320 Royal Society, * 



of Dover, but was found to shift from west to cast as the tide rises 

 and falls at Dover, beginning at Beachy Head and ending at the 

 North Foreland ; so that the space occupied by the Channel -stream 

 always preserves the same dimensions, notwithstanding its limits ex- 

 tend over a distance of 360 miles. The strait of Dover was found 

 never to have slack water throughout its whole extent at any time, 

 as was the case in the other ports of the Channel, from which it dif- 

 fers in this respect ; and the streams in this locality have in conse- 

 quence been designated as those of the " Intermediate tide." 



As the simultaneous turn of the stream throughout the Channel id 

 a point of considerable interest and entirely new, the author takes 

 considerable pains to point out the methods by which this important 

 fact was ascertained, and refers to the observations kept on board 

 the light vessels along the coast, and to others made at various im- 

 portant stations; and whenever any contradictory evidence appears, 

 the cause of the discrepancy is inquired into and explained. It was 

 found, for instance, that in a port of the North Sea, near the node 

 referred to by Dr. Whewell, that there was a retardation of an 

 hour in the turn of the stream ; and, upon an investigation as to the 

 cause of this delay, it is seen to be owing to the stream running 

 round the Texel and entering the North Sea at a time when the 

 Channel-stream had ceased ; but as soon as the Channel-stream ac- 

 quired sufficient strength, it speedily drove the Texel stream back 

 and confined it to its proper limits. In the English Channel also a 

 similar discrepancy is observable near the coast of France ; but this 

 also the author considers to be fully accounted for by causes inci- 

 dental to that part of the Channel, and not to be of sufficient con- 

 sequence to derogate from the character ascribed to the general 

 motion of the water throughout the strait. 



A reference is made to the erroneous opinions which have 

 hitherto been entertained with respect to the motion of the streams 

 of our channels ; and the author concludes his paper by explaining 

 his views as to the manner in which the turn of the stream is ren- 

 dered simultaneous by the rapid rise of the combined wave in the 

 centre of the strait, and expresses a hope that he has satisfactorily 

 shown from the observations, that throughout the English Channel 

 and North Sea the movement of the stream may safely be referred to 

 a common standard. This, it is considered, will be of great import- 

 ance to navigation ; as thus the seaman's progress through these 

 moving waters will be freed from the numerous and perplexing re- 

 ferences he was before obliged to make, and which too often — and, 

 it is to be feand, in many instances too fatally — caused the tides to 

 be wholly disregarded. All uncertainty as to the effect of the stream 

 will henceforward, it is expected, be obviated by a simple reference 

 to a tide table. 



The paper, which is accompanied by numerous plans and charts, 

 forms a practical illustration of the tidal streams of straits, under 



the influence of a combined wave. ;^' ' ' 



-,.-. J- .... 



B lo 9eq 



