TIDES. 



53 



to 3 or 4 feet at the head of the Adriatic Sea, probably from the 

 same cause as that referred to in connection with the great range 

 in the Bristol Channel and elsewhere. In view, however, of the 

 general shape of the Adriatic, one would scarcely have expected 

 to find the tidal range there affected to such an extent. 



Double Tides. What is known as a double tide, or double 

 high water, is usually caused by portions of the tidal wave 

 reaching a given locality by different routes, their respective 

 times of arrival depending upon the distance traversed, difference 

 in velocity which is generally occasioned by variation in depth 

 or by other physical conditions. 



Ordinary Neap Tide. 



Diagram showing commencement of long series of Earthquake Waves caused by volcanic 

 eruption at the Straits of Sunda, as recorded by the tide-gauge at Port Elizabeth. 

 August 27, and following days (1883). 



The dotted line shows the normal curve of tide. Abnormal waves did not disappear from 

 the diagrams for seven days. 



FIG. lO.Tidal curves, Port Elizabeth (South Africa). 



A well-known example of this one of many is to be found 

 at Southampton, where the western channel of the Solent affords 

 a deeper and more direct course to the town than the eastern 

 arm. The portion of the tidal wave which passes up this 

 channel therefore reaches Southampton earlier than that which 

 passes up the eastern channel, and so an apparently double tide 

 is formed, as indicated by the diagram (Fig. 11, C) on next page. 



