Theodolite
date: label: date made
content: early 1890s
notes: label: Description
content: This theodolite marked "U. S. C. & G. S. No. 145," this is one of two identical 12–inch instruments that the Instrument Division of the United States Coast and Geodetic Survey made in the early 1890s, for use in the transcontinental triangulation. After a critical examination, the Survey concluded that, "With respect to design and perfection of mechanical construction," these theodolites "rank with the highest in their class." Moreover, "so far as purely instrumental and observational errors are concerned, a mean measured angle from four equidistant positions of the circle of either instrument will have a precision equal to the requirements of the highest order of primary triangulation."
label: Description
content: This theodolite is composed of several different metals: cast iron for the base; hardened steel for the bearing center and sockets; brass for the frame; silver for the graduated horizontal circle; and aluminum where suitable, to reduce the weight supported on the centers. The beveled edge of the horizontal circle is graduated to 5 minutes, and read by micrometer to 5 seconds. The noted optician, John A. Brashear, made the telescope objective.
label: Description
content: Ref: Edwin Smith, "Notes on Some Instruments Recently Made in the Instrument Division of the Coast and Geodetic Survey Office," <i>United States Coast and Geodetic Survey Report for 1894</i>, Appendix No. 8, pp. 265–275, and plate 1.
label: Location
content: Currently not on view
place: label: place made
content: United States: District of Columbia, Washington
setName: label: See more items in
content: Medicine and Science: Physical Sciences
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content: Surveying and Geodesy
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content: Measuring & Mapping
publisher: label: Related Publication
content: United States Coast and Geodetic Survey Report for 1894
dataSource: label: Data Source
content: National Museum of American History
identifier: label: ID Number
content: PH.314630
label: accession number
content: 208213
label: catalog number
content: 314630
objectType: label: Object Name
content: theodolite (geodetic)
physicalDescription: label: Physical Description
content: cast iron (overall material)
label: Physical Description
content: steel (overall material)
label: Physical Description
content: brass (overall material)
label: Physical Description
content: silver (overall material)
label: Physical Description
content: aluminum (overall material)
label: Physical Description
content: glass (overall material)
label: Measurements
content: overall: 21 in; 53.34 cm
label: Measurements
content: horizontal circle: 12 in; 30.48 cm
label: Measurements
content: vertical circle: 3 in; 7.62 cm
label: Measurements
content: telescope aperture: 2 13/32 in; 6.096 cm
label: Measurements
content: telescope focus: 29 in; 73.66 cm
label: Measurements
content: striding level: 11 1/2 in; 29.21 cm