274 PROCEEDINGS OF THE AMERICAN ACADEMY 



structed from Graham's scale by Bird, in 1760. It is marked, " Stand- 

 ard 1760." 



The reason assigned for selecting Bird's "Standard 1760" was its 

 close agreement with Shuckburgh's scale (0-36 in *), made by Trough- 

 ton in 1798, with which the pendulum and the meter had been com- 

 pared, and of which a fac-simile was known to exist at Geneva. It is 

 interesting to note, in passing, that, previous to Shuckburgh, all trans- 

 fers were made by means of beam compasses, and all comparisons were 

 made in the same way. The first use of optical means of comparison 

 must be credited to Troughton in 1798, when he transferred Bird's 

 scale for Shuckburgh. The following is the act legalizing the stand- 

 ards : — 



" Suction I. Be it enacted . . . that from and after the first day 

 of May one thousand eight hundred and twenty-five, the Straight Line 

 or Distance between the Centres of the Two Points in the Gold Studs 

 iu the Straight Brass Rod, now in the Custody of the Clerk of the 

 House of Commons, whereon the Words and Figures ' Standard Yard 

 1760 ' are engraved, 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 

 between 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-two 

 Degrees by Fahrenheit's Thermometer, shall be and is hereby denomi- 

 nated the 'Imperial Standard Yard.' .... 



" Section III. And whereas it is expedient that the said Standard 

 Yard, if lost, destroyed, defaced, or otherwise injured, should be restored 

 to 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 Thirty-Nine Inches and one thou- 

 sand 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 otherwise 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 Standard Yard bears to 

 such Pendulum." 



On the 16th of October, 1834, both houses of Parliament were con- 



