20 



MR. AIRY ON THE LAWS OF THE TIDES 



After the statement which I have given (in the second section) of the difficulty of 

 fixing upon times of high and low water, it will not be surprising that considerable 

 irregularities exist among these numbers. Their agreement nevertheless is sufficient 

 to show that the diurnal tide in time of low water is great at Limerick, and very 

 great at all the stations from Buncrana to Ballycastle. At Mullaghmore and Bally- 

 castle it is also great at high water. The increase in numbers at low water from 

 Kilrush to Foynes Island and Limerick, would seem to show that diurnal tide in 

 time at low water increases considerably in ascending a river. It would appear, 

 however (as seems, a priori, probable), that this holds only when there is at the same 

 time a considerable diurnal tide in height, of such a nature that a depression of height 

 accompanies a retardation of time. This is supported entirely by the analogy of the 

 course of low water at ordinary semidiurnal tide : where, as will appear in this paper, 

 and as is known from other observations, and as also appears from theory*, the pro- 

 gress of the phase of low water up a river is slower as the water is shallower at low 

 water. At New Ross, considered with relation to Dunmore East, the diurnal tide in 

 time of low water is not sensibly increased ; and here there is no large diurnal tide 

 in height. The large numbers in the neighbourhood of Ballycastle do not depend 

 on this cause. 



Maximum Coefficient of Diurnal Tide in Height, First Division, as inferred from 



Diurnal Tide in Time. 



Kilbaha 



Kilrush 



Foynes Island. . . , 



Limerick 



Casleh Bay 



Galway , 



Old Head 



Mullaghmore . . . . 



Buncrana 



Port Rush 



Carrowkeel 



Ballycastle 



Glenarm , 



Donaghadee ... 



Ardglass 



Clogher Head . , 



Kingstown 



Dunmore East . 



New Ross 



Passage West ... 

 Castle Townsend. 



High water (from times of low water). 



July 1—14. July 14— 31. July 31— Aug.l2 



ft. 

 + 0-46 

 + 0-11 

 + 0-41 

 4-1-88 

 + 0-24 

 -fO-60 

 + 0-28 

 + 0-16 

 + 0-97 

 + 0-77 

 + 0-97 

 + 0-75 

 -0-07 

 4-0-06 

 4-0-27 

 + 0-45 

 + 0-44 

 + 0-04 

 -0-19 

 + 0-26 

 — 0-45 



ft. 



— 0-18 



— 0-14 



— 0-40 

 -M6 

 -0-16 



— 0-51 

 -0-19 



— 0-42 



— 0-15 



— 0-13 

 —0-20 

 -0-42 



— 0-31 



— 0-46 



— 0-40 



— 0-45 



— 0-40 



— 0-20 

 -006 

 -fO-17 

 4-0-12 



ft. 

 -fO-37 

 4-0-12 

 -I-0-61 

 4-1-35 

 4-0-30 

 + 0-45 

 + 0-07 

 + 1-02 

 4 0-75 

 + 0-73 

 + 0-85 

 + 0-50 

 + 0-25 

 + 0-10 

 + 0-33 

 + 0-32 

 + 0-57 

 + 0-34 

 + 0-37 

 + 0-09 

 — 0-15 



Low water (from times of high water). 



July 4—17. July 17—32. Aug. 1—13 



ft. 

 —059 

 -0-62 

 -0-68 

 —061 

 -0-92 

 —0-87 

 -0-40 

 -0-78 

 -0-15 



— 0-14 

 -0-25 

 -0-11 

 + 0-05 

 -0-39 



— 0-04 

 -0-03 

 -039 

 + 0-31 

 + 0-26 

 + 0-02 

 -0-17 



ft. 

 + 0-28 

 + 0-30 

 + 0-19 

 + 0-06 

 + 0-46 

 + 028 

 + 0-24 



+ 0-17 



+ 0-04 

 + 0-14 

 + 0-11 

 + 0-28 

 + 0-13 

 + 0-11 

 + 0-37 

 -0-19 

 + 0-46 

 — 0-02 

 -0-20 

 + 0-08 

 + 0-09 



ft. 



— 0-13 

 -0-37 



— 0-50 



— 0-81 

 -0-45 

 -068 

 + 0-02 

 -0-33 

 -0-25 



— 0-13 

 -0-08 

 -0-08 

 -0-13 

 -0-45 

 -0-11 



— 0-41 



— 0-38 



— 0-20 



— 0-43 

 -0-04 

 -0-24 



These numbers ought, upon the theoretical expressions for the tides given in an 

 earlier part ^f this section, to agree with the numbers in the first table in page 19. 



* Encycl. Metropol., Tides and Waves, Art. 208. 



