Troughton & Simms Altitude and Azimuth Instrument

The altitude and azimuth instruments made by Edward Troughton in London from the 1790s were remarkably stable and accurate, and Troughton & Simms continued this tradition. Indeed, Frederick W. Simms described the portable Troughton & Simms instruments as being "the most generally useful of all instruments for measuring angles, being applicable to geodesical as well as astronomical purposes."
This example, made in 1837 for Columbia College (now University), is of this sort. It has a large and powerful achromatic telescope. The horizontal and vertical circles are silvered, graduated to 5 minutes, and read by microscopes with micrometers to 5 seconds. The graduated vertical circle is counterbalanced by a second circle on the other side of the telescope. The telescope assembly and horizontal axis rest on two conical pillars, supported by wyes and friction rollers. A long level is mounted between the microscopes reading the vertical circle. The inscriptions read "Troughton & Simms, London, 1837" and "Property of Columbia College."
Ref: Frederick W. Simms, A Treatise on the Principal Mathematical Instruments (Baltimore, 1836), pp. 81–98.
Currently not on view
Object Name
altitude and azimuth instrument
Date made
Troughton and Simms
telescope aperture: 2 in; 5.08 cm
telescope: 24 in; 60.96 cm
horizontal circle: 16 in; 40.64 cm
vertical circle: 16 in; 40.64 cm
level: 11 in; 27.94 cm
place made
United Kingdom: England, London
ID Number
catalog number
accession number
See more items in
Medicine and Science: Physical Sciences
Measuring & Mapping
Surveying and Geodesy
Data Source
National Museum of American History, Kenneth E. Behring Center


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