ON OBTAINING THE MERIDIAN 
51 
From the table for change of declination, and for the 
locality eastern New York, the values 5° 28' and 11° 34' 
are obtained, showing that the needle in the 110 years 
swung 6° 00' to the westward. The desired bearing 
therefore should prove to be N 6° E nearly. 
SECTION VII 
ON OBTAINING THE MERIDIAN 
When for any reason it is necessary to determine a true 
meridian, that is best obtained from the north star. This 
star, easily identified by the range of the “pointers,” is not 
exactly at the pole of the heavens, but in 1923 was 1° 06' 
26" from it. This angle is called the “polar distance” of 
the star. It is decreasing at the rate of about one third of 
a minute yearly. 
The north star, like other stars, is thus circling around 
the pole once in about 24 hours. When directly over or 
under the pole it is said to be in culmination, upper or 
lower as the case may be. The star is then in the meridian, 
and bringing it down with plumb line or transit gives the 
meridian directly. 
When the north star is farthest from the meridian it is 
said to be in elongation, east when the star is east of the 
meridian, west when on the opposite side. A plane through 
the observer, the zenith, and the north star when at elonga¬ 
tion, prolonged downward to the horizon, makes an angle 
with the meridian which is called the azimuth of the star 
at that time. This angle may be obtained for any time and 
position from tables, and setting off the angle, the true 
meridian is found. Upon this meridian the needle can be 
read or marks can be left for reference at any future time. 
The operation of bringing down the star may be per¬ 
formed either with the plumb line or, more accurately and 
conveniently, with a well-adjusted transit. When the 
transit is used it is necessary to illuminate the cross wires. 
This may often be done by holding a lantern or candle 
in front of the transit tube and a little to one side, when 
the field should appear light with the cross hairs show- 
