This reflecting circle belonged to Georgetown University in Washington, D.C.
and may have been purchased when Georgetown built an astronomical observatory in the early 1840s. It is of the "English" form designed by Edward Troughton in 1796. Here the telescope, mirror, and filters are on one side of the circle, while the silver scale is on the other side. This scale is graduated to 20 minutes, and read by three verniers (one has a micrometer screw) to 20 seconds. The circle is supported on a heavy brass stand with a counterweight.
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."
