When searching the internet for more information about Beech Cottage, I came across the bench mark database, which mentioned a flush bracket on the north face of the cottage, used in the second geodetic levelling of England and Wales between 1912 and 1921.
I had no idea what a flush bracket was and had never heard of the second geodetic levelling, so decided to dig around for the detail.
It turns out that all across the UK there are symbols carved into stone, and brackets bolted onto buildings that were used to calculate heights and distances way before GPS, to ensure that the three dimensional properties of the landscape were captured correctly and maps were drawn accurately.
The first geodetic levelling of England, Wales and Scotland was carried out between 1841 and 1860.
The second geodetic levelling was carried out between 1912 and 1921, where fundamental bench marks were sunk into the ground, 25 miles apart, at the ends of long levelling lines that stretched up and across the country.
Between fundamental bench marks, flush brackets were cemented into the faces of buildings, acting as intermediary points where the height of the landscape could be measured.
Fundamental Bench Marks
Fundamental bench marks are highly stable bench marks, comprising of brass bolts at ground level, set into the top of a buried granite pillar which is encased in concrete. These are incredibly accurate immovable objects that resist any shifts in the landscape. 115 were created, and 100 years later they are still being used as the baseline for levelling of the landscape.
Flush brackets are bronze plaques which are found along levelling lines between fundamental bench marks, fixed to buildings, bridges and triangulation pillars.
Originally there were 3,000 of these, though many have been lost and destroyed as roads have been widened, bridges have been replaced and houses knocked down or remodeled.
Each benchmark contains a serial number. A record of all the remaining flush brackets can be found on the bench mark database, where enthusiasts visits the sites of flush brackets to record their condition.
I wondered why these plaques were called flush brackets. It’s fairly obvious when you know. They are cemented flush onto a wall and are used as brackets to which a small bench is attached. A staff is then rested onto the top of the bench so that a theodolite can be used to calculate the height of the landscape.
The reason they are called bench marks is because of the reference point on the flush bracket. This is a slot or mark which the bench slots into; hence ‘bench mark’.
The Wetherby To Bulmer Levelling Line
Our Georgian cottage sits on the Wetherby to Bulmer levelling line.
We travelled out to the junction between Kearby Cliff, Kirkby Lane and Mill Lane to take a look at the fundamental benchmark that marks the Wetherby end of our levelling line.
According to records, at some point between December 1918 and July 1919, flush bracket number 2389 was added to the front of our cottage.
It was recorded at a height of 117.1820 feet (35.7171 metres) above mean sea level.
Of the 37 flush brackets that were originally installed along the Wetherby to Bulmer levelling line, 25 are currently still known to be in existence.
The flush bracket on the front of our cottage is a bit of a mess at the moment, though I’ll be cleaning it up as we spend some time renovating the exterior of the cottage.
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Black and white photo and diagrams are taken from “The Second Geodetic Levelling of England & Wales 1912-1921” by Colonel Sir Charles Close, KBE, CB, CMG, FRS Director-General of the Ordnance Survey, Southampton, 1921