RE-MEASUREMENT OF THE OLD 10-FT.LENGTH STANDARDS O1 AND OI1 OF THE ORDNANCE SURVEY,AND SOME NOTES ON THE RELATIVE STABILITY OF CERTAIN STANDARDS OF LENGTH

Abstract

The old 10-ft. length standards of wrought iron, O₁ and OI₁, made for the Ordnance Survey in 1826 and 1856 respectively, are briefly described and some account is given of the purpose for which they were constructed.

Both these 10-ft. standards were measured in terms of the Yard in 1864, and one of them in terms of the Metre in 1906. They have recently been re-measured at the National Physical Laboratory, and it was found that, allowing for the known shortening of the Imperial Standard Yard since 1895, the 10-ft. Ordnance Survey standards have remained unchanged in length during the last 50 years or so. Furthermore, if it is assumed that the Imperial Standard Yard shortened rather more rapidly between 1853 and 1895 than it has since that date, then the 10-ft. standards can be said to have remained substantially unchanged in length for nearly a century.

Additional evidence for the change in the length of the Yard between 1853 and 1895 is provided by the results of measurements made in 1864 on some of the old Toise standards used for geodetic surveys on the Continent, and by some recent measurements made at the N.P.L. of another yard standard contemporary with the Imperial Standard.