5+0 Royal Society. 



Channel, as the English Channel does the Gulf of St. Malo, it was 

 found that the observations there also fully bear out the idea. So 

 that there was afterwards but little difficulty in tracing the course of 

 the water, and bringing into order what before appeared to be all 

 confusion. 



The author then traces the great similarity of tidal phenomena 

 of the two channels, and proceeds to describe them. For this pur- 

 pose he considers the Irish Channel as extending from a line con- 

 necting the Land's End with Cape Clear to the end of its tidal stream, 

 or virtual head of the tide at Peel ; and the English Channel from a 

 line joining the Land's End and Ushant, to the end of its tidal stream 

 off Uungeness. With these preliminary lines, he shows that both 

 channels receive their tides from the Atlantic, and that they each 

 flow up until met by counter-streams ; that from the outer limit of 

 the English Channel to the virtual head of its tide the distance is 

 262 geographical miles ; and in the Irish Channel, from its entrance 

 to the virtual head of its tide, it is 265 miles. 



In both channels there is a contraction about midway ; by Cape 

 La Hague in the one, and by St. David's Head in the other, and at 

 nearly the same distance from the entrance. In both cases this con- 

 traction is the commencement of the regular stream, the time of the 

 movement of which is regulated by the vertical movement of the 

 water at the virtual head of the channel ; situated in both cases 145 

 miles above the contraction, and the actual time of this change, 

 or Vulgar Establishment, is the same in both cases. Below the con- 

 traction of the strait, in both cases the stream varies its direction 

 according to the preponderance of force exerted over it by the ofRng 

 stream. In both cases, between the contraction and the southern 

 horn of the channel, there is a deep estuary (the Bristol Channel and 

 the Gulf of St. Malo) in which the times of high water are nearl)'' 

 the same, and where, in both, the streams, meeting in the channel, 

 pour their waters into these gulfs, and in both raise the tide to the 

 extraordinary elevation of forty-seven feet. From the Land's End 

 to the meeting of these streams in one case is seventy-five miles, and 

 in the other the same. 



In one channel, at Courtown, a little way above the contraction, 

 and at 150 miles from the entrance, there is little or no rise of the 

 water ; and in the other, about Swanage, at the same distance from 

 the entrance, there is but a small rise of tide also (five feet at springs). 

 In both cases these spots are the node or hinge of the tide-wave, on 

 either side of which the times of high water are reversed. And 

 again, near the virtual head of the tide, in both cases there is an in- 

 creased elevation of the water on the south-east side of the channel 

 of about one-third of the column ; the rise at Liverpool being thirty- 

 one feet, and at Cayeux thirty-four feet 



The author traces a further identity in the progress of the tide- 

 wave along the sides of both channels opposite to tliat of tlie node. 

 In the first part of the channel the wave in each travels at about 

 fifty miles per hour ; in the next, just above the node, this rate is 

 brought down to about thirty miles per hour in one, and to sixteen 



