ntr. iv.] DISSERTATION SF.CONl). ID 



sea revolving with the earth, are nearly in the condition 

 of a satellite revolving about its primary ; and are liable 

 to the same kind of disturbance from the attraction of a 

 third body. The fact in the history of the tides which 

 seems most difficult to be explained, received, on this 

 supposition, a very easy solution. It is known, that high 

 water always takes place in the hemisphere where the 

 moon is, and in the opposite hemisphere where the moon 

 is not, nearly at the same time. This seems, at first sight, 

 very unlike an effect of the moon's attraction ; for, though 

 the water in the hemisphere where the moon is, and 

 which, therefore, is nearest the moon, may be drawn up 

 toward that body, the same ought not to happen in the 

 opposite hemisphere, where the earth's surface is most 

 distant from the moon. But if the action of the moon 

 disturb the equilibrium of the ocean, just as the action of 

 one planet disturbs the motion of a satellite moving round 

 another, it is exactly what might be expected. It had 

 been shown, that the moon, in conjunction with the sun, 

 has her gravitation to the earth diminished, and when in 

 opposition to the sun has it diminished very nearly by the 

 same quantity. The reason is, that at the conjunction, or 

 the new moon, the moon is drawn to the sun more than 

 the earth is ; and that, at the opposition, or full moon, 

 the earth is drawn toward the sun more than the moon 

 nearly by the same quantity; the relative motion of the 

 two bodies is therefore affected the same way in both ca- 

 ses, and the gravity of the moon to the earth, or her 

 tendency to descend toward it, is in both cases lessened. 

 It is plain, that the action of the moon on the waters 

 of the ocean must be regulated by the same principle. 

 In the hemisphere where the moon is, the water is more 

 drawn toward the moon than the mass of the earth is. 

 and its gravity being lessened, the columns toward flic 



