ME. G. T. TAYLOR ON TIDAL FRICTION IN THE IRISH SEA. 
25 
velocity of the tidal wave. On examining- the data at onr dis])osal it will be found 
that they are hardly sufficient to place the co-tidal lines for 6, 7, 8, 9 and 
10 hours sufficiently accurately on the map to make an accurate determination of the 
velocity of tlie co-tidal line in the neighbourhood of the line AB. 
On looking at maps of co-tidal lines for the Irish Sea, however, such as that given 
in Krummel’s ‘ Ozeanographie,’"'^" it will be seen that the co-tidal lines for successive 
hours are crowded together in the neighbourhood of the Arklow-Bardsey line. 
is therefore a minimum in that region, as we should expect from (42). 
Though we cannot measure accurately the velocity of the co-tidal line as it passes 
the Arklow-Bardsey section, there are two sections of the channel where the positions 
of single co-tidal lines can be determined with considerable accuracy. We can 
therefore determine the mean velocity of the co-tidal line between these two sections 
andean compare this with theory. The line AB, which is practically a co-tidal line for 
8h. lOm. is one example. Bardsey hsland at its eastern end is separated from the 
mainland, so that the error due to a shelving shore is lessened. The time of H.W. at 
Courtown, a few miles south of the point where the western end of AB strikes the 
Irish coast, is 8h., while the time of H.W. at Arklow Bank and Arklow, both a little 
north of AB, and therefore a little later in their tides, is 8h. 25m. Greenwich mean 
time. 
The co-tidal line for 8h. lOm. is therefore well determined and is practically 
coincident with AB. As l)efore we shall take it as being coincident with .r = 0. 
The other co-tidal line referred to is the one for 6h. 15m. It is H.W. at 
Carnsore Point at 6h. 25m., and at Tuskar Bock, 4f miles off the Irish coast, at 
6h. 10m., Avhile tlie other end of the line is determined by Ramsey Sound, off* the 
Welsh coast, where it is H.W. at 6h. 21m. The co-tidal line for 6h. 15m. is shown as 
the line TS in the map, fig. (3). 
Let us then apply the foianula (41) to find the ratio of the amplitudes of the two 
tidal waves. The distance between the mid points, M and L of the two co-tidal lines 
AB and TS, is about 43 nautical miles, so that in (4l) ./■ = — 43 miles. ‘The mean 
depth of the water between the two sections is 45 fathoms, and the velocity of a long¬ 
wave in water of this depth is 56 nautical miles per houi-. Remembering that T, tlie 
period of the semi-diurnal tide is I2h. 25m. or 12'4h., it will be found that 
cot^’= cot = cot (-22-3°) 2-44. 
ci o6 X 12 4 
■ ( 13 ) 
Also A = 6h. 15m. — 8h. lOm. = — l’92h. and 
cot = cot = cot ( — 56°) = —0'67 
T 12-4 ^ 
( 44 ) 
* ‘ Haiidbiich der Ozeanographie,’ vol. ' 1 , }). 33(3 (1911 edition). 
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VOL. COXX.-A. 
