Royal Society. 539 



those of the Ordnance made at the suggestion of Professor Airy, 

 show that there are two spots in the Irish Sea, in one of which the 

 stream runs with considerable rapidity, without there being any rise 

 or fall of the water, and in the other the water rises and falls without 

 having any perceptible stream ; that the same stream makes high and 

 low water in different parts of the channel at the same time ; and 

 that during certain portions of the tide, the stream, opposing the 

 wave, runs up an ascent of one foot in three miles, with a velocity of 

 three miles an hour. 



The author then enters minutely into the course of the stream ; 

 shows that the point of union of the streams from the ojjposite chan- 

 nels takes place on a line drawn from Carlingford through Peel in the 

 Isle of Man on to Morecombe Bay ; and concludes his remarks on 

 this part of the subject, by adverting to the great benefit navigation 

 will derive from the present inquiry. 



The author then notices a chart of lines of equal range of tide, 

 which has been compiled partly from the ranges published by the 

 Royal Society*, and partly from observations made on the present 

 occasion ; and has annexed a table f, by the aid of which the seaman 

 will be able to compare his soundings taken at any time of the tide 

 with the depths marked upon the Admiralty charts. 



Next folloM's the mention of a feature in the motion of the tide- 

 wave, which Captain Beechey thinks has hitherto escaped observation ; 

 viz. that the upper portions of the water fall quicker than the lower, 

 or in other words, that the half-tide level does not coincide with the 

 place of the water at the half-tide interval ; that this difference in 

 the Bristol Channel amounts to as much as four feetj, and that the 

 law seems to be applicable to all the tides of the Irish Sea§. 



We are next presented with a table (No. 5) exhibiting the various 

 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 ai)ply to the tides of the English Channel the law which 

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

 of the oljservations of Captain M. White and others for this purpose. 

 There was no difficult}^ 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 oj)position to each other ; viz. that there is a great offing 

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

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

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

 removed from, the jjoints 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 comprise within its limits the Bristol 



* Philosophical Transactions, 1836, part 1. t Table X. 



X See Diagram, No. 9. § Diagram, No. ]J. 



