Friday, 15 November 2013
From a transit of Venus to a slave-state boundary
Charles Mason and Jeremiah Dixon arrived in Philadelphia on November 15th 1763 to begin a survey to settle a dispute between the early colonists of North America. The boundaries that resulted between Maryland, Pennsylvania and what was to become Delaware came to have symbolic status. Mason and Dixon were skilled geometers. They had been appointed after the diputants had sought the advice of James Bradley, the then astronomer-royal. Mason was Bradley’s assistant at the observatory, an Anglican widower with two sons. Dixon was a skilled surveyor from Durham, a Quaker bachelor whose Meeting had ousted him for his unwillingness to abstain from liquor. In 1761 Mason and Dixon had sailed together for Sumatra, but only made it to the Cape of Good Hope, to record a transit of Venus across the sun to support the Royal Society’s calculations of distance by parallax between the Earth and sun. There is more historical detail here.