XXI.] THE SUN. 373 



globe. But while the water is thus held to the earth, it is 

 also attracted by all the other components of the universe ; 

 and, as the particles of water are free to move, the position 

 of any given particle, and, hence, the form of the surface of 

 the whole ocean, must be determined, other things being 

 alike, by the balance of all these attractions. Most of the 

 bodies which lie outside the earth are so distant, that their 

 influence is inappreciable ; but it is otherwise with the sun 

 and the moon. Each of these pulls the water, which lies 

 on the face of the globe which is turned towards it, away 

 from the solid earth ; w hile, at the same time, it pulls the 

 solid earth away from the water which lies on the opposite 

 face of the globe. 



In any parallel of latitude, which traverses nothing but 

 sea, the contour of the latter, if left to the attraction of the 

 earth alone, will be, sensibly, a circle. Now suppose the 

 sun or the moon to come to any meridian of that parallel, 

 then the attraction of these bodies will convert the contour 

 of the ocean into an ellipse, of which the long diameter 

 will pass through the meridian in question, and that i8o'^ 

 from it; while the short diameter will traverse meridians 

 at 90° from these two. 



If, before the intervention of the sun or moon, the water 

 were everywhere of the same depth, it would now be 

 deepest at the two meridians, 0° and 180°; and shallowest 

 at 90° and 270°. In other words, it would be Jdgh water at 

 the former, and low water at the latter meridians. 



Supposing the sun or the moon to be stationary, it is 

 obvious that, in the course of the diurnal rotation of the 

 earth, every point of the ocean under the parallel of latitude 

 in question will have been twice raised to the height of high 

 water, and twice lowered to the depth of low water ; which 

 comes to the same thing, as if a wave, with a crest the 



