Oy THE TIDES. 581 



supposition of the time of high water in the open sea being within an hour 

 of the moon's southing, as it must be if the depth were very great: so that 

 neither the height of the tides nor the time of high water will allow us to 

 suppose the sea any where quite so deep as 4 miles. 



The tide entering the Atlantic appears to advance northwards at the rate of 

 about 500 miles an hour, corresponding to a depth of about 3 miles, so as to 

 reach Sierra Leone at the 8th hour after the moon's southing; rliis part of 

 Africa being not very remote from thc'meridian of the middle of the south 

 Atlantic ocean, and having little share in the primitive tides of that ocean. 

 The southern tide seems then to pass by Cape Blanco and Cape Bojador, to 

 arrive at Gibraltar at the 13th hour, and to unite its eifects with those of other 

 tides at various parts of the coast of Europe. 



Wc may therefore consider the Atlantic as a detached sea about 3500 miles 

 broad and 3 miles deep; and a sea of these dimensions is susceptible of tides 

 considerably larger than those of the ocean, but how much larger we 

 cannot determine without more accurate measures. These tides would happen 

 on the European coasts, if there were no resistance, a little less than 5 hours 

 after the moon's southing, and on the coast of America, a little more than 

 seven hours after; but the resistance opposed to the motion of the sea may 

 easily accelerate the time of high water in both cases about two hours, so 

 that it may be a little before the third hour on the western coasts of Europe 

 and of Africa, arid before the fifth on the most exposed parts of"the eastern 

 coast of America; and in the whole of the Atlantic, this tide may be com- 

 bined more or less both with the general southern tide, and with the par- 

 tial effects of local elevations or depressions of the bottom of the sea, which 

 may cause irregularities of various kinds. The southern tide is, however, 

 probably less considerable than has sometimes been supposed, for, in tlie 

 latitudes in which it must originate, the extent of the elevation , can only 

 be half as great as at the equator; and the Islands of Kergulen's Land 

 and South Georgia, in the latitudes of about 50" and 55°, have their 

 tides delayed till the 10th and 11th hours, apparently because they receive 

 them principally from distant parts of the ocean, which are nearer to the 

 equator. 



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