AND ON THE DIURNAL INEQUALITY. 
27 
Diurnal inequality. 
Port Dalrymple . . . High water ? Low water, 3 ft. 
Circular Head . . . High water ? Low water, 2| ft. 
Hummock Head . . High water, 1 ft. Low water, 1 ft. 
Adelaide High water, 3 ft. Low water, 1 ft. 
48. For Port Adelaide I have been furnished with twelve months’ observations 
made by Mr. Bealton, Tide Surveyor at that Port. 
Of these I have thrown the high water heights of ten semilunations into curves, 
and the result is very striking to the eye. There is a diurnal inequality w'hich, for 
the months of December and January 1839, amounts to no less than four feet. In 
the succeeding months it is smaller, but equally regular as to its law. It follows 
the moon's declination with great regularity, at an interval of two days, altering from 
tide to alternate tide as the declination alters from north to south, and reversely. 
Its amount when greatest is nearly an inch for each degree of lunar declination. 
Probably a further discussion of these observations would show why the diurnal 
inequality for January, February, March 1840, is less than that for the two preceding 
months : but my present purpose does not require this labour. We may hope that 
these tides will receive a full discussion from some local mathematician. 
49. At King George’s Sound, near the south-west point of Australia, there is a 
large diurnal inequality of the times, which sometimes reduces the two daily tides to 
one*. Proceeding onwards to the western coast of Australia, and the settlement of 
Swan River, we find the diurnal inequality assuming new forms. The islands called 
Houtman’s Abrolhos, in latitude 29° S., have been surveyed by Captain Stokes, and 
tide observations made at East Wallaby Island ; of which the following is the result : — 
East Wallaby Island. — High water heights: diurnal inequality = 1 J ft. Low 
water heights: diurnal inequality = ^ ft. High water times: diurnal inequality 
= 5 hours. Low water times : diurnal inequality = 2 hours. 
As the rise of the surface at this point is only about two feet altogether, there may 
be some doubt of the times ; but the observations are remarkably regular and con- 
sistent. 
The observations made at Rat Island, another of the same group, agree in the 
general character of the results. 
If we proceed to the north along this coast, and pass round the N.W. Cape of 
Australia to Depuck Island, in latitude 20°^ S., longitude 7 ^ 51' E., we have (still 
from Captain Stokes’s observations) a marked diurnal inequality of the heights, both 
high and low water, amounting to two feet in a tide of 14^ ft. ; but we discern no 
regular diurnal inequality of the times. 
As apparently more connected with the South of Australia than with any other con- 
tinental coast, I may here notice Kerguelen’s Island in latitude 49° S. longitude 4^^ E. 
It appears by the observations of Sir J. Ross in 1840, that here also there is a large 
* Philosophical Transactions, 1837, Part 1. p. 83. 
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