Gregorian reflecting telescope, 1734-50.

UNITED KINGDOM - APRIL 14: Made by the famous London instrument maker George Adams the Elder (1709-1772), this reflecting telescope uses the Gregorian optical configuration which produces upright images; a convenience for a telescope that was as likely to be used for terrestrial viewing as for looking at objects in the sky. The tube is covered in shagreen, polished ray skin. The claw-foot tripod stand allows the telescope to be used with a table, while a tapering screw thread is exposed if the pillar is detached from the tripod. This allows the telescope to be used outdoors by screwing the pillar stand into the trunk of a tree. (Photo by SSPL/Getty Images)