In 1763, Charles Mason and Jeremiah Dixon came to the New World to settle a bloody 80-year boundary dispute between Pennsylvania and Maryland. Dispatched by the Royal Society after a Court of Chancery decree set the border exactly 15 miles south of the southernmost point in Philadelphia, they faced the problem that no one knew that point's location. They chose the forks of the Brandywine Creek in Embreeville, due west of Philadelphia, as a clear geographical location and established an observatory there to make their observations. Using a device with a six-foot-long brass telescope to determine their position relative to the stars, they observed the night sky through frigid winters and oppressive summers for nearly five years. Their survey established the official line between the two colonies and stands among the greatest scientific achievements of its time. A marker called Star Gazers' Stone was placed to mark the astronomical meridian line north of the observatory, and it and the Harlan House where Mason and Dixon stayed are listed on the National Register of Historic Places. Star Gazers' Stone is also designated a National Historic Civil Engineering Landmark, one of 125 sites in the country.
