CnAr. IX.] SOLAR AND LUNAR GRAVITATION. 105 



and as it rotates its gravitation tends to carry the 

 earth with it, the latter endeavouring to maintain its 

 position in relation to the nearest part of the surface 

 of the sun. But as the sun's gravitation endeavours 

 to carry the earth eastwards, it endeavours to draw it 

 from the position in which astral gravitation tends to 

 hold it. And this latter force prevents the earth from 

 maintaining its position in relation to the rotating 

 surface of the sun. And though the earth is drawn 

 onwards in its orbit by solar gravitation, it is, in con- 

 sequence of the retarding action of astral gravitation, 

 constantly falling westwards in relation to the surface 

 of the sun. 



As the attraction of solar gravitation draws the 

 earth onwards in its orbit, it draws the solar tide 

 (westwards in relation to the surface of the earth) to 

 that part of the surface of the earth which is in advance 

 in the earth's orbital motion. This is a meridian 

 somewhat nearer that of the sun than the meridian of 

 6^ A.M. Let us, for the present arbitrarily, suppose 

 this to be the meridian of 6^^ a.m. And astral gravi- 

 tation — acting in exactly the opposite direction to that 

 in which the sun's attraction tends to carry the earth — 

 draws the counter-tide westwards, to the part of the 

 earth opposite that to which the solar tide is drawn. 

 This is a meridian more remote from the sun than the 

 meridian of 6^ p.m., and doubly remote from that 

 which is most behind in the central line of the earth's 

 orbital motion. The positions of the solar tide c d, 



