ACTUAL STATE OF EARTH. 33 



and 136 feet in advance on leaving it. It is, therefore, in 



272 



that quadrant about y seconds = about '18" short of a 



quarter of a lunar day. This would give a result similar 

 to that already found. 



The preceding calculations are obviously applicable to the 

 case of a globe uniformly covered with water, since each 

 section parallel to the equator would give the same results. 

 The meridional wave would have no effect on the rotation. 



It is not worth while to extend our calculation to the 

 case of the moon not being in the equator. The nett 

 result would be to diminish the retardation. 



6. Application to the actual state of the earth's 

 surface. 



In attempting to apply the preceding results to the 

 actual condition of things on the earth's surface, the fol- 

 lowing points must be noted : 



First. On the earth as it actually is the effect of friction 

 proper on the tides is trifling compared with that of ob- 

 stacles. Against these the tidal current impinges, and in 

 addition the increased elevation gives the moon an in- 

 creased pull, which, if acting towards the obstacle, exerts 

 its full moment on the earth, but only for a fraction of a 

 day. 



Secondly. The existence of a retarding influence de- 

 pends, as we have seen, on the place of high water being 

 in what I have called the retarding quadrants, i.e. less 

 than six hours in time later than the moon's meridian 

 passage. If this condition is violated, the influence might 



D 



