'The Transactions of the Bombay Geographical Society. From January 1863 to December 1864. (Edited by the Secretary.) Volume XVII.' [‎13] (42/524)

BOMBAY GEOGRAPHICAL SOCIETY.
Xlll
Institution, and not by tlie late Captain Montriou, I.N. ; and tliat at
the time he published it, he himself allowed that it was not accurate
within half an hour, either one way or the other, or in other words,
the extent of its inaccuracy was about one whole hour. The person
to whom we are indebted for tne election of the tide guage at Colaba,
was, I believe, our lamented friend the late Dr. Buist, and it was first
brought into operation in January 1846. Whether the site for its
erection was chosen hurriedly, or was the best at command within the
Observatory compound, I cannot say, but I rather think tne latter.
Professor Orlebar makes the following remarks thereon :—
“ The instrument indicates neither the tide of the open sea or that
of the harbour, but something between the two. It is necessary to re
mark here, that the position of the tide gauge was not judiciously
chosen. It ought to have been established either on the sea coast or in
the harbour.”
These remarks, coming to my knowledge when I first took charge of
the Observatory, I placed little value either in the registration of the
Observatory’s tide gauge, or in Professor Orlebar’s formula. The tide
gauge had been working for nearly six years when I assumed charge of
the Observatory, and was not then in good working order, and all efforts
since to render it permanently efficient have more or less failed. Ihis,
however, gave me no anxiety, as I had a formula of my own, by which
1 could determine the time of high-water on any given day within say
44 ten minutes” of the truth, which is near enough for all practical
purposes, that is to say “ nautical purposes” which I consider is all
that is required.
My formula or rule for determining the time of high-water on any
given day at Bombay or any other port, the establishment of which is
known, is based upon the difference of its establishment and that of
London Bridge. For instance, the establishment of London Bridge is
2 hours and 7 minutes Mean Time, and that of Bombay is 11 hours 17
minutes Civil Time; the difference between these two is 2 hours 50
minutes (minus'), and this forms a Constant, which, if applied as follows
to the time of high-water at London Bridge for any given day, will
give the time of high-water at Bombay : and I may here add that, by
personal testing and observation for many years, I have found the ie~
suits from the foregoing rule to be as correct as could be desired, and I