MR. (I. r. TAYLOR ON TIDAL FRICTION 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 1300t ergs per square centimetre per second. 
It will be seen that the agreement between the two methods of estimatino- 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 tlian 
has previously been supposed. 
Proportion of the Tidal Wave which is Ahso)i)ed 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 specidations as to how large a proportion of the 
energy of the tidal wave is absorbed, and how much of it is reflected back to the 
Atlantic. 
It has generally been believed that tidal friction plays only a very small part in 
tidal phenomena. Heasoning on the lines of tlie present work, howevei-, the mere 
fact that it is possible to And 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 whicli 
enters the Irish Sea directly, because at all points the eflects of the entering and of 
the emerging wave will be felt simultaneously. It is necessary therefore to disentangle 
those eflects. 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, winch are “loops” in the 
oscillation, is small, while the current is a maximum at tliese points. In the middle 
of the Irisli Sea in the neighbourlrood 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. 
M^e have seen that the eflect of the deflecting force due to the earth’s rotation is to 
increase the tide on one side of the cliannel and to decrease it on the other, leaving 
the rise-and-fall of the central part of the channel unaflected. We shall deal flrst 
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). 
