150 
HINTS TO TRAVELLERS, 
Time. 
Measures of time.—hi these pages reference is made to Mean, Apparent, 
and Sidereal times, and it is possible that a few remarks on these 
different measures of time may be useful to those travellers who have not 
had the advantage of previous instruction. The first of these, Mean 
time , is the easiest to understand, as it is that usually shown by watches 
and clocks, and is reckoned by the average length of all the solar days 
throughout the year. For the purposes of everyday life, the day is 
divided into two periods of twelve hours each, and commences at 
midnight. This is called the civil day , to distinguish it from the 
astronomical day, which commences at noon , and is counted through the 
whole twenty-four hours from one noon to another. 
Apparent time is time measured by the sun, as, for instance, the time 
shown by a sundial, and the difference between this time and the time 
shown by an ordinary watch, is called the equation of time, or the interval 
of time necessary to convert Mean time into Apparent time, or the 
contrary. 
Sidereal time is measured by the interval occupied by a star between 
two consecutive passages over the same meridian, which is equal to 
23h. 56m. 4* 09s. of our ordinary, or mean time. It will thus be seen 
that the sidereal hour is 9*83s. shorter than the Mean time hour, and the 
Sidereal day 3m. 55* 91s. shorter than the Mean solar day. Table XXXI. 
is for converting Mean time into Sidereal time, and Table XXXII. for 
converting Sidereal time into Mean time. 
To find a lost Date. —It will sometimes happen that from one cause or 
another, a traveller may lose count of the day of the month, in which 
case (if provided with a sextant, artificial horizon, and f Nautical Almanac ’ 
for the year), he may find it by one of the following methods:— 
Find the latitude of the place by the meridian altitude of a fixed star 
(for this it is not necessary to know the day, as a star’s declination varies 
but little). On the next day, at the same place, observe the meridian 
altitude of the sun, from which find the true altitude, and subtract it 
from 90° to get the sun’s zenith distance; then with the latitude found by 
the star, and this zenith distance, the sun’s declination may be found as 
