ON THE DATUM LEVEL OF THE ORDNANCE SURVEY. 



227 



Municipal Offices, 

 Liverpool, 7th Sept., 187G. 



Dear Sir, — Enclosed I forward tracings showing relative heights of 

 O.B.M. on Custom House, ccc. 



( trdnance Datura. Also copy of particulars 28th August, 1876. 



I took observations this morning from O.B.M., north-west corner of Custom 

 House to gauge on the east side of the Canning Dock, and find the bottom of 

 the 22nd figure to be 17 - 78 feet (against 17'8 feet Ordnance, which is prac- 

 tically the same thing). 



Their 22-0 feet bottom of figure on Gauge, = 17 - 8 feet Ordnance Datum, 

 gives 4-2 ,, the figure used in this Department since 1847. 

 Also Tidal datum as transferred to river-face of Canning Island in 1843 

 from Old Dock sill (see observations taken Aug. 1876). 

 Sill 4-06 feet, say 4-8 feet, below Ordnance Datum. 



You will observe these Datums do not agree. 



Yours obediently, 



(Signed) Thomas Hough. 



P.S. Figures on Gauge. 



feet. 

 1826 



Above Ordnance Datum... 17'80 



Copy of Correspondence with the Engineer of the Mersey Docks and 



Harbour Board. 



Dock Yard, Liverpool, 

 30th July, 1874. 



Dear Sik, — I have your letter of the 28th instant making inquiry respect- 

 ing the actual difference of level between the datum of the Old Dock sill and 

 that of the Ordnance Survey, in reply to which I may say I have not by 

 me the result of any critical examination of the relative levels ; but I enclose 

 a copy of that part of our tabular statement referring thereto, from which 

 you will find that the Ordnance is called by us 5 feet above the level of the 

 Old Dock sill. 



J. N. Shoolbred, Esq. 



Yours faithfully, 



(Signed) George Fosbery Lyster, 

 per J. A. S. 



Q2 



