78 
THE REV. W. WHEWELL ON THE 
moon begins to have north declination, the tide which follows her, and which is 
therefore the greatest, is three hours before the sun, and is a morning tide. When 
the moon’s right ascension becomes three hours, (that is, after about one eighth of a 
lunation,) the tide following the moon, which is still the greater, (because the decli- 
nation is still north,) becomes the evening tide. The evening tide continues the 
greater till the moon’s right ascension becomes twelve hours, when she passes to the 
south of the equator, and the tide following the moon, which is nine hours after the 
sun, and still the evening tide, becomes the smaller ; and this continues till the moon 
is seven hours from the sun, or in fifteen hours right ascension, at which period the 
tide which follows her becomes the morning tide, and the evening tide is again the 
greater. Thus in this position the morning tide is greater during six hours of the 
moon’s motion in right ascension (from the sun), and the evening tide is greater 
during the remaining eighteen hours ; that is, the evening tide is the greater during 
three fourths of the lunation. 
We might in the same manner trace the changes which take place in other posi- 
tions of the sun ; but this is unnecessary. The effect of the inequality may be calcu- 
lated by the tables which are added at the end of this paper. 
The height of low water at Plymouth is also affected by a diurnal inequality. It 
follows the same law as the inequality of high water ; its epoch is the same ; and its 
multiplier for May, June, July, August, 1834, is f, |, f, i, respectively. 
Sect. II. Diurnal Inequality at Singapore. 
By the Hydrographical Office of the Admiralty I was furnished with about a year’s 
observations of the tides of Singapore, from August 1834 to August 1835, made by 
Mr. W. Scott, the Master Attendant at that port, in pursuance of directions given 
by the Directors of the East India Company. 
These observations, from the very curious nature of the results to which they lead, 
I consider as more remarkable and valuable than any series of equal extent which 
has fallen under my notice. 
On laying down the heights of high water, it appeared that the early part of the 
series was very irregular, obviously from the imperfection of the observations ; but 
beginning with January 1835, the curve was tolerably regular ; and during the greater 
part of the subsequent time, the inequalities (which the observers could not know) 
were so clearly marked, and so steady in their course, that it was impossible to doubt 
the goodness of the observations. 
I proceeded to examine these in the manner already described for the Plymouth 
observations, and found a diurnal inequality nearly agreeing in law and in amount 
with that at Plymouth ; the only difference being, that instead of four days it was 
here found necessary to take the lunar declination a day and a half preceding the 
tide, or, more exactly, at the interpolated or north lunar transit which intervened be- 
tween the second and third south transit preceding the tide. 
