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 

 vessel. 



[5 



Hours before I 4 

 H.W. at > 3 

 Dover 2 



[1 

 H.W. at Dover . 



[1 



Hours after 



H.W. at 

 Dover 



16 



Diurnal 

 magnitude. 



X. 43 E. 

 X. 43 E. 

 X. 43 E. 

 X. 43 E. 

 X. 43 E. 

 X. 43 E. 

 S. 43 W. 

 S. 43 W. 

 S. 43 W. 

 S. 43 W. 

 S. 43 W. 

 S. 43 W 



Rate. 



Knots. 



1-7 

 3-5 

 3-7 



3-2 

 2-2 

 0-7 

 1 "2 



4-0 

 3-5 

 2-0 

 0-7 



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 



'.) (18) 



where V is the maximum current velocity, which in the case of the section AB is 

 3 "2 knots, t has 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 H.W., Dover, at full and change of moon is at llh. 7m., therefore, 

 T = 8h. 20m. approximately. 



