MR. LUBBOCK ON THE TIDES. 145 



Mr. W. Peirce, of the London Docks, under whose care the observations have been 

 made, has kindly communicated to me the following information. 



The observations were originally instituted at the instigation of Mr. W. Vaughan, 

 of Fenchurch-street, then one of the directors, in consequence of having seen aa 

 account of the tides kept at Liverpool. The time was always taken by Wapping 

 church clock, which is considered in Wapping as good a timekeeper as any in Lon- 

 don. The observations, previously to the opening of the Docks, viz. from 1801 to 

 January 1805, were taken by Mr. Peirce in the day, and by a foreman in the night. 

 After the Docks opened, from 1805 to 1828, inclusive, they were taken by the watch- 

 man in the day, and by Mr. Peirce and two foremen, who attended alternately, four 

 teen nights each. From 1823 up to the present time they are taken in the day by the 

 foreman at the entrance lock, in the night by two foremen alternately. The time has, 

 at my instigation, been more particularly attended to since I had the accounts (1829), 

 when Mr. Peirce gave the foreman charge to be particularly careful. The heights, 

 previously to the opening of the Docks (viz. 1801 to 1805), were taken by the 

 averaged eighteen-feet tide at the Trinity marks, or, as it is called. Trinity datum. 

 The marks were fixed in a wall where the entrance now is. The lock being made five 

 feet deeper than Trinity datum, there are twenty-three feet at the lock when the water 

 is at the eighteen-feet mark Trinity datum ; therefore the difference between the lines 

 from which the heights are reckoned in the books containing the observations" is five 

 feet ; so that eighteen feet previously to 1805 is the same height or depth as twenty- 

 three feet after that time. In similar accounts of tide observations, the initials or the 

 name at full length of the observer should be affixed to each observation, in order to 

 afford a check upon the care with which they are made. 



Sir John Hall has kindly favoured me with the following information relative to 

 the influence of the wind upon the tides in the port of London. Sir John Hall 

 procured the joint opinion of some nautical men, including the dock-master of the 

 St. Katharine Docks, and the senior harbour-master of the port. The following is the 

 result of their sentiments respecting the influence of the wind upon the tides in the 

 river Thames. 



During strong north-westerly gales, the tide marks high water earlier than other- 

 wise, and does not give so much water, whilst the ebb-tide runs out later, and marks 

 lower ; but upon the gales abating, and the weather moderating, the tides put in, and 

 rise much higher, whilst they also run longer before high water is marked, and with 

 more velocity of current, nor do they run out so long or so low. The reason assigned 

 for all this is, that the strong north-west winds drive the sea along the Dutch coast, 

 through the straits of Dover, and consequently away from the mouth of the Thames ; 

 so that the tides, during north-west winds, are always much higher (producing fre- 

 quently ruinous flooding,) on the Dutch than upon the English coast. A south- 

 westerly gale has a contrary effect generally, and an easterly one gives some water ; 

 but the tides, in all these cases, always improve the moment the weather moderates. 



MDCCCXXXIV. u 



