MR. G. I. TAYLOR ON TIDAL PKICTION IN THE IRISH SEA. 21 



per second are used in doing work against the moon's attraction. The remainder 

 1640 110 = 1530 ergs per second are dissipated by tidal friction. 



It will be remembered that the estimates previously given from a direct consideration 

 of skin friction were 1040* and 1300f ergs per square centimetre per second. 



It will be seen that the agreement between the two methods of estimating the 

 energy dissipation due to tidal friction is quite remarkable. The conclusion appears 

 inevitable that the dissipation of energy by tidal friction is very much larger than 

 has previously been supposed. 



Proportion of the Tidal Wave which is Absorbed in the Irish Sea. 



The large amount of tidal energy which these calculations show to be absorbed in 

 the Irish Sea naturally gives rise to speculations as to how large a proportion of the 

 energy of the tidal wave is absorbed, and how much of it is reflected buck to the 

 Atlantic. 



It has generally been believed that tidal friction plays only a very small part in 

 tidal phenomena. Reasoning on the lines of the present work, however, the mere 

 fact that it is possible to find a section where the rise and fall of tide is appreciable 

 and where the phases of the tidal current and tidal height are the same, is a proof 

 that an appreciable proportion of the energy of the tidal wave entering through the 

 South Channel is absorbed. We cannot measure the size of the tidal wave which 

 enters the Irish Sea directly, because at all points the effects of the entering and of 

 the emerging wave will be felt simultaneously. It is necessary therefore to disentangle 

 those, effects. When this has been done it will be found that apparently complex 

 tidal phenomena in the South Channel are really very simple. 



It has often been pointed out that the Irish Sea behaves like a resonator with two 

 open ends. The rise and fall of tide at the two open ends, which are " loops" in the 

 oscillation, is small, while the current is a maximum at these points. In the middle 

 of the Irish Sea in the neighbourhood of the Isle of Man, the currents are small while 

 the rise and fall of tide is large. If the motion of the sea at the two channels is at 

 all similar to a "loop" in a stationary oscillation, it may evidently be analysed into 

 two waves, one going in and the other coming out. 



We shall assume that the motion of the water in the South Channel is all backwards 

 and forwards along the channel, as in fact the current observations show it to be. 

 We have seen that the effect of the deflecting force clue to the earth's rotation is to 

 increase the tide on one side of the channel and to decrease it on the other, leaving 

 the rise-and-fall of the central part of the channel unaffected. We shall deal first 

 with the tidal phenomena which do not depend on this deflecting force, by considering 

 the motion in the central part of the channel. 



* See equation (10). 

 t See equation (9). 



