110 THE OCEAN. [Book IV. 



CHAPTER X. 



MOVEMENTS OF THE TIDES IN RELATION TO THE 

 SURFACE OF THE EARTH. 



We have thus far determined the positions, in rela- 

 tion to the sun and moon respectively, in which those 

 bodies tend to raise their tides, supposing the earth 

 simply to be moved onwards in its orbit round the 

 sun, or in an orbit round the moon. Let us now 

 consider how these positions will be affected by the 

 earth's axial rotation, and what course this rotation 

 will give them over the surface of the earth. 



In the position of the tides in Fig. 2, Plate XIII., 

 the effect of the axial rotation of the earth has not been 

 taken into consideration at all. We have seen that 

 the solar and lunar tides are in conjunction when the 

 relative positions of the sun aud moon are such that 

 the earth's motion eastwards round the sun, or west- 

 wards round the moon, are in the same line. And 

 therefore, if the earth did not rotate on its axis, the 

 solar and lunar tides at the time of conjunction would 

 be on that part of the earth which is in advance in 

 those motions, the two counter- tides bemg together 

 on the opposite side, as in Fig. 2. But, as the earth 

 rotates eastwards on its axis, it tends to carry the 



