745 



curves assumed by the tide-wave, and with the durations of the ebb 

 and flood at each place. 



Having explained these observations in the Irish Sea, the author 

 proceeds to apply to the tides of the English Channel the law which 

 he found to regulate the stream of the Irish Channel, availing himself 

 of the observations of Captain IM. White and others for this purpose. 

 There was no difficulty in adapting the rule in the upper part of the 

 Channel ; but below the contraction of the strait, the apparent dis- 

 cordance was so great, that nothing but a reliance on the general 

 accuracy of the observations prevented the inquiry being abandoned. 



It seemed that the streams are operated upon by two great forces, 

 acting in opposition to each other ; viz. that there is a great ofiing 

 stream setting along the western side of the British Isles, and flowing 

 in opposition to the tides of the Channel above the contraction, turn- 

 ing the stream with greater or less effect as the site is near to, or 

 removed from, the points of influence. By pursuing this idea, it was 

 immediately seen that the observations in the English Channel re- 

 spond to it ; and then applying it to the offing of the Irish Sea, and 

 considering that channel to com])rise within its limits the Bristol 

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

 found that the observations there also fully hear 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 ])ur- 

 pose lie 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 Dungeness. 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, Belov/ 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 offing 

 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 nearly 

 the sam«, and where, in both, the streams, meeting in the channel. 



