268 Mr. J. Nixon on the Tides in the Bay of Morecambe. 



house. With this distance, and the vertical angles measured 

 at the wall by the sector, we get 



Height of wall above breakwater pole top, (the \ Feet, 

 mean of three observations in 1829 and 1832, > 43*2 

 varying from 43*1 to 43*2) J 



Height of wall above pole base, (the mean of) 



eight observations, in 1829, 1830, and 1832, V 71*2 

 varying from 70'9 to 71*4) J 



Hence the canal will be 30*2 feet above the top, and 58*2 

 above the base of the pole. 



Notwithstanding the present dilapidated state of the break- 

 water, the measurements do not indicate any alteration of level 

 in the pedestal of the pole. 



Height of Neap and Spring Tides at Hey sham. 



The tide deserts Hest sands soon after half-ebb, and at 

 Poulton, two miles to the west-south-west, it either ebbs out 

 at spring tides, or is cut off by a two- foot bar of sand. In 

 Heysham lake, 5 miles south-west of Hest-bank, there is, 

 however, constantly deep water, communicating without cur- 

 rent (?) with the open sea. 



July 20, 1832, two days before the neap tides were at a 

 minimum, a stake was driven just within the margin of the 

 lake down to the exact level of its unruffled surface when at 

 the lowest (or about 10 h 2 m a.m., mean time). The height of 

 high water was marked (in a dead calm) true to an inch or 

 two (at 3 h 57 m p.m.) by a similar stake driven (820 yards to the 

 eastward of the other) into the sands near the road from 

 Upper Heysham to the shore. The difference of level of the 

 two marks was found by the six-inch theodolite and two six- 

 feet levelling staves, divided on both sides into inches, of which 

 the fractional parts, as the staves were unfurnished with slid- 

 ing vanes carrying verniers, were visually estimated. The 

 level (bubble) of the theodolite was properly adjusted, but 

 from a defect in the screw-key, the line of collimation, which 

 pointed too high by one tenth of an inch in a distance of fifty 

 feet, could not be rectified. To meet the evil, the instrument 

 was invariably placed (between and) equidistant from the two 

 staves previously set up perpendicularly (by a plumb-line) at 

 distances from each other not exceeding 100 feet*. Two 

 staves were indispensable on account of the slight, yet gradual 



* Or, when the sum of the distances from the instrument to the staff in 

 one direction equal the sum of those to the staff in the other direction, a 

 compensation of errors takes place. 



