\fdO'^ - Old Forge Coal Mines

278 RAILROAD LOCATION.
curve (which we will call Sta. 0) is 110 ft., the elevations ot
the grades for all the stations of the curve are the following:
Stations. Elevation of Grade.
110.00
1 110.85
2 111.40
3 111.65
4 111.60
5 111.25
110.60
(807) In Fig. 72, A 6^ is an ascending grade of 1 per
cent., and C B is sl descending grade of 0.8 per cent,, which
,,-'- — « 6 « d • f~ g
Fig. 78.
are the grades specified in Question 806. To draw these
grade lines, first draw a horizontal line A D ^ in. long,
which will include both grade lines to a scale of 100 ft. to
the inch. Divide this line into six equal parts, with the
letters «, b, c, etc., at the points of division. Now, ^ being
300 ft. from A, the height of the original grade line above ^
is the rate of grade. ^= 1.0 ft. X 3 = 3 ft., which distance
we scale off above d to a. vertical scale of 5 ft. to the inch,
locating the point C. The grade of C B is — 0.8 ft. per
100 ft. Consequently, B, which is 300 ft. from C, is 0.8 ft.
X 3 = 2.4 ft. below C, and the height of B above A D is
equal to 3.0 ft. — 2.4 ft. = 0.6 ft. We scale off above D the
distance 0.6 ft., locating B. Joining A C and B C, we have
the original grade lines, which are to be united by a vertical
curve. Now, the elevation of the grade at Sta. is 110 ft,
The line A D has the same elevation. We have already
determined the heights of the curve above this line at the
several stations on the curve. Accordingly, we lay off
these distances, viz., at ^, corresponding to Sta. 1, 0.85 ft. ;
at r, Sta. 2, 1.4 ft. ; at d^ Sta. 3, 1.65 ft., etc., marking each