Charles Mason

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Charles Mason
Born April 1728 (baptised 1 May)[1]
Oakridge Lynch, Gloucestershire, England
Died 25 October 1786(1786-10-25) (aged 58)
Philadelphia, Commonwealth of Pennsylvania, United States of America
Nationality Kingdom of Great Britain
Fields Astronomy, surveying
Known for Mason–Dixon line

Charles Mason (April 1728 [baptised 1 May][1] – 25 October 1786) was an English astronomer who made significant contributions to 18th-century science and American history, particularly through his involvement with the survey of the Mason-Dixon line, which came to mark the border between Maryland and Pennsylvania (1764–1768). The border between Delaware and Maryland is also defined by a part of the Mason-Dixon line.

Early career

Mason's early career was spent at the Royal Greenwich Observatory near London. He served as assistant astronomer from 1756 to 1760 under the Reverend James Bradley, the Astronomer Royal.

While employed at the Greenwich Observatory, Mason became familiar with Professor Tobias Mayer’s Tables of the Moon. The Lunar Tables were designed to solve the problem of determining longitude at sea, a challenge that frustrated scientists and navigators for decades. Mason worked throughout his life to perfect the Lunar Tables as a method of improving navigation at sea. In 1787, Mason was awarded £750 by the Board of Longitude for his work on perfecting the Tables.[2]

1761 transit of Venus

In 1761, Mason was assigned to travel to the island of Sumatra to observe the transit of Venus as part of an international effort to record data that would enable scientists to determine the distance from the earth to the sun. Mason was joined by Jeremiah Dixon, a surveyor and amateur astronomer from Cockfield in the County of Durham. Owing to an attack by a French man-of-war, they did not reach their destination in time for the transit and were forced to record their observations from the Cape of Good Hope. On the way back from the Cape they visited St. Helena where they made a series of observations with the astronomer Nevil Maskelyne.

The Mason–Dixon line survey

" A Plan of the West Line or Parallel of Latitude" by Charles Mason, 1768

From November 1763 to 1768, Mason and Jeremiah Dixon established the boundary line between the American provinces of Pennsylvania and Maryland.[3] Colonial surveyors had been unable to accurately establish the boundary due to their poor training and inadequate scientific instruments. Mason and Dixon, accompanied by a large party of assistants, established three important boundaries: (1) the south boundary line of Pennsylvania separating it from Maryland and Virginia; (2) the west boundary of the three lower counties of Pennsylvania (now Delaware) separating it from Maryland; and (3) the south boundary of the three lower counties. The pair also conducted a number of experiments for the Royal Society such as measuring a degree of longitude. Mason’s journal provides the most complete record of the survey and its progress. The journal includes his astronomical observations and personal notes about the American frontier environment and his experiences in colonial America.

Mason and Dixon failed to measure the entire length of the south boundary of Pennsylvania as determined by its charter. In the summer of 1767, the surveying party crossed the Monongahela River and the Great Catawba War Path, violating a treaty limiting the westward expansion of English settlements. Not wishing to risk inciting native hostilities, Mason and Dixon were forced to return east after making their final observations at the crest of Brown's Hill.

Career after the Mason–Dixon line survey

After completing the boundary survey in America, Mason returned to Greenwich where he continued work on Mayer's Lunar Tables. He also contributed to the Nautical Almanac, working under Nevil Maskelyne, Astronomer Royal.

On September 27, 1786, Mason wrote to Benjamin Franklin claiming to have returned to Philadelphia with his wife, seven sons, and one daughter. Mason was very ill and confined to his bed. Mason also shared with Franklin the design for an astronomical project. Mason provided no explanation for his return to America, and nothing more is known of Mason's proposed project.[4]

Mason died on October 26, 1786, in Philadelphia.

Posthumous recognition

The crater Mason on the Moon is named after him.

Mason is one of the titular characters of Thomas Pynchon's 1997 novel Mason & Dixon.

The song "Sailing to Philadelphia" from Mark Knopfler's album of the same name, also has strong references to Mason and Dixon, and was inspired by Pynchon's book.

Surveying organizations dedicated a memorial at his previously unmarked grave on August 31, 2013, using a Mason-Dixon line stone that was found displaced from its position.[5]


  1. 1.0 1.1 mdlpp: A NOTE ON CHARLES MASON'S ANCESTRY AND HIS FAMILY, H. W. ROBINSON, Lately Librarian of the Royal Society of London. Retrieved 6 July 2015
  2. Cope, Thomas D. and H. W. Robinson. "Charles Mason, Jeremiah Dixon and the Royal Society." Notes and Records of the Royal Society of London. vol 9, no 7, 1951. p 75.
  3. "A Plan of the West Line or Parallel of Latitude". World Digital Library. 1768. Retrieved 2013-07-01.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  4. Cope, Thomas D. "Some Contacts of Benjamin Franklin with Mason and Dixon in Their Work". Proceedings of the American Philosophical Society. 95 (1951) p 238
  5. "Rendezvous 2013". Surveyors Historical Society.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>

External links