. -rijpeSUng the Cmlfe of the- Tide-s. i^.^J 



with equal force, and in parallel directions, the whole mafs 

 would be moved together without experiencing any alteration 

 in its figure. But this is not the cafe with relpeet to the moon'-. 

 action on our globe : the power of gravity diminifhes as the 

 fquare of the alliance increafes, ard therefore the waters, 

 (at Z, Plate V. fig. 1.) on the fide of the earth (A,B,C,D) 

 next the moon (M), are more attracted by the moon than the 

 central parts of the earth (O), and the central parts more at- 

 tracted than the waters on the oppofite fide (at n) ; and there- 

 fore the diftance between the earth's centre and the waters 

 on its furface under and oppofite to the moon will be in- 

 creafed. For, fuppofe three bodies in the fame line (H,0,D), 

 if they are all equally attracted by any power (as M), they 

 will all move towards it with equal rapidity, their mutual 

 diftances continuing the fame; but if the attraction of this 

 power (M) is unequal, the body moft forcibly attracted will 

 move fafteft, and their reciprocal diftances will be propor- 

 tionally increafed : thus, the power of gravitation acting un- 

 equally on the three bodies (H,0,D), the diftance of the 

 firft (II) from the fecond (O), and of the fecond from the 

 third (D), will be increafed in proportion to the difference 

 of the gravitating power at the diftance of the three bodies 

 (H,0,D) refpectively : now, fuppofe a number of bodies 

 (ABCD) placed round the centre (0) fo as to form a fluid 

 ring, unequally attracted by fome power CM), the parts. 

 neareft and furtheft (il and D) from this power will have 

 their diftance from the centre (O) increafed, while the fides, 

 of this ring (B and F), being nearly equidiftant from the 

 power (M), the centre (O) will not recede, but rather 

 approach the centre (O), and form an ellipfis (nLfzN). 

 To apply this reasoning lo the cafe under consideration, 

 while the earth, by its gravity, tends toward the moon, the 

 water directly below her will fwell and rife gradually; the 

 water on the oppofite fide will recede from the centre (or, 

 more properly, the centre will advance), and rife, or appear to 

 rife, while the water at the fides is deprefled, and falls below 

 the former level : hence, as the earth revolves on its axis from 

 the moon to the moon again in 24 hours 50 minutes, there will 

 be two tides of ebb and two of flood in that period. In con- 



fequence 



