PHYSICAL ASTRONOMY. 



has been on the meridian, either above or un- 

 der the horizon. 



On the shores of the larger continents, and where 

 there are shallows and obstructions, there are 

 great irregularities in this respect, and when these 

 exceed six hours, it may seem as if the high- water 

 preceded the Moon's transit over the meridian* 



For any given place, the hour of high- water is al- 

 ways nearly at the same distance from that of the 

 Moon's passage over the meridian. 



This constant dependence on the Moon, is the rea- 

 son why the tides are considered as astronomical 

 phenomena. 



329. Though the tides seem to be chiefly re- 

 gulated by the Moon, they appear also, in a 

 certain degree, to be under the influence of the 

 Sun. Thus, at the syzygies, when the Sun and 

 Moon come to the meridian together, the tides, 

 cceteris paribus, are the highest ; at the quadra- 

 tures, or when the Sun and Moon are 90 dis- 

 tant, the tides are least. The former are call- 

 ed the Spring, the latter the Neap Tides. 



The highest of the Spring Tides is not the tide that 

 immediately follows the syzygy, but is in general 

 die third, and, in some cases, the fourth. 



At 



