THE MEDITERRANEAN — THE ADRIATIC. 43 



any signs of wind or storm. A deafening noise announces and 

 accompanies this sudden swelling of the waters, which owes its 

 first origin to the silent action of gravitation, and is the result 

 of the diminishing velocity of the tide-wave over a shallow 

 bottom. 



While the tide-wave advances over the deep and open seas 

 with an astonishing rapidity, its progress up the channel of a 

 river is comparatively very slow, partly on account of the reason 

 just mentioned, and partly from its meeting a current flowing 

 in an opposite direction. 



Thus, the tide takes no less than twelve hours for its progress 

 from the mouth of the Thames to London, about the time it 

 requires to travel all the way from Van Diemen's Land to 

 the Cape of Good Hope. Consequently, when it is high-water 

 at the mouth of the Thames at three o'clock in the afternoon, 

 for instance, we have not high-water at London Bridge before 

 three o'clock in the following morning, when it is again high 

 water at the Nore. But, in the mean time, there has been low 

 water at the Nore and high water about half-way to London, 

 and while the high water is proceeding to London, it is ebbing 

 at the intermediate places, and is low water there when it is 

 high water at London and at the Nore. If the tide extended 

 as far beyond London as London is from the Nore, we should 

 have three high waters with two low waters interposed. The 

 most remarkable instance of this kind is afforded by the gi- 

 gantic river of the Amazons, as it appears by the observations 

 of Condamine and others, that, between Para, at the mouth of 

 the colossal stream, and the conflux of the Madera and MaraSon, 

 there are no less than seven simultaneous high waters with six 

 low waters botween them. Thus, four days after the tide-wave 

 was first raised in the Southern Ocean, its last undulations 

 expire deep in the bosom of the South American wilds. 



The Mediterranean is generally supposed to be tideless, but 

 this opinion is erroneous ; and in the Adriatic, the flux of the 

 sea is far from being inconsiderable, for, at Venice, the dif- 

 ference between high and low water is sometimes no less than 

 six or even nine feet. Mr. W. Trevelyan, during a summer 

 residence in the old port of Antrum, on the Eoman coast, found 

 from a series of accurate observations, that the tides regularly 

 succeed each other and attain a height of fourteen inches. 



