1733-1779

1728-1786

English astronomers famous for surveying the disputed boundary between Maryland and Pennsylvania (1763-68). The boundary they established, which has since come to be known as the Mason-Dixon line, settled the quarrel and remains the most famous boundary in the United States. As part of international efforts to accurately determine solar parallax, Mason and Dixon participated in a Royal Society expedition to observe the 1761 Venus transit. They separately observed the 1769 Venus transit.