604 MISCELLANEOUS PAPERS. 



yard E.* In the year 170L', 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 divisions of the various instru- 

 ments 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 were made by the aid of micro- 

 meter microscopes, to be so exact that no variations could possibly be 

 detected in them either frojn the original or from each other. Among 

 the earliest of the scales so made by Troughton vfuS the one used by Sir 

 George Shuckburgh in 1796-98 in his important scientific operations 

 for the improvement of the standards. Subsequently, the length of the 

 meter was determined by comparison with this scale and with the 

 supposed facsimile of it made by Troughton for Professor 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 5-foot scale made for Sir George Shuck- 

 burgh by Troughton in 1796; two iron standard yards, marked lA. and 

 2A, made for the English 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 Cap- 

 tain 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 trans- 

 ferred 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-nuikers of the time with all the 

 accuracy then attainable. Thns 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 vs^ith the Exchequer 

 standard and with the Royal Society's yard E, and was of a length be- 

 tween 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 

 with Sir George Shuckburgh's scale by Captain Kater in 1830, and by 

 Mr. Francis Baily in 1834; with the Ordnance yards lA and 2A in 1834 

 by Lieutenant Murphy, R. E., Lieutenant Johnson, R. N., and Messrs. 



* 15, p. 326. 



