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. 310.—Optical details of the apomecometer.

Fig. 311.—Scheme for measuring heights.

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696.—The distance of an inaccessible object may be measured, as for instance a buoy at sea, by measuring in any straight line double the distance and taking equal angles thereto by the apomecometer on any direct line. An approximate idea may be formed by walking over measuring points. As for instance, b being a buoy at sea, Fig. 312, walk from e, at which a walking-stick may be set up, towards an object o. At E the buoy and object o will appear to be coincident. Then drop a stone or make a mark directly under the instrument. Walk on till beyond E′ and turn to face e. Now in returning, the buoy and the object e will appear coincident at E′. The distance EE′ is double that of the intermediate a to b.

Fig. 312.—Scheme for measuring distances.

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