12 
MR. G. I. TAYLOR ON TIDAL FRICTION IN THE IRISH SEA. 
The considerations just advanced show that if a channel is so narrow that the 
water is forced to travel straight up and down it, then the difference in level between 
the water on the two sides may be calculated on the assumption that the sea slopes 
to an extent which gives rise to a pressure gradient across the channel which is 
exactly equal to the deflecting force due to the earth’s rotation. If the channel is 
rather wider the central parts of the stream may be able to move across the channel 
slightly. This wmdd reduce the slope. In the case of the South Channel of the 
Irish Sea, however, these cross currents are very small, as may be seen by examining 
the flgures given in the table on p. 14, where it is shown that the direction of the 
current is practically constant during the ebb and during the flood streams. We are 
therefore justified in assuming that the South Channel is narrow enough to allow us 
to apply the calculations given above. 
Velocity of' the Tidal Currents. —We now come to the measurements of tidal 
currents. These are tlie principal factors which determine our choice of sections 
suitable for measuring the flow of energy into the Irish Sea. 
South Channel .—In the South Channel the best section is that shown as AB in the 
map (fig. 3 ). It runs from Bardsey Island through the south end of Arklow Bank. 
Along this section tidal measurements have been made at the points marked in the 
map as Sj, Sg, Sg, S 4 . 
In the position Si, 5 miles from Arklow Bank, the maximum velocities of the ebb 
and flood streams are both 3’6 knots. The direction of the flood stream is N. 32° E., 
while that of the ebb is S. 26° W. 
At S 2 , 15 miles from Arklow Bank, the maximum flood stream is N. 35° E. at 
3 ’2 knots, while the maximum ebb stream is S. 32° W. at 3'3 knots. 
At S 3 , 15 miles from Bardsey Island, the maximum flood stream is N. 25° E., 
3 "2 knots, while the maximum ebb is S. 28° W., 3'0 knots. 
At S 4 , 5 miles from Bardsey Island, the maximum flood stream is N. 16° E., 
3'0 knots, while the maximum ebb is S. 16° W., 2 ‘3 knots. 
It will be seen, therefore, that the maximum current velocity is nearly constant 
along the section, its average value being 3 ’2 knots. The direction also varies very 
little ; the average direction of the flood stream being N. 27° E., while that of the 
ebb S. 26° W. These are practically opposite directions. They will (for simplicity) 
be assumed to be exactly opposite during the rest of this discussion. 
No measurements of the speed and direction of the currents at the points 
Si, S 2 , S 3 , S 4 , are given for the intermediate hours; but several such measure¬ 
ments are given for other points in the neighbourhood. I have selected three 
of these sets which were taken at the nearest points to the section AB. They 
were made at the South Arklow, North Arklow and C^arnarvon Bay light-ships, 
respectively. 
In the accompanying table'^ are given the velocities and directions of the current 
* Taken from ‘ Tides and Tidal Stream.s of the British Islands,’ lirst edition, 1909. 
