THE NORTH SEA AND ENGLISH CHANNEL. 
715 
but, on the contrary, a large tract of still water which the streams scarcely ever 
disturb, but this arises from the different conformation of the inner part of the 
strait. The Irish Sea, for instance, maybe said to be contracted at its entrances, and 
to expand into a large inland sea in its centre, whereas the other channel has wide 
entrances and a very contracted centre. They are, however, both canals in which 
the waves from two tidal seas enter at opposite ends and meet in the centre, where 
they form a combined wave, and hence they have the property of reversing their 
streams simultaneously. 
There cannot therefore be any doubt that the waves which are formed in the 
centre of these straits exert a powerful influence over the course of the waters on 
both sides of them, and in fact that they both govern their movements and regulate 
the limits of their streams. 
It was the consideration of this influence that determined me to refer all the 
movements of the streams of these Channels to the time when the combined wave 
was matured. In the Irish Sea I adopted Liverpool as the standard*, and as Dover 
was situated so near to the apex of the v/ave in the English Channel, and had tables 
of its tides already printed and in general circulation, I adopted the time of high 
water at that place as a standard to which all the observations there should be re- 
ferred. 
I shall now compare the general inclination or slope of the surfaces of the com- 
bined wave on both sides with the direction of the streams passing along the Channel 
at the moment, for the purpose of showing the mechanical action of the water, and of 
tracing the intimate connection that exists between these slopes and the simultaneous 
turn of the stream. 
If we direct our view to the inclination of the surfaces of these waves. Plans 3 and 
Tidal pheno- 
mena of the 
Irish Sea and 
of the En- 
glish Chan- 
nel com- 
pared. 
Comparison 
of the incli- 
nation of the 
surface of the 
wave with 
the direction 
of the stream 
along it. 
4, Plates XLII. XLIII., we shall see that the directions in which the streams run 
do not always correspond with the existing slopes of the surfaces, as they might be 
supposed to do from the known law of gravitation, but that during the last half of 
the tide they are to be traced to the effect of a previous and contrary depression. 
The maximum rate of the stream may be seen to occur when the surface has its 
smallest depression'!’, and that there is no stream at all at the moment of the greatest 
elevation and depression. It will be seen that the rate of the stream depends upon 
the amount and continuance of the inclination ; and also that a stream, when once 
produced, will continue its progress for a length of time, although the inclination 
that produced it may have been reversed by the passage or descent of the crest 
of the w’ave. Consequently from the time of the passage of the wave, or the reversal 
of the inclination of its surface, until the stream finally ceases to flow, the water 
will be seen to run up an inclined plane, and will continue lo do so for nearly as 
* See my paper in Philosopliical Transactions, Part I. 1848. 
t The maximum rate of the stream is shown in the Table at page 711 to occur at half-tide, at which time 
the wave is seen to have the smallest depression. 
