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XXIII. On the Error in Standards of Linear Measure, arising from the thickness 
of the har on which they are traced. By Captain Henry Kater, V.P. and 
Treasurer of the Royal Society. 
Read June 17th, 1830. 
AN the course of the adjustment and verification of the copies of the Imperial 
standard yard, destined for the Exchequer, Guildhall, Dublin, and Edinburgh, 
I discovered a source of error till then, I believe, wholly unsuspected, arising 
from the thickness of the bar upon the surface of which measures of linear 
dimension are traced. The difficulties which I experienced, and the remedy 
which suggested itself upon that occasion, and which was found efficient, are 
shortly detailed in the account of the construction and adjustment of the new 
standards of weights and measures of the United Kingdom of Great Britain 
and Ireland, published in the Philosophical Transactions for 1826. 
But as the notice there given occupies little more than a single page, and 
might therefore pass unremarked, I cannot but think that a fact of such im- 
portance in inquiries where linear measures are concerned, and which may be 
sufficient to account for the discrepancies to be found in the experiments of 
different observers, ought to be placed before the Royal Society in a more pro- 
minent point of view than that which it at present occupies. I shall, therefore, 
first extract from the paper alluded to the part to which I refer, and then add 
an account of such experiments as I have since made on the subject ; and 
describe a scale which I have caused to be constructed so as almost entirely 
to obviate the source of error of which I am treating. 
It may be seen in the paper before mentioned, “ On the Construction of the 
Standard Measures,” that Sir George Shuckburgh’s scale was employed as 
the medium of comparison ; the distance from the zero point of which to that 
marked thirty-six inches, had been found by comparisons detailed in the Phi- 
3 A 
MDCCCXXX. 
