58f LECTURE XLVri. 



On the western coasts of Europe, from Ireland to Cadiz, on those of Africa, 

 from Cape Coast to the Cape of Good Hope, and on the Coast of America, from 

 California to the streights of Magellan, as well as in the neighbouring islands, 

 it is usually high water at some time between two and four hours after the 

 moon's southing; on the eastern coast of South America between four and six, 

 on that of North America between seven and eleven; and on the eastern coasts 

 of Asia and New Holland between four and eight The Society islands arc 

 perhaps too near the middle of the Pacific ocean to partake of the effects of 

 its primitive tide, and their tide, being secondary, is probably for this 

 reason a few hours later. At the Almirantes,near the eastern coast of Africa, 

 the tide is at the sixth hour; but there seem to be some irregularities in the 

 tides of the neighbouring islands. 



The progress of a tide may be very distinctly traced from its source in 

 the ocean into the narrow and shallow branches of the sea which constitute 

 our channels. Thus the tide is an hour or two later at the Scilly Islands 

 than in the Atlantic, at Plymouth three, at Cork, Bristol, and Weymouth 

 four, at Caen and Havre six, at Dublin and Brighthelmstone seven, at 

 Boulogne and Liverpool eight, at Dover near nine, at the Nore eleven, and 

 at London bridge twelve and a half. Another portion appears to proceed 

 round Ireland and Scotland into the North Sea; it arrives from the Atlantic 

 at' Londonderry in about three hours, at the Orkneys in six, at Aberdeen in 

 eleven, at Leith in fourteen, at LeostofFe in twenty, and at the Nore in 

 about twenty four, so as to meet there the subsequent tide coming from the 

 south. From the time occupied by the tide in travelling from the mouth of 

 the English channel to Boulogne, at the rate of about 50 miles an hour, we 

 may calculate that the mean depth of the channel is about 2S fathoms, in- 

 dependently of the magnitude of the resistances of various kinds to be over- 

 come, which require us to suppose the depth from 30 to 40 fathoms. In 

 the great river of Amazons, the eifects of the tides are still sensible at the 

 streights of Pauxis, 500 miles from the sea, after an interval of several days 

 spent in their passage up: for the slower progressive motion of the water no 

 more impedes the progress of a wave against the stream, than the velocity 

 of the wind prevents the transmission of sound in a contrary direction^ 

 (Plate XXXVIIL Fig. 521.) 



