354 Astronomy. [Lecture 22. 



two, as in truth we find to be the case. Thus, 

 when the moon passes from the syzigies to the 

 quadratures, (that is, when she is not ninety 

 degrees from the sun,) the highest elevation of 

 the waters ought to take place at the setting of 

 the moon; the contrary happens when the 

 moon passes from the quadratures to the syzigies. 

 In the first case the time of high water ought to 

 precede the three lunar hours : for on one side 

 the vis inerticc of the waters produces the 

 elevation three hours after the moon passes the 

 meridian ; and on the other, the relative situation 

 of the sun and moon affects this elevation before 

 the moon passes the meridian. On the contrary, 

 in the second case, and for similar reasons, the 

 time of high water must happen rather after the 

 three hours. 



As there is some retardation of the jtide by 

 the vis inertias of the waters, and their tendency 

 to preserve an equilibrium, the highest tides do 

 not take place exactly at the time of the op- 

 positions and conjunctions of the sun and moon, 

 but two or three tides after. In the same manner, 

 the lowest neap tides happen a little after the 

 quadratures. 



Since in the winter the sun is a little nearer 

 the earth than in the summer, it is observed 

 that, when all other circumstances are equal, the 

 tides about the winter solstice are rather higher 

 than those of the summer solstice. 



Such would be the regular phaenomena of 



