THE ART OF WEIGHING AND MEASURING. 608 



Society's coininittce aesuuu'd tlie rod to be tlie true stuudard of 30 

 iuclies, and upou that assuuiption Graham's measurements gave for the 

 lenjuth of the matrix 30.0102 inches, and for tlie length of the Royal 

 Society's yard 30.0075 inches. The Parliamentary Committee of 1758 

 l)robably assumed the standard to consist of the rod an-.l matrix 

 together, which seems the better view; and by laying the rod in its 

 matrix and measuring to the joint between them Bird would have got 

 a length of about 36.0051 inches. The mean between that and 36.0075 

 would be 36.0063, which differs very little from the length of Bird's 

 standard resulting from Sir George Shuckburgh's measurements. 

 Thus the committee's statement is justified, and there has been no falsi- 

 fication of the ancient standards. 



On December 1, 1758, Parliament created another committee on 

 weights and measures which in April, 1759, repeated the recommenda- 

 tion that Bird's standard of 1758 should be legalized, and further recom- 

 mended that a copy of it shouhl be made and dei)osited in some public 

 office, to be used only on special occasions.* The copy was made by 

 Bird in 1760, but owing to circumstances entirely unconnected with 

 the subject, no legislation followed for sixty-four years. 



The Koyal Commission appointed during the reign of George III to 

 consider the subject of weights and measures made its first report on 

 June 24, 1819, and therein recommended the adoption of the standard 

 of length which had been used by General Roy in measuring the base 

 on Hounslow Heath ;t but in a second report, made July 13, 1820, they 

 wrote: " We - - - have examined, since our last report, the rela- 

 tion of the best authenticated standards of length at present in exist- 

 ence, to the instruments employed for measuring the base on Hounslow 

 Heath, and in the late trigonometrical operations : — But we have very 

 unexpectedly discovered, that an error has been committed in the con- 

 struction of some of these instruments.^ We are therefore obliged to 

 recur to the originals which they were intended to represent; and we 

 have found reason to prefer the Parliamentary standard executed by 

 Bird in 1760, which we had not before received, both as being laid down 

 in the most accurate manner, and as the best agreeing with the most 

 extensive comparisons, which have been hitherto executed by various 

 observers, and circulated through Europe ; and in particular with the 

 scale employed by th.e late Sir George Shuckburgh."§ 



Accordingly, when in 1824, Parliament at length took action, Bird's 

 standard of 1760 was adopted instead of that of 1758. The former be- 

 ing a copy of a copy, its selection as a national standard of length seems 

 so singular that the circumstances which brought about that result 

 should scarcely be passed over in silence. Bird had a very accurate 

 brass scale 90 inches long, which he used in all his dividing operations, 

 whether upon circles or straight lines, and which Dr. Maskdyne said 

 was 0.001 of an inch shorter on three feet than Graham's Royal Society 



* 14, p. 4G3. t 26, p. 4, t 30, p. 92. ^ 27, p. '^ ; also 25 ami 26. 



