THE TIDES. 



Liverpool, 15-5 feet; at Portsmouth, 12 -5 feet ; at Plymouth, also 

 12-5 feet ; at Bristol, 33 feet. 



18. Besides the numerous causes of irregularity depending on 

 the local circumstances, the tides are also affected by the state of 

 the atmosphere. At Brest, the height of high water varies 

 inversely as the height of the barometer, and rises more than 

 eight inches for a fall of about half an inch of the barometer. At 

 Liverpool, a fall of one-tenth of an inch in the barometer cor- 

 responds to a rise in the river Mersey of about an inch ; and at 

 the London Docks, a fall of one-tenth of an inch corresponds to a 

 rise in the Thames of about seven-tenths of an inch. "With a 

 low barometer, therefore, the tide may be expected to be high, 

 and vice versa. The tide is also liable to be disturbed by winds. 

 Sir John Lubbock states, that in the violent hurricane of January 

 8th, 1839, there was no tide at Gainsborough, which is twenty- 

 five miles up the Trent a circumstance unknown before. At 

 Saltmarsh, only five miles up the Ouse from the Hurnber, the 

 tide went on ebbing, and never flowed until the river was dry 

 in some places ; while at Ostend, towards which the wind was 

 blowing, contrary effects were observed. During strong north- 

 westerly gales the tide marks high water earlier in the Thames 

 than otherwise, and does not give so much water, while the ebb 

 tide runs out late, and marks lower ; but upon the gales abating 

 and weather moderating, the tides put in and rise much higher, 

 while 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. 





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