Ixviii EXPLANATION OF THE PtATES. 



bccanfe the Sun warms by turns, in the courfe of one year, 

 the fouthern and northern Hemifpheres ; and there are two 

 tides every day, becaufe the Sun warms, by turns, every 

 twenty-four hours, the caftern and the weftern fide of the 

 Pole that is in fufion. The fame efFe6l exactly is vifible in 

 many lakes fituated in the vicinity of icy mountains, which 

 have currents, and a flux and reflux in the day-time only. 

 But it cannot admit of doubt, that, if the Sun warmed, 

 during the night, the other fide of thofe mountains, they 

 would produce, likewife, another flux and reflux in their 

 lakes, and, confequently, two tides in twenty-four hours, 

 like the Ocean. 



The retardation of the tides of the Ocean, which is about 

 twenty four minutes the one from the other, arifes from 

 the daily diminution of the diameter of the icy cupola of the 

 Pole in fufion. Accordingly, the focus of the tides is re- 

 moving farther and farther from our coafts. If their inten- 

 fity is fuch, according to Boiiguer, that our evening tides 

 are the ftrongefl: in Summer, it is becaufe they are the diur- 

 nal efi'ufions of our Pole, produced by the heat of the day in 

 the fultry feafon. If, at that feafon, they are lefs ftrong in 

 the morning than in the evening, it is becaufe they are the 

 nodlurnal cfFufions which come from the other part of the 

 Pole, and difcharge themfelves into the fources, in the fpiral 

 diredlion of the Atlantic Ocean, but in a fmaller quantity. 



If, on the contrary, at the end of fix months, the ftrongefl 

 tides, that is, thofe of the evening, becoine the weakeft ; and 

 the weakeft, that is, thofe of the morning, become the 

 flronged : it is becaufe they are then produced by the ac- 

 tion of the Sun on the South Pole, and the caufe being op- 

 pofite, the efFe6ls mufl be fo likewife. If the tides are 



ft ronger 



