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XIX. An Account of the Construction and Verification of a Copy of the 
Imperial Standard Yard made for the Royal Society. By Captain Henry 
Kater, F.R.S. 
Read May 19, 1831. 
The Royal Society having done me the honour to request that I would un- 
dertake the construction and verification of a copy of the Imperial Standard 
Yard for their use, it becomes necessary to place upon record the manner in 
which this was executed, in order that some judgement may be formed of the 
degree of confidence which may be placed in the result. 
The scale in question is constructed in the manner which I have described 
in the Philosophical Transactions for 1830 * for diminishing the errors arising 
from the thickness of the bar upon which it has hitherto been customary to 
trace the divisions. The support of the scale is of brass, forty inches long, 
If inches wide, and Toths of an inch in thickness. A brass plate of seven 
hundredths of an inch thick was made to slide freely upon the support in a 
dovetail groove formed by two side plates, and was then fixed to the support 
by a screw passing through its middle. 
This plate carries the divisions, which are fine dots upon gold disks let into 
the brass ; the scale is divided into inches, and there is one inch to the left of 
zero, which is subdivided into tenths. The scale is the work of Mr. Dollond. 
As the points designating the Imperial Standard Yard are upon a brass bar 
one inch in thickness, it was necessary to be extremely careful that the bar 
during the comparisons should be placed upon a surface as nearly as possible 
plane ; since it has been shown in the paper before alluded to, that a curvature 
of which the versed sine is only one-hundredth of an inch in a yard would 
occasion a variation in the length of this standard amounting to nearly five- 
thousandths of an inch. 
* Page 359. 
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