14 
MR. G. I. TAYLOR ON TIDAL FRICTION IN THE IRISH SEA. 
at various hours referred to H.W., Dover. It will be seen that in all three sets of 
measurements the current remains constant in direction during the flood and during 
the ebb streams, except for a short period, just about the time of H.W., in the case 
of the South Arklow measurements when there is a change in direction of about 10°. 
The direction of the flood stream is exactly opposite to that of the ebb stream in 
this region. 
Table showing the Direction and Velocity of the Tidal Streams at Three Light- 
Ships at Various States of the Tide. 
North Arklow light 
South Arklow light 
Carnarvon Bay light 
vessel. 
vessel. 
vessel. 
Diurnal 
Rate. 
Diurnal 
Rate. 
Diurnal 
Rate. 
magnitude. 
Knots. 
magnitude. , 
Knots. 
magnitude. 
Knots. 
f5 . 
1 i ■ 
N. 43° E. 
1-7 
N. 43° E. 
1-0 
81ack 
Hours before 
N. 43° E. 
3-5 
N. 43° E. 
2-5 
N. 21° E. 
1-2 
i H.W. at 
I 3 . 
N. 43° E. 
3-7 
N. 43° E. 
3-2 
N. 21° E. 
2-0 
Dover 
1 ^ 
N. 43° E. 
3-2 
N. 43° E. 
3-0 
N. 21° E. 
2-2 
[1 ■ 
N. 43° E. 
2 • 2 
N. 43° E. 
2-0 
N. 21° E 
2-0 
H.W. at Dov 
er . . 
N. 43° E. 
0-7 
N. 54° E. 
1-0 
N. 21° E. 
1-0 1 
fl • 
K. 43° W. 
1-2 
8. 32° W. 
1-5 
Slack 
- j 
■ Hours after 
j H.W. at 
Dover 
1 
1 3 . 
J3 . 
i ^ • 
8. 43° W. 
S. 43° W. 
8. 43° W. 
3- 2 
4- 0 
3-5 
8. 43° W. 
8. 43° W. 
8. 43° W. 
2- 7 
3- 5 
3-2 
S. 21° W. 
8. 21° W. 
8. 21° W. 
1-2 
2-0 
2-0 
1 5 . 
8. 43° W. 
2-0 
8 43° W. 
2-5 
8. 21° W. 
1-7 
1 
[6 . 
8. 43° W 
0-7 
8. 43° W. 
1-2 
8. 21° W. 
1-0 ! 
The variation of current velocity with the state of the tide is shown in the curves 
in fig. 2, which are drawn from the measurements recorded in the above table. 
On inspecting the curves of fig. 2 it will be seen that in the neighbourhood of the 
section AB the tidal streams can be represented sufficiently accurately for many 
purposes by a sine curve. We can, therefore, express the current by the mathematical 
expression 
u = V cos^(^ + To) .(18) 
where V is the maximum current velocity, which in the case of the sectioii AB is 
3'2 knots, t lias the same meaning as before (see p. 9), and T^ is the time of maximum 
current at full and change of the moon. In the case of the section AB this must be 
2h. 45m. before H.W., Dover, since the stream changes direction at 15m. after H.W., 
Dover. Since IT.W., Dover, at full and change of moon is at llli. 7m., therefore, 
T|| = 81). 20m. approximately. 
