Physics of the Earth - II The Figure of the Earth Bulletin of the National Research Council (1931) / Chapter Skim
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Chapter XII. Geodetic Instruments
Chapter XII. Geodetic Instruments
Pages 191-200
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From page 191... ...
References are given to reports and papers in which detailed descriptions of the instruments appear ASTRONOMICAL INSTRUMENTS Transit arid accessories.-The transit is used in the determination of local sidereal tine, in connection with the determ.ina.tion of the a.stronomical longitude of a station. The local time thus obtained is compa,red with the time signals sent through a radio station from the Naval 13 191
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From page 192... ...
Attached to the eye end of the telescope is an " impersonal micrometer " or " transit micrometer " with oldish an automatic record is made on a chronograph sheet as the star moves across Else field of the telescope. The screw of the micrometer moves a carriage to which is fixed a single wire, or strand of spider web.
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From page 193... ...
An accurate level mounted on the telescope in the plane of the meridian its an essential part of an instrument to be used with this method. The zenith telescope has a vertical column risings, above a three-arm base provided with three foot-screws for leveling.
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From page 194... ...
The observed angle between Polaris and the mark or line of triangulation is corrected for this inclination. When a pointing is made on Polaris the time of the observation is noted on a clock, chronometer, or watch, whose error and rate on local sidereal time have been determined by radio time signals or by observations on the stars with the astronomical transit or with the theodolite.
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From page 195... ...
In malting the measurements the rear mark is brought into coincidence with the mark on the strip on the rear stake, and then the graduation at the forward end of the tape is transferred to a strip of soft metal fastened to the top of the forward stake. The transfer to the strip is made with a sharp pointed scriber or awl, the error seldom being greater than + 0.!
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From page 196... ...
The Coast and Geodetic Survey employers simple staves to which the tape ends are attached. Heliotrope aced signal lamps.
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From page 197... ...
Over difficult lines two lamps are sometimes used, one lamp being, placed on top of' the other to avoid horizontal eccentricity. In the Ignited States an electric light has been observed upon over a triangulation line 1,53 miles long.
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From page 198... ...
The method of illumination is the same as that used in the astronomical transit. Electric bulbs fixed in place are now used on some types of t,heodolites to illuminate the graduated circle and the micrometer head.
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From page 199... ...
The telescope is provided with one vertical and three horizontal wires, the latter being equally spaced. In practice the observer levels the instrument and turns the telescope horizontally until the vertical wire falls on the leveling rod.
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From page 200... ...
. The United States Coast and Geodetic Survey, its work, methods and organization.
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