Tides of the Oceans 487 



Kerguelen Island to the Antarctic (Gauss Station, phase 229°). With high 

 amplitudes everywhere it seems to be an oscillation opposite in phase to the 

 western and eastern sections of this ocean. 



(4) From the Gulf of Aden to the coast of Baluchistan and then to the 

 12°N. parallel on the coast of southern India there is a very small change 

 in phase. 



(5) The entire inner part of the Bay of Bengal, including the Andaman 

 Sea, is characterized by a nearly constant phase of 75°. 



The transitions between these regions are clearly defined by the coastal 

 values, but the drawing of the co-tidal lines is, however, only possible in a few 

 cases and is left to subjective interpretation. The best defined conditions are at 

 the entrance of the Bay of Bengal. From the east coast of Ceylon a crowded 

 bunch of co-tidal lines to the northern point of Sumatra with a sudden trans- 

 ition in the phase of 180°, while the amplitudes are reduced to small values 

 for M 2 (in the western section 13 cm, in the eastern section 4 cm). This points 

 clearly to a well-developed nodal line and a uniform oscillation of the entire 

 bay with a phase opposite to that of the open Indian Ocean, in the south. 



The other transitions have the forms of amphidromies of which the one 

 in front of the Arabian sea is rotating to the right and is supported by the 

 amplitude distribution in the west and the east. The two other amphidromies 

 are located at about 30° S. the western one, with its centre south of the 

 Mascarenes (amplitude here only 13 cm) rotating to the left; the one in the 

 eastern part, with its centre west of south-west Australia (amplitude only 

 5 cm) rotating to the right. 



The co-tidal lines given by Dietrich for this southern section of the Indian 

 Ocean are not as reliable and accurate as those in the northern region, but 

 they fit in with the available observations and permit an interpretation. They 

 agree with the map of Sterneck, whereas Prufer (1939) in working up almost 

 the same observations, had a different conception. Prufer completely omits 

 the western amphidromy in the southern Indian Ocean and draws the co- 

 tidal lines down to the Antarctic Continent and moves the eastern amphi- 

 dromy much farther to the north. The more recent observations rather seem 

 to confirm Dietrich's conception. Harris's map does not indicate any am- 

 phidromy at all in the south whereas in the northern Indian Ocean there 

 is good agreement with Dietrich's map. 



An excellent representation, also on a theoretical basis, of the diurnal 

 tides along the equator in the Indian Ocean was given by Fairbairn (1954). 

 The distribution of the semi-diurnal tidal constituent K 2 along the equator 

 has been calculated with the aid of known harmonic constants at approxi- 

 mately fifty coastal stations in the northern part of the Indian Ocean. This 

 has been achieved by use of a theorem in tidal dynamics, which connects 

 integrals involving the tidal elevations and currents along the boundaries 

 of an oceanic region and the equilibrium elevation over its surface (see p. 362). 



