PROVISIONAL REPORTS, AND NOTICES. 437 
can obtain the absolute mean semimenstrual inequality, and 
consequently the absolute correction for declination applicable 
to all years alike. This being known to be the case, I was dis- 
posed to take advantage of an opportunity which occurred of 
discussing a series of several years’ tide observations, with a 
view to the verifying in fact these theoretical features of the 
correction tables, and determining the correction for declina- 
tion. Mr. Dall, the Harbour Master at Leith, had made a se- 
ries of tide observations, extending from 1827 to 1839, which I 
had every reason to believe to be accurate; and Mr. Ross, of 
the Hydrographer’s office, had, for his own satisfaction, begun 
to arrange these observations, with a view to discussions rela- 
tive to lunar declination and parallax. The latter gentleman 
undertook, at my request, to conduct his discussion in such a 
manner that it might bring into view such results as I have above 
described. The arrangement and discussion of thirteen years’ 
observations of tides (involving the management of above 18,000 
numbers given by observation, and double the number extracted 
from tables,) was, of course, a business of very great labour and 
time; but as this task was not originally suggested by the Bri- 
tish Association, nor directed exclusively to objects pointed out 
by it, I thought it my duty to confine my expenditure within a 
sum very disproportionate to the magnitude of the labour. Mr. 
Ross has been paid 20/. for his discussion of the above-men- 
tioned heights, with a view to the declination correction. The 
result of this discussion is very nearly what I had anticipated. 
The semimenstrual lines taken for different years, differ by the 
effect of the different mean declination. Thus the correct mean 
of the height of high water for each hour of transit, is about 
six inches less in 1837 than in 1829, and this difference is ba- 
lanced by a difference in the declination correction which is to 
be applied to this mean. The declination correction is greater 
in 1837 than in 1829 for equal declinations. The difference, 
however, is net constant, but increases with the declination, 
which agrees with what the theory indicates. The curves which 
express this correction, deviate considerably from each other at 
the higher declinations. This result suggests an improved me- 
thod of applying the declination correction to tide observations, 
which, however, requires to be further considered and examined 
before it can be confidently recommended: I mean, a method 
of using a different semimenstrual inequality and different de- 
clination correction for every different period of the moon’s 
nodes. On this subject it may hereafter be possible to speak 
more decidedly. 
W. WaHEWELL, 
