MR. G. [. TAYLOR ON TIDAL FRICTION IN THE IRISH SEA. 
27 
involves only measurements of depth and time of H.W. It does not involve 
measurements of current or tidal ran^e at all. 
The reniarkable ao-reement between these two methods of estimating the loss of 
energy in tlie tidal wave during its passage into and out of the Irish Sea is strong 
evidence that three-quarters of the energy of the tidal wave entering by the Soiith 
Channel is dissipated in the Irish Sea. The main purpose of this paper is therefore 
accomplished. 
To complete the investigation, however, it is worth while to show that certain 
other tidal phenomena of the South Channel, hitherto apparently not very well 
undei'stood. are simple consequences of the superposition of two tidal waves of 
different amplitudes moving in opposite directions. 
The first of these is the difference between the velocities of the co-tidal line on the 
two sides of tlie channel. This difference is very marked. The distance from Tuskar 
Hock to the south end of Arklow Bank, traversed by the co-tidal line up the Irish 
Coast during the interval between 6h. 15m. and 8h. 10m. is only 30 nautical miles, 
while the distance from Hamsey Island to Bardsey Island traversed by the co-tidal 
line in the same interval on the Welsh (foast is 59 miles, so that the velocity of the 
co-tidal line on one side of the channel is about double its velocity on the other. 
This difference evidently causes the co-tidal line to turn through a large angle, 
independently of any turning which the wave fronts themselves may experience in 
passing through the channel owing to a difference between the depths on the two 
sides. 
In the case of the South Channel the depths are practically equal on the two sides, 
so the fronts of the waves will not turn, though of course they may be very slightly 
convex, owing to the greater depth in mid-channel. 
The direction of the line AB from South Arklow to Bardsey is N. 86° W. The 
direction of the line TS from Tuskar to Ramsey is S. 57|-° W. The angle turned 
through by the co-tidal line from 6h. I 5m. to 8h. 10m. is therefore N. 86° W. mmus 
S. 57° W. = 36i°. 
As a matter of fact the angle, turned through by the co-tidal line is, if anything, 
rather greater than this, because the true co-tidal line for 8h. 10m. must be a little 
nortli of Bardsey and south of Soutli Arklow, while the true co-tidal line for 6h. 15m. 
must run from a point slightly north of Tuskar Rock to a point slightly south of 
Ramsey Island. The true angle between the co-tidal lines for 6h. 15m. and 8h. 10m. 
is therefore slightly greater than 36|-°. 
Now let us turn to the explanation. It has been pointed out already (see p. 9) 
that the “ geostrophic ” or deflecting force due to the earth’s rotation increases the 
rise and fall of tide on the side of the channel which lies on the right-hand side of an 
observer who faces in the direction in which the tidal stream is running at H.W. In 
the case of a progressive tidal wave the current at high water is moving in the 
direction in which the wave is travelling. 
r: 2 
