The Sun.
London, England, 1827-04-23 00:00:00

Just Published—in quarto.

HORARY TABLES, for finding the Time
by Inspection, to facilitate the operations for obtain-
ing the Longitude at Sea by Chronometers and Lunar Ob-
servations ; also for finding both the Latitude and Time, by
noting the exact interval by a good watch or chronometer,
between two observed Altitudes of the Sun, or a fixed Star ;
or by the simultaneous observations of the Altitudes
of any two celestial objects. To which is added, by Way
of Appendix, an easy method of Clearing the Observed
Distance of the effects of Refraction and Parallax, with new
Tables for the purpose, computed according to Mr. Lyon's
Theory, and with Dr. Thomas Young's Refractions.
By THOMAS LYNN,

Late Commander in the Sea-service of the Eait India
Company, and Examiner (appointed by the Honourable
Court of Directors,) of the Officers of that service.
Author of " The Improved System of Telegraphic Com_
munication."—" Star Tables."—Nautical and Astronomi-
cal Tables."—" Supplementary Tables of the Moon's Place,
for every three hours, in right ascension and declination,
ikc." to be printed annually for two years in advance. Ste-
reotyped and printed for the Author.
Sold by himself, at 148, Leadenhall-street ; by Messrs.
Par bury and Allen, and by all other Booksellers. Price
2/. 2s. bds.

The plan of these tables is in itself simple and obvious.
The degrees of Latitude from the Equator to 60 North and
South, occupy a prominent situation at the head of each
page. The degrees of declination, from oto 24, run from
left to right, on the top and bottom of the columns, and
the Altitudes increase as they descend in the marginal
column. The Horary Angles, standing opposite to 0, or
Zero, in the Altitude column, show the apparent time to
the nearest second that the Sun'a centre is in the true or
rational horizon ; or the time of his Rising and Setting ;
or the semidiunaal arcs of any Celestial objects. Opposite
to the true Altitudes (to the number of sixty in each page),
and under and over the degrees of Declination, are the cor-
responding Horary Angles, or Apparent Times fro:a Noon,
computed to the nearest second. When the Meridian Al-
titude falls short of 60 degrees, the pages are kept full by
the introduction of smaller portions of Altitudes, chiefly of
10 minutes each ; which enhances the value of the Tables,
inasmuch as more frequent opportunities are afforded, to
obtain the time with the least possible trouble ; and that,
in general, when best adapted to the times and circum-
stances when observations for Time are most desirable.
The Horary Tables tints computed (exclusively of 58 pages
of subsidiary Tables, and 48 of prefatory matter and in-
structions) contain '282 pages, each page consisting of 13
columns, and each column of 61 Horary Angles, making
sum of not less than 191 thousand results, or computed
numbers.

The most scrupulous attention has been paid to the accuracy
of the numbers. The computations were conducted by two
able persons, separated from each other, and working by
different methOds, entirely independent of any former work
of the kind. The operations were verified by comparison
—before the pages went to press, they were twice read,
and the differences afterwards taken to insure still greater
accuracy, and the beautiful agreement of the results, hear
ample testimony to the care and skill of the Operators.
The main original object of these Tables, was to find the
Apparent Time from an Altitude of the Sun, or other Ce-
lestial object, in a known Latitude, and for which purpose
they will be found extremely simple. But this convenience
may be considered in a secondary point of view, in com-
parison of their utility in obtaining both Latitude and Time,
independently of the Latitude by Account, at any hour of
the day, after the Sun is 5 degrees high, or at any hour of
the night, when the horizon is sufficiently defined to take
the altitudes of the Stare. The method will be best shown
by the following Example :—Admit a ship to be entering
the British Channel, on a day when the Sun's declination
is 20 deg. South. and in the morning at 8 h. 0 m. 1-0 see.
by a good watch or chronometer, let the Sun's true alti-
tude be 5 degrees—and again at bh. 42 m., 36 sec., by
the same watch, let the Sun's true altitude be 10 degrees.
--Required the Latitude and Apparent Time at the last
observation ? N.B. in this Example the ship is supposed
to be stationary. - If otherwise, the first altitude must he
corrected for the change of station, as in the common
method of double altitudes.