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Fig. No. 9.

General View of Base-measuring Apparatus set up heady for use. A. Tape-winder. Steel-wire frame, covered with stout leather, 18 in. F. Spring balance. inside diameter. G. Tension-gear. (For details see Fig. Xo. 10.) B. Cast-iron universal-jointed support-stands (Crabs). (For details see H. Tape. Fig. No. 11.) I. Tension-wires. C. Measuring-stand. (For details sec Fig. No. 8.) •>■ Weight. _ D. Measuring-tripod. Galvanized-iron tube legs, gun-metal top. (For de- K. Winch-handle of slow-motion screw of tension-gear. tails see Fig. No. 7.) I J - Slow-motion screw of chaining-stand. E. Five-inch Troughton and Simms transit theodolite, with brass and steel M. Scale attached to axis of vertical arc of theodolite. reading-scales attached to the vertical arc. (For details see Fig. Xo. 6.) When measurements are being made in the field, the observer at the scale stands abreast of the theodolite and reads the position of the graduated mark on the tape where it passes the scale M or A clearly shown in Fig. Xo. (1. always using a strong magnifying-glass. The observer at the rear end. or tripod D, stands abreast of the tripod and makes the contact of the rear graduated tape-mark with the zero-mark on the tripod-head (see Fig. Xo. 7) by means of the slow-motion screw at L or B in Fig. Xo. 8. The fine scale on tripod is only in the position shown when the tape is on the comparator. ~,,, _ , , . ■ The tension-recorder stands abreast of F and keeps the index-mark of the balance true by means of the winch-handle X of the slow-motion tensionscrew.