1829.] 
On the Tides of the River Htig/i. 
321 
From every view of the question I have always been led to the same conclusion, 
that the highest tide in these marshes must be below the highest levels of the parent 
tides from which they are fed. Prima facie, it certainly appears bold to hazard a sup- 
position that the waters of the Bay are frequently several feet above these waters, 
which are so far inland as 70 to 100 miles, taking the course of the creeks. But it 
cannot be otherwise, from the principle upou which they are fed, and their surface 
remains comparatively so constant. 
Diagram 1st will perhaps explain this to your readers more clearly than words 
could express. The case to which it applies is the simplest form of a tide-channel, 
viz. that in which there is supposed no supply of upland waters. 
SYSJ-/ 
Let 0 be the mean level of the Bay tide, which rises and falls daily to A and B, 
respectively. At a certain distance up the creek, as at O', the daily variation of 
surface is found to be reduced considerably, measuring only ab, and still further 
reduced at the successive points 0", O'", where the daily variation is, respective- 
ly, cd, ef. At last a point -f- is discovered, if the creek be sufficiently extended, 
where the daily variation disappears altogether, and we observe only a variation of 
surface between the full and new moons and their quarterings. The question then 
occurs, where are the levels of O', 0", 0"' relatively with 0. That they are above 0 
is plain, because the last ebb cannot run as freely as the top flood ; and the free- 
dom of expenditure, must invariably be in favour of the flood. 
The next question which strikes us, is, whether the flood levels «, c, e, must not 
rise every where to the same level A A, or whether it might not be supposed to rise 
even above A A, by the effect of afflux. 
In the first case, the final point where the daily variation disappears + would be 
found on the line A A , and it would be simple to fill up the remaining curves of 
the diagram 0 0' 0" O'" + and B b 4 f -f . But this, I believe not to be the 
case ; and although I cannot fix with precision the exact place where -f- would be 
found I must, from what data are before me, assign some intermediate level between 
A and 0 for the + of every simple tide, creek, or channel, where no inland supply of 
water exists. Nor is it difficult to reconcile this with the common principles of 
hydraulics The only moving power to the fluid, is the variation A B, which we 
may suppose constant at the mouth of a long extended channel or creek. Now it is 
plain that this channel, being tolerably free for the passage of the tide, and not con- 
verging too rapidly*, before the tide can have reached any very remote point, the 
first cause of its flowing is removed, as the parent tide at the mouth, or A, has 
already subsided. This principle, which affects every intermediate point, according 
to its distance from the parent tide A 0 B, must at last leave -f- where the daily 
variation is at last dissipated below A A. , . 
I find this confirmed in the Dutch table of tides, reduced to the Amsterdam guage or 
pile The ordinary rise and frill in the Ye, near Amsterdam, an arm of the sea run- 
ning into the land from the Zuyder Zee, being only 1ft. 6in. t while the ordinary rise 
and fall in the German sea is a feet. The mean level in the V e, from these data, is 
several inches above the mean level of the German sea. The sea ot Haerlem and 
the Dutch canals, of which we possess the levels.cannot be adduced as instances, both 
being under the influence of sluices, to keep down their mean levels. Many other 
cases, however, may be found much nearer to us, which appear to confirm this view, 
* It is evident, that if the creek converged too rapidly, the principle ofafflux would 
have effect in raising the top level, and such may still be the case in the first mouths 
of all these creeks, as well as of other rivers. 
f Vide Lalande’s ‘ Canaux de Navigation.’ 
