109 



TIDES. 



[Sect. IV 



r 



Sect 



from each other, as may be convenieiiL They must 

 observe the tides at these places on the same days, morn- 

 ing and eveningj by the methods already described. Tlie 

 times of high water at the different places on each half-d ay, 



being compared, will give the progress of the tide-wave. 



40. In order to trace the progress of the tide-wave still 

 more widely, the observers described in the last article, 

 after having made the observations there spoken of, mav 

 be removed to new positions of the same kind, and thus 

 trace the tide farther. 



When this course is adopted, it will be well to liave one 



standard station, at which tide 



(or more) fixed or 



observations are constantly made ; and the observations 

 made at any time at any other place may be compared 

 with those made at the standard station. 



4L The tides which take place far up deep bays, 

 sounds, and rivers, are later than the tides at the entrance 

 of such inlets ; but they are not more irregular : on the 



contrary, the tides in such situations are often remarkably 

 regular. 



42. The progress of the tide-wave up inlets may be 

 determined by the method described in Art. 39. 



43. The tide in its progress up inlets and rivers is often 

 much maernified and modified by local circumstances. 



s it is magnified so that the wave which brings 



the tide at one period of its rise advances with an abmpt 

 front of broken water. This is called a bore (as in tL- 

 Severn^ the Garonne, the Amazons River). 



S 



ometinies the tide is divided into two half-day tides in 

 its progress up a river (as in t^<^ Forth in Scotland). 

 In all cases, after a certain point, the tide dies away 



m 



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 6,11 



give 



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 same 



47 



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effect, 



48. 

 baroix 



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