﻿12 



Solar Semidiurnal Tide. 



We thus find that in these high latitudes the solar tide is more magnified than the lunar, and is inverted. 

 Thus in latitude 60° the solar tide is much larger than the lunar and is inverted, whereas in latitude 70° 

 they are nearly of equal magnitude and the inversion of the solar tide still continues. 



For an ocean of twice the depth both the tides are direct, and they are not so much magnified. 



Although the Antarctic Ocean runs all round the globe it is of course unjustifiable to apply these results 

 directly to the oscillations of the actual ocean, but they serve to show that we have no reason to expect 

 considerable semidiurnal tides so near to the pole, and also that the great discrepancy between the phases 

 of Mo and So is not so surprising a fact as it might appear at first sight. 



It is useless to carry out a similar investigation for the diurnal tides, because the variations in the depth 

 of ocean exercise so large an influence on the result. We know, in fact, that for an ocean of uniform depth 

 the Ki-tide vanishes completely, and the 0-tide nearly vanishes. 



I find that the equilibrium 0-tide is 3i inches in latitude 60° and falls to 2 inches in latitude 75°. Thus 

 the amplitudes of the diurnal tides observed by the " Discovery " are very much larger than the 

 equilibrium values. 



The Scottish Antarctic Expedition passed the winter of 1903 in S. latitude 60° 44' and W. longitude 

 44° 39' at the South Orkney Islands; they were thus nearly opposite to the station of the "Discovery." 

 Their station was well adapted for determining the general character of the tides in the Antarctic Ocean. 

 The reduction of their observations was made by Mr. Selby at the National Physical Laboratory, and 

 gave the following results : — 



It will be noticed that these results are quite normal, save that the So-tide is rather large compared with 

 M2, and there is a well-marked diurnal inequality. They acquire a special interest when considered in 

 connection with the " Discovery's " results. We see that the semidiurnal tides are " inverted," but have 

 little or no retardation, whereas the Mo of the " Discovery " is small, but " direct," also with little 

 retardation. We are thus led to suspect that to the northward of the latitude of the South Orknej's, 

 where the " Scotia " wintered, the semidiurnal tides are inverted with small retardation ; that somewhere 

 between the South Orkneys and near to the Antarctic Continent there is a nodal line for the Mo-tide. 

 There must be also a similar node for the Sj-tide, and we may, perhaps, suppose that the node of the 

 S2-tide is nearer to Ross Island than that of the Mo-tide. 



When we turn to the diurnal tides we find an entirely diff"erent condition, for at both places the phases 

 are virtually identical, and there seems a. prima facie case for maintaining that the phase of the diurnal tide 

 throughout the whole Antarctic Ocean is approximately the same as in the equilibrium theory. I cannot 

 venture to offer any theory in explanation of the greater magnitude of the diurnal tide at Eoss Island than 

 at the South Orkneys. 



