114 



A TEXTBOOK OF OCEANOGRAPHY 



LN is less than LO. The différences between the earth's 

 centrifugal force and the attraction of the moon at the points 

 X and L on the earth's. surface are shown by the arrows. At 

 X movable portions of the earth (sea-water) are pulled towards 

 the moon ; at L a residuum of force pulls the sea-water out- 

 wards and upwards in contrary direction to that at X. 



At P and P' a pair of forces are présent, which resuit in a 

 pull towards the earth's centre. Consequently, if we imagine 

 the earth to be covered with a liquid, there must be a heaping 

 up at X and L and a dépression at P and P'. 



George Darwin has prepared a diagram which shows the 



^.. 



FiG. 19D. — Direction and Strength of the Tide-producing Forces 



DUE TO THE MoON. (AfTER G. H. DaRWIN.) 



direction and relative strengths of thèse forces at varions points 

 on the earth's surface. 



On the water surface it is only the horizontal components 

 of the tide-producing- force which are effective. The horizontal 

 components of the tide-producing forces produce their effect 

 of " pull " precisely at those two points where the line joining 

 the tide-producing body (sun or moon) to the earth's centre 

 cuts the earth's surface. Its maximum force is attained at a 

 distance of 45° from thèse points. 



The distribution of thèse forces on a planet whose surface 

 was entirely water is shown on the accompanying figure. 



The tide-producing force, be it of the sun or the moon, 



