The Greenwich Meridian

Currently viewing images from 05 May 2018

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One of three similar plaques located immediately to the north and south of Greenwich Park. Two face south and have east marked on the right and west on the left. This one faces north and has the east and west markings reversed.

In 1984, a theodolite was set up on the roof above the Airy Transit Circle in order to determine the path of the Line across Greenwich Park so that it could be marked for the ‘Meridian Day’ celebrations. It was at this point that it became apparent that the plaque had been mounted about six metres to the east of where it should have been. It had long been believed that Ordnance Survey maps were based on the Airy Meridian. That they were still based on the earlier Bradley Meridian only re-emerged in the 1950s during the retriangulation of Britain. As a result, a small offset needs to be applied when using an OS map. Although this fact remains largely unknown, whoever was responsible for fixing the plaque was aware of it, and not realising that the offset had already been applied, applied it again. It seems likely that the same error applied to the other two plaques, and that like this one, they were subsequently relocated. The scarring on the wall from where the plaque was originally positioned is still visible (seen best in raking light) and has been marked in red in the 2009 image set. The vertical line linking the plaque with the line on the pavement below was added when the wall was re-rendered in the summer of 2013.