TIDES AND OCEANIC HIGHWAYS. 



357 



and fifty feet. At St. Maloes, on the north coast of France, the tide attains the height 

 of fifty feet, and even sixty in the Bay of Fundy in the United States, where its rise is 

 at the same time so rapid, that cattle feeding on the shores have been surrounded and 

 swept off by it. On the contrary, in narrow seas situated like the Mediterranean and the 

 Baltic, there is scarcely any tide whatever ; while in Hudson's and Baffin's Bays and the 

 Red Sea, the influence of the tidal current is strongly felt. A slight inspection of their 

 geographical position will explain the reason of this. The mouths of the latter 

 oceanic estuaries open in the direction of its advancing tide-waves, while the entrances 

 of the Mediterranean and the Baltic are at acute angles with reference to them, 

 arid being turned from the main direction of the Atlantic tide, but a small portion 

 of its waters passes through them, not sufficient to produce any marked alteration in 

 the level of those seas. In addition to this, their dimensions are too limited to allow of 

 the moon's action being unequally exerted upon them, were they in the direct line of her 

 attraction, so that the equilibrium of the surface is not greatly disturbed. The highest 

 tidal rise in the Mediterranean occurs to the eastward of Sicily, where a wave is raised 

 which flows up the Adriatic, elevating the waters of that close sea nearly four feet at 

 new and full moon, and half that height at neap tides, alternately covering and laying bare 

 the bottom of the Venetian lagoons. At Antium, Mr. Trevalyan found, by a series of 

 observations, regular tides in the summer of 1836, rising there to fourteen inches ; and a 

 tide was noticed by M. D'Angos, at Toulon, on the coast of France, where the sea rose a 

 foot about three hours and a half after the moon passed the meridian. In the east of the 

 Mediterranean also the tides are felt, and slightly so in the Grecian Archipelago, where 

 a gentle rise of the waters in the port of ^gina and the gulf of Corinth has been 

 observed. But the general level of the Mediterranean fluctuates only a few inches. 



Port of Egina. 



Hence the soldiers of Alexander were alarmed on beholding the high tide at the mouth 

 of the Indus, and the troops of Caesar were filled with consternation on witnessing a 

 similar spectacle upon our own coast, their previous knowledge of oceanic phenomena 

 having been confined to the seas of Italy and Greece. 



Winds have a powerful influence upon the tidal currents, especially in narrow seas and 

 river channels, keeping them back when blowing from an opposite quarter, and acce- 

 lerating their flow when pursuing the same direction ; so that the tide will rise above its 

 usual level, or fall below it, according as a strong wind co-operates with it or not. An 

 experiment made by Smeaton shows, that in a canal four miles long, the level of the 



A A 3 



