Cassegrain reflecting telescope, 1762-1774.
© Science Museum / Science & Society Picture Library
A reflecting telescope made by the London instrument maker Jesse Ramsden (1735-1800) with a 6 inch speculum (metal) mirror. This telescope uses the Cassegrain optical configuration. It is mounted on an improved version of James Short's so-called 'universal'; a portable equatorial stand with a brass fork holding the tube and an adjustable polar axis. As it is used on a table or similar surface, the portable telescope has three levelling screws and a pair of sprit levels. Such a lavish instrument would only have been affordable to wealthy amateurs. Ramsden worked for various well-known instrument makers such as Sisson, Adams and Dollond, before starting on his own business in 1762. He went on to become the foremost instrument maker of his day.