ON THE COASTS OF IRELAND. 109 



The apparent age from times is at every littoral station, except Dunmore, consider- 

 ably less than the age from range. At Port Rush the apparent age is small ; and at 

 Ballycastle, the diminution proceeds so far as to change the sign of the apparent age. 

 I cannot entirely explain this difference. It indicates that large tides arrive earlier 

 (with reference to the hour-angles of the sun and moon) than small ones ; but I know 

 not why this should happen. 



Section XV. — Comparison of the results as to mean height , range, semimenstrual in- 

 equality in height, age of tide obtained from height, establishment, semimenstrual 

 inequality in time, and age of tide obtained from times, deduced from high and 

 low waters only, in Sections V., VI., VII., VIII., with those deduced from the ana- 

 lysis of individual tides in Sections XL, XII., XIII., XIV. 



With regard to the mean heights, we have to compare the results in Section V. with 

 those in Section XI. And first for the mean height on the whole series of observa- 

 tions. The stations which appear best adapted to enable us to decide on the adop- 

 tion of Mean Heights or Apparent Mean Heights as our standard (that is, as most 

 nearly related to the height of water unaffected by tides) are those upon the Shannon. 

 And these leave no doubt that the Mean Heights (deduced from the analysis) ought 

 to be adopted. In a current river, it is inconceivable that the height at a lower 

 station (as Foynes Island) should be equal to that at the highest station (Limerick), 

 as it would be if we relied on apparent mean heights. These are the only stations 

 which throw much light on this subject, for at Dunmore East and New Ross (river 

 stations) the two results agree ; and, at the littoral stations, there is on the whole no 

 difference of a critical kind. At the two quasi-river-stations of Buncrana and Car- 

 rowkeel, we have on both systems discordant results, one giving a mean level higher 

 and the other lower than that of the more exposed stations. The extreme diminution 

 of the range of tide between Port Rush and Glenarm causes no sensible alteration of 

 the mean level, in either system of results. The greater elevation of the mean level 

 at the northern part of the island is equally well-marked in both. For the variation 

 of mean height under different circumstances of large and small tides, large and 

 small declinations of the moon, and increasing and decreasing declinations of the 

 moon, the comparison of the numbers on the two systems gives little subject for 

 remark, except that the difference between large and small tides in the Shannon sta- 

 tions seems to be more strongly marked in the mean heights than in the apparent 

 mean heights. This however does not well accord with the idea of a standard height. 

 It will be remarked that at Limerick the difference between the mean height and the 

 apparent mean height is nearly a foot. 



With regard to the range of the tide, we have to compare the " Mean Range" in 

 the 8th column of the Table in page 35 with the double of " Mean or M" in the 5th 

 column of the Table on page 106. Neglecting the differences of 0*01, we may assert 

 that, at all the stations except Mullaghmore and Dunmore East, the apparent range 



