[Footnote: From Proceedings of the Association of County Surveyors of
Ohio, Columbus, January, 1882.]
The following process has been used by the undersigned for many years.
The true meridian can thus be found within one minute of arc:
_Directions_.--Nail a slat to the north side of an upper window--the
higher the better. Let it be 25 feet from the ground or more. Let it
project 3 feet. Kear the end suspend a plumb-bob, and have it swing in a
bucket of water. A lamp set in the window will render the upper part of
the string visible. Place a small table or stand about 20 feet south of
the plumb-bob, and on its south edge stick the small blade of a pocket
knife; place the eye close to the blade, and move the stand so as to
bring the blade, string, and polar star into line. Place the table so
that the star shall be seen very near the slat in the window. Let this
be done half an hour before the greatest elongation of the star. Within
four or five minutes after the first alignment the star will have moved
to the east or west of the string. Slip the table or the knife a little
to one side, and align carefully as before. After a few alignments the
star will move along the string--down, if the elongation is west; up, if
east. On the first of June the eastern elongation occurs about half-past
two in the morning, and as daylight comes on shortly after the
observation is completed, I prefer that time of year. The time of
meridian passage or of the elongation can be found in almost any work on
surveying. Of course the observer should choose a calm night.
In the morning the transit can be ranged with the knife blade and
string, and the proper angle turned off to the left, if the elongation
is east; to the right, if west.
Instead of turning off the angle, as above described, I measure 200 or
300 feet northtward, in the direction of the string, and compute the
offset in feet and inches, set a stake in the ground, and drive a tack
in the usual way.
Suppose the distance is 250 feet and the angle 1° 40', then the offset
will be 7,271 feet, or 7 feet 3¼ inches. A minute of arc at the distance
of 250 feet is seven-eighths of an inch; and this is the most accurate
way, for the vernier will not mark so small a space accurately.