626 
ME. AIEY’S ACCOLYS'T OF THE COXSTEUCTIOX OF 
Degrees by Faheekheit’s Thermometer, shall be and is hereby denominated the * Impe- 
rial Standard Yard.’ ” 
Section III. “ And whereas it is expedient that the said Standard Yard, if lost. 
destroyed, defaced, or otherwise injm’ed, should be restored of the same Length, by 
reference to some invariable natural Standard : And whereas it has been ascertained by 
the Commissioners appointed by His Majesty to inquire into the subject of Weights and 
Measures, that the said Yard hereby declared to be the Imperial Standard Yard, when 
compared with a Pendulum vibrating Seconds of Mean Time in the Latitude of London, 
in a Vacuum at the Level of the Sea, is in the proportion of Thirty Six Inches to Thirt}' 
Nine inches and one thousand three hundred and ninety-three ten-thousandth Parts of 
an Inch ; Be it therefore enacted and declared. That if at any Time hereafter the said 
Imperial Standard Yard shall be lost, or shall be in any Manner destroyed, defaced, or 
otherudse injured, it shall and may be restored by making a new Standard Yard. 
bearing the same Proportion to such Pendulum as aforesaid, as the said Imperial Stand- 
ard Yard bears to such Pendulum.” 
Section II. — Compm''isons of Standards between the passing of the Act o/1824 and the 
appointment of a Commission for consideration of Standards after the destnictiofi of 
the Imperial Standard in 1834; with remarks suggested by the advance of collateral 
theory and experiment in that interval. 
In the Philosophical Transactions, 1826, Part II., page 1, &c., is EAter’s account of 
the preparation of the new [Secondary] Standards of Weights and Measures. The 
only part of this which is important to the present pm’pose is the follo'^Lag. Four 
brass bars were prepared, each 1 ^ inch wide and ^ inch thick, with gold pins bearing 
points (I refer to the original for the excentric mounting of these points). In the coui'se 
of the comparisons of these secondary standards with Sir G. Shuckbuegh’s scale, it was 
found that discordances to the amount of inch were produced by almost undiscover- 
able inequalities in the surface of the table on which they were laid. In the new 
secondary standards, this defect was cured by removing the upper half of the thickness 
of the bar, in those parts where the defining points are planted, so that the defining 
points are in reality at the middle of the depth of the bar. But it was impossible to 
apply this remedy to Shuckburgh’s scale; and consequently all measures made with 
that scale are liable to some uncertainty. 
Philosophical Transactions, 1830, page 359, &c. Captain Kater piusues the subject 
of curvature of bars produced by the inequalities of the supporting surface. He shows 
that in one instance (Dollond’s scale), in which great care had been used, an error of 
inch had nevertheless been committed. He describes a practical method of testing 
the planeness of surfaces. He shows that, when the greatest precautions are used, the 
length of Shuckburgh’s scale 0 — 36 appears sensibly equal to the Imperial Standard, 
liemarking that, when the supporting surface is nearly plane, a bar of any moderate 
thickness will accommodate its form to the small inequalities, and the errors of dhisions 
