6 Captain Kater's account of the 



disappearances alone is productive of no error, if the ob- 

 servations are made as nearly as may be under similar 

 circumstances. 



With respect to the absolute length of the pendulum in 

 London, as determined by means of the convertible pendu- 

 lum, it must be evident from what has been advanced, that 

 the method of observation by disappearances alone could, 

 on that occasion, have been productive of no error, as the 

 disk subtended precisely the same angle as the tail-piece of 

 the pendulum. 



In the Philosophical Transactions for 1821 will be found 

 " An account of the comparison of various British Standards 

 of linear measure \" and it will there be seen that the differ- 

 ence between Sir George Shuckburgh's standard scale and 

 a standard yard of 1 760, made by Bird, and in the custody of 

 the Clerk of the House of Commons, is so very small, that 

 they may be considered as " perfectly identical." This 

 yard, under the denomination of " the Imperial Standard 

 Yard,'' has been declared by Parliament, on the recommen- 

 dation of the Commissioners of Weights and Measures,* to 

 be the " unit, or only standard measure of extension" of the 

 United Kingdom ; consequently, the length of the pendulum 

 before given is expressed in parts of the Imperial Standard 

 Yard. 



The measures of capacity being dependant upon the weight 

 of a cubic inch of distilled water, it became necessary to 



* A commission was appointed by letters patent under the Great Seal of the 

 United Kingdom in 1818, '* For considering how far it might be practicable and 

 advisable to establish a more uniform system of Weights and Measures," the 

 members of which were, the late Sir Joseph Banks, Sir George Clerk, Mr. Davies 

 Gilbert, Dr. W. H. WoUaston, Dr. Thomas Young, and Capt. Henry Kater. 



