Nevil Maskelyne

The Reverend Dr Nevil Maskelyne FRS (6 October 1732 – 9 February 1811) was the fifth English Astronomer Royal. He held the office from 1765 to 1811.

Biography

Maskelyne was born in London, the third son of Edmund Maskelyne of Purton, Wiltshire. Maskelyne's father died when he was 12, leaving the family in reduced circumstances. Maskelyne attended Westminster School and was still a pupil there when his mother died in 1748. His interest in astronomy had begun while at Westminster School, shortly after the eclipse of 25 July 1748.

Maskelyne entered St Catharine's College, Cambridge in 1749, graduating as seventh wrangler in 1754.[1] Ordained as a minister in 1755, he became a fellow of Trinity College, Cambridge in 1756.

About 1785 Maskelyne married Sophia Rose of Cotterstock, Northamptonshire. Their only child, Margaret (1786–1858), was the mother of Mervyn Herbert Nevil Story-Maskelyne (1823–1911) professor of mineralogy at Oxford (1856–95). Maskelyne's sister, Margaret, married Robert Clive.

Nevil Maskelyne is buried in the churchyard of St Mary the Virgin, the parish church of the village of Purton, Wiltshire, England.[2]

Career

Measurement of longitude

In 1758 Maskelyne was admitted to the Royal Society, which in 1761 despatched him to the island of St. Helena to observe the transit of Venus. This was an important observation since accurate measurements would allow the accurate calculation of Earth's distance from the Sun, which would in turn allow the scale of the solar system to be calculated.

Bad weather prevented any useful observations, however Maskelyne used his journey to develop a method of determining longitude using the position of the moon, the lunar distance method. He returned to England, resuming his position as curate at Chipping Barnet in 1761, and began work on a book, publishing the lunar distance method of longitude calculation in 1763 in The British Mariner's Guide, which included the suggestion that to facilitate the finding of longitude at sea, lunar distances should be calculated beforehand for each year and published in a form accessible to navigators. This proposal, the germ of the Nautical Almanac, was approved by the government, and under the care of Maskelyne the Nautical Almanac for 1767 was published in 1766. He further induced the government to print his observations annually.

Despite a possible conflict of interests, Maskelyne being an advocate of the lunar distance method of determining longitude, the Board of Longitude sent him to Barbados in 1763 to calculate the longitude of the capital, Bridgetown by observation of Jupiter's satellites, and also to test his lunar distance method and compare its accuracy to John Harrison's chronometer, the No. 4 timekeeper. Even after a successful trial in Barbados in 1764 observed by Maskelyne, Harrison was required to produce detailed drawings and build two more chronometers, one of which was eventually tested by King George III himself.

The results of the voyage were made public at a meeting of the Board of Longitude in early 1765, where it was disclosed that Harrison's chronometer had produced Bridgetown's longitude with an error of less than ten miles after a sea voyage of more than 5,000 miles. Maskelyne's method on the other hand showed an error of 30 miles. However, four of the naval officers present stated that their calculations had been performed to Maskelyne's instructions and were therefore subject to their inexperience. Also, since the lunar distance method relied on tables that only Maskelyne was capable of calculating, the method was not yet in a position to take the prize.

However, two Astronomers Royal had recently died in quick succession and Maskelyne was appointed to the position soon after his return to England. The position automatically made him an ex-officio member of the Board of Longitude and it was not long before a negative report was made on Harrison's chronometer, Maskelyne refusing to allow for the known rate at which Harrison's chronometer gained or lost time and thus dismissing it as inaccurate.[3][4][5] He was not alone in his position on lunar distances; other members of the Board of Longitude and the Royal Society were also strongly biased toward lunars, as they saw the scientific solution being conceptually and intellectually superior to the mechanic's solution. When eventually Harrison was paid the money owing to him, it was by a special Act of Parliament rather than the Board of Longitude.

Nonetheless, while chronometers were indeed more accurate, the lunar distance method was cheaper and was the predominant method used well into the 19th century. Since Maskelyne's observations and calculations were made at the Royal Greenwich Observatory, the Greenwich meridian eventually became a common base for longitude worldwide and was adopted internationally as the Prime Meridian in 1884.[6]

Measurement of latitude

Maskelyne took a great interest in various geodetical operations, notably the measurement of the length of a degree of latitude in Maryland and Pennsylvania,[7] executed by Mason and Dixon in 1766 - 1768, and later the determination of the relative longitude of Greenwich and Paris.[8] On the French side the work was conducted by Count Cassini, Legendre, and Méchain; on the English side by General Roy. This triangulation was the beginning of the great trigonometrical survey which was subsequently extended all over Britain. His observations appeared in four large folio volumes from 1776–1811, some of them being reprinted in Samuel Vince’s Elements of Astronomy.[9]

Schiehallion experiment

In 1772 Maskelyne proposed to the Royal Society what was to become known as the Schiehallion experiment (named after the mountain on which it was performed), for the determination of the Earth’s density using a plumb line. He was not the first to suggest this, Pierre Bouguer and Charles-Marie de la Condamine having attempted the same experiment in 1738.

Maskelyne performed his experiment in 1774 on Schiehallion in Perthshire, Scotland[10], the mountain being chosen due to its regular conical shape which permitted a reasonably accurate determination of its volume. The apparent difference of latitude between two stations on opposite sides of the mountain were compared with the real difference of latitude obtained by triangulation.

From Maskelyne’s observations Charles Hutton deduced a density for the earth 4.5 times that of water (the modern value is 5.515).

Other work

Maskelyne’s first contribution to astronomical literature was A Proposal for Discovering the Annual Parallax of Sirius, published in 1760.[11] Subsequent contributions to the Transactions contained his observations of the transits of Venus (1761 and 1769), on the tides at Saint Helena (1762), and on various astronomical phenomena at Saint Helena (1764) and at Barbados (1764).

Maskelyne also introduced several practical improvements, such as the measurement of time to tenths of a second; and prevailed upon the government to replace Bird’s mural quadrant by a repeating circle 6 feet (1.8 m) in diameter. The new instrument was constructed by Edward Troughton but Maskelyne did not live to see it completed.

Maskelyne in literature and the arts

* Maskelyne features prominently in Dava Sobel's 1995 book, Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time, as well as the A&E miniseries based on the same.

* Maskelyne is a supporting character in Mason & Dixon by Thomas Pynchon.

* Maskelyne is portayed as "Dr. Vickery" in Kate Grenville's semi-historical novel The Lieutenant.

Honours

* 1775 - Awarded the Royal Society's Copley medal

* The lunar crater Maskelyne is named for him.

References

1. ^ Nevil Maskelyne in Venn, J. & J. A., Alumni Cantabrigienses, Cambridge University Press, 10 vols, 1922–1958.
2. ^ Maskelyne's grave can be seen by going through the church gates and veering to the right, against the right outside wall of the church.
3. ^ Sobel, Dava, Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time, Walker and Company, New York, 1995 ISBN 0-8027-1312-2
4. ^ Landes, David S., Revolution in Time, Belknap Press of Harvard University Press, Cambridge Mass., 1983, ISBN 0-674-76800-0
5. ^ Gould, Rupert T. The Marine Chronometer. Its History and Development London: J. D. Potter, 1923, ISBN 0-907462-05-7
6. ^ (JR Wills The Royal Society)
7. ^ Philosophical Transactions of the Royal Society. lviii. 323
8. ^ Philosophical Transactions of the Royal Society. lxxvii. 151
9. ^ Vince, Samuel (1811). The Elements of Astronomy: Designed for the Use of Students in the University. J. Smith.
10. ^ Philosophical Transactions of the Royal Society. 1. 495
11. ^ Philosophical Transactions of the Royal Society. ii. 889

* W. W. Rouse Ball, A History of the Study of Mathematics at Cambridge University, 1889, repr. Cambridge University Press, 2009, ISBN 978-1-108-00207-3, p. 108