The Tides. 353 



therefore, always proceeds in this direction. But 

 the general motion of the sea between the tropics 

 from east to west is more difficult to explain. 

 This motion is evinced by the direction in which 

 all floating bodies proceed there. It is observed 

 also that, all other things being equal, it is much 

 easier to navigate towards the west than in the 

 contrary direction. M. D'Alembert has de- 

 monstrated, in his Inquiry into the Causes of 

 Winds, that the action of the sun and moon 

 must cause a motion in the waters under the 

 equator from east to west. This action must, 

 according to the same writer, equally affect the 

 air, and is one of the principal causes of the 

 trade-winds. 



If the moon remained always in the equator, 

 it is evident she would then be always ninety 

 degrees distant from the poles, and that there 

 could be there neither flux nor reflux ; for the 

 waters at the poles would always be low. Though 

 the moon, however, is not always in the equator, 

 she is never more distant from it than twenty- 

 eight degrees. We are not to wonder, therefore, 

 that near the poles, and even at the latitude of 

 sixty-five degrees, the tide is not perceptible. 



As it only happens twice in a month that the 

 sun and moon are in the same line or direction, 

 (that is, when they are in conjunction or opposi- 

 tion,) the elevation of the water ought in general 

 to take place neither immediately under the sun 

 nor under the moon, but in a point between the 



