FINDING THE LOCUS OF GEOGRAPHICAL POSITION. 245 
radial and the number of the circumference that pass through 
the point so plotted, and, haying subtracted the co-latitude 
of the place of observation expressed in minutes from the 
number of the noted radial, find the intersection of the noted 
circumference with the radial whose number is the remain¬ 
der thus found by subtraction, and read from the gradua¬ 
tions of the projection the declination of this point and its 
hour-angle from the left-hand bounding meridian. The 
hour-angle of the observed star thus found must be converted 
into right ascension by the following rule: 
From the local mean time of observation and the star’s hour- 
angle , to find the star’s right ascension. To the right ascension 
of the mean sun (or sidereal time, American Nautical Alma¬ 
nac, page ii, last column; also British Nautical Almanac, 
page ii, last column), corrected for the Greenwich mean time 
of observation, add the local mean time of observation. The 
result will be the local sidereal time of observation. If star 
is east of the meridian, add its hour-angle to the local sidereal 
time of observation; if west of the meridian, subtract its 
hour-angle therefrom. The result will be the right ascension 
of the star. 
Then scan the star tables of the Nautical Almanac and 
find the name of the star whose tabulated right ascension 
and declination come nearest to the values of the right ascen¬ 
sion and declination that have been deduced. The stars 
that are of a sufficient magnitude to be observed by navi¬ 
gators are so widely separated that there will be no difficulty 
in making the selection from the tables, even when we pro¬ 
ceed no further than the use of the Index to Plates in effecting 
the required solution, as has been done in the following- 
example : 
At sea, February 26, 1901, local mean time (L. M. T.) 
6 h 30 m p. m. Weather overcast and cloudy. Observed the 
altitude of an unknown star through a break in the clouds 
to be 29° 30' (true), bearing N. 74° W. (true). What is the 
name of the star? Ship’s position by dead-reckoning, Lat. 
35° N., Long. 60° W. 
