MR. G. I. TAYLOR ON TIDAL FRICTION IN THE IRISH SEA. 17 



AB runs in a direction N. 86 E., while the current runs in a direction N. 26 E., 



so that = 60 and sin 6 = 0'87. 



T = 12'4h., T! = 8h. 10m., T = 8h. 20m. 

 so that 



T,-T = 10m. =i">h., 

 and 



cos T.-T,,) = cos = cos 2-4 = 1 '0, 



D = 37 fathoms = 6800 cm. 

 H, = 4f feet = 145 cm. 

 L = 50 nautical miles = 9'1 x 10 6 cm. 



Hence the mean rate at which energy is transmitted across the section AB is 



W^ = |x981x l'03x 163xO'87x 1'0 x 6800 x 145 x 9'1 x 10 6 



= 6 '4 x 10 17 ergs per second ............. (24) 



North Channel. The same method may be applied to the North Channel, but it 

 is at once obvious that practically no energy enters the Irish Sea through this 

 channel. The tidal streams set strongly through the North Channel, running in 

 from 5h. to lib. and out from lib. to 5h. at full and change of the moon. The neck 

 between the Mull of (Jan tyre and the Irish Coast forms a loop in a stationary 

 oscillation. It is H.W. at Midi of Cantyre at LOh. 58m. At lied Bay, on the Irish 

 Coast, it is H.W. at lOh. 55m. The co-tidal line for lOh. 55m., therefore, runs from 

 the Midi of Cantyre to Red Bay, and it is for this reason that it has been chosen for 

 the section HC (see fig. 3) along which the integral for W uc (the energy which flows 

 across RC) will be taken. Since the streams change direction at H.W., Dover, i.e., at 

 llh. 7m., the phase difference between the tidal stream and the height of the tide is 

 only 12m. of time short of the quarter period, i.e., 87 expressed as an angle. 



The maximum current runs throxigh the North Channel at a rate of 4 knots. The 

 rise and fall of tide in the North Channel is very small ; at Red Bay it is 4 feet, and 

 at Ballycastle Bay, to the N.W. of Red Bay, it is only 3 feet. At the Mull of 

 Cantyre it is also 4 feet. The equality of the heights of the tide on the two sides of 

 the channel is probably due to the fact that, at the times the stream is running at its 

 maximum speed, when therefore we should expect the maximum difference in level on 

 the two sides of the Channel owing to geostrophic force, the water is at its mean 

 level. At H.W. and L.W. the streams are slack, so that no geostrophic effect is to be 

 anticipated at those times. 



In the formula 



W KC .= P g ~ cos cos (T -l\)x (length of RC) . . . (25) 

 VOL. CCXX. A. D 



