'The Transactions of the Bombay Geographical Society. From January 1863 to December 1864. (Edited by the Secretary.) Volume XVII.' [‎3] (164/524)

BOMBAY TIDAL OBSERVATIONS FOR 1861.
3
years’ observations only, there would be slight discrepancies varying
with the hour of the moon’s transit, but probably occurring in accord
ance with some law. Different methods might have been pur-
sued in the examination. The following plan was adopted. The
mean difference was found between the time of observed high-water
and the moon’s meridian transit for every hour of the day and for
both transits separately.* Thus, it was found that at new moon the
mean tide precedes the moon’s upper transit at 12 o’clock by
33 J- minutes, and the lower transit by 33|- minutes, and at full moon
it precedes the upper transit by 31and the lower by 28^ minutes.
The differences between these numbers are comparatively small;
none of them varvine; 3 minutes from their mean value, about 32
minutes. So again it was found, that when the transits occur at 1
o’clock, these times are 51*2, 53'8, 411, and 56 # 4 minutes, the average
being about 52, ar.d the variations from the mean value not very
large ; but at the later transits the discrepancies in these differences
become larger, nor do the variations in the different groups seem
to follow any distinct laws ; whence it may be inferred that, as
each number is the average result of from 10 to at most 1/ observa
tions, the discrepancies may, partially at least, arise from obser
vational errors of individual tides. In order, if possible, to elicit
some results, it was therefore necessary to combine the observations
«/
in larger numbers. This was done in four ways.
1«$£.—Those of the first half of the lunation were combined with
the corresponding quantities for the second half for each transit.
2nd.—Those of the upper were combined with those of the
lower transits.
3rd.—All the observations of either transit, belonging to times of
transit between 6-30 a.m. and 6-30 ivm., were combined into twelve
horary groups.
4/7u—The observations for both transits and both halves of the luna
tion were combined into 12 groups of about 56 observations each.
The transit immediately succeeding the time of high-water was employed only
because it is the one used by Professor Orlebar.