TIDES OF PORT DARWIN. 67 
THE TIDES OF PORT DARWIN. 
By R. W. Capmany, M.A., F.R.A.S., anp Captain INcLIs. 
Tue tidal waves which produce the oscillations of sea-level 
along the N.W. coast of Australia come from the Indian 
Ocean, and appear to strike the outlying headlands of ‘the 
coast at about the same time, the co-tidal line running pretty 
well parallel with the coast. The range of the tide along 
the W. coast of Australia, from Fremantle up to North- 
West Cape, is very small, the mean spring range at Fre 
mantle being only 2? feet. | But beyond North-West Cape 
the range of the tide gets very much greater, running up to 
as much as 36 feet in Cambridge Gulf. At Port Darwin 
the mean spring range is about 24 feet, but is sometimes as 
high as 30 feet. A tide-gauge of Lord Kelvin’s pattern 
was set up at Port Darwin in 1892 by the South Australian 
Government, and good records are available up to 1897, 
since when it has been dismantled, awaiting the building 
of a new jetty. The records of the tide-gauge show a very 
marked diurnal inequality, especially at the low waters, the 
general sequence throughout the year, with some few excep- 
tions, being—High High, High Low, Low High, Low Low. 
From December to July the H.H. follows the lower transit 
from the third quarter to the first quarter, and the upper 
transit from the first quarter to the third. During the other 
half of the year this is reversed. The Diurnal Inequality 
is greater at the Low Waters than it is at the High Waters 
throughout the year, the maximum effect occurring in 
December and January, when che diurnal inequality 
between the high waters is about 43 feet, and between the 
.two low waters it amounts to as much as 9 or 10 feet. In 
June and July there is about 3 feet inequality between the 
high waters and about 7 feet between the low waters. In 
March and April, when the moon is from 8 to 10, or from 
20 to 24 days old, three tides amalgamate to make one long 
high wacer. W hen approaching this stage the two high 
waters get more and more nearly equal, and the two low 
waters more unequal, until] the H.L.W. equals the two 
H.W.s. In September and the first part of Occober two 
tides amalgamate and merge intc one, the L.H. and H.L. 
We selected the tide-gauge recurus for the vear 1896 as 
the latest reizabie ones, and subjected them to uarmonic 
analysis, measuring the heighis at hourly interva!s. ‘The 
results of the analysis are given below in the iritish Assoria- 
