![]() ![]() Colonial surveyors already had established a temporary “Tangent (or Tangency) Line,” but Mason and Dixon had to resurvey and connect it with the 12-mile radius circle arc that formed the northern border of Delaware. The survey team then traveled south to plot the boundary between Maryland and Delaware. This “Post mark’d West,” as they called it, served as the “true latitude” reference point for the Pennsylvania-Maryland boundary line westward along the latitude of 39 degrees 43 minutes and 18 seconds. In April, Mason and Dixon proceeded fifteen miles due south from Stargazer stone to the Alexander Bryan plantation, where they set their main reference point for the Pennsylvania-Maryland border and there erected an oak post with the word “West” carved into the west face. Page from the Journal of Charles Mason and Jeremiah Dixon, November 15, 1763. ![]() Calculating their position by the night sky, they then established the latitude and erected a stone marker (known as the “Stargazer’s Stone”) to mark the site. There they encountered John Harlan’s farm where they established their headquarters and set up a mobile observatory. Due south would have taken them across the Delaware River into New Jersey, so the following day, they instead traveled thirty miles west to establish a reference site on the same latitude as Cedar (South) Street. On Januthe surveyors placed their first mark at the south wall of the Plumstead and Huddle house on Cedar Street in Philadelphia (now 30 South Street) and from there proceeded exactly fifteen miles south, where they began establishing the boundary dividing Pennsylvania and Maryland. After receiving formal instructions from the commissioners from Pennsylvania and Maryland they began their work by determining the latitude of “the southernmost point of the city of Philadelphia.” On November 15, 1763, Mason and Dixon landed in Philadelphia with their books, charts, tables, and the best astronomical tools available. This solution held until the early 1760s when colonial surveyors attempts to finalize an exact border broke down due to cost overruns and miscalculations as they attempted to “run lines.” So in 1763 the Penns and Calverts hired English astronomers and surveyors Charles Mason and Jeremiah Dixon to finish the work. Stargazers' Stone on the John Harlan or Stargazers' Farm, near Stargazers'. ![]()
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