388 Tides in the Mediterranean and Adjacent Seas 



St. George canal, subsists. In the northern part of the North Channel, there is 

 an amphidromy (exactly as in the Hoofden). Figure 162 gives a comparison 

 between the observations and the theoretical computations. The Irish tides can 

 be explained by the impulses received by their water-masses from the Atlantic 

 Ocean. There is also very good agreement between theory and observations 

 on the tidal currents. For the tidal currents in the North Channel see also 

 Proudman (1939). 



Doodson, Rossiter and Corkan (1954) have made a rather interesting 

 investigation of the tides of the Irish Sea, in which they used methods similar 

 to the so-called "relaxation methods", using finite differences in all variables 

 and attempting to satisfy all the conditions of motion within the sea, proceed- 

 ing by successive approximations. Only coastal observations of tidal ele- 

 vations are supposed to be known. There are many difficulties, peculiar to 

 the tidal problem, in the application of these methods, due to the very ir- 

 regular coast lines and depths, gaps in the coasts, shallow water near the 

 coasts, frictional forces, and the very serious complication due to the fact 

 that the tides are oscillating and thus require two phases to be investigated 

 simultaneously owing to their reactions one upon the other. 



The resulting chart is shown to be very closely the same as the existing 

 chart, thus proving the validity of the method. 



5. The Tides of the Mediterranean 



The tides of the Mediterranean, including the adjacent seas, have been 

 investigated exhaustively in more recent times, although they are com- 

 paratively weak. A satisfactory explanation was found, but it took numerous 

 new observations to arrive at a basic theory of these tides. 



A compilation has been made of all the available coastal observations 

 on establishments and tidal ranges of the western and eastern basin, and 

 of the Strait of Gibraltar and the Strait of Tunis (where the 1 5° E. meridian, 

 which divides the Mediterranean in two, has been taken as a reference). In 

 Fig. 163, drawn by Sterneck (1915, p. 905) (see also Defant, 1916, p. 462) 

 is shown schematically the distribution of the establishments; not considering 

 the Straits of Messina and of Tunis. The majority of the establishments fall in 

 two groups, namely, 3-3 and 9 3 h. At the ends of the various basins we have 

 entered the average establishment of the stations located there. The lines of 

 demarcation between the areas with the establishments 3 and 9 h are to be 

 considered as nodal lines of standing oscillations. This indicates that the 

 tides in the Mediterranean can be represented by two standing waves, one 

 covering the western, the other the eastern basin. The arrows in the figure 

 indicate the direction of the tidal currents from 3 to 9 h at the time of the 

 syzygies. In the Straits of Messina and Tunis, the rotation of the earth causes 

 strong transverse oscillations which, according to the observations, transform 

 the nodal lines into amphidromies contra solem. The other nodal lines are 



