"معاملات الجمعية الجغرافية في بومباي. من يناير ١٨٦٣ حتى ديسمبر ١٨٦٤. (تحرير السكرتير.) المجلد XVII." [‎٨‎٩] (٥٢٤/١١٨)

BOMBAY GEOGRAPHICAL SOCIETY.
Ixxxix
ages greatly differ. Thus, for ports in the Irish Sea and St. George’s
Channel, the times derived from those of Liverpool will always be
approximately correct, hut for the coasts of Africa or the Indian
Ocean, there must be considerable errors in computing the times of
tide from those of any British port.
In his second letter, dated 16th April, Captain Wherland seems to
have come to the same conclusion as I had in regard to the effects of
the wind.
He makes an important suggestion however in his first letter, which
I hope the Society will not lose sight of; namely, the necessity of
making observations in the offing as to the time when the stream turns,
for the guidance of Captains, “ particularly when making the port in
thick weather.”
His valuable communication on the Magnetimeter I trust will receive
the consideration it seems to deserve.
Hoping that other intelligent Captains who visit our port will be
stimulated by the example of Captain Wherland’s zeal to contribute
their quotas of information to the Society for general use.
I am, my dear Sir,
Ever yours sincerely,
J. Burgess.
The first Paper read was on a Method of Coipputing the Times of the
Moon’s Bising and Setting, by J. Burgess, Esq., F.F.J.S.
Mr. Burgess said :—
Owing to the rapid variations of the moon’s declination, angular
motion from the sun, and horizontal parallax, the determination of the
times of her rising and setting is much more complicated than the
analogous problem for sunrise and sunset. The necessity of repeating
the calculation, after finding an approximate time, renders the usual
method of computation tedious. The writer showed, that by construct
ing a table of the lunar semi-diurnal arcs for any proposed latitude,
employing the mean values of the moon’s angular motion from the sun
and horizontal parallax, the times of rising and setting might be obtained
f rom the time of southing at once with a considerable degree of accuracy,
and the correction for variations of parallax and of angular motion
14 p