OF ARTS AND SCIENCES. 275 



sumofl by fire. The bar of 17G0 was recovered, but in a condition 

 which rendered it useless as a standard, one of the gold plugs having 

 been melted out. It now became necessary to decide whether it should 

 be restored in accordance with the act of June 17, 1824. Since 

 the passage of the act, it had been shown that all the elements 

 which were defined in the act for restoration were subject to some 

 doubt. Dr. Young had shown that the reduction to the level of the 

 sea was doubtful. Both Bessel and Baily had shown that the reduc- 

 tion for the weight of the air was erroneous. Baily had thrown doubt 

 upon the estimated specific gravity of the pendulum employed, and 

 upon the accuracy of the agate planes, while Kater himself showed that 

 sensible errors had been introduced in comparing the pendulum with 

 Shuckburgh's scale. 



In view of these facts, all attempts to restore the lost standard in 

 accordance with the act of June, 1824, were abandoned. Instead, it 

 was decided to attempt the restoration of the lost standard from the 

 various standards which had been previously compared with it. There 

 were available for this purpose, — 



Shuckburgh's scale (0-36 in -) ; 



Shuckburgh's scale, with Kater's authority ; 



The yard of the Royal Society, constructed by Kater ; 



The Royal Astronomical Society's brass tubular scale ; 



Two iron bars, marked A x and A 2 , belonging to the Ordnance 

 Department, and preserved in the office of the Trigonometrical Survey. 



The restoration of the standard was placed in the hands of Sir 

 Francis Baily. At his death, in August, 1844, he had done little 

 more than complete the provisional inquiries required before attempt- 

 ing the final construction. He had, however, after many experiments, 

 decided upon the material of which the new standard should be com- 

 posed. It has since his time been known as Baily's metal. Its com- 

 position is, copper 16, tin 2|, zinc 1. 



Upon the death of Mr. Baily, the work of restoration was committed 

 to the Rev. R. Sheepshanks. Sir George Airy, in his account of the 

 construction of the new national standards of length, has given an ex- 

 ceedingly interesting communication from Mr. Sheepshanks (Philo- 

 sophical Transactions, 1857, p. G61), detailing the means he employed 

 for the restoration of the lost standard. He first constructed a brass 

 bar, as a working standard. This "brass bar 2" was compared with 

 all the standards which Mr. Sheepshanks considered properly available 

 for this purpose, with the following results : — 



