69 



simultaneously throughout the strait with the times of high and low 

 water on the shore at the point of combination or virtual head of 

 the tide. 



Accordingly the observations were conducted upon this plan, and 

 all the movements of the stream were referred to the time of high 

 water at Dover, which had been determined upon as the standard 

 from its being situated nearly at the point where the combined wave 

 is formed. It appeared from the intervals which this mode of com- 

 parison afforded, that whilst the water was rising at Dover, the 

 stream of the channels on both sides ran foicards that place ; and on 

 the contrary, in the opposite direction whilst the water was falling 

 there ; and that these streams pursued a steady course throughout the 

 tide, and extended from a line joining the Texel and Lynn, in the 

 North Sea, to a line joining the Start and Jersey in the English 

 Channel. Beyond these limits the streams of the Channel vv'ere 

 found to encounter those of the offing or parent w^ave, and to occa- 

 sion the tides in those localities to partake of a rotatory character, 

 revolving for the most part with the sun, and having scarcely any 

 interval of slack water. 



The line of meeting of these streams was found not to be a sta- 

 tionary line, neither in those parts where the Channel-stream en- 

 counters the offing stream, nor where the streams meet in the strait 

 of Dover, but was found to shift from west to east 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 Avater 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 is 

 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, 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- 



