662 TIDES AND CURRENTS. 



Superposed on the semi-diurnal tides at Port Foulke is the 

 diurnal tide. The diurnal inequality in height of high water 

 amounts to about two feet, and in the November observations is 

 very regular. 



In discussing the observations in June 1861, the diurnal inequality 

 in times of high water and of low water are somewhat irregular, 

 but their periods agree with the computed inequality in time of 

 low water. 



In November and December 1860 the day high tides were higher 

 than the night high tides, whereas in June 1861 the night high 

 tides were higher than the day high tides. The range of the half- 

 monthly inequality in time amounts to Ih. 26m. At Van Rensse- 

 laer it amounted to Ih. 52m., a very large value. 



General Character oj Port Foulke Tides. 



The general character of the half-monthly and diurnal in- 

 equalities is very much the same as at Van Rensselaer Harbour ; 

 the establishment is half-an-hour less at Port Foulke. The aver- 

 age range of the tide is about the same at the two places, and the 

 diurnal inequality in the height of high water is greater than in 

 the height of low water. 



Note. — Comparing the heights of the highest spring tides in 

 Baffin's Bay, generally about 7^ feet, with the height in Van 

 Rensselaer Harbour, 1 1 feet, it would appear possible that the 

 tide at Van Rensselaer may result from both the southern and 

 northern tides. The fact that the duration of the fall of the tide 

 is less at Van Rensselaer than at Port Foulke, would also seem 

 to show that Van Rensselaer is nearer to the open ocean than 

 Port Foulke. Also at Van Rensselaer Harbour the extreme 

 fluctuation of low water is very much greater than at Port 

 Foulke. 



8. Theory of Tides. Half-Monthly Inequality. Phil. 

 Trans., 1834 and 1836. 



The Theory of Bernouilli. — The pole of the fluid spheroid 

 follows the pole of the spheroid of equilibrium at a distance (at 

 the hour angle X), and the spheroid of equilibrium corresponds to 

 the configuration of the sun and moon, not at the moment of the 

 tide, but at a previous moment at which the right ascension of the 

 moon was less by a quantity a. 



Thus tan 2(0. -x,) = - ^"'°^^^-"^ 



-^ + COS 2{(p — a) 



^1 is the hour angle of the place of high water from the moon's 

 place; (f the hour angle of the moon from the sun; ^, A^, the 

 heights of solar and lunar tides ; X^ the hour angle by which the 

 tide follows the pole of equilibrium ; a the retardation or diff. of 

 R.A. due to the age of the tide. 



