Chap X.] SOLAR AND LUNAR GRAVITATION. Ill 



tides with it towards the position shown in Fig. 4. 

 They constantly endeavour to get into the positions 

 in which the lunar and solar forces respectively tend 

 to place them ; hut the surface of the earth, on which 

 they rest, as it revolves eastwards, is as constantly 

 endeavouring to carry the tides eastwards with it. 



And therefore, whatever may be the normal 

 velocity with which water would move through the 

 ocean under the action of the luni-solar force towards 

 the meridian on which that force tends to place the 

 tide, it must be constantly rising towards that meridian 

 from the east in the equatorial regions, and from the 

 west in the higher latitudes in which the velocity 

 with which the surface rotates eastwards is less than 

 the normal velocity of the tide. 



Thus, as shown in Plate XIV., the high spring 

 tide would lie diagonally across the meridian of 

 6^^' A.M., so that in the temperate regions the 

 surface of the earth would reach it in the early 

 morning, and in the equatorial regions not until 

 during the forenoon. And therefore, if an unbroken 

 expanse of ocean covered the earth, the hours of high 

 water at different places would mcrease as the distance 

 from the equator decreased, for the tide would first 

 touch the meridian in high latitudes, and then travel 

 down it from the north and south to the equator, and 

 then fall on the equator as it rose again along the 

 meridian in higher latitudes. 



Thus the luni-solar tide on the side of the earth 



