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WKIUHTS AND MEASURES, STANDARD. 



WEIGHTS AND MEASURES, STANDARD. 



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standard, more especially the Royal Astronomical Society's wale, and 

 the iron ban belonging to the Board of Ordnance, and they asserted 

 that by the aid of theee the value* of the original standard might be 

 restored without tenable error. They further expressed their firm 

 belief that by employing due care it will always be possible to effect 

 the restoration of a standard by the aid of material copies which have 

 been accurately compared with them, more securely than by experi- 

 ment* having reference to any natural constants. They accordingly 

 offered a series of suggestions, of which the following are the most 

 important : t 



1. That so much of the act 5 Geo. IV. c. 74 as provides for the 

 restoration of the standards in the manner therein mentioned, be 

 repealed ; and that the standard of length be denned in subsequent 

 enactment* of the legislature, either by the whole length of a certain 

 piece of metal or other durable substance, supported in a certain 

 manner, at a certain temperature ; or by the distance between two 

 points or lines engraved on the surface of a certain piece of metal or 

 other durable substance, supported in a certain manner, at a certain 

 temperature ; but that the standard be in no way defined by reference 

 to any natural basis, such as the length of a degree of meridian on the 

 earth's surface in an assigned latitude, or the length of a pendulum 

 vibrating seconds in a specified place. 



5. That four sets of copies (to be denominated the parliamentary 

 copies) of the standards of length and weight be made, in all respects 

 similar to the legal standards of length and weight (which are herein- 

 after denominated the parliamentary standards), and as nearly as 

 possible equivalent to them ; their difference from the parliamentary 

 standards, if appreciable, being carefully ascertained ; and that the 

 several parliamentary copies be distinguished by proper marks. 



6. That one set of the parliamentary copies be enclosed in a case 

 hermetically sealed and embedded within the masonry of some public 

 building ; and that the place in which it is enclosed be pointed out by 

 a conspicuous inscription on the outside ; and that this set of copies 

 be not disturbed without the sanction of an act of parliament. 



17. That the superintendence of the construction of the new par- 

 liamentary standards be intrusted to a committee of scientific men, to 

 be named by her Majesty, subject to the general instructions which 

 follow. 



18. That the superintending committee be instructed to combine, in 

 the way which may appear most advantageous, the evidence afforded 

 by the Royal Astronomical Society's scale No. 46, and by the 3 feet 

 bars of the Ordnance Survey ; and by the use of these to construct a 

 new standard of length, representing as nearly as possible the same 

 measure as the lost standard. 



The government, acting upon this report, appointed a committee of 

 scientific men to superintend the carrying into effect of the operations 

 recommended by the commissioners. The committee thus formed 

 consisted in fact of the commissioners themselves, who were requested 

 by the government to continue their services. The following is a 

 list of the individuals of which it was composed : The Astronomer 

 Royal, the Marquis of Northampton, the Lord Wrottesley, F. Baily, 

 .1. E. D. Bethune, J. G. S. Lefevre, Sir J. W. Lubbock, the Rev. G. 

 Peacock, Kev. R. Sheepshanks, Sir John Herschel, and Professor Miller. 



The Earl of Rosse was subsequently appointed a member of the 

 committee. Mr. Baily undertook to execute the operations for restoring 

 the standard of length. The work relating to the standards of weight 

 was undertaken by Professor Miller of Cambridge. [MILLKK, WILLIAM 

 HALLOWS, in Bioo. Div.] 



The committee having carefully considered the advantages and 

 disadvantages of line measures, as compared with end measures, 

 decided upon making the standard of length a line measure. 



The next point to be considered was the material of which the new 

 standard was to be composed. A series of interesting experiments 

 was made by Mr. Baily, with a view to this object. The committee 

 finally decided upon adopting for the material of the standard of length, 

 an alloy of copper, tin, and zinc, in the following proportions : 



Copper 16 



Tin 2J 



Zinc 1 



Mr. Baily next made a series of valuable experiments on the circum- 

 stances which exercise a disturbing influence on the length of a bar. 

 Captain Kater bad found that the length of the bar is sensibly affected 

 by small inequalities of the surface on which it recta. It resulted from 

 this circumstance, that the same bar when compared with other bars 

 at different times, might not indicate the same length. This was fully 

 verified by the experiments of Mr. Baily. It followed as a necessary 

 consequence of this circumstance, that no reliance could be placed on 

 the existing copies of Shuckburgh's scale as representatives of the 

 scientific standard of length, since we possegnd no security that we 

 were thereby referring to a consistent system. 



Besides Shuckburgh's scale, which was found to be unworthy of 

 confidence, there existed five other standards, which had been carefully 

 compared with the imperial standard. Mr. Baily having obtained 

 temporary possession of four of these, the Royal Society's 8-foot braiw 

 scale, the Astronomical Society's tubular scale, and the two :j i.i.it 

 iron bars of the Ordnance Survey, instituted a series of careful com- 

 parison! of their lengths under different conditions. The results of 



these experiments were by no means satisfactory as regards the degree 

 of reliance to be placed on these ban, as representatives of the imperial 



-t.m.i ..i.i. 



Mr. Baily died in the autumn of 1844. At the request of the 

 committee, Mr. Sheepshanks undertook to continue the operations. 



It appeared to the committee that no reliance could be placed 

 on Shuckburgh's scale, or on any other existing copy of the imperial 

 standard, the experiment* of Mr. Baily having shown that the com- 

 parisons of those measures could not fail to have been sensibly affected 

 by errors of different kinds. " It was plain therefore that either in the 

 scientific or the legal sense, the restoration of the standard wa- 

 teruiinate. The formation of a new standard must be an operation 

 de noto ; the length must be confined within certain limits (wide in 

 the scientific, narrow in the commercial sense), but within these it 

 might have any definite value, and when that definite value was fixed, 

 it must in no way be again referred to the old standards or scales, 

 whether original or intermediary. The principal object now was to 

 ensure constancy and definiteness to the new standard and its copies, 

 and means of reducing without sensible error the comparisons which 

 might be made with them. As far as depended on the standard itself, 

 it was hoped that the construction adopted gave sufficient security. 

 As regarded the means of making comparisons, a far firmer apparatus 

 than had hitherto' been used was requisite. As regards the effects of 

 temperature, it was necessary to create an entirely new system of 

 thermometers, founded upon the natural constants, to be determined 

 by appropriate physical experiments ; and to use them in new deter- 

 minations of thermotuetric expansion."* 



It was found in the course of the experiments that a change of 0'01 

 Fahr. produces a sensible effect in the measure of a bar. It was there- 

 fore necessary to employ thermometers which would serve to indicate 

 variations of temperature of no greater magnitude than this. At the 

 time when Mr. Sheepshanks commenced his experiments there were 

 not to be found in England any thermometers of such delicacy. He 

 was consequently induced to undertake the construction of an original 

 system of thermometers adapted to the important object of his labours. 

 He then proceeded to determine the thennometric expansion of a great 

 number of bars of different metals, t This object being accomplished, 

 the next step was, by means of the existing standards, to determine 

 the relation of the length of one of the new bars to the lost imperial 

 standard. After many comparisons, he finally decided upon adopting 

 a bar designated by him bronze 28, as a suitable representative of the 

 imperial standard. He remarked, with reference to the circumstances 

 which led him to adopt this resolution, that bronze 28 was as nearly 

 as possible equal in length to the imperial standard, measuring in fact 

 35-999992 in., that it floated evenly in quicksilver, and that it was 

 nicely divided. 



Having now obtained a satisfactory representative of the imperial 

 standard, Mr. Sheepshanks made a great number of comparisons of the 

 length of the new standard with other bars, in order to select from 

 them four Parliamentary copies of the standard, to be disposed of in 

 the way recommended by the committee to the government. He also 

 made careful comparisons of these with a great number of other bars, 

 which were intended for distribution throughout the empire and in 

 foreign countries. It would be out of place here to enter into tho 

 details of his arduous and persevering labours in connection with this 

 great national work. It may give the reader some idea of their magni- 

 tude when we state, upon the authority of Mr. Airy, that in the course 

 of them he executed about two hundred thousand micrometric measures. 

 He still continued to labour at his task when, in the summer of 1855, 

 symptoms of a serious nature affecting his health began to manifest 

 themselves. On the 28th of July in that year he was engaged on the 

 comparing apparatus, and returned in the evening to his residence at 

 Heading. On the following day he was struck with apoplexy, and died 

 on the 4th of August We quote tho following tribute to his character 

 by Mr. Airy : 



" Thus died almost in the scene of bis labours, and with his 

 thoughts still intent on them a man whose equal in talent and perse- 

 verance, in disinterestedness, in love of justice and truth, I have scarcely 

 known. * He had, however, brought to a satisfactory termination the 

 great division of the standard-work which best suited his taste, having 

 well overcome the last of the difficulties which had presented them- 

 selves, and leaving the work in such a state that not a single additional 

 comparison of line-measures was compared. All that was necessary 

 was to collect and arrange the papers, to complete some few means and 

 abstracts which he had been unable to finish, and to draw up such an 

 account as I have attempted here." (' Phil. Trans.,' 1857, p. 684.) 



The form adopted for the standard, and for all its copies, is that of a 

 solid square bar, 38 inches long and 1 inch square in transverse 

 section. Near to each end a cylindrical hole is sunk (the distance 

 between the centres of the two holes being 36 inches) to the depth of 

 0'5 inch. At the bottom of this hole is inserted in a smaller hole a 

 gold plug or pin about O'l inch diameter, and upon the surface of this 

 pin there are cut three fine lines at intervals of about O'Ol inch trans- 



* 'Phil. Trans.,' 1847, p. 648. 



f They wore chiefly of nun-metal, M recommended by the committee ; but 

 then were alo nreral of cut-Iron and steel. 



Mr. Sheepihanlu' public service*, in connection with the restoration of the 

 national standard of length, were wholly gratuitous 



