ON OBTAINING THE MERIDIAN 
59 
subtract from the time of west elongation 0.16 min. for 
every degree north of 40°. For eastern elongations sub¬ 
tract 0.10 min. for every degree south of 40°, and add 0.16 
min. for every degree north of 40°. 
E. To refer to any other than the tabular longitude: Add 
0.16 min.for each 15° east of the ninetieth meridian and sub¬ 
tract 0.16 min. for each 15° west of the ninetieth meridian. 
The deduced time of elongation will seldom be in error 
more than 0.3 min. 
For Evening Observation. Study of the tables will 
show that at certain times of the year a choice of methods 
is offered. Since, however, evening observation is usually 
most convenient, the following directions have been ar¬ 
ranged with that in view. The time limits for these 
observations, it will be understood, vary somewhat with 
the latitude. 
On the tenth of January observe western elongation 
at midnight and for each fifteen days thereafter earlier 
by one hour. This may be done until late March. 
From late March to early June, use lower culmination 
with the help of Delta of Cassiopeia. On April 1st the 
culmination occurs at 12* 1 50 m and after that for each fifteen 
days earlier by one hour. 
From early June to early October use eastern elonga¬ 
tion. On June 15th it occurs at 2 a.m. 
From early October to middle January use upper cul¬ 
mination with Zeta of the Great Bear. 
