158 THE OCEAX. [Book VI. 



CHAPTER Xiy. 



EVIDENCE OF THE TIDAL ACTION DESCRIBED IN 

 CHAPTER IX. 



AYe have seen, in the preceding chapter, that the 

 actual course of the tide-waves, in relation to the 

 surface of the earth, accords with the theory which 

 gives theni a motion westwards in the equatorial 

 regions, and eastwards in the temperate zones : that 

 the relative rise and fall on different coasts accords 

 with the theory which requires that the tide which 

 rolls westwards in the equatorial regions must coun- 

 terbalance that which rolls eastwards m the tem- 

 perate zones, so as to preserve the equilibrium of the 

 ocean as a whole ; and that the advanced position 

 of the tide in high latitudes is indicated by a con- 

 vergence from those latitudes towards the equator. 



As regards the hours of the spring-tides raised by 

 the sun and moon in the positions given in Fig. 4, 

 Plate XIII., we cannot, in consequence of the contor- 

 tions of coast-lines, expect, without a very elaborate 

 analysis of the subject, to arrive at more than rough 

 approximation to the theory sketched in Chapter X. 



Let us suppose that when the central part of the 

 Atlantic, midway between the coast of America on 

 the west, and that of Africa and Europe on the east, 



