378 



NATURE 



\August 15, 1889 



little from the length of Bird's standard resulting fro n Sir George 

 Shuckbnrgh's measurements. Thus the Committee's statement 

 is justified, and there has been no falsification of the ancient 

 standards. 



On December i, 1758, Parliament created another Committee 

 ■on Weights and Measures, which, in April 1759, repeated the 

 •recommendation that Bird's standard of 1758 should be legalized, 

 and further recommended that a copy of it should be made and 

 ■deposited in some public office, to be used only on special occa- 

 sions. The copy was made by Bird in 1760, but, owing to cir- 

 cumstances entirely unconnected with the subject, no legislation 

 followed for sixty-four years. 



The Royal 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 ; but in 

 a second Rejxyrt, made July 13, 1820, they wrote : — " We . . . 

 have examined, since our last Report, the relation of the best 

 authenticated standards of length at present in existence, 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 construction of some of these instruments. We are there- 

 fore obliged to recur to the originals which they were intended 

 to represent, and we have found reason to prefer the Parlia- 

 mentary 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 com- 

 parisons which have been hitherto executed by various observers, 

 and circulated through Europe ; and in particular with the scale 

 employed by the late Sir George Shuckburgh." 



Accordingly, when in 1824 Parliament at length took action, 

 Bird's standai-d of 1760 was adopted instead of that of 1758. 

 The former being 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. Maskelyne said was O'ooi 

 •of an inch shorter on 3 feet than Graham's Royal Society 

 yard E. In the year 1792, or 1793, the celebrated Edward 

 Troughton made for himself a 5-foot scale, which conformed to 

 Bird's, and which he afterwards used in laying down the divi- 

 sions of the various instrume its that passed through his hands. 

 This was the original of all the standard scales he ever made, 

 and at the beginning of the present century he believed these 

 copies, which wete made by the aid of micrometer microscopes, 

 to be so exact that no variations could possibly be detected in 

 them, either from the original or from each other. Among the 

 earliest of the scales so made by Troughton was the r ne U'ed by 

 Sir George Shuckburgh in 1796-98 in his important scientific 

 •operations for the improvement of the standards. Subsequently, 

 the length of the metre was determined by comparison with this 

 scale and with the supposed facsimile of it made by Troughton 

 for Prof. Pictet, of Geneva ; and thus it happened that on the 

 continent of Europe all measures were converted into English 

 units by a reference to .Sir George .Shuckburgh's scale. The 

 Royal Commission of 1819 believed Bird's standard of 1760 to 

 be identical with Shuckburgh's scale, and they legalized it rather 

 than the standard of 1758, in order to avoid disturbing the value 

 •of the English yard, which was then generally accepted for 

 scientific purposes. 



There are yet four other scales of importance in the history of 

 English standards — namely, the brass S-foot scale made for Sir 

 ■George Shuckburgh by Troughton in 1796 ; two iron standard 

 yards, marked ia and 2A, made for the Engli-h Ordnance 

 .Survey Department by Messrs. Troughton and Simms in 1826- 

 27 ; and the Royal Society's standard yard, constructed by Mr. 

 George Dollond, under the direction of Capt. Henry Kater, in 

 1831. 



Bearing in mind the preceding history, the genesis of the 

 present English standard yard may be thus summarized. In 

 1742, Graham transferred to a bar made for the Royal Society a 

 length which he intended should be that of the Tower yard, but 

 which was really intermediate between the Exchequer standard 

 yard of Elizabeth and its matrix. That length he marked with 

 the letter E, and, although destitute of legal authority, it was 

 immediately accepted as the scientific standard, and was copied 

 •by the famous instrument-makers of the time with all the 



accuracy then attainable. Thus it is in fact the prototype to 

 which all the accurate scales made in England between 1742 and 

 1850 can be traced. Bird's standard of 1758 was compared with 

 the Exchequer standard and with the Royal Society's yard E., 

 and was of a length between the two. Bird's standard of 1760, 

 legalized as the Imperial standard, in June 1824, was copied 

 from his standard of 1758. After becoming the Imperial 

 standard. Bird's standard of 1760 was compared wirh Sir 

 George Shuckburgh's scale by Capt. Kater, in 1830, and by Mr. 

 Francis Baily, in 1834; with the Ordnance yards ia and ZK, in 

 1834, by Lieut. Murphy, R.E., Lieut. Johnson, R.N., and 

 Messrs. F. Baily and Donkin ; and with Kater's Royal Society 

 yard by Capt. Kater, in 1831. On October 16, 1834, the Im- 

 perial standard (Bird's standard of 1760) was destroyed by the 

 burning of the Houses of Parliament, in which it was lodged ; 

 and very soon thereafter the Lords of the Treasury took measures 

 to recover its length. Preliminary inquiries were begun f n 

 May II, 1838-; and on June 20, 1843, they resuhed in the 

 appointment of a Commission to superintend the construction of 

 new Parliamentary standards of length and weight, among whose 

 members the Astronomer-Royal (now Sir George B. Airy), 

 Messrs. F. Baily, R. Sheepshanks, and Prof. W. H. Miller, 

 were prominent. The laborious investigations and experiments 

 carried out by that Commission cannot be described here, but it 

 will suffice to say that for determining the true length of the new 

 standard Mr. Sheepshanks employed a provisional yard, marked 

 upon a new brass bar designated " Brass 2," which he compared 

 as accurately as possible with Sir George Shuckburgh's scale, 

 the two Ordnance yards, and Kater's Royal Society yard. The 

 results in terms of the lost Imperial standard were as follows : — 



Brass bar 2 =: 36*000084 from comparison with Shuckburgh's scale, 0-36 in. 

 36'ooo28o ., ,, ,, ,, 10-46 in. 



36"ooo303 from comparison with the Ordnance yard, ia. 

 36'ooo275 ,, ,, ., ,. 2A. 



36'ooo229 from Capt. Kater's Royal .Society yard. 



Mean — 36 '0002 34 



Respecting this mean, Mr. Sheepshanks wrote : — "This should 

 be pretty near the truth ; but I prel'er 36 00025, if i" such a 

 matter such a difference be worth notice. I propose, therefore, 

 in constructing the new standard to assume that — 



Brass bar 2 = 36 '00325 inches of lost Ifnperial standard at 62° F." 



And upon that ba is the standard now in use was constructed. 



Turning now to the French standards of length, it is known 

 that the ancient toise de viacoits of Paris was probably the toise of 

 Charlemagne (A. D. 742 to 814), or at least of some Emperor 

 Charles, and that its etalon was situated in the courtyard of the 

 old Chatelet, on the outside of one of the pillars of the building. 

 It still existed in 17 14, but entirely falsified by the bending of 

 the upper part of the pillar. In 1668 the ancient toise of the 

 masons was reformed by shortening it five lines ; but whether 

 this reformation was an arbitrary change, or merely a change to 

 remedy the effects of long use and restore the etalon to con- 

 formity with some more carefully-preserved standard, is not 

 quite clear. These old itaUnis were iron bars having their two 

 ends turned up at right angles so as to form talons, and the 

 standardizing of end measures was effected by fitting them 

 between the talons. Being placed on the outside of some public 

 building, they were ex]50sed to wear from constant u=:e, to rust, 

 and even to intentional injury by malicious persons. Under such 

 conditions every etalon would, sooner or later, become too lon:^ 

 and require shortening. 



Respec'ing the ancient toise of the masons there are two con- 

 tradictory stories. On December i, 1714, La Hire showed to 

 the French Academy what he characterized as "a very ancient 

 instrument of mathematics, which has been made by one of our 

 most accomplished workmen with very great care, where the 

 foot is marked, and which has served to re- establish the toise of 

 the Chatelet, as I have been informed by our old mathe- 

 maticians." Forty- four years later, on July 29, 1758) L^ 

 Condamine stated to the Academy that " We know only by tra- 

 dition that to adjust the length of the new standard, the width of 

 the arcade or interior gate of the grand pavilion, which served as 

 an entrance to the old Louvre, on the side of the rue Fromenteau, 

 was used. This opening, according to the plan, should have 

 been 12 feet wide. Half of it was taken to fix the length of the 

 new toise, which thus became five lines shorter than the old 

 one." Of these two contradictory statements that of La Hire 

 seems altogether most trustworthy, and the ordinary rules of 



