Surveying and Levelling Instruments, Theoretically and Practically Described. / For construction, qualities, selection, preservation, adjustments, and uses; with other apparatus and appliances used by civil engineers and surveyors in the field.

by William Ford Stanley

Fig. 217.—Improved Hedley's dial, mounted on Hoffmann's head.

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528.—In Fig. 217 an improved Hedley's dial is mounted upon an improved form of Hoffmann's head. The whole arrangement is very compact, rigid, and rapid in action. The height of this dial is 9½ inches; the weight 8 lbs. for a 6-inch instrument, in aluminium 5 lbs.

Fig. 218.—Improved Hedley, with cradle ring.

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529.—Hedley's Dial with Cranked Rocking Centre.—One defect of the Hedley's dial, which in certain cases makes Lean's preferred, is that with the rocking ring the sights cannot be brought vertical for looking up or down a shaft. The author has devised a means of getting over this difficulty by making the ring of cradle form, thus throwing the bearing surfaces to sufficient height to cause the ring, when the arc is raised to about 90°, to fall under the compass-box and its adjustments, Fig. 218. This dial presents possibly the greatest refinements of the Hedley principle at the time of its patent, No. 9134, 1898. Since this date the reviser has introduced a few further refinements as illustrated at Fig. 219.

Fig. 219.—Stanley's improved dial.

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