Mason–Dixon line (nonfiction)

The original Mason–Dixon line.

The Mason–Dixon line, also called the Mason and Dixon line or Mason's and Dixon's line, was surveyed between 1763 and 1767 by Charles Mason and Jeremiah Dixon in the resolution of a border dispute involving Maryland, Pennsylvania, and Delaware in Colonial America. It is still a demarcation line between four U.S. states, forming part of the borders of Pennsylvania, Maryland, Delaware, and West Virginia (part of Virginia until 1863). Later it became known informally as the border between the free (Northern) states and the slave (Southern) states. The Virginia portion was the northern border of the Confederacy. It came into use during the debate around the Missouri Compromise of 1820, when the boundary between slave and free states was an issue. It is still used today in the figurative sense of a line that separates the North and South politically and socially (see Dixie).

History

The line was established to end a boundary dispute between the British colonies of Maryland and Pennsylvania/Delaware. Maryland had been granted the territory north of the Potomac River up to the fortieth parallel. Pennsylvania's grant defined the colony's southern boundary as following a 12-mile (radius) circle (19 km) counter-clockwise from the Delaware River until it hit "the beginning of the fortieth degree of Northern latitude." From there the boundary was to follow the fortieth parallel due west for five degrees of longitude. But the fortieth parallel does not, in fact, intersect the 12-mile circle, instead lying significantly farther north. Thus Pennsylvania's southern boundary as defined in its charter was contradictory and unclear. The most serious problem was that the Maryland claim would put Philadelphia, the major city in Pennsylvania, within Maryland.

The dispute was peacefully resolved in 1767 when the boundary was fixed as follows:

• Between Pennsylvania and Maryland:
  • The parallel (latitude line) 15 miles (24 km) south of the then southernmost point in Philadelphia, measured to be at about 39°43′ N and agreed upon as the Maryland–Pennsylvania line.
• Between Delaware and Maryland:
  • The existing east–west transpeninsular line from the Atlantic Ocean to the Chesapeake Bay, as far as its midpoint from the Atlantic.
  • A 12-mile (radius) circle (12 mi (19 km)) around the city of New Castle, Delaware.
  • A "tangent line" connecting the midpoint of the transpeninsular line to the western side of the 12-mile circle.
  • A "north line" along the meridian (line of longitude) from the tangent point to the Maryland-Pennsylvania border.
  • Should any land within the 12-mile circle fall west of the north line, it would remain part of Delaware. (This was indeed the case, and this border is the "arc line".)

The disputants engaged an expert British team, astronomer Charles Mason and surveyor Jeremiah Dixon, to survey what became known as the Mason–Dixon line.[10] It cost the Calverts of Maryland and the Penns of Pennsylvania £3,512 9/– (equivalent to £455,944 in 2019) to have 244 miles (393 km) surveyed with such accuracy. To them the money was well spent, for in a new country there was no other way of establishing ownership.

The Mason–Dixon line is made up of four segments corresponding to the terms of the settlement:

• the tangent line
• the north line
• the arc line
• the 39°43′ N parallel

The most difficult task was fixing the tangent line, as they had to confirm the accuracy of the transpeninsular line midpoint and the 12-mile circle, determine the tangent point along the circle, and then actually survey and monument the border. They then surveyed the north and arc lines. They did this work between 1763 and 1767. This actually left a small wedge of land in dispute between Delaware and Pennsylvania until 1921.

In April 1765, Mason and Dixon began their survey of the more famous Maryland–Pennsylvania line. They were commissioned to run it for a distance of five degrees of longitude west from the Delaware River, fixing the western boundary of Pennsylvania (see the entry for Yohogania County). However, in October 1767, at Dunkard Creek near Mount Morris, Pennsylvania, nearly 244 miles (393 km) west of the Delaware, their Iroquois guides refused to go any further, having reached the border of their lands with the Lenape, with whom they were engaged in hostilities. As such the group was forced to quit, and on October 11, they made their final observations, 233 miles (375 km) from their starting point.

In 1784, surveyors David Rittenhouse and Andrew Ellicott and their crew completed the survey of the Mason–Dixon line to the southwest corner of Pennsylvania, five degrees from the Delaware River. Other surveyors continued west to the Ohio River. The section of the line between the southwestern corner of Pennsylvania and the river is the county line between Marshall and Wetzel counties, West Virginia.

The Mason–Dixon line has been resurveyed three times: in 1849, 1900, and in the 1960s. On November 14, 1963, during the bicentennial of the Mason–Dixon line, U.S. President John F. Kennedy opened a newly completed section of Interstate 95 where it crossed the Maryland–Delaware border. It was one of his last public appearances before his assassination in Dallas, Texas. The Delaware Turnpike and the Maryland portion of the new road were later designated as the John F. Kennedy Memorial Highway.

Systematic errors and experiments to weigh the Earth

Mason and Dixon could only do the work as accurately as they did due to the work of Nevil Maskelyne, some of whose instruments they used. There was keen interest in their work and much communication between the surveyors, Maskelyne and other members of the British Scientific establishment in the Royal Society in Britain, notably Henry Cavendish. During such survey work, it is normal to survey from point to point along the line and then survey back to the starting point, where if there were no errors the origin and re-surveyed position would coincide. Normally the return errors would be random – i.e. the return survey errors compared to the intermediate points back to the start point would be spatially randomly distributed around the start point. Mason and Dixon found that there were larger than expected systematic errors, i.e. non-random errors, that led the return survey consistently being in one direction away from the starting point. When this information got back to the Royal Society members, Henry Cavendish realized that this may have been due to the gravitational pull of the Allegheny Mountains deflecting the theodolite plumb-bobs and spirit levels. Maskelyne then proposed measuring the gravitational force causing this deflection induced by the pull of a nearby mountain upon a plumb-bob in 1772 and sent Mason (who had returned to Britain) on a site survey through central England and Scotland to find a suitable location during the summer of 1773. Mason selected Schiehallion at which to conduct what became known as the Schiehallion experiment, which was carried out primarily by Maskelyne and determined the density of the Scottish mountain. Several years later Cavendish used a very sensitive torsion balance to carry out the Cavendish experiment and determine the average density of Earth.

See also

• Diary (May 7, 2020)#Song_of_the_Day_for_Howard_Kranz

Fiction cross-reference

• Gnomon algorithm
• Gnomon Chronicles

Nonfiction cross-reference

• Jeremiah Dixon (nonfiction)
• Charles Mason (nonfiction)
• Schiehallion experiment (nonfiction)

External links

• Mason–Dixon line @ Wikipedia