4-92 FOURTH REPORT 1834. 



the rise of the tides at Sheerness, with the mean of Mr. Lub- 

 bocks at the London Docks, it appears that 



The spring tide high water at the London Docks 1 o-O'lfil 



above the same at Sheerness, is . . . ) 0-2068 



The mean high water ditto ditto 



The neap tide ditto ditto 



The spring tide low water ditto 



The mean level of the tides ditto 



Or, taking more correctly the half difference between "i 



spring high and low water at Sheei-ness, the I 1-7249 



mean spring level is ..... J 



It seems from the above summary, that as the water decreases 

 in height, so the height of the water's surface at London Docks 

 above the same at Sheerness also decreases, with the exception 

 of spring tides at the London Docks and the neap tide. These are 

 the means, not of the highest tides, but of the tides at a parti- 

 cular time of the moon's southing : at Trinity high-water mark 

 at London Bridge, it was found by Mr. Lloyd to be 1-9040 

 above mean spring tide high-water mark at Sheerness. 



With respect to the influence of the winds on the tides in the 

 river Thames, Mr. Lubbock states, on the authority of Sir 

 John Hall, of the St. Katharine Docks, that " during strong 

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

 otherwise, 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 long before high water is marked, 

 and with more velocity of current ; nor do they run out so long 

 or so low, &c. 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." 



The very valuable tables of Mr. Lubbock, compiled with his 

 corrections from upwards of ten thousand observations, have 

 contributed very largely to our knowledge on this subject. 



From a series of levels and observations made on the tides in 

 September and October 1820, between the entrance of London 

 Docks and Westminster Bridge, by Mr. Francis Giles, for the 

 Select Committee of the Bridge-house lands, the following were 

 found to be the facts : 



1st, The high water of spring tides at the entrance of the 



