222 report— 1877. 



site of a gauge purporting to be a reproduction of the Old Dock sill), the fol- 

 lowing remark occurs : — " 17'8 Bottom of 22nd figure on gauge." By exa- 

 mination of this gauge it appears that this would give 4*20 feet as the height 

 of the Ordnance Datum above the zero of the Old Dock sill. Tet on page 2 

 of the 'Abstract of Levelling' above quoted, the difference is given as 4 - 67 

 feet. Both levels cannot, of course, be correct. 



The Liverpool Borough Engineer's Office had ever since 1847, when the 

 above tracings were supplied, observed the 4-20 feet difference for the levels 

 throughout the town ; while the Waterworks Office (until lately distinct from 

 the former, though now combined with it) had made use of the 4-67 feet 

 difference. It may here also be remarked (as will be seen further on) that 

 the Engineer's Department of the Mersey Docks and Harbour Board made 

 use of and published 5 feet as the difference between the Ordnance Datum and 

 the Old Dock sill level. 



2. The existence of the two gauges, each purporting to be referred to the Old 

 Dock sill. 



A few words as to the history of the Old Dock sill may not here appear 

 inappropriate. 



The Old Dock at Liverpool (whence the Old Dock sill datum takes 

 its name) was opened on August 31st, 1715, and closed on August 31st, 

 1826. During this interval a " Dry Dock " had been added on the river 

 side of the " Old Dock." This dock having been altered into a wet dock, 

 and opened on December 12th, 1829, the level of the Old Dock sill, thence- 

 forward covered with water, was transferred to the S.E. corner of the new 

 dock ; in 1832 this new dock assumed the name of the " Canning Dock." It 

 was subsequently enlarged and reopened on May 9th, 1842. During this 

 operation the Old Dock sill gauge must have been temporarily removed else- 

 where, since the present eastern wall (near to the S.E. corner of which this 

 gauge now stands) is considerably further inland than was the eastern wall 

 of the " Dry Dock " against which it formerly stood. 



In 1844 the approaches to the Canning Dock, having been enlarged, were 

 opened under the name of the Canning Half-tide Dock, the two entrances 

 from the river having between them the " Canning Island." To the river- 

 face of this " Canning Island " was also transferred the level of the Old Dock 

 sill by Mr. John B. Hartley, the Engineer to the Liverpool Dock Committee, 

 and subsequently to the Mersey Docks and Harbour Board. Captain Graham 

 H. Hills, B.N., the present Marine Surveyor to the Mersey Docks and 

 Harbour Board, was informed in 1861, by Mr. J. B. Hartley, that this was 

 the only trustworthy tide-gauge, as representing the Old Dock sill one. This 

 gauge is placed in a conspicuous position facing the river, with the following 

 heading in large letters over it, " Tidal datum, as transferred in 1843 from 

 the Old Dock sill ;" while the gauge at the S.E. corner of the Canning Dock 

 (which must have been re-transferred there when the dock was enlarged, and 

 during which process the error might have occurred) is placed unostentatiously 

 in an obscure corner, where its existence is almost forgotten. 



A series of check-levels*, taken under the direction of Mr. G. P. Deacon 

 of Liverpool, whose attention was naturally drawn to the anomaly in 1871, 

 when the Borough Engineer's and the Waterworks Departments were both 

 placed under his charge, show that the zero of the Old Dock sill gauge at the 

 Canning Island (the prominent one) is 4 # 66 feet below the Ordnance Datum 

 (thus conciding nearly with the 4-67 feet of the Ordnance Book of Levels); 



* See Appendix. 



I 



