MEETING OF THE TIDES. 



Ill 



into the Irish Channel, meets at the end of the Gulf where the 

 Severn discharges itself, another wave older by twelve hours, which 

 has just made the entire circuit of Ireland. These two waves, 

 united into one, take the common direction which results from their 

 original impulsion, and flow together into the Gulf of the Severn. In 



t.Ooe&saxti 





Kxresi 



V^«^?^ 



m 



Fig. 38.— Tides of the English Channel. 



the same manner, the tide which enters the Channel meets off Jersey 

 with another wave, which has made the tour of the British Isles in 

 twenty-four hours, and the two joining each other, dash their 

 enormous liquid mass against the strand and rocks of Brittany. 



If two tides coming from opposite points, and meeting at the time 

 of high tide, are thus combined in one, they, on the contrary, 

 neutralize and suppress each other, when the ebb of the one crosses 

 the flow of the other. A phenomenon of interference occurs then 

 comparable to that of two luminous vibrations extinguishing each 

 other. Fitzroy was the first who pointed out a region of the 

 ocean where contrary tides maintain the surface of the water in 

 equilibrium. This region is the estuary of La Plata. At sight of 

 this gulf, which is no less than 150 miles at the entrance, one would 

 be tempted to believe^ that the amplitude of the ebb and flow would 

 be as enormous there as in the Bay of Fundy or the Gulf of St. Malo. 

 But, on the contrary, the tides there are scarcely anything. The 

 strong oscillations of the level that have been observed in that 



