THK 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 
lave 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 Maranon, 
there are no less than seven simultaneous high waters with six 
low waters hetween 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 Antium, on the Roman coast, found 
from a svries of accurate observations, that the tides regularly 
succeed each other and attain a height of fourteen inches. 
