Charles Mason (59)

Charles Mason (c. 1 May 1728–25 October 1786) was an astronomer and surveyor, best known for establishing the Pennsylvania-Maryland border (the Mason-Dixon line), as well as a member of the American Society, elected in 1767. Born in Gloucestershire, England, he started his career as assistant to the Astronomer Royal, James Bradley, at the Royal Greenwich Observatory in 1756. Mason’s partnership with Jeremiah Dixon began in 1760 when the Royal Society sent them to the Indonesian island of Sumatra to observe the 1761 Transit of Venus. When a military engagement between a French ship and their own delayed their arrival, they conducted their observations from the Cape of Good Hope instead. En route back to England, Mason assisted future Astronomer Royal (and future APS member) Nevil Maskelyne with tidal observations in the south Atlantic island of St. Helena. In 1763 Mason and Dixon contracted with the proprietors of Maryland and Pennsylvania to survey the disputed boundary between the two provinces. Beginning at the northeast corner of Maryland, they would run their line a total of 244 miles west, establishing mile-markers and managing the workmen who cut “vistos” through the forest along the way. The Mason-Dixon Line would come to represent the boundary between the northern and southern U.S. Before returning to England, the pair also measured a degree of latitude on Maryland’s Delmarva Peninsula for the Royal Society. In 1768 Mason was tasked with observing another Transit of Venus, this time from Ireland, and in 1773 he conducted additional fieldwork in Scotland. He then resumed his lifelong efforts to improve Tobias Mayer’s solar and lunar tables for the Board of Longitude, with the result appearing in the Nautical Almanac. Mason immigrated to Philadelphia in 1786 but died shortly after his arrival. (PI, DNB)