438 



Tides in the Mediterranean and Adjacent Seas 



The theoretical fundaments can be found in the paper of Grace already men- 

 tioned and its practical application causes no further difficulties. The compar- 

 ison between the results of the theory and the observations for the two partial 

 tides K ± and M 2 is given in Table 65. For the K x tide the agreement is better; 

 the average error, without considering the sign, amounts to 10° for the phase 

 and 3-3 cm (23%) for the amplitudes. The tidal currents computed for the 

 cross-sections at the openings are of the same order of magnitude as the 

 observed ones, which date from 1887 and probably are very inaccurate, but 

 in the phases there are considerable differences. In making such a comparison, 

 it should be borne in mind that the theory gives an average current for the 

 entire cross-section, but that the observations are values at a certain point, 

 which were obtained intentionally at the point where the current is strongest. 

 Besides, they are based on measurements extending only over a few days 

 and can be considerably disturbed by wind and stowing. Figure 186 gives 



Fig. 



186. Co-tidal lines and amplitudes of the K t tide in the Gulf of Mexico. — 

 referred to the centre meridian 89-9° W.; , amplitude in cm (Grace). 



-, phases 



the co-tidal and co-range lines of the K x tide constructed from the theoretical 

 values. With the exception of the areas in the vicinity of the opening, this 

 tide occurs almost simultaneously in the entire Gulf. The amplitude increases 

 from 10 cm in the east in a counter-clockwise revolution, to about 20 cm 

 in the south. The wave apparently penetrates through the Strait of Florida 

 and circulates around the Gulf in the positive sense, leaving it in the Strait 

 of Yucatan. It can be concluded from the tides of the single components 

 that the diurnal tides are almost exclusively co-oscillating tides, whereas the 

 independent tide becomes of less importance. 



The computations for the M 2 tide are more difficult. It was necessary to 

 reject the observations at the north-east coast, which has high amplitudes of 

 more than 30 cm (1 ft) because these stations are apparently disturbed by 

 local influences (extensive, shallow areas off the coast). There was an average 



