MASON, CHARLES, 1730-87; b. England, and long employed as an assistant at the Greenwich observatory; was sent with Jeremiah Dixon to the cape of Good Hope in 1761 to observe the transit of Venus. In 1763 the same gentlemen were employed by the proprietors of Maryland and Pennsylvania to survey the boundary line between their resrketive possessions; a task upon which they were engaged until Dec. 26, 1767. Tin boundary fixed by them has since been known as "Mason and Dixon's line" (q.v.), They also, at the request of the Royal society, fixed " the precise measure of a degree of latitude in America, ' for which service the society granted them £200. The particular4 .of this work are recorded in vol. Iviii. of the society's Transactions. In the same volume may be found Astronomical Observations made at the Forks of the Brandywine for the pur pose of " determining the going of a clock sent thither by the Royal society in order to find the difference of gravity between the observatory at Greenwich and the spot where the clock was set up in Pennsylvania." Mr. Mason recorded in his private journal a minute account of his proceedings in America, his haps and mishaps, as well as of his scientific observations on a great variety of subjects, with interesting notices of the Indians of various tribes whom he met on his route or who rendered assistance to him and his companions. He describes with enthusiasm the beauty and grandeur of Ameri
can scenery, and gives a tolerably accurate account of the valley of the Mississippi, as received by him from an aged Indian chief. Mason and Dixon returned to England in the autumn of 1768. In the following year Mason went to Cavan, Ireland, to observe tho transit of Venus, his report of which appeared in the Philosophical Transactions for 1770. He was also employed by the bureau of longitudes to verify the lunar tables of Tobias Mayer, in which he made some corrections. At an unknown date he returned to America, and died in Philadelphia in 1787. His private journal, field notes, etc., were found among a pile of waste paper in the cellar of the government-house at Halifax, Nova Scotia, in 1860, and an account of their contents was publisherl by Porter C. Miss in the Historical Magazine for July, 1861.