Troughton and Simms Reflecting Circle

Edward Troughton, of London, introduced this type of reflecting circle in 1796. The telescope, mirror, and filters are on one side of the circle, while the silver scale is on the other. This scale is graduated to 20 minutes, and read by three verniers (one has a tangent screw) to 20 seconds. The circle is supported on a heavy brass stand with a counterweight. The inscription reads "Troughton & Simms 240 LONDON." Troughton & Simms were still offering instruments of this sort in the 1850s–at a cost of £23. This example belonged to Worcester Polytechnic Institute, and was probably made in the late 1830s.
Ref: Abraham Rees, The Cyclopaedia; or, Universal Dictionary of Arts, Sciences, and Literature (London, 1819), vol. 8, art. "Circle," and Plate III of "Astronomical Instruments."
"Directions for observing with Troughton’s Reflecting Circle," quoted in F. W. Simms, A Treatise on the Principal Mathematical Instruments (Baltimore, 1836), pp. 51-54.
"Catalogue of Instruments Made By Troughton & Simms," appended to William Simms, The Achromatic Telescope (London, 1852).
Currently not on view
Object Name
reflecting circle
date made
late 1830s
Troughton and Simms
reflecting circle: 10 in; 25.4 cm
place made
United Kingdom: England, London
ID Number
catalog number
accession number
Measuring & Mapping
See more items in
Medicine and Science: Physical Sciences
Data Source
National Museum of American History, Kenneth E. Behring Center
Credit Line
Worcester Polytechnic Institute

Visitor Comments

7/21/2015 5:42:54 PM
I have one of these without the stand, it came in a box. It is labelled Troughton and Simms but has no serial #. Is it True that they didn't start serializing them until 1796 ish time frame and if so would it then make my circle older than that. Your feedback would be appreciated. Cheers, Frank
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