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XXX. Account of the Construction of the New National Standard of Length, and of its 
principal Copies. By G. B. Aiey, Esq., Astronomer Royal. 
Eeceived May 2, — Head June 18, 1857. 
Ix presenting this Eeport to the Royal Society, I must solicit their indulgence for many 
imperfections, arising from the circumstances under which the task of writing it has 
deTolved on me. Through the whole account, I have to record the proceedings of 
others, and (in a great measure) I have to describe the trains of thought in the minds 
of others, which have determined those proceedings. The first part of the investiga- 
tions for restoration of the Standard was made by Mr. F. Baily ; but the largest pro- 
portion by very far was effected by my much-valued friend the Rev. R. Sheepshanks. 
These have successively been removed by death from their labours on the Standards. 
On the eve of the day on which Mr. Sheepshanks was struck down with mortal disease, 
he was engaged in micrometrical comparisons of Copies of the Standards ; on the day 
foUoufing the deadly stroke, the Royal Assent was given to the Bill for legalizing the 
Official Standards which he had constructed. Under circumstances like these, it is evi- 
dent that the documents relating to the final operations must have been left in great 
confusion. In the earlier portions (the papers relating to which had been, in a measure, 
roughly brought into order), the difficulty is mainly of another kind. Although from 
official relation and private friendship I was in constant and unreserved intercourse both 
with Mr. Baily and wfith Mr. Sheepshanks, and though I was cognizant of every step 
taken, and sometimes examined the apparatus used, yet I never actually made an obser- 
vation. It is possible therefore that my want of familiarity with the operation may 
sometimes make my statements imperfect. I trust, however, that in the main my account 
will be substantially correct. 
It will be necessary for me briefly to revise the history of the British Standards for 
some time anterior to the work which forms the essential subject of this paper. 
I propose to divide my Account under the following heads : — 
Section I. — History of the British and of some Foreign Standards, and of the methods 
of using them in Base-Measures and Pendulum-Measures, anterior to the legalization of 
the Imperial Standards by the Act of Parliament of 1824; definition of the Standard of 
Leirgth by that Act ; and provision for its restoration hr case of loss. 
Section II. — Comparisons of Standards, between the passing of the Act of 1824 and the 
appointment of a Commission for consideration of Standards after the destruction of the 
Imperial Standard in 1834 ; with remarks suggested by the advance of collateral theory 
and experiment in that interval. 
4 M 
MDCCCLVII. 
