Instead of setting up the instrument at the back of the normal with the telescope set to line with the plane of the slope, and to range the pegs in by means of a rod or staff held at the inclination of the slope, as before described, it may be set up in any position in the line of slope where a reading can be taken on the peg, as at a on the sketch (Fig. 264), and at the point read, as at b, a disc should be clamped to the staff, as this can be much more clearly seen than the staff graduations when sighting long distances. The staff should then be transferred to the next normal and held on the peg. If the telescope be now turned in this direction and the cross web adjusted to cut the disc, any point on the intermediate surface where the disc can be intersected is the outcrop of the slope and position of the slope peg.
Fig. 264.
Larger image
It is necessary to observe in the setting out of slope pegs that when there is a change of gradient the operation must cease, but if the point where this occurs be made the position of a normal the operation may be proceeded with, if the instrument be set up at this point.
600.—To set out Slope Pegs on both sides of the Line simultaneously without moving the Instrument from the Centre Line.—Conditions. Single Line. (ab) Formation 15 feet. (cd) Depth of cutting 14 feet. Slope 1 to 1.
The point e, Fig. 265, is the extension of the slope lines to cut the centre line, and its depths below formation for 1 to 1 slope is half the formation width, or 7′ 6″.
Fig. 265.
Larger image