ADVERTISEMENT, Iv 



and from Afia, toward the 21 ft degree of North 

 Latitude. When this place is more expofed to 

 the Current of the one Continent, than to that of 

 the other, it's two femi-diurnal tides are unequal, 

 as at the entrance of Nootka, on the coaft of Ame- 

 rica ; but when it is completely out of the influ- 

 ence of the one, and entirely under that of the 

 other, it receives only one tide a day, as at Kam- 

 chatka, on the coaft of Afia, and this tide is then 

 of twelve hours, as the adion of the Sun on the 

 half of the Pole, the effufions of which, in this cafe, 

 undergo no divifion. 



Hence it is evident, that two harbours may be 

 fituated in the fame fea, and under the ûme pa- 

 rallel, and have, the one two tides a day, and the 

 other only one, and that the duration of thofe tides, 

 whether double or fingle, whether double equal, or 

 double unequal, whether regular or retarded, is al- 

 ways of twelve hours, every twenty-four hours; 

 that is, precifely the time which the Sun employs 

 in heating that half of the polar cupola from which 

 they flow ; which cannot poflibly be referred to the 

 unequal courfe of the Sun between the Tropics, 

 and ftill much lefs to that of the Moon, which is 

 frequently but a few hours above the Horizon of 

 fiich harbour. 



d 4 I have 



