136 
HINTS TO tRAVteLLfiRfi. 
days, the daily rate of the watch can be obtained; and, supposing the 
watch to be in good order, and well taken care of on the march, this rate 
will for some days afford a means of finding the difference of longitude 
of any two places when observations for time have been taken. 
The precise method of doing this will be hereafter described, but it is 
not often that in an ordinary journey it can be employed, as it requires 
a halt of several days from time to time, and, moreover, it is not easy to 
ensure the watch from accidents. It is therefore important to become 
acquainted with “ absolute ” methods for obtaining the longitude. 
It must be remembered that in all observations with the sextant, 
unless they are so taken as to eliminate the errors of the instrument, 
great errors of result may occur. 
With a sextant in good order and adjustment the errors are small, and, 
if known, may be applied; but the heat of the sun may induce temporary 
errors, and shocks more serious and permanent errors, which, in some 
observations, will have a disastrous effect. 
The ordinary observations are 
Sextant Observations . 
For latitude 
For longitude .. 
For trtie hearing and 
error of compass 
For longitude ,. 
With the exception of lunar observations, oceultations of stars by the 
moon, and the eclipses of Jupiter's satellites, all these observations can 
Meridian altitude of sun 
a » star 
Circum-meridian altitude of sun 
5, >9 star 
Bouble altitude of sun or stars 
Time by single altitudes of sun 
„ „ „ star 
h equal altitudes of sun 
59 99 99 star 
Lunar Observations. 
By altitude of the sun 
By observed angular distance of a peak, or any 
other object from the sun 
Telescope Observations :— 
Oceultations of stars by the moon 
Eclipses of Jupiter’s satellites 
Moon culminating stars with Transit Theodolite. 
