436 Tides in the Mediterranean and Adjacent Seas 



Ferrel (1874, p. 245) mentioned the diurnal nature of the Mexican tides. 

 Harris (1900, Part IV A, p. 661) has expressed the opinion that, for the 

 diurnal tide, the Gulf of Mexico and the Caribbean form one single oscillat- 

 ing system with a nodal line extending from Western Haiti to Nicaragua. 

 The consequence of this would be that the tides of the Gulf are essentially 

 simultaneous. Endros (1908, p. 86) has shown that, with a nearly convex 

 parabolic normal curve the period of the free oscillation of the system comes 

 close to 24 h, which would explain the prominence of the diurnal components. 

 Wegemann (1908, p. 532) has also assumed a resonance effect of the diurnal 

 components in the Gulf of Mexico. He computed as period of the free 

 oscillation 24-8 h for a west-east oscillation of the Gulf (Cuba- Vera Cruz 

 / = 1650 km = (1000 land miles) mean depth 875 m (2625 ft) with an open- 

 ing correction of \\. v = 0-4 and when the water-masses of the Gulf co- 

 oscillate with the diurnal tides of the Atlantic Ocean, there will be a simul- 

 taneous rise and fall of the water surface in the Gulf which conforms to 

 the observations. For the semi-diurnal tides, v = 8, i.e. the semi-diurnal 

 tides co-oscillating with the Atlantic Ocean will have one nodal line ap- 

 proximately on a line Mississippi River delta — Yucatan peninsula which, is 

 transformed into a weak amphidromy rotating to the right by the rotation 

 of the earth. Sterneck (1920, p. 131; 1921, p. 363) has assumed for the semi- 

 diurnal an amphidromy rotating to the left having its centre in the middle 

 of the Gulf, and for the diurnal tides a co-oscillation with the Atlantic Ocean 

 but with an opposite phase (see also Defant, 1925). 



Grace (1932, p. 70; 1933, p. 156) has developed an entirely new method 

 to investigate the tides in deep adjacent and boundary seas, which he tested 

 for the first time for the Gulf of Mexico. It consists essentially in dividing 

 the sea under consideration into a number of rectangular basins of ap- 

 proximately uniform depth ; some of these are closed at one or more of their 

 sides, whereas the other sides are open. Grace then applies his solutions of 

 the tidal motion in a deep rectangular basin (Grace, 1931, p. 385) to this 

 system of regularly shaped basins. For such a basin open on one side, he 

 assumes a tidal current of the tidal period under consideration entering 

 through this side and computes theoretically the average range on each side 

 of the basin; that is the part directly generated by the tide-producing forces 

 (independent tide) in a basin imagined to be closed, as well as the part gener- 

 ated by the assumed tidal current at the open end (opening). After all the 

 computations have been made for all partial basins, we obtain the theoretical 

 tide at each coastal point as the total sum of all the influences of all adjoining 

 partial basins, and a comparison with the observed values makes it possible to 

 compute the unknown tidal currents at the opening. The totality then should 

 give the tidal picture for this sea as it is formed by the independent and co- 

 oscillating tides. Figure 185 shows how the Gulf of Mexico is schematized 

 by a succession of lines A , B, C, ... , K, the sides CD, DE, FG being considered 



