244 
LITTLEHALES. 
computing the difference of latitude between the two points 
in accordance with the following formula: 
, d A h 
a (f =-o— cosec. 
^2 + 
2 
cosec. 
COURSES AND DISTANCES IN GREAT-CIRCLE SAILING. 
In figure 2, if L be taken to represent the latitude of the 
point of departure laid off along the bounding meridian and 
M the latitude of the point of destination laid off along a 
meridian making an angle with the bounding meridian 
equal to the difference of longitude between the point of 
departure and the point of destination,"then the length of 
the side LM of the spherical triangle PLM will be the great- 
circle distance between the point of departure and the point 
of destination, and the angle PLM will be the initial course 
for a vessel proceeding along the great-circle track between 
L and M. It will therefore be apparent that the course and 
distance in great-circle sailing may be found with very great 
facility by the method of solution which has just been 
described. 
TO FIND THE NAME OF AN OBSERVED STAR. 
Frequently a star that is favorably placed for observation 
cannot be identified because clouds obscure the surrounding 
parts of the sky. If, when the altitude of such a star is 
measured, its compass bearing be observed, and the approxi¬ 
mate true azimuth be obtained by correcting the bearing for 
the variation and deviation of the compass, the identity of 
the star may at once be ascertained by reversing the order 
of proceeding that has been described for finding the alti¬ 
tude and azimuth from the declination and hour-angle— 
that is, having plotted the corrected altitude of the star on 
the meridian of the projection which makes an angle with 
the right-hand bounding meridian equal to the star’s azi¬ 
muth counted from the north pole, note the number of the 
