OF TIDES, 335 



the same hours after a period of about fifteen days, or between one 

 spring tide and another. 



This theory, however, is not without objections and difficulties j 

 which has encouraged a Frenchman of some eminence, St. Pierre, 

 to frame a new and singular hypothesis, ascribing all the phaeno- 

 mena of the tides to the periodical effusions of the polar ices. I 

 shall first mention the most material facts and considerations which 

 appear to militate against the common theory, as stated by St. 

 Pierre ; and I shall then endeavour to explain the theory he has 

 substituted (which it has cost me some pains to collect, abstract, 

 and arrange), as nearly as possible in a literal translation of his own 

 language. 



It is said that, if the moon acted by her attraction, her influence 

 must extend to the Mediterranean, the Baltic, the Caspian, and 

 the vast lakes of North America, in some degree at least; but all 

 these have no sensible tides *. Tiiis tranquillity renders her attrac- 

 tion liable to suspicion; and we shall, perhaps, tind that the 

 greatest part of the tides in the ocean have nothing more than an 

 apparent relation either to her influence or her course. 



The phases of the moon do not correspond all over the globe 

 with the movements of the seas. On our coasts the flux and reflux 

 follow the moon rather than her real motion: in various places 

 they are subject to different laws, which obliged Newton to admit 

 (chap. 25,) " that in the periodical return of the tides there yiiist 

 be some other mixed cause, hitherto undiscovered." 



The currents and tides in the vicinity of the polar circle come 

 from the pole, as appears from the testimony of Fred. Martens, 

 who asserts, that the currents amidst the ices set in towards the 

 south ; but adds, that he can state nothing with certainty respect- 

 ing the flux and reflux of the tides. Voyage (awards the North 

 Pole, 16*71. 



Henry Ellis observed that the tides in Hudson's bay came from 

 the north, and were accelerated as the latitude increased. It is 

 impossible these tides should come from the line or the Atlantic. 

 He ascribes them to a pretended communication with the South 



* The Caspian sea is about 860 miles long, and, in one place, 260 miles 

 broad : there are strong currents, but no tides. 

 There is no regular flux and reflux in the Baltic. 

 In some particular spots of the Mediterranean there is a small tide, 



