744 



Laud's-End and up the English Channel/' Embodied in a letter to 

 the Hydrograi)her. by Captain F. W. Beechey, R.N., F.R.S. Com- 

 municated by G. B. Airy, Esq., F.R.S., Astronomer Royal. 



The author commences by stating, that the set of the tides in the 

 Irish Sea had always been misunderstood, owing to the disposition 

 to associate the turn of the stream with the rise and fall of the water 

 on the shore. This misapprehension, in a channel varying so much 

 in its times of high water, could not fail to produce much mischief ; 

 and to this cause may be ascribed, in all probability, a large proportion 

 of the wrecks in Caernarvon Bay. 



The present inquiry has dispelled these errors, and has furnished 

 science with some new and interesting facts. It has shown that, 

 notwithstanding the variety of times of high water, the turn of the 

 stream throughout the north and south Channels occurs at the same 

 hour, and that this time happens to coincide with the times of high 

 and low water at Moricombe Bay, a place remarkable as being the 

 spot where the streams comJng round the opposite extremities of 

 Ireland finally unite. These experiments, taken in connexion with 

 those of the Ordnance made at the suggestion of Professor A^iry, 

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

 stream runs with considerable rajudit}^, without there being Ruy 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 opposite chan- 

 nels takes place on a line drawn fi'om 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 tablet, by the aid of which the seaman 

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

 with the depths marked upon the Admiralty charts. 



Next follows 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 M-ater at the half-tide interval ; that this difierence in 

 the Bristol Channel amounts to as much as four feet^, 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 



* Philosqpliical Transactions, 1836, part 1. f Table X. 



X See Diagram, No. 9. § Diagram, No, 11. 



