People: Charles Mason

Name Mason, Charles
Place of work Greenwich
Employment dates
c.Oct 1756 – c. Nov 1760

Posts Assistant

Born 1728 (baptised May 1)
Died 1786, Oct 25
Burried Christ Church burial-ground, Philadelphia, USA
Objects named after him The Mason-Dixon line in America
Crater Mason on the Moon

Charles Mason was James Bradley’s second assistant at Greenwich. He replaced John Bradley, and was himself replaced by Charles Green.

Like James Bradley and his wife, (who were married in 1744), Charles Mason came from Gloucestershire. The son of a baker, he was born at Wherr (now Wear) in the same parish of Bisley as Susannah Peach, the later Mrs Bradley, who was raised nearby in the village of Chalford. It seems likely that it was through this local connection that Mason came to Bradley’s attention.

Little is know of Mason’s life before he came to Greenwich. It has however been suggested that he received at least some of his mathematical education from Robert Stratford, a schoolmaster in the neighbouring village of Sapperton where Mason had been baptised. Mason made his earliest recorded observation at Greenwich in October 1756 and his last in November 1760. Amongst his important achievements was his help in assessing the accuracy of Tobias Mayer’s solar and lunar tables which had been submitted to the board of longitude in 1757, a task which drew heavily on his calculating skills. Mason’s career at Greenwich came to an end in 1760, when on Bradley’s recommendation, he was selected by the Royal Society to travel with Jeremiah Dixon to observe the 1761 Transit of Venus in Sumatra.

Unusually for an eighteenth century Greenwich assistant, Mason was a married man. His wife Rebekah, died at Greenwich at the age of 30 on 13 February 1759, leaving two sons, William and Doctor Isaac. It seems likely that Mason was already married at the time he came to Greenwich as his wife is burried in the churchyard at Sapperton. There has been a longstanding assumption that from the 1750s until the early years of the nineteenth century, that the Greenwich assistants lived in the small apartment that Bradley had had constructed on the first floor of his new observatory building (now part of the Meridian Building). Given that Mason had children and that there was no kitchen in the apartment, the correctness of the assumption has to be in some doubt. It seems more likely that Mason’s family was provided with some sort of accommodation elsewhere, with the apartment being used only occasionally by him for sleeping. How Mason coped with being widowed is not known. Bradley is likely however to have been sympathetic to his position, having himself been widowed in 1757, and left with his eleven year old daughter, Susannah, to raise on his own.

Although Mason was sent to Sumatra to observe the 1761 Transit, the original intention in July 1760 had been to send him to St Helena as Maskelyne’s assistant. The Royal Society however changed its mind and decided to send Robert Waddington to accompany Maskelyne and to send Mason with Jeremiah Dixon as his assistant to Bencoolen in Sumatra. Many doubted that the Royal Society had left sufficient time for Mason and Dixon to reach their destination as the Transit was due on 6 June 1761. In late November 1760, their instruments were loaded onto HMS Sea-Horse at Portsmouth, with the party eventually setting sail in early January. At this time, England was at war with France and reports had been received that Bencoolen had fallen to the French. Matters were compounded when on 12 January the Sea-Horse was attacked with all the masts being damaged, 11 men lost and 37 being wounded. The Sea-Horse returned to port for repairs. At the Royal Society’s insistence it eventually set sail again. By 27 April, it had only reached Table Bay off South Africa. With no possibility of reaching Sumatra in time, Mason and Dixon set up their observatory at the Cape of Good Hope were they made successful observations of the Transit. On his way back to England, Mason  joined Maskelyne at St Helena to assist with a series of tidal and gravitational measurements, eventually arriving back in England on 7 April 1762.

Following his return to England, Mason resumed work on the lunar tables and a catalogue of stars which was printed in the Nautical Almanac for the year 1773 (Click here to view the catalogue). He next embarked on a trip to America, where with Dixon, he helped settle the boundary between the states of Pennsylvania and Maryland (later known as the Mason-Dixon line). At the same time, he undertook the measurement of the length of a degree of latitude for the Royal Society. He returned to England in late 1768. In 1769, he was asked by the Royal Society to go to Ireland to observe the Transit of Venus that was due to occur on 3 June. Later projects include selecting the mountain of Schehallien in Scotland for Maskelyne's determination of the density of the Earth.

In 1770, Mason remarried, with the wedding taking place in Sapperton. Several children followed, as did work for the Board of Longitude. In 1786, Mason decided to emigrate with his family to Philadelphia. After falling ill on the voyage, he died in America on 25 October 1786. His wife returned to England where in 1791 she appealed with some success for support from the Board of Longitude in compensation for her husband’s services.


Further reading

Mason, Charles (1728–1786), Derek Howse, Oxford Dictionary of National Biography, Oxford University Press, 2004

A note on Charles Mason’s ancestry and his family. H. W. Robinson, Proceedings of the American Philosophical Society Vol. 93, No. 2, (May 16, 1949), pp. 134–136. Downloads as a pdf

Charles Mason. From: Patriot-improvers: Biographical sketches of memebers of the American Philosophical Society. Volume one, 1743-1768. pp.366–373. Whitfield J, Bell JR (Philadelphia 1997)

Miscellaneous Works and Correspondence of the Rev. James Bradley, James Bradley and Stephen Peter Rigaud. Oxford, 1832

Supplement to Dr. Bradley’s Miscellaneous Works, James Bradley and Stephen Peter Rigaud. Oxford, 1833