124 THE OCEAN. 



CHAPTER XY. 



EBB AND FLOW IN LAKES AND INLAND SEAS, — CURRENTS OF THE EURIPUS. — 

 SCYLLA AND CHARYBDIS. 



The attraction of the sun and moon act no less on enclosed seas 

 than on the great ocean ; but in basins of small extent, the tide has 

 not the necessary space to rise, and develop itself in an appreciable 

 manner. Lake Michigan, which, although not less than 56,000 

 square miles in extent, is the smallest surface we are acquainted with 

 where the regular return of the ebb and flow have been established 

 with precision; the amplitude of the tide there, is, according to 

 Lieut. Graham, less than 3 inches. Still, it is undoubted that the 

 smaller lake-basins also experience normal oscillations every 12 

 hours ; measures carefully made will probably reveal them one day. 



Even in the vast Mediterranean the tides are very little perceived, 

 excepting in the Gulfs of Syrtes, between the ancient Pentapolis and 

 Tunis. In this part the phenomenon of the ebb and flow occurs 

 with the greatest regularity, and one can study its progress as in the 

 ocean. At the mouth of Oued-Gabes, almost at the end of the 

 lesser Syrtes, the water alternately rises and falls at least 6 J feet. 

 More to the north, in the port of Sfax, the average difierence be- 

 tween high and low water is about 5 feet, but at the epoch of the 

 equinoxes this difierence attains to nearly 8 feet. Finally, at the Island 

 of Dj erbah, the ancient island of the Lotophagi, the mean amplitude 

 of the tide is not less than 9 feet 10 inches.* This remarkable 

 height of the tide on the shores of the Syrtes doubtless arises from 

 the Mediterranean presenting in its southern part, from Port Said 

 to Ceuta, a single basin, wdth a slightly sinuous bank, while on the 

 coast of Europe it is divided into a number of smaller seas, those of 

 Sardinia, the Adriatic Gulf, the Ionian Sea, and the Archipelago. 

 Besides, the winds being much more regular on the African coast, the 

 alternate play of the tides is not disturbed there, as on the coasts of 

 Europe, which belong to the zone of variable winds. 



* Victor Guerin, Voyage Archeologique en Tunisie, t. 1st. 



