The Tides in Relation to Geophysical and Cosmic Problems 509 



eliminated the less reliable harmonic constants of certain localities and there 

 were a still sufficient number of data left to allow the determination of the 

 four unknown quantities. 



The result was that, y = \ — h + k = —042. This value is entirely at 

 variance with the other values and no explanation can be found for it. How- 

 ever, it is certain that in considering the tides of the solid earth we can re- 

 present much better the observations. 



The application of the first method shows perhaps the reasons why the 

 second method gives such a different result for y (see also Thorade, 1933; 

 see p. 411 and Fig. 173). If according to the second method, the assumption 

 that the tides of the solid earth are proportional to the equilibrium tide is 

 correct, then the relative tide of the earth (the excess of the tide of the earth 

 over the rise caused by mutual attraction of water spheroids) should have 

 the same form as the equilibrium tide itself. In reality this is not the case: 

 the curves are very much disturbed, which must probably be attributed to 

 inaccuracies in the observations. If one compares very roughly the difference 

 between the two curves, one gets, according to Grace, a ratio 1 : 4, from which 

 it follows that 



h-k =0-25 or y = l-h + k = 0:75 . 



The agreement with the value of Prey would be very good. However, this 

 estimation is very inaccurate and all one can tell for sure is that the tides 

 of the Red Sea can hardly be explained with sufficient accuracy without 

 considering the tides of the solid earth, and that the accelerations produced 

 by these latter tides will be approximately of the same order of magnitude 

 as that of the tide generating forces. 



2. Deformations of the Solid Earth by Tidal Load 



The tides of the solid earth are disturbed and cause the values of y to vary. 

 The disturbing effect is caused above all by the oceanic tides exercising varying 

 pressures on the shores, which cause deformations of the earth's crust. 



These deformations show the same period as the oceanic tides and super- 

 impose themselves on the tides of the solid earth. According to the amplitude 

 of these deformations, the tides of the solid earth may be hardly noticeable. 

 Thus, a coastal gauge will record also oscillations, which besides the general 

 tides can be explained by the attraction exercised by the water-masses which 

 are being periodically moved towards the coast by the tides and by the 

 varying loads exercised by the tides. It can be shown that, when the rocks 

 have the same degree of rigidity as glass, the direct attraction by the water- 

 masses is only one-sixth of the disturbance of the plumb line caused by the 

 loads of the tides. The effects of the variations of the slope are, therefore, by 

 far the more important. 



In order to make the effect of the tidal load clearer, Darwin (1882; 1910, 



