Edward Troughton, a prominent instrument maker in 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. The 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." This example belonged to Worcester Polytechnic Institute, and was probably made in the late 1830s. Troughton & Simms was still offering instruments of this sort in the 1850s–at a cost of £23.
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).
Our collection database is a work in progress. We may update this record based on further research and review. Learn more about our approach to sharing our collection online.
If you would like to know how you can use content on this page, see the Smithsonian's Terms of Use. If you need to request an image for publication or other use, please visit Rights and Reproductions.