716 
CAPTAIN F. W. BEECHEY ON THE TIDAL STREAMS OF 
Cause of the 
stream ex- 
plained. 
Conclusion. 
Beneficial 
results of this 
inquiry to the 
seaman. 
long- an interval before it be brought to rest as it did to acquire its momentum, the 
relative inclinations at the beginning and end being about the same. 
The reversal of the stream throughout the strait at the same time will not therefore 
be a matter of surprise, as it will be seen to be only the effect of gravitation due to 
the general slope of the surface. That it is the general slope of the surface of the 
combined wave that occasions the stream throughout these channels, is even more 
manifest in the North Sea than in the English Channel, from the fact of the stream 
there pursuing a steady course between two shores, of which the order of their 
tidal establishments is inverted without reference to either. 
If it be required to trace the streams of the Channel through their gradations, it 
may be done on Plan 3, thus : at XL o’clock, it is high water at Dover, the wave has 
consequently attained its zenith, and the depressions of the surfaces on either side 
are at their maximum. There is now no stream, because the momentum acquired 
during a former depression has only now ceased, notwithstanding the increasing ob- 
struction for two hours which has been presented by the reversed inclination of the 
wave. The water at Dover now falls, the stream begins, and as the depression of 
the surface continues, the stream gradually acquires strength until about half-tide, 
when the depression is at its minimum and the strength of the stream at its maxi- 
mum : after this the inclination of the surface is unfavourable to a continuation of the 
stream. From this time, therefore, the rate of the stream begins to diminish, be- 
cause the reversed inclination is progressively becoming more adverse to its pro- 
gress, and at low water at Dover, after having run up an elevation for two hours, 
its effort is exhausted and there is slack water throughout the wave, as at first*. 
In conclusion, I trust it will appear to their Lordships, that the means which 
they have been pleased to place at my di.sposal have been advantageously em- 
ployed ; and I venture to express a hope, that whilst science will be benefited 
by the inquiry, the navigation of our channels will be so far improved that the 
seaman wdll in future find his course through these moving waters rendered simple 
and plain. Hitherto the numerous and perplexing references which he has been 
compelled to make to establishments of ports, with some of which he was not even 
furnished, and which, under any circumstances, rendered a calculation necessary, 
have in too many instances, it is feared, caused the set of the tides to be wholly dis- 
regarded, or what is worse, misapplied, the consequences of which, it is now seen, 
are very likely to have been attended with disastrous results. For instance, the 
meeting of the streams off the Casquets and the Start in the English Channel, and 
the direction there given to the water at a particular time of the tide, will fully ac- 
count for the numerous wrecks about the Channel Islands ; whilst near the Strait of 
Dover an unexpected set of the stream directly down upon the Somme, and in a part 
of the Channel where from its narrowness a true stream might be expected, is evi- 
* In my report upon the streams of the Irish Sea, Philosophical Transactions, Part I. 1848, at figures A 
and B the effect is there shown to be precisely the same. 
