Charnock’s drawing gives a good idea of some of the telescopic instruments in use at one of Europe’s leading observatories in the late 18th century. On the right is a large mural quadrant [AST0971], which was commissioned by the third astronomer Royal, James Bradley, in 1750. Its design copied an existing instrument at Greenwich, which was in turn copied by many other European observatories. The quadrants were for making accurate readings of the positions of stars as they crossed the meridian (north-south line) along which the instruments were aligned, and each had a telescopic sight.

On the left is a zenith sector [AST0992], a telescopic instrument that points directly overhead and is used to measure the angular distance of a star from the observer’s zenith (the point directly above the observer). Before coming to Greenwich, Bradley had discovered the aberration of light and nutation (wobbling) of the Earth’s axis with this instrument, which was also copied by observatories elsewhere.

The other images are of an equatorial sector and its accessories.