THE TIDES. (APP. A.} 197 



moon nearest to the earth tend to fall most rapidly, 

 the parts furthest from the earth, least rapidly ; in 

 its own circle, each is falling away and the result is 

 as if we had the moon falling directly. 



But while the moon is always falling towards the 

 earth, the earth is always falling towards the moon ; 

 and each preserves a constant distance, or very 

 nearly a constant distance from the common centre 

 of gravity of the two. The parts of the earth 

 nearest to the moon are drawn towards the 

 moon with more force than an equal mass at 

 the average distance ; the most distant parts are 

 drawn towards the moon with less force than 

 corresponds to the average distance. The solid 

 mass of the earth, as a whole, experiences y 

 according to its mass, a force depending on the 

 average distance ; while each portion of the water 

 on the surface of the earth experiences an attractive 

 force due to its own distance from the moon. The 

 result clearly is, then, a tendency to protuberance 

 towards the moon and from the moon ; and thus, 

 in a necessarily most imperfect manner, I have 

 explained to you how it is that the waters are not 

 heaped up on the side next the moon, but are 

 drawn up towards the moon and left away from 

 the moon so as to tend to form an oval figure. 

 The diagram (Fig. 21, p. 161) shows the pro- 

 tuberance of water towards and from the moon. 

 It shows also the sun on the far side, I need 

 scarcely say, with an enormous distortion of 



