Groombridge Transit Circle
Groombridge Transit Circle was a meridian transit circle made by Edward Troughton for Stephen Groombridge in 1806, which Groombridge used to compile data for the star catalogue, Catalogue of Circumpolar Stars. The advantage of a transit circle over a mural circle (which can measure polar distances) is that it allows measuring right ascension and declination at the same time.
It had an aperture of 3.5 inches and a 5-foot focal length, mounted inside two 4 foot circles on stone piers. Groombridge used the instrument to determine the positions of over 4000 circumpolar stars.
- Groombridge Transit Circle, 1820. -- Science and Society Picture Library
- King, Henry C., (1955/2003). The History of the Telescope. Cambridge, Massachusetts: Sky Publishing Corporation. Retrieved from Google Books in 2010: The History of the Telescope, by Henry C. King, page 234-6