THE TIDES. 



277 



earth facing the sun and moon at this point of hor orbit must have an 

 equally high tide at this time. The centripetal force here is produced 

 by the gravity of both sun and moon acting jointly. 



Let us now suppose the moon to be in quadrature, as at B. Then 

 the two centrifugal forces, the one produced by revolution around the 

 sun, the other by revolution around the centre of gravity of these two 



Mf) B 



O 



Fig. 2. 



bodies, do not act in the same line of direction, but at right angles 

 with each other. The phenomena of solar and lunar tides are then 

 about 90 apart ; the solar being the smaller and the lunar the larger. 

 Here the centres of both earth and moon are in the path described 

 by their centre of gra-vity. 



In the last place, let us suppose the moon and sun to be in oppo- 

 sition, as at C. Then, according to my theory, the earth feels, on 

 her side farthest from the sun, an influence which diminishes the 

 centrifugal force produced by her orbital revolution. For at this 

 point the earth's centre is icithin and the moon's centre is without the 

 elliptic path described by their centre of gravity. Here the revolu- 

 tion of the earth around this centre of gravity is contrary to her gen- 

 eral motion around the sun. But what is thus lost in centrifugal force 

 on her side turned away from the sun is more than made up by the 



