104 THEORY OF THE TIDES. [SECT. xni. 



is diminished by this tendency. On the contrary, the nioon 

 attracts the centre of the earth more powerfully than she 

 attracts the particles of water in the hemisphere opposite to 

 her ; so that the earth has a tendency to leave the waters, 

 but is retained by gravitation, which is again diminished by 

 this tendency. Thus the waters immediately under the 

 moon are drawn from the earth, at the same time that the 

 earth is drawn from those which are diametrically opposite 

 to her, in both instances producing an elevation of the ocean 

 of nearly the same height above the surface of equilibrium ; 

 for the diminution of the gravitation of the particles in each 

 position is almost the same, on account of the distance of the 

 moon being great in comparison of the radius of the earth. 

 Were the earth entirely covered by the sea, the waters thus 

 attracted by the moon would assume the form of an oblong 

 spheroid whose greater axis would point towards the moon ; 

 since the columns of water under the moon, and in the 

 direction diametrically opposite to her, are rendered lighter 

 in consequence of the diminution of their gravitation ; and, in 

 order to preserve the equilibrium, the axes 90 distant would 

 be shortened. The elevation, on account of the smaller space 

 to which it is confined, is twice as great as the depression, 

 because the contents of the spheroid always remain the 

 same. If the waters were capable of assuming the form of 

 equilibrium instantaneously, that is, the form of the spheroid, 

 its summit would always point to the moon notwithstanding 

 the earth's rotation. But, on account of their resistance, the 

 rapid motion produced in them by rotation prevents them 

 from assuming at every instant the form which the equili- 

 brium of the forces acting upon them requires. Hence, on 

 account of the inertia of the waters, if the tides be considered 

 relatively to the whole earth and open seas, there is a 

 meridian about 30 eastward of the moon, where it is always 

 high water both in the hemisphere where the moon is and in 

 that which is opposite. On the west side of this circle the 

 tide is flowing, on the east it is ebbing, and on every part of 



