Trinity High-water Mark
Trinity High-water Mark is placed in various parts of London, as described in the Register of Tides in the River Thames, printed by order of the Honourable Court of Commissioners, of the 26th of October, 1849; and every bench-mark in London is shown in feet and decimals of feet above an oblate spheroidal datum plane, decreasing in radii towards the north pole from the centre of gravity between the parallels of latitude at London and Liverpool, about 2·02 feet, or 24¼ inches, which is evidently worthy of consideration, at a rate of 2 feet to the mile in 40 miles of sewer. The difference at Liverpool is also given in the aforesaid Report; and this may prove of public utility if reported on by the engineer employed in the levelling of the main drainage of London. The Ravensbourne drainage is a specimen of such levelling. The approximate mean water at Liverpool is 12½ feet below the level of Trinity High-Water at London, as described identical with the level of the datum plane of the Ordnance survey of London, which is also 12½ feet below the level of Trinity High-Water mark.