Broad Sound .] TERRA AUSTRALIS. 
but it may be proper to say what I conceive to be the cause of the 
extraordinary rise in Broad Sound. From Cape Howe, at the southern 
extremity of the East Coast, to Port Curtis at the edge of the tropic, 
the time of high water falls between seven and nine hours after the 
moon's passage, and the rise does not exceed nine feet; but from 
thence to the northward, commencing with Keppel Bay, the time 
becomes later, and the rise augments, till, at Broad Sound, they reach 
eleven hours, and between thirty and thirty-five feet. The principal 
flood tide upon the coast is supposed to come from the south-east, 
and the ebb from the north, or north-west ; but from the particular 
formation of Keppel and Shoal-water Bays, and of Broad Sound, 
whose entrances face the north, or north-west, this ebb tide sets into 
them, and accumulates the water for some time, becoming to them a 
flood. This will, in some degree, account for the later time and 
greater rise of the tide ; and is conformable to what captain Cook 
says upon the same subject ( Hawkesworth, III. 244,) ; but I think 
there is still a super-adding cause. At the distance of about thirty 
leagues to the N. N. W. from Brettk-sea Spit, commences a vast 
mass of reefs, which lie from twenty to thirty leagues from the coast, 
and extend past Broad Sound. These reefs, being mostly dry at low 
water, will impede the free access of the tide ; and the greater pro- 
portion of it will come in between Break-sea Spit and the reefs, and 
be late in reaching the remoter parts ; and if we suppose the reefs to 
terminate to the north, or north-west of the Sound, or that a large 
opening in them there exist, another flood tide will come from the 
northward, and meet the former; and the accumulation of water 
from this meeting, will cause an extraordinary rise in Broad Sound 
and the neighbouring bays, in the same manner as the meeting of the 
tides in the English and Irish Channels causes a great rise upon the 
north coast of France and the west coast of England. 
That an opening exists in the reefs will hereafter appear; and 
captain Cook’s observations prove, that for more than a degree to 
75 
1802. 
September. 
