Chapter XV 



The Tides in Relation to Geophysical 

 and Cosmic Problems 



In this chapter we will discuss a few problems which are related only in- 

 directly to the tides of the ocean and rather deal with the effect of these tides 

 on the solid earth and its movements. We have treated this matter very 

 summarily, only touching upon the most essential points, because we thought 

 that these questions should be briefly mentioned in a textbook on oceano- 

 graphy. For details we refer to the textbooks on geophysics. 



1. The Detection of the Tides of the Solid Earth from Tidal Observations in 



Shallow Adjacent Seas 



In the theory of the tides, as well in the discussion of tidal observations, 

 it is mostly tacitly assumed that the earth is completely rigid and, therefore, 

 not yielding to the tide generating forces. According to observations in 

 geophysics, this assumption is incorrect. In Fig. 208 it is shown how the 

 tides of the oceans are influenced by the tide of the solid earth if the tides 

 obey completely the equilibrium theory (see Thorade, 1933, p. 49). Assume 

 that the ocean bottom BB is rigid and a gauge PP is established at the 

 point P. High water will occur at that point and the water surface will have 

 risen from mean sea level MM to H'H , when the tide generating body is in the 

 prolongation PP (in the zenith); the gauge will register a height of water 

 AN = r\ above mean sea level at A. At A the surface will be horizontal 

 (maximum) and according to the direction of the tide generating forces (indi- 

 cated schematically on top of the figure), the surface will slope down on both 

 sides ; if this slope is a, the horizontal component of the tide generating force, 

 which must balance the pressure force, will be gtana or, a being very small, ga. 



This simple picture changes: 



(1) When one considers the variation in the height of the tide caused by 

 the tidal protuberance (see p. 284); and 



(2) If we assume a certain elasticity in the solid earth which yields to the 

 tide generating forces. The addition of the potential of the protuberance 

 causes a rise of the water level to HH and an increase in the range at the 



