ref peeling the Caufe of the Tides. I39 



high water ; and the fame is faid to be the cafe on the weftern 

 coaft of America : fo that tides happen to different places at 

 all diftances of the moon from the meridian, and confe- 

 quentlv at all hours of the day. 



To allow the tides their full motion, the fpace in which 

 they arc produced ought to extend from eaft to weft 90 at 

 lead ; fuch being the diftance between the places molt railed 

 and deprefled by the moon's influence. Hence it appears 

 that fuch tides can only be produced in large oceans, and 

 why thofe of the Pacific exceed thofe of the Atlantic ocean : 

 hence alfo it is obvious why the tides in the torrid zone be- 

 tween Africa and America, where the ocean is narrower, are 

 exceeded by thofe of the temperate zones on either fide : and 

 hence we may comprehend why the tides are fo fmall in 

 illands at a great diftance from the fhores, fince the water 

 cannot rife on one fhore without defcending on the other: 

 fo that at the intermediate illands it muft continue at a mean 

 height between its elevations on thofe fhores. 



The tide produced on the weftern coaft of Europe corre- 

 sponds to this theory. Thus, it is high water on the weftern 

 coafts of Ireland, Spain, and Portugal, about the third hour 

 after the moon has puffed the meridian ; from thence it flows 

 into the adjacent channels, as it finds the eafieft paffage. One 

 current, for example, runs up by the Couth of England, and 

 another by the north of Scotland; taking considerable time 

 to move all this wav, and occafioning high water fooncr in 

 the places at which it firft arrives, and begins to fall at thefe 

 places while the current is proceeding to others further di- 

 ftant in its courCe. On its return it is unable to raiCe a tide, 

 becauCe the water runs fafter off than it returns, till, by the 

 propagation of a new tide from the ocean, the current is ftont, 

 and begins to rife again. The tide propagated by the moon 

 in the German ocean, when fhe is three hours paft the me- 

 ridian, takes twelve hours to come from thence to London 

 bridge; fo that, when it is high water there, a new tide has 

 already attained its height in the ocean, and in Come inter- 

 mediate place it muft be low water at the fame time. When, 

 the tide runs over fhoals, and flows upon flat fhores, the water 

 T 2 is 



