### Quick Info

Born
5 October 1732
Kensington Gore, London, England
Died
9 February 1811
Greenwich, England

Summary
Nevil Maskelyne was an English astronomer who measured the Earth's density in a famous experiment at Schiehallion.

### Biography

Nevil Maskelyne's father, Edmund Maskelyne, was a practising barrister-at-law and Counsel to the Secretary of State's Office. He lived at Purton Down, Wiltshire, England. Edmund Maskelyne married Elizabeth Booth, daughter of John Booth and Elizabeth Proger, on 4 February 1724. They had four children, William Maskelyne (1725-1772), Edmund Maskelyne (1728-1775), Nevil Maskelyne (the subject of this biography), and Margaret Maskelyne (1735-1817). Nevil Maskelyne wrote autobiographical notes in 1800 in which he gave some information about the origins of the family. He said he was (see for example [1]):-
... the last male heir of an ancient family long settled at Purton in the County of Wiltshire, which from the name probably came from Normandy, where there is or was 50 years ago a family of that name Masqueline.
All four children were born in Kensington but, in 1736, the family moved to Tothill Street, Westminster. This meant that the two eldest boys, William and Edmund, were close to Westminster School where they were pupils and their father, Edmund Sr., was close to his place of work. In January 1741 Nevil began his education at Westminster School. Edmund Sr., died in March 1744 when Nevil was 12 years old leaving the family rather poor. Nevil was still being educated at Westminster School when his mother Elizabeth died in 1748. After this Nevil boarded at Vincent Bourne's house in Westminster while he continued his school education. Just before the death of his mother his interest in astronomy had begun after seeing the eclipse of 25 July 1748. Maskelyne writing about his school education said (see for example [1]):-
Great mathematicians have become astronomers from the facility mathematics gave them in the attainment of astronomy; but here the love of astronomy was the motive of application to mathematics without which our astronomer soon found he could not make the progress he wished in his favourite science; in a few months, without any assistance he made himself master of the elements of geometry and algebra. With these helps he soon read the principal books in astronomy and optics and also in ... mechanics, pneumatics and hydrostatics. The considerable progress he had made in these sciences led him naturally to the University of Cambridge...
Maskelyne entered St Catharine's College, Cambridge in November 1749. In the summer of the following year he moved to Pembroke College and in 1752 he moved again, this time to Trinity College where he studied the mathematical tripos and graduated with a B.A. in 1754. He was ranked as seventh wrangler in the mathematical tripos. As part of his move to gain a fellowship, he was ordained a minister in 1755, becoming a curate at Chipping Barnet in Hertfordshire. Then he became a fellow of Trinity College, Cambridge in 1756. By this time he was in close contact with James Bradley who was the Savilian professor of astronomy at Oxford and the Astronomer Royal. Maskelyne learned much from working with Bradley and assisted him in producing a table of refractions.

With Bradley as one of his supporters, on 27 April 1758 Maskelyne was admitted to the Royal Society of London, his recommendation describing him as
... a person well versed in mathematical learning and natural philosophy ...
On 14 July 1761 the Royal Society agreed to send Maskelyne to the island of St Helena to observe a transit of Venus which would take place on 6 June 1761. Maskelyne had earlier proposed that the same expedition should try to measure the parallax of the star Sirius.

This Venus transit was important since accurate measurements would allow the distance from the Earth to the Sun to be accurately measured and the scale of the solar system determined. He set sail on the ship Prince Henry on 18 January 1761. During the voyage he experimented with the lunar position method of determining longitude using the lunar tables produced by Tobias Mayer. He arrived in St Helena on 6 April 1761 in plenty of time to find a good site for observing and to set up his instruments. Sadly, the 6 June was cloudy and he was unable to make measurements of the transit. He spent several months on St Helena trying to compute the parallax of Sirius but eventually decided that his instruments were faulty. Disappointed, Maskelyne set sail for England on the ship Warwick in February 1762. Reaching Plymouth on 15 May, he went back to Chipping Barnet, where he was a curate, and worked on publishing a book. He published the lunar distance method for determining longitude in The British Mariner's Guide (1763) where he also included Tobias Mayer's tables.

In 1763 he went on a voyage to Barbados to carry out trials of John Harrison's timepiece H4. Maskelyne, although not a member of the Board of Longitude who were evaluating methods of computing longitude for which a large prize was on offer, was considered a suitable judge since he could compute the longitude of Barbados accurately using Jupiter's satellites, and compare this accurate result with that given by Harrison's H4 and also the result given by his lunar distance method. Maskelyne sailed on the HMS Princess Louisa on 23 September as the ship's chaplain reaching Bridgetown, Barbados, on 7 November. William Harrison, John Harrison's son, arrived with the timepiece H4 on 13 May 1764. He objected to Maskelyne's involvement in the H4 trials since Maskelyne was championing his own lunar distances method. They agreed a compromise in terms of who made the measurements and the trials were carried out. Harrison's H4 came out best with an error of around 10 miles, with the lunar distance method producing an error of around 30 miles. Back in England, he presented the results to the Royal Society on 20 December 1764. On 9 February 1765 the Board of Longitude gave its approval to both Harrison's H4 and to the lunar distance method.

Soon after his return, on 26 February 1765, he was appointed Astronomer Royal to succeed Nathaniel Bliss who had only held the post for two years when he died in September 1764. All four men to hold the post of Astronomer Royal before Maskelyne had done so with minimal salary as people of independent means. Maskelyne, on the other hand, was given a salary to make the post his main occupation (£350 per annum). This had the effect of making his observations public property whereas the earlier holders of the post considered their observations their private property. He published the first volume of the Nautical Almanac in December 1766 and continued to work on this project up to the time of his death. The original purpose was to present tables to allow longitude to be computed by the lunar distance method [15]:-
[The Nautical Almanac's] essential feature was a table of lunar distances computed to a nominal precision of 1" for three-hourly intervals throughout the year [of 1767], supplemented by additional requisite tables, explanations, instructions and examples worked out by Maskelyne himself. The difficulties were thereby reduced to the computation of local time-equivalent to finding an azimuth - and the correction of the observed lunar distances (by means of either of two methods described in the almanac) for the effects of refraction and parallax.
The work that Maskelyne carried out as Astronomer Royal at the Greenwich Observatory is described by Mary Croarken [8]:-
The principal work at Greenwich was to observe the positions of the Sun, Moon, planets and stars and to publish these data. This was a considerable undertaking because not only did the observations need to made, frequently at night, but they also needed to be reduced, i.e. corrected for refraction, parallax, instrument error, and so on, and a fair copy had to be made. To perform most of these duties Maskelyne hired an assistant. ... Maskelyne, like many of his scientific contemporaries an ordained minister of the Church of England, annually visited his parish living in Wiltshire and regularly attended Royal Society and other meetings in London, where he was very much part of the scientific establishment. In practice this meant that his assistant was expected to carry most of the observing load, although in fairness the observing books show that Maskelyne also regularly observed when in residence.
Also in [18] there is an interesting description of the skills Maskelyne required of his assistants, set down by him in 1787:-
To understand Arithmetic, Geometry, Algebra, Plane and Spherical Trigonometry, and Logarithms; to have a good eye and good ears, be well grown, and have a good constitution to enable him to apply several hours in the day to calculation, and to get up to the observations that happen at late hours in the night. To write a good hand, and be a ready and steady arithmetical computer. If he know something of Astronomy and had a mechanical turn so much the better. To be sober and diligent, and able to bear confinement. Age from 20 to 40.
Of course, Maskelyne's appointment as Astronomer Royal was rather a blow to John Harrison who considered him his major competitor for the longitude prize. Being Astronomer Royal meant that Maskelyne became a member of the Board of Longitude [11]:-
... the resulting report on H4 was entirely negative. It seems Maskelyne prevaricated over the meaning of "accuracy" to condemn Harrison's creation. In this era, all clocks gained or lost time at some rate, but so long as that rate was constant and known, one could derive an accurate time. Maskelyne refused to allow these corrections.
Harrison died in 1776 believing to the end that Maskelyne was biased in his judgement of H4.

Maskelyne proposed to the Royal Society in 1772, an experiment for determining the Earth's density with the use of a plumb line. He was not the first to suggest such an experiment. Bouguer and La Condamine had tried such an experiment over 30 years before. The Royal Society set up the Committee for the Attraction of Mountains which sent various scientists to seek suitable mountains in England and Scotland which had to be:-
... of sufficient height, tolerably detached from other hills, and considerably larger from East to West than from North to South.
Maskelyne, after seeking permission from King George II to be absent from his duties at Greenwich, carried out the experiment in 1774 on Schiehallion, a mountain in Perthshire, Scotland. Schiehallion was chosen by the Committee for the Attraction of Mountains because it was surprisingly regular and conical in shape so its volume could be determined accurately. He set up an observatory on the south side of the mountain, marked a meridian line, set up a plumb-line linked to a telescope and observed 39 stars with 169 observations as they crossed the meridian [5]:-
The angular distance of each star from the "zenith" (as indicated by the plumb-line) was noted with great care.
After making these observations, he set up an observatory on the north side of the mountain and made a similar series of observations. From his observations, which had to be corrected for refraction, precession, aberration, deviation and nutation, Maskelyne computed that the plumb-line was pulled 11.7" by the gravitational attraction of the mountain. From that he deduced that the Earth's density is approximately 4.5 times that of water. He was awarded the Copley medal of the Royal Society in 1775 for his:-
Curious and Laborious Observations on the Attraction of Mountains.
Excerpts from his papers on this subject are given at THIS LINK.

We have noted that Maskelyne was ordained in 1755. In 1768 he was awarded the degree of bachelor of divinity by the University of Cambridge and, in 1775, he was given the living of Shrawardine in Shropshire. His brother William died in 1772 and Maskelyne inherited Pond's Farm, Purton Stoke, Wiltshire at this time. In 1777 he was awarded the degree of doctor of divinity by the University of Cambridge and, in 1782, he was given the living of North Runcton, Norfolk by Trinity College. He married Sophia Rose (1752-1821), the second daughter of John Pate Rose of Cotterstock, Northamptonshire, on 21 August 1784 in St Andrew's, Holborn. They had a daughter Margaret (born at Greenwich on 27 June 1785). After their marriage, the Maskelynes made much use of Pond's Farm as a country retreat.

We mention a few other aspects of Maskelyne's work:
1. Of course, optics was a topic of great interest and relevance to him and in 1761 he published a "Theorem of the Aberration of the Rays of Light refracted through a Lens, on account of the Imperfection of the Spherical Figure".
2. Although he did not visit North America, Maskelyne was very much involved in astronomical and surveying measurements made by Charles Mason and Jeremiah Dixon in Pennsylvania during 1765-68 (see [6] for details).
3. The discovery of night myopia, the fact that one tends to be short-sighted in the dark, was made by Lord Rayleigh in 1883. However, as John Levene points out in [21], this was discovered by Maskelyne and published in his paper An attempt to explain a Difficulty in the Theory of Vision, depending on the Different Refrangibility of Light of 1789.
4. Although not greatly interested in original mathematical ideas, he did prove some new geometry theorems. For example, in 1808 he published a paper giving a proof of the following theorem:
Let the circumference of a circle be divided any how into three arches $A, B, C$; that is, let $A + B + C$ be equal to the whole circumference. I say, the square of the radius multiplied into the sum of the tangents of the three arches $A, B, C$, is equal to the product of the tangents multiplied together.
As to his character he is described as [4]:-
... urbane, shrewd and likeable (especially if one happened to be on his side). As one of a line of squirearchial Nevil Maskelynes and brother-in-law to Clive of India, he knew his place in an ordered society and was an adroit mover in a world of gentlemen scientists and sailors.
Derek Howse writes [1]:-
The evidence from the large body of correspondence that has survived proves that, pompous and a bit of a bore as he might have seemed to some, Maskelyne was almost universally liked and admired by his contemporaries - except perhaps by some chronometer makers and their families. The reputation that survives in some popular twentieth-century books of Maskelyne as the evil genius who tried to deprive the poor illiterate carpenter of his just rewards-out of personal spite and because of his own involvement in the rival lunar-distance method of finding longitude-was certainly not one that was held generally in his own day, nor is it in any way justified by modern research: he was a member of the board of longitude, appointed by parliament to advise on the award of large sums of public money; there is no evidence whatsoever that he at any time abused his position as a public servant, still less lined his own pocket.
Maskelyne was honoured for his contributions by many societies and academies throughout the world. He was elected to the American Academy of Arts and Sciences, the Paris Academy of Sciences, the Hanover Academy of Sciences and academies in Russia and Poland.

### References (show)

1. D Howse, Nevil Maskelyne: The seaman's astronomer (Cambridge University Press, Cambridge, 1989).
2. W Appelbaum, Review: Nevil Maskelyne: The seaman's astronomer, by Derek Howse, American Scientist 79 (1) (1991), 88.
3. A Apt, Review: Nevil Maskelyne: The seaman's astronomer, by Derek Howse, Isis 82 (2) (1991), 379-380.
4. A Chapman, Review: Nevil Maskelyne: The seaman's astronomer, by Derek Howse, British J. Hist. Sci. 23 (3) (1990), 377-379.
5. T D Cope, A mountain in Perthshire, Pennsylvania History 21 (3) (1954), 228-238.
6. T D Cope, 'A Clock Sent Thither by the Royal Society', Proc. Amer. Philos. Soc. 94 (3) (1950), 260-268.
7. M Croarken, Tabulating the heavens: computing the Nautical almanac in 18th-century England, IEEE Ann. Hist. Comput. 25 (3) (2003), 48-61.
8. M Croarken, Astronomical Labourers: Maskelyne's Assistants at the Royal Observatory, Greenwich, 1765-1811, Notes and Records Roy. Soc. London 57 (3) (2003), 285-298.
9. C J Cunningham, Discovery of the missing correspondence between Carl Friedrich Gauss and the Rev. Nevil Maskelyne (1802-5), Ann. of Sci. 61 (4) (2004), 469-481.
10. D W Dewhirst, The Greenwich-Cambridge axis. The origins, achievement and influence of the Royal Observatory, Greenwich: 1675-1975, Vistas Astronom. 20 (1-2) (1976), 109-111.
11. J D Fernie, The Harrison-Maskelyne Affair, American Scientist 91 (5) (2003), 403-405.
12. E G Forbes, The correspondence between Carl Friedrich Gauss and the Rev Nevil Maskelyne (1802-5), Annals of Science 27 (1971), 213-237.
13. E G Forbes, Schultz's proposal for finding longitude at sea, J. Hist. Astronom. 2 (1) (1971), 35-41.
14. E G Forbes, Gauss and the discovery of Ceres, J. Hist. Astronom. 2 (3) (1971), 195-199.
15. E G Forbes, The Bicentenary of the 'Nautical Almanac' (1767), The British Journal for the History of Science 3 (4) (1967), 393-394.
16. O Gingerich, Review: Nevil Maskelyne: The seaman's astronomer, by Derek Howse, Technology and Culture 31 (4) (1990), 869-670.
17. D B Herrmann, Some aspects of positional astronomy from Bradley to Bessel, The origins, achievement and influence of the Royal Observatory, Greenwich: 1675-1975, Vistas Astronom. 20 (1-2) (1976), 183-186.
18. H C King, Instrumentation of the nineteenth and early twentieth centuries. The origins, achievement and influence of the Royal Observatory, Greenwich: 1675-1975, Vistas Astronom. 20 (1-2) (1976), 157-163.
19. A W Lane Hall, Nevil Maskelyne, J. British Astronomical Association 43 (1932), 67-77.
20. G S Leadstone, Maskelyne's Schehallien experiment of 1774, Physics Education 9 (1974), 452-458.
21. J R Levene, Nevil Maskelyne, F.R.S., and the Discovery of Night Myopia, Notes and Records Roy. Soc. London 20 (1) (1965), 100-108.
22. W H McCrea, The Royal Observatory and the study of gravitation, Notes and Records Roy. Soc. London 30 (2) (1975/76), 133-140.
23. W H McCrea, Review: Nevil Maskelyne: The seaman's astronomer, by Derek Howse, Notes and Records Roy. Soc. London 45 (1) (1991), 118-120.