ON THE COASTS OF IRELAND. 



45 



A glance at this table will show how different are the velocities of the diurnal 

 tide-wave and the semidiurnal tide-wave. From Kilbaha to Port Rush, the diurnal 

 tide travels in a direction so different, or with a velocity so small, that it loses 5^ 

 hours in time upon the semidiurnal wave. But it passes through the North Channel 

 with such speed that at Donaghadee it has regained about 4^ hours. Its course how- 

 ever will be better understood by forming the actual time of high diurnal tide, or 

 rather its interval after the moon's transit. I have treated the numbers in the fol- 

 lowing manner: — Increasing the numbers for July 23rd by 12'' 24'", or half a tidal 

 day (because the moon's declination then was in a direction opposite to that on July 

 9th and August 6th), I have three comparable intervals from semidiurnal higfi 

 water to diurnal high water. I take the mean of these, and apply it to the mean 

 interval from moon's transit to semidiurnal high water in the table of page 39. I 

 also take the mean of the three coefficients. Thus the following Table is formed ; in 

 which it is to be remembered that the coefficients are to be taken positive for July 

 9th and August 6th, and negative for July 23rd. 



