712 
CAPTAIN F. W. BEECHEY ON THE TIDAL STREAMS OF 
Direction in 
Avhich the 
stream turns. 
On a sup- 
posed tide 
and half-tide. 
Peculiarity 
of the wave 
of the En- 
glish Chan- 
nel and 
North Sea. 
The direction in which the stream turns will next engage our attention. This is 
a question more curious than useful to the navigator ; it is nevertheless one of 
interest, and I have given it my attention. 
Upon Plate XXXII., I have shown, by curved arrows, the direction in which the 
streams in all parts of the Channel pass through their various rhombs, and I cannot 
discover that there is any general rule with respect to 'particular sides of the Channel. 
On the contrary, the direction appears to be wholly dependent either upon the course 
of that stream which commences first or continues the longest, or upon that which be- 
comes the most powerful, and which, acting obliquely upon the weaker stream, com- 
pels it to partake of its own direction. A good example of this may be seen in the 
chart of the streams at three hours after high water (Plate XXXV.), where the in- 
coming Ocean stream off the Lemon and Ower is dividing the Channel stream and 
causing all the tides to the eastward of that spot to turn ivith the sun, and those to 
the westward of it in a contrary direction. 
[ have now only to mention a popular error which still exists with reference 
to the streams of our channels, viz. a belief in a “ tide and half -tide by which it 
is understood that the stream runs half a tide longer near the centre of the Channel 
than it does near the coast. So general an opinion requires substantial proof to in- 
validate it, and I must refer once more to the diagrams which accompany this re- 
port. It will be seen there that in no part of either channel does the change of 
stream in the centre differ eveji an hour from the change of stream as near the land 
as a vessel would be safe in navigating, except in that part of the North Sea which is 
affected by the tide sweeping round the Texel ; and then, at the most, it amounts 
only to a quarter-tide. It is not difficult to discover that this error has arisen from 
the confusion of high water on the shore with the time of slack water in the offing. 
I have now described the principal features of the tidal streams of this strait, and 
it is evident from the observations which have been collected that the laws by which 
the streams of these channels are governed, differ materially from those which regu- 
late the streams of ordinary tides. 
It will be interesting to see in what this consists, and to endeavour to account for 
the cause. 
Under ordinary circumstances, such as those which attend the passage of a single 
tide-wave up an estuary or deep gulf, or even along an open coast, we find a 'pro- 
gressive turn of the stream to accompany a progressive increase of establishment. 
But in the channels under discussion the stream is found to turn nearly simul- 
taneously throughout the strait, wholly regardless of the order of its establishments, 
and to reverse with the time at which a wave peculiar to such channels is matured. 
This Avave, which exercises so singular an influence over the streams of these 
Channels, is occasioned by one portion of the oceanic tide-wave of the Atlantic 
passing round the north end of the British Islands, while the other finds its way up 
the English Channel and meets it in the Strait of Dover. In consequence of this 
meeting or opposition, the character of the wave is changed ; its dimensions become 
