Gregorian reflecting telescope, 1748-1768.
© Science Museum / Science & Society Picture Library
This reflecting telescope uses the Gregorian optical configuration, first proposed by 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 James Short (1710-1768), the telescope has a bras tube and a three inch speculum (metal) mirror. The claw-foot tripod stand allows the telescope to be used on a table, while focusing is achieved by moving the mirror at the top of the tube. The telescope is provided with naked-eye viewing sights to help locate the objects under observation.