The Tides. 351 



degrees from the sun. This, then, is the time 

 of the lowest or neap tides ; and the highest or 

 spring tides happen at new and full moon, when 

 the two luminaries are in conjunction or op- 

 position. 



In the course of every natural day there are 

 two tides, which depend upon the action of the 

 sun, as in every lunar day there are two which 

 depend on that of the moon ; all follow, how- 

 ever, the same laws. In general, the nearer the 

 moon happens to be to the earth, the greater is 

 its attraction, and the same may be said of the 

 sun. 



Laying aside for the present the action of the 

 sun on the ocean, the highest tide would be at 

 the moment when the moon passed the meridian, 

 if the waters had not, like all bodies in motion, a 

 vis inertice, by which they are inclined to retain 

 the impression they have received. But this 

 force must necessarily produce two effects. It 

 must retard the time of high water, and it must 

 in general diminish the height of the tide. As 

 a proof, let us for a moment suppose the earth 

 at rest, and the moon above it in a certain point. 

 Abstracting, then, the action of the sun, the 

 force of which upon the tides is much less than 

 that of the moon, the water would unquestion- 

 able rise in that part which was under the moon. 

 Let us suppose again that the earth turns upon 

 its axis : on one side it turns very rapidly as to 

 the motion of the moon ; and on the other, the 



