Gregorian telescope, c 1745.
© Science Museum / Science & Society Picture Library
This telescope is believed to be made by William Robertson, although James Gregory invented this design of reflecting telescope in 1663. It comprises a primary concave mirror with a central hole and a smaller secondary concave mirror which share a common focus. The image is viewed through the hole in the primary mirror using an eyepiece lens. This telescope may be asociated with Dr Stephen Demainbray (1710-1782), a famous science lecturer of the 18th century.