Tides in the Mediterranean and Adjacent Seas 381 



are lines of convergence for all phases after high water near Dover (including 

 low water at that point), and lines of divergence for the phases at or before 

 high water near Dover. The opposite holds for the channel boundary. In the 

 vicinity of the boundary lines there is, of course, no current. The velocities 

 of the current are in the vicinity of the pseudo-nodal lines between St. Albans 

 Head and Cape de la Hague, always greater than east and west thereof 

 (3-5 knots in the centre of the channel up to 5 knots at the French coast). 

 A second place where the current velocities are greater is located in the Strait 

 of Dover, where at times velocities of 5-6 knots are attained. (For flow of 

 water through the Strait of Dover related to wind and differences in sea 

 level, see Bowden, 1956). The French coast of the English Channel has 

 higher current velocities than the English side; east of the Strait of Dover 

 (Hoofden) conditions are reversed, but the velocity here is reduced to 

 l|-3 knots. 



Most tidal charts of the Channel are based upon the assumption that 

 the tide wave travels faster in the central part of the Channel because of the 

 greater depths, so that the co-tidal lines across the channel seem to be curved. 

 According to whether the bottom influence was given more or less importance, 

 the co-tidal lines are more or less convex towards the east. As explained 

 previously (p. 148), this assumption, however, is absolutely false and, there- 

 fore, such charts should be discarded. Modern methods in Hydrodynamics 

 did not substantiate such curvature in the co-tidal lines and as a matter of 

 fact the curvature, if any, would be in the opposite direction. Hydrodynamical 

 investigations were made by Doodson and Corkan (1932), who used the 

 Proudman method which has already given satisfactory results for the North 

 Sea. The small number of current observations and of stations with harmonic 

 constants in the Channel required the use also of somewhat less accurate 

 coastal tidal constants which were previously reduced. The computations 

 refer to the M 2 tide. The result for the English Channel is given in Fig. 

 158. The course of the main partial tide along the entire Channel is readily 

 seen from this figure, and it is shown that the previously given results, 

 based on coastal observations only, apply also to the central parts of the 

 Channel. 



Borgen (1898) has tried to explain the tidal phenomena in the English 

 Channel. He assumed that two progressive waves, one coming from the 

 Atlantic Ocean, the other one from the North Sea, cross each other after 

 repeated reflections in the Channel. According to recent views on the be- 

 haviour of tide waves in the vicinity of land, it is obvious that a hydro- 

 dynamical theory of the tides of the Channel must start with the fact that 

 the water-masses co-oscillate with the tides of the oceans in front of the two 

 openings. Airy had already assumed this, but did not explore it further. 

 Borgen denies this explanation, probably because in his time there were no 

 methods to verify it by means of computations. Defant (1919, see also 



