Tides in the Mediterranean and Adjacent Seas 



383 



Thorade, 1921, p. 105) has developed this method to compute the tidal 

 phenomena, and it agrees very well with the observations. 



The period of the free oscillation of the Channel supposed to be closed 

 at both ends is 29-5 h and, therefore, the independent tides are absolutely 

 unimportant in respect to the co-oscillating tides. The latter can be assumed 

 to be composed of (a) the co-oscillation of the water-masses of the Channel 

 with the Atlantic Ocean if the North Sea is supposed to leave no tides, and (b) 

 co-oscillation with the North Sea if the Atlantic Ocean is supposed to be free 

 of tides at the western opening of the Channel. Both parts can be computed 

 step-wise, according to the methods already explained. If at first the friction 

 is neglected, both are standing waves which, v being = 2-4, have two nodal 

 lines inside the Channel. Of course, they do not coincide; besides, these 

 standing waves have a phase difference of llh, so that their superposition 



800 



600 



400 



200 



(bi 



Fig. 159. Semi-diurnal tide in the English Channel and in the Hoofden. (Spring tide values 

 from the tide tables.) (a) shows the range, (b) shows the establishments in lunar hours. 



gives the picture of a wave travelling from west to east. If friction is 

 considered, it causes the transformation of the nodal lines of each co-oscillat- 

 ing tide into a crowding of the co-tidal lines, but this does not essentially 

 modify the picture. The computed horizontal water movements permit the 

 approximate determination of the influence of the Coriolis force. A noticeable 

 fact is that the rotation of the earth is not able to transform the crowding 

 of the co-tidal lines into an amphidromy in the narrow part of the Channel 



