OBSERVATIONS FOR TIME AND LONGITUDE, 
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follows:—The difference between the latitude by star and the sun’s zenith 
distance equals the sun’s declination. With the declination thus found 
search page 1 for the month in the f Nautical Almanac/ and opposite the 
declination that most nearly agrees with the declination found as above, is 
the day of the month. 
This method cannot always be used in the tropics, unless the traveller 
is provided with a transit theodolite , as the meridian altitude of the sun 
will, at times, be too great to be measured with a sextant, when using an 
artificial horizon; neither can it be used with any degree of certainty at 
those periods just before or after the sun has obtained its greatest 
declination, viz., June 21st and December 21st. 
Another simple method of finding the lost day, is to measure with a 
sextant the angular distance between the moon and one of the heavenly 
bodies whose distance from the moon is given in the lunar distance tables 
of the ‘ Nautical Almanac.’ This observed distance must then be reduced 
to the apparent distance in the following manner:—When the sun is one 
of the objects, add the semi-diameters of the sun and the moon to the 
observed distance, but when a star or a planet is observed the moon’s 
semi-diameter must be subtracted when the distance to the moon’s far 
limb has been observed, but added when the near limb has been observed; 
the result in each case will be the apparent distance. Then (since the 
true and apparent distances cannot differ by more than the sum of the 
corrections of their altitudes), with the apparent distance found as above, 
search the f Nautical Almanac ’ tables for the nearest given distance (of 
the same body) to it, opposite which will be found the day of the month. 
It must be remembered that the hours given in the lunar distance tables 
are counted from noon, when the astronomical day begins: thus July 18th, 
XVh., astronomical date, is July 19th, 3h. a.m., civil date. 
Observations for finding the Time and Longitude. 
These are of two kinds. (1) Observations which have for their object 
to find the difference of longitude between the place of the observer and 
that of a place whose longitude is known. 
(2) Observations to find the longitude directly, by the determination 
of Greenwich time astronomically, without the aid of a watch showing 
Greenwich time, or, as it is termed, absolutely. 
