Engraving from the book 'Machina Coelestis' (1673) by Johannes Hevelius (1611-1687). The image shows the German astronomer Hevelius using the bras sextant made by Gunter in 1658. Hevelius established the foremost observatory in Danzig in 1641, rebuilding it after a fire in 1679. He catalogued 1500 stars, discovered four comets and was one of the first to observe the transit of Mercury.
© Science Museum / Science & Society Picture Library