Tides in the Mediterranean and Adjacent Seas 399 



eddies with a vertical axis. There are three points where they develop: (1) in 

 front of C. Peloro, i.e. the Charybdis; (2) in front of Scilla, i.e. the Scilla 

 eddies; and (3) near the Punta San Ranieri in front of the harbour entrance 

 of Messina. The eddies off Charybdis and in front of Messina are the most 

 important and they develop through the rotational movement in the eddies, 

 whereby the heavier water sinks under the lighter water; the direction of 

 rotation is mostly cyclonic. There are, however, also anticyclonic eddies, in 

 which the water rises in the centre. They are visible by a smooth, apparently 

 oily area in the centre of the eddy (macchie d'oglio). The eddies off Scilla 

 are nowadays insignificant. In earlier days their intensity and extension must 

 possibly have been greater. This decrease in intensity might be connected 

 with morphological modifications of the bottom relief off Scilla. 



7. The Tides of the Adriatic 



The Adriatic Sea has the form of a canal about 500 miles (820 km) long 

 penetrating far into the continent and ending in the Ionian Sea, through 

 the Strait of Otranto. The mean width is 100 miles (166-5 km), the opening 

 is about half this width and its cross-section has a surface of around 37 km 2 . 

 The depth chart shows two different kinds of basins ; the bottom in the north- 

 ern basin slopes down regularly towards the south, up to a cross barrier 

 which separates it from the southern basin. The latter has the shape of 

 a kettle with maximum depths of a little over 3900 ft (1200 m) in the centre. 

 The mean depth of the cross-section of the opening is only 1457 ft (444 m), 

 whereas at the cross-section the maximum depth is nearly twice this figure, 

 2516 ft (767 m). Table 50 contains a compilation of the amplitudes and 

 phases of the principal components (referred to 15°E.). [Kesslitz (1919), 

 Tenani (1929)]. 



The distribution of the harmonic constants of the semi-diurnal tides along 

 the coasts indicates the presence of a well-developed amphidromy. It results 

 from the superposition of a longitudinal oscillation with a nodal line south 

 of Punta Bianche (Dugi) and the transverse oscillations caused by the rotation 

 of the earth. The ratio of the amplitudes of M 2 and S 2 is smaller than 2 for 

 all the adriatic stations, and, consequently, reaches nowhere the theoretical 

 value of 2-3. There is practically no difference between the phases, so that 

 in the Adria there is no "age of the tide". 



The diurnal tides show a quite different picture. Their amplitude de- 

 creases uniformly to the south-east and seems to become nearly zero near 

 the Strait of Otranto. The differences in phase are small and form the north- 

 ern part of a weak amphidromy, whose centre is in the vicinity of the Strait 

 of Otranto. The amplitude of the K x component exceeds that of the other 

 diurnal tides very strikingly. 



As the phases of the semi-diurnal tides vary very much in the different 

 sections of this sea and those of the diurnal tides differ only slightly, there 



