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 
44 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 1760, 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 44 perfectly identical.” This 
yard, under the denomination of 44 the Imperial Standard 
Yard,” has been declared by Parliament, on the recommen- 
dation of the Commissioners of Weights and Measures,* to 
be the 44 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. Wollaston, Dr. Thomas Young, and Capt. Henry Kater, 
