94 THE TIDAL WAVE. SECT. XIII. 



enters the Indian Ocean, strikes with violence on the coasts of 

 Hindostan and the shores at the mouths of the Ganges, and 

 causes the terrific bore in the Hoogly. The part of this tidal 

 wave that enters the Atlantic passes impetuously along the 

 coasts of Africa and America, arriving later and later at each 

 place. It is modified, however, by a tide raised in the Atlantic, 

 which is deep and free from islands ; and this combined tidal 

 wave, still coming northward, pours its surge into the Gulf of 

 Fundy to the height of fifty feet ; then being deflected by the 

 coast of America at right angles, it rushes eastward, bringing 

 high water to the western coasts of Ireland and England. It 

 then goes round Scotland, brings high water to Aberdeen and 

 the opposite coasts of Norway and Denmark, and, continuing its 

 course to the south, arrives at the mouth of the Thames and 

 fills the channels of that river on the morning of the third day 

 after leaving the Antarctic Ocean. 



Thus the tides in our ports are owing to an impulse from the 

 waters of the Antarctic seas raised by the action of the sun and 

 moon. No doubt a similar action raised that tide in the North 

 Polar Ocean which Dr. Kane saw rolling on the northern coast 

 of Greenland in 82 N. latitude, but which, in the present state 

 of the globe, is imprisoned by bars of ice and ice-bound lands. 



The tidal wave extends to the bottom of the ocean, and moves 

 uniformly and with great speed in very deep water, variably and 

 slow in shallow water ; the time of propagation depends upon 

 the depth of the sea, as well as on the nature and form of the 

 coasts. It varies inversely as the square of the depth a law 

 which theoretically affords the means of ascertaining the propor- 

 tionate depth of the sea in different parts. It is one of the great 

 constants of nature, and is to fluids what the pendulum is to 

 solids a connecting link between time and force. 



For example: the tidal wave moves across the Southern 

 Ocean with the velocity of 1000 miles an hour, and in the 

 Atlantic it is scarcely less on account of the deep trough which 

 runs through the centre of that ocean ; but the sea is so shallow 

 on the British coast that it takes more time to come from Aber- 

 deen to London than to travel over an arc of 120, between 60 

 S. lat. and 60 N. lat. 



In deep water the tidal wave is merely a rise and fall of the 

 surface ; the water does not advance, though the wave does. In- 



