File:Topographic surveying; including geographic, exploratory, and military mapping, with hints on camping, emergency surgery, and photography (1905) (14759285396).jpg

Identifier: topographicsurve00wils (find matches)
Title: Topographic surveying; including geographic, exploratory, and military mapping, with hints on camping, emergency surgery, and photography
Year: 1905 (1900s)
Authors: Wilson, Herbert Michael, 1860-1920
Subjects: Topographical surveying Topographical drawing Photographic surveying Map drawing Camping
Publisher: New York : J. Wiley
Contributing Library: University of California Libraries
Digitizing Sponsor: Internet Archive

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class of instrument consist indetermining, first, the distance on the slope, and then the hori-zontal and vertical angle without taking account as a separateobservation of the space subtended on the rod from whichthe inclined distance is determined. From these data theazimuth of the desired point is determined, then the reduceddistance and relative height from the point of observation.These operations are all mechanical and graphical, calling forno computations whatever. The manipulation of the instru-tnent is simple and, with practice, rapid. It is adjusted tothe occupied station, and the height of the latter set uponthe scale of heights. The determination of separate points isthen proceeded with in the following order: The rodman sets his rod at the desired point; the instru-mentman brings the middle wire upon the zero point of the WAGNER-FENNEL TACHYMETER. 281 rod, reads the space on the rod intercepted by the distance-wires, and records in his note-book the corresponding inclined
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Fig. 83.—Wagner-Fennel Theodolite Tachvmeter. distance. These he sets off ujion the rule parallel to the lineof sight, pressing the projection angle against the vernier of 282 ANGULAR TACHYMETRY. heights, and from the latter reads the required height, andfrom the horizontal rule the reduced distance of the observedpoint. Lastly, the horizontal angle is read with the tachym-eter or the tachygeometer and plane-table. The first por-tion of the operations with the two instruments are the same,excepting that with the latter the horizontal projection of theobserved point is pricked upon the drawing-paper in its cor-rect position by pressing a needle suitably arranged againstthe horizontal scale instead of recording the same in a note-book. These various operations take from one and a half totwo minutes. This instrument can be used satisfactorily for^distances of a thousand feet, making the central base of theinstrument two thousand feet. .^ Il6. Range-finding.—Range-finders are instrume

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