"معاملات الجمعية الجغرافية في بومباي. من يناير ١٨٦٣ حتى ديسمبر ١٨٦٤. (تحرير السكرتير.) المجلد XVII." [‎١‎٤] (٥٢٤/٤٣)

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proceedings of the
have also learned from the Dock Master s Department at Bombay, that
the time riven in the Bombay Calendar or Newspapers is all that they
need for docking ships, &c. I find also, that the times of high-water
given in the “ Times of India,” agree with my own calculation to a
minute for several consecutive days, and at utmost only varying ten
minutes, when the sun and moon are approaching conjunction.
My rule is as follows:—The morning or forenoon high tide at
Bombay is on the same day (Civil Time) as at London Bridge, when
the tide table for it, at pages 488 and 489 of the Nautical Almanac,
gives the first tide less than 2 hours and 50 minutes, otherwise the pre
vious day’s second tide when above 14 hours 50 minutes; in both cases
applying the Constants, minus 2 hours 50 minutes. Afternoon high-
tides at Bombay are on the same day as at London Bridge, when the
first tide in its table is above 2h. 50m., and the second tide less than
4k. 50m.
Now, an error of ten minutes for the time of high-water is less sig
nificant than generally supposed, l mean to say for all practical pur
poses ; for instance, we will say that the tide runs for six hours fiood, and
that the rise and fall is 12 feet, or 2 feet per hour ; well, an error of ten
minutes would only give two inches error in the height of the tide, and
this, for most nautical purposes would, in 999 cases out of 1,000, be
insignificant and inappreciable. However, I will go further.
Supposing we even have a formula by which we can calculate the
time of high-water, or the height of water at any required hour to
within one minute, as Mr. Eurgess appears to think so desirable.
What shall we be the gainers ? How often are scientific theories
exploded and rendered null by the inscrutable ways of Nature, and
where is it oftener the case than with the tidal system ? An abnormal
wind will sometimes effect a tide a whole hour the swell of the sea,
when contrary to the tide, will do the same. Therefore, of what
practical use is it to have formulas for predicting tides or the tidal
range with gi eater accuracy, than that suited for practical purposes,
w en such. is the case ? Professor Orlebar was no doubt a good
mathematician, but he was a landsman, and knew more of tides in
^ practl ? e ; but lf> tlie law pertaining to tides never varied, he
accuracy 1,8 C ° U C ^ ^ means predicting them with the utmost