\fdO'^ - Old Forge Coal Mines

SURVEYING. 253
The difference of the columns, viz., 140.95 ft., agrees
with the elevation of the T. P. following Sta. 53, which is
the last one determined. A check mark |/ is placed opposite
the elevation checked, to show that the figures have been
verified. The rate of grade is determined as follows: In one
mile there are 5,280 ft. = 52.8 stations. A descending grade
of 80 ft. per mile gives per station a descent of -r^-^" =1.515
52. o
ft. The elevation of the grade at Sta. 40 is fixed at 162.0
ft. As the grade descends from Sta. 40 at the rate of 1.515
ft. per station, the grade at Sta. 41 is found by subtracting
1.515 ft. from 162.0 ft., which gives 160.485 ft., and the
grade for each succeeding station is found by subtracting
the rate of grade from the grade of the immediately
preceding station.
A section of profile paper is given in Fig. 69 in which the
level notes are platted, and upon which the given grade line
^ FIO. 69. 60
is drawn. The profile is made to the following scales: viz.,
horizontal, 400 ft. = 1 in. ; vertical, 20 ft. = 1 in.
Every fifth horizontal line is heavier than the rest, and
each twenty-fifth horizontal line is of double xvcight. Every
tenth vertical line is of double iveight. The spaces between
the vertical lines represent JOO ft., and those between the