'The Transactions of the Bombay Geographical Society. From January 1863 to December 1864. (Edited by the Secretary.) Volume XVII.' [‎11] (172/524)

BOMBAY TIDAL OBSERVATIONS FOR 1861.
11
with the investigation of the tidal theory, is not open to any such
objection, and would certainly be a good port for reference in the way
proposed. But, secondly, the age of the tide at London is upwards
of two days, whilst at Bombay it must lie between one and one and a
half days. Hence the local dates of similar tides at London and
Bombay cannot differ less than 14^., nor probably more than 28^.;
more accurately, the London tide must he at least about 14A. 59m.,
or possibly even 21 h. 24m.* later in local time than the corresponding
tide at Bombay. These I shall call the third and fourth constants
respectively : a considerable number of observations only could decide
which constant ought to be used. The tides for which they will differ
most are those which accompany the transits between 6|A. and 8^A.,
whilst those for which Lieutenant FergussoiTs and Captain Barker’s
methods vary most, accompany the transits between 1\ and 9|- hours
Civil Time. If to these we add Professor Orlebar’s formula, we have
in all five different methods of approximating to the times of high-water.
The question now to be answered is :—“ Do the observations made and
recorded at Colaba agree generally with any one of these approxima
tions ?” If they do, we are at once in possession of an easy method
of computing the times of high-water witn tolerable accuracy for gene
ral purposes; and what is of more importance, we may employ the
observations with confidence in the determination of correct formula
for the prediction of the local tides, and so far accomplish the object
for which they are carried on by Government. Besides, if one of these
approximations represent generally the observed times of tide, within
say even 20 minutes, we shall be justified in rejecting as erroneous any
observations which appear exceptional or very much beyond the
utmost limits of error. With such objects in view, I have compared
each of the 335 observations of the times of high-water at the upper
transit, as registered in the volume for 1861, with the results of Pro
fessor Orlebar’s formula, and with the times derived from those of the
London tides, by the application of each of the four time-constants
alluded to. Founded, as the latter are, on the difference of the establish
ments of the port at London and Bombay, they necessarily all give
nearly the same dates for the tides at new and full moon, but often
differ considerably in the times of intermediate high-waters*
The following are the results of the examination
* More correctly perhaps 157i. 4m. and 27A. 27m.