530 



XIV. "Account of the Construction of the New National 

 Standard of Length, and of its principal Copies/' By 

 G. B. AIRY, Esq., F.R.S., Astronomer Royal. Received 

 May 2, 1857. 



(Abstract.) 



The author premises that the work to which this account relates 

 was executed almost entirely by Mr. Baily and Mr. Sheepshanks. 

 He then proceeds with the Account, which is divided under nine 

 Sections. 



Section I. contains the 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 ; the definition of the 

 Standard of Length by that Act ; and the provision for its restora- 

 tion in case of loss. The first record cited is that of the laying 

 down of the English Standard Yard on the Royal Society's brass 

 bar, described in the Philosophical Transactions, 1/42-3; then 

 allusion is made to the comparisons by Graham, Maskelyne, Ray, 

 Shuckburgh, those of the Base du Systeme Metrique, and those by 

 Kater (1818 and 1821). The Sections of the Act of Parliament of 

 1824, which define the British Yard and prescribe the method for 

 restoring it in case of loss, by reference to the length of the Seconds' 

 Pendulum, are cited. 



Section II. gives some description of the Comparisons of Standards 

 made 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. Extracts 

 are given from Kater's papers of 1826, 1830, and 1831, in which 

 new difficulties were described and new constructions planned to 

 obviate them. Allusion is made to the characteristics of the prin- 

 cipal Base-measures in Britain and on the Continent. The con- 

 structions of the Ordnance Standard Bars and of the Royal Astro- 

 nomical Society's Tubular Scale are described, and reference is made 

 to the accounts of their comparisons. Bessel's measure of the 

 seconds' pendulum, Bessel's construction of the Prussian 3-foot 



