAveen the Centres of the said Two Points in the 
said Gold Studs in the said Brass Rod, the Brass being at the temperature of Sixty-tAvo 
