MR. G. I. TAYLOH ON TIDAL FRICTION IN THE IRISH SEA. 



31 



Effect of the Shape of the Coast in Determining the Time of II. W. at Points 



on the Coast. 



This is too complicated a matter to treat quantitatively, there is, however, one 

 point in connection with local peculiarities of the tides of the South Channel of the 

 Irish Sea which can be explained qualitatively by the analysis contained in this paper, 

 and that is the effect of a point of land projecting into the channel in altering the 

 times of H. W. on the two sides of it. 



Consider the effect of a point of land on the range, of tide due to a tidal wave 

 passing along a channel. Let AB, fig. (4), represent a portion of one side of a 

 channel and let CDE be a point of land projecting into it. 



Suppose the tidal wave moves along in the direction from A to B. At H.W. the 

 tidal stream is moving from A to B, it might be expected therefore that, owing to 

 the piling up of the water on side facing the current, the level of the water would be 

 higher at C than at E at H.W., that is to say, the range of tide should be greater 





Sea. 



Direction of tidal wave 



Fig. 4. Effect of a cape on times of H.W. on either side of it. 



on the side of the cape which faces the direction from which the tidal wave comes 

 than it would be on the side which faces away from the direction of the tidal wave. 

 This effect does not materially alter the time of H.W. when there is only one tidal 

 wave in the channel. When, however, there are two nearly equal waves, one going 

 up and the other going down, the case is altered. 

 The time t x of H.W. at distance x is given by 



cot 



a b 



T 



2-ir.r 



(41) 



Suppose now, that, without altering x, a is decreased while b is increased by the 

 action of some local peculiarity* as it is on the side DE of the cape (fig. 4). 



If a; is positive and ^?<- then equation (41) shows that a decrease in a and an 

 C L Z 



increase in b will lead to an increase in t t , the time of H.W. 



* This increase must not be so great as to reverse the tides. 



