File:Topographic surveying; including geographic, exploratory, and military mapping, with hints on camping, emergency surgery, and photography (1905) (14779179161).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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erminationof both latitude and time is a conibinatioji transit and zenithtelescope^ such as is used by the U. S. Geological Survey (Fig.181). This embodies the latest improvements in both instru-ments. It consists of a circular base resting upon three level-ing screws, and upon this base the whole instrument may re-volve when in use as a zenith telescope. About the base is alarge graduated circle, provided with micrometer screw forslow motion to be used in setting the instrument and in ad-justing it in azimuth. The telescope of the above instrumenthas a focal distance of 27 inches, a clear aperture of 2.5 inches,and its magnifying power with diagonal eyepiece is 74 diam-eters. For use as a zenith telescope there is attached a verti-cal circle reading by vernier to 20, to which is fastened adelicate level. In the focus of the object-glass is a threadmovable by means of a micrometer screw for the measurementof differences of zenith distances. ASTRONOMIC TRANSIT AND ZENITH TELESCOPE. J2J
Text Appearing After Image:
Fig. i8i.—Astronomic Transit and Zenith Telescope. 728 LA TITUDE. For use as a transit the telescope is provided with a del-icate striding-level for measurement of inclination of the axis,and a reversing apparatus for turning the telescope in thewyes. The stationary reticule in the focus of the instrumentconsists of five threads for observing as many transits of thestar. The reticule is illuminated by lamps, the light of whichenters the hollow axis of the telescope and is reflected bya mirror into the eye. 320. Latitude by Differences of Zenith Distances ofTwo Stars.—The zenith distance of a star on the meridianis the difference between the latitude of the station of ob-servation and the declination of the star; therefore the meas-urement of the meridional zenith distance of a known starfurnishes a determination of the latitude. The most accuratemethod of determining the latitude of a place, and that gener-ally employed in geodetic operations, is that known as theHorrebow-Talcott

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