Bras Gregorian reflecting telescope, 1852.
© Science Museum / Science & Society Picture Library
This reflecting telescope uses the Gregorian optical configuration, first proposed by the Scottish mathematician James Gregory (1638-1675) in 1663, to produce upright images. This is a convenience for a telescope that was as likely to be used for terrestrial viewing as for looking at objects in the sky. Made by the London instrument maker John Cuthbert, the telescope has a short bras tube. The tripod stand with levelling screws allows the telescope to be used on a table while focusing is achieved by moving the tiny mirror at the top of the tube. With a metal mirror and bras construction, it differs little from telescopes made a hundred years earlier in the 18th century.