LECTURE XXII. 



ASTRONOMY. 



THE TIDES. 



As a phenomenon affecting this earth, the 

 consideration of the tides will properly follow 

 what we have advanced on that subject. It is 

 almost unnecessary to explain to you what is 

 meant by the word tide. If a definition were 

 called for, it might be said that it is a daily 

 regular and periodical rising and falling of the 

 waters of the sea. 



In great oceans this rising and falling, in 

 other words the flux and reflux of the sea, take 

 place twice a day. That is, about every six hours 

 the waters of the ocean extend themselves over 

 its shores : this is called \hejlux or flood ; in this 

 state they remain a short space of time, after 

 which they retire or fall back ; and this is called 

 the reflux, or ebb tide. 



During the flood tide the waters of those 

 rivers which communicate with the ocean are 

 stopped in their course by the advance of the sea 

 water ; the rivers swell, and overflow their banks ; 

 during the reflux or ebb tide the stream resumes 

 its usual course. 



