SIZE OF THE TIDAL WAVE. 107 



as far as the eye can see over vast tracts^ which emerge again at the 

 time of ebb. This astonishing contrast in the amplitude of the 

 tides results from differences of speed in the progress of the oscilla- 

 tions in the seas and bays of the coast-line. In fact, the great 

 swelling caused by the heavenly bodies may be considered as formed 

 of a great number of successive waves occupying a considerable 

 breadth on the surface of the sea. In the open ocean, all these waves 

 move with great speed ; but in proportion as they approach the shores, 

 they slacken their movement, and consequently must gain in height 

 what they lose in rapidity. From the mere sight of a tidal chart we 

 can affirm that the tide will rise several feet high in all the gulfs 

 where we see the cotidal lines crowded together, in consequence 

 of the gradual retardation of the wave of intumescence. 



In this respect, facts fully confirm theory. The Gulfs of Bengal 

 and Oman, the Chinese Sea, the indentations of the eastern coast of 

 Patagonia, the Bay of Panama, that of Fundy, between New Bruns- 

 wick and Nova Scotia, the Channel and the Irish Sea, are parts 

 where the waves of equal intumescence follow each other very closely, 

 and it is there too that a greater extent of coast is alternately 

 covered and revealed by the tide. In the port of Panama the tides 

 rise nearly 23 feet, concealing and discovering by turns an immense 

 strand in their diurnal movements, while at hardly 37 miles distant 

 on the other coast of the isthmus the ebb and flow are scarcely 

 perceptible. 



In the Persian Gulf and the Chinese Sea the amplitude of the 

 equinoctial tide is nearly 36 feet at the extremity of the gulfs. In 

 the mouth of the Severn and the French bay of Mount St. Michael 

 the difference of height between the spring-tides and low-water is 

 from 45 to 48 feet. To the south of the American Continent, in 

 the Gulfs of San- Jorge and Santa Cruz, at the entrance of the Straits 

 of Magellan, Fitzroy has measured tides of from 48 to nearly 66 feet 

 high ; finally, in the Bay of Fundy, so well calculated, by the con- 

 tour of its coast and the surface of its bed, to retard progressively the 

 march of the tide, the difference between high and low water, which 

 is about 9 feet at the entrance, gradually increases to nearly 69 

 feet towards the extremity of the channel. This is probably the 

 part of the coast where the regular oscillations of the waters are ac- 

 complished in the grandest manner. Twice a day immense neutral 

 shores, which are neither land nor sea, change into deep gulfs^ and 

 stranded ships rise and float with sails spread, whilst towns lost in the 

 * De Boucheporn, Fhilosophie Naturelle. 



