ON THE COASTS OF IRELAND. 31 



I regard this as a most important result, and I cannot with confidence offer any ex- 

 planation of it. 



The last column seems to show that the Apparent Mean Height is greater for large 

 ranges of tide than for small ones, or that in spring tides the increase of elevation of 

 the high water is greater than the increase of depression of the low water. A similar 

 result has been found in the Thames. It does not appear to admit of explanation 

 with our present theoretical knowledge. But in a period of two months it is impos- 

 sible to separate the effects of varying range from those of varying declination of the 

 moon and other varying circumstances. 



For investigation of the effect of the moon's declination on the apparent mean 

 height, the following process was used. It is to be remarked that (setting aside the 

 differences of the moon's distance) the effect of southern declination is the same 

 as that of northern declination ; and the effect is proportional nearly to the square 

 of declination ; and therefore the groups into which our observations are to be di- 

 vided are to be classified by large declinations (of either kind) and by small declina- 

 tions ; the separating time being nearly that at which the moon's declination =— ^x 



moon's maximum declination. The times being thus found, one day was added to 

 each, and thus the following separation of groups was made. 



d h d h 



1st Group, June 26 3 to July 3 14, small declination. 



2nd Group, July 3 14 to July 10 2, large declination. 



3rd Group, July 10 2 to July 16 8, small declination. 



4th Group, July 16 8 to July 23 10, large declination. 



6th Group, July 23 10 to July 30 22, small declination. 



6th Group, July 30 22 to August 6 12, large declination. 



7th Group, August 6 12 to August 12 15, small declination. 



8th Group, August 12 15 to August i9 16, large declination. 

 For each of these groups, the mean of the heights at high water was taken, and 

 the mean of the heights at low water ; and the mean of these gave a mean Apparent 

 Mean Height in each group. The mean of the results from the 1st, 3rd, 5th and 7th 

 groups, was used for small declinations, and the mean of the results from the 2nd, 

 4th, 6th and 8th, was used for large declinations. At Ballycastle the first group was 

 wanting. Thus the following Table was found. 



