We have now in the planed edges a of the targets a rigid substitute for the stretched line, forming a guide for the horizontal adjustment, and to provide a guide for the vertical adjustment we take a wooden straight-edge long enough to reach from one post to another. Then beginning at one end of the shafting, we place the flat side of the straight-edge against the planed edge of two targets at a distance of about 15 inches below the top of the shafting; and after levelling the straight-edge with a spirit-level, we mark (even with the edge of the straight-edge) a line on the planed edge of each target, and we then move the straight-edge to the next pair of targets, and place the edge even with the mark already made on the second target. We then level the straightedge with a spirit-level, and mark a line on the third target, continuing the process until we have marked a straight and horizontally level line across all the targets, the operation being shown in [Fig. 2589], in which a represents the line of shafting, b the hangers, and c the targets. d represents the line on the first target, and e the line on second. f is the straightedge, levelled ready to form a guide whereby the line d may be carried forward, as at e, level and straight, to the third target, and so on across all the targets.
Fig. 2590.
Fig. 2591.
The line thus marked is the standard whereby the shafting is to be adjusted vertically; and for the purpose of this adjustment, we must take a piece of wood, or a square, such as is shown in [Fig. 2590], the edges a and b being true and at a right angle to each other. The line d, in [Fig. 2589], marked across the targets being 15 inches below the centre line of the shaft at the end from which it was started, we mark upon our piece of wood the line c in [Fig. 2590], 15 inches from the edge a (as denoted by the dotted line); and it is evident that we have only to adjust our shaft for vertical height so that, the gauge being applied at each target in the manner shown in [Fig. 2591], the shaft will be set exactly true, when the mark c on the piece of wood comes exactly fair with the lines d marked on the targets.
