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SIR Q. B. AIRY ON THE TIDES AT MALTA. 
Section V. — Examination of the Tidal Results for Malta obtained in the last Section. 
The first result claiming attention is that for the daily mean heights of the water 
abstracted in columns 7 and 8, column 8 giving the difference of the value for each 
eighth part of lunation from the mean of all. And the numbers in column 8 are to be 
compared with those in column 5 for the moon’s declination. There cannot be a 
doubt that they exhibit an accurate luni-menstrual variation of height, depending on 
the moon’s declination. Viewing the extreme slowness of the formation of this 
inequality, I think it probable that the amount at Malta is very little smaller than 
that on the Atlantic coasts of Spain and Morocco, and that its epoch is very little in 
retard, and that thus we have gained a term in the expression for the ocean-tides 
which it might not have been easy to obtain from direct observation. 
The second result is that for the retard of high water on moon’s transit in 
column 9 ; the difference of each number from the mean of all, in column 10, shows 
the semi-menstrual inequality of time at Malta, which is perfectly well defined. On 
comparing it with the tabular semi-menstrual inequality of time at London, in 
column 2, it appears that its amount is nearly the same as that at London (at first 
sight it appears larger, but that is perhaps the effect of small irregularities), and its 
epoch is certainly about three days earlier than the tabular epoch for London. How 
far the London retardation may depend on friction (which was shown in the treatise 
on Tides and Waves in the ‘ Encyclopedia Metropolitana ’ to be the probable cause of 
the “ age of tide ”) I am unable to say. 
The mean retard of semi-menstrual tide on the moon’s transit appears to be about 
16 h 4 m , which may be taken as the “ Establishment” of Malta. 
The third result is that for the semi-range in height of Malta tide in column 11, 
and its variations in column 12. And here again is a perfectly clear semi-menstrual 
inequality. This is to be compared with the tabular London semi-menstrual inequality 
in column 4. In regard to the proportion of inequality of height to the whole semi- 
range in height, if we divide the sum of inequalities without regard of sign by the 
mean semi-range, the quotient for Malta is 278, while that for London is 1T3 
(supposing that no error has been committed in regard to the zero of London heights). 
I cannot explain this difference. In regard to the epoch of inequality, the heights 
agree with the times in making the epoch for Malta about three days earlier than 
that for London. 
It appears curious that such results should be obtained, apparently with certainty, 
in a single lunation from these miniature tides, in which the semi-range, even for 
spring tides, is less than a hand-breadth. 
The remaining results relate to the diurnal tides, and these are not so clear as 
those which we have already treated. We may first consider what we ought to 
expect in diurnal tides. Referring everything to lunar time (not quite the same 
thing as tidal time) we should expect that the lunar diurnal tide would occur at the 
