\fdO'^ - Old Forge Coal Mines

244 SURVEYING.
in dotted lines. In platting the remaining angles, he
will produce the lines in pencil only, erasing then, as
soon as the forward angle is laid oflf. Write the proper
station number in pencil at the end of each line as soon as
platted, and the angle with its direction, R. or L., before
laying off the following angle. Write the bearing of each
line distinctly, the letters reading in the same direction in
which the line is being run. The magnetic meridian is
platted as follows: The bearing
of the course from Sta.
33 + 77 to Sta. 44 + 80 is S 61° 45' W, i. e., the course is
61° 45' to the left of a north and south line, which is the
direction we wish to indicate on the map. Accordingly, we
place a protractor with its center at Sta. 33 + 77 and its
zero on the following course, and read off the angle 61° 45'
to the right. Through this point of angle measurement and
Sta. 33 + 77 draw a straight line N S. This line is the
required meridian.
(654) Angle B = 39° 25'. From the principles of trigonometry
(see Art. 1 243), we have the following proportion:
sin 39° 25' : sin 60' 15' :: 415 ft. : side A B.
sin 60° 15' = .8682.
415 ft. X .8682 = 360.303 ft.
sin 39° 25' = .63496.
360.303 -^ .63496 = 567.442 ft., the side A B. Ans.
C
Fig. 66.
and the line A B produced as required.
(655) (See Fig. 66.) At
A we turn an angle B A (7 of
60° and set a plug at C 100'
from A. At C we turn an
angle A C B oi 60° and set a
plug at B 100' from C. The
point B will be in the line
A B, and setting up the instrument
at B, we turn the
angle C B A = 60°. The
instrument is then reversed,