Thursday, 13 May 2021

Hidden Henley

Hidden Henley

SET in the steadily eroding stonework of Henley Bridge is this Ordnance Survey flush bracket with an arrow pointer, the cast lettering of “O S B M” and the number 1026.

From my research, it seems that this was part of the OS geodetic levelling surveys, including assessing its height above sea level of approximately 35m, included in the Windsor Castle to Wallingford levelling line.

This is highly specialised and beyond your diarist but what I do know is that the indents at the top of the brass plate were used to fit the surveyor’s instruments to provide an accurate reading. Modern technology has made this procedure all but redundant but there are still many of these flush brackets and trig (triangulation) points around.

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