PHYSICAL ASTRONOMY. 329 



When the Moon is in the northern signs, the tide of 

 the day, in all northern latitudes, is somewhat 

 greater than the tide of the night. 



The contrary happens when the Moon is in the 

 southern signs. 



332. If the tides be considered relatively to 

 the whole Earth, and to the open Sea, it is evi- 

 dent, that there is a meridian, about 30 east- 

 ward of the Moon, where it is always high- wa- 

 ter, both in the hemisphere where the Moon 

 is, and in the opposite ; on the west side of this 

 circle, the tide is flowing ; on the east, it is 

 ebbing ; and on the meridian, at right angles to 

 the same, it is everywhere low-water. 



These meridians move westward, preserving nearly 

 the same distance from the Moon, only approach- 

 ing nearer to her at the syzygies, and going farther 

 off at the quadratures. 



In high latitudes, whether south or north, the rise 

 and fall of the tides are inconsiderable. It is pro- 

 bable that at the poles there are no tides. 



The great Wave which, in this manner, constitutes 

 the tide, is to be considered as an undulation, or 

 reciprocation of the waters of the ocean, in which 

 there is, except when it passes over shallows, or ap- 

 proaches 



