82 
THK HEV. \\\ WmWELh ON THE 
tides of remote places, as produced successively by the motion of the same " tide- 
wuve but it is already established beyond doubtj by the observations made on the 
two sides of the Atlantic in 1835, that tides which were supposed to be brought by the 
same tide-wave differ materially in their circumstances. As I have already stated*, 
" On the 9th, iOth, and 1 1th of June 1835, when the diurnal inequality was great in 
America it was nothing in the West of Europe; and on the 18th and 19th, when this 
ini'i|uality had vanished in America; it was great in Europe,'* Are we to doubt 
whether the tide- wave which brings high water to America and to Europe at the 
saine moment be the same wave ? A sound hydrodynamical view of all the circum- 
stances must enable us to decide ; but for this purpose more observations are needed, 
especially observations on the coast of America, wliere the diurnal inequality is great, 
and wliere, on several accounts, a knowledge of its laws would be interesting to us. 
Anotlier remarkable cireumstance in the progress of the diurnal inequidity is, that 
it appears much more distinctly and steadily at some places than at others which are 
near them : nor does it seem easy to assign any rule which it follows in this respect. 
It is very marked and almost universal on the coast of the United States, and was 
conspicuous in the observations of June 1835 on the coasts of Spain and Portugal, 
tlie west coast of France, and parts of the west coast of Ireland. Yet at places inter- 
jacent among those at which it was thus displayed it couhl not be detected j nor did 
the circumstances easily allow of my ascribing this to any defect of exactness in the 
observations. In like manner it is large on the east coast of New Holland, tis we 
know from Cook*s account of his getting his ship off a reef by means of it ; and 
the north and south coasts of Australia appear to exhibit the extreme case of it, as 
we shall see. We might therefore suppose that it affects the whole of the Indian 
Ocean : yet at Keeling Island, in the centre of that ocean, it does not decidedly show 
itself. Such, at least. Is tiie result of oliservations matle by Captain Fitz Roy, from 
April 2 to April 8, 1836, with which I have been furnished by his kindness. 
Sect. IV. On extreme Cases of great Diurnal InequalHif. 
If we consider the motion of the surface of the water in cases where, as at Singa- 
pore, the diurnal inerpndity is very great, we shall see that this motion is very different 
from the alternate equal ascent and descent which would occur if there were no such 
inequality. In order to exhibit this peculiarity, I have represented this motion in 
Plate IV. for Plymouth and for Singapore, as observed in the months of May and 
June. It will be seen that at Piy mouth the curve of the motion of the surface oscil- 
lating upwards and downwards by nearly equal distances ; the main feature of in- 
equality is the difference of spring and neap tides, although the diurnal inequality is 
very clearly visible. But at Singapore the alternate oscillations make no approach 
to equality; at some parts of the series the alternate tides seem to be on the point 
* Pliilomphicixl Traneacdons, 183e, Part II. \\. 302, 
