Nevil, a most industrious and accurate astronomer, born in London on the 6th of October 1732, was the son of Mr Edmund Maskelyne, a gentleman of respectable family in Wiltshire.

At the age of nine he was sent to Westminster School, and continued to apply with diligence to the usual pursuits of that place, until the occurrence of the great solar eclipse of 1748, which made a strong impression on his mind, and was the immediate cause of his directing his attention to astronomy, and beginning with great ardour the study of the mathematics, as subservient to that of astronomy. It is remarkable, that the same eclipse is said to have made an astronomer of Lalande, who was only three months older than Maskelyne. He soon afterwards entered as a member of Catherine Hall, Cambridge, but in a short time removed to Trinity. He took a degree as bachelor of arts with great credit in 1754, and proceeded regularly afterwards through the succeeding stages of academical rank in divinity. He was ordained in 1755 to a curacy at Barnet, and the next year he obtained a fellowship at Trinity. In 1758 he was elected a fellow of the Royal Society; having previously become intimate with Dr Bradley, and determined to make astronomy the principal pursuit of his life, feeling its perfect compatibility with an enlightened devotion to the duties of his own profession.

In 1761 he was engaged by the Royal Society to undertake a voyage to St Helena, in order to observe the transit of Venus. He remained ten months in that island, but the weather prevented his observing the transit to advantage; and the faulty attachment of the plumb-line of his quadrant, which was of the construction then usually employed, rendered his observations on the stars less conclusive with respect to annual parallax than he had expected. His voyage Maskelyne was, however, of great use to navigation, by promoting the introduction of lunar observations for ascertaining the longitude; and he taught the officers of the ship which conveyed him the proper use of the instruments, as well as the mode of making the computations.

He performed a second voyage, in 1763, to the island of Barbadoes, in order to determine the rates of Harrison's watches, and also to make experiments with Irwin's marine chair, on board of the Princess Louisa, Admiral Tyrrel, acting at the same time as chaplain to the ship. The chair he found of very little use for observing the eclipses of Jupiter's satellites; and the maker of the chronometers was not satisfied with his report of their performance, fancying that he was too partial to the exclusive employment of lunar observations for determining the longitude. The liberality of the British government, however, bestowed on Harrison the whole reward that he claimed; and Maskelyne having been appointed to the situation of astronomer-royal, and having thus become a member of the Board of Longitude, was extremely active in obtaining a few thousand pounds for the family of Professor Mayer, who had computed lunar tables, and a compliment of L300 for Euler, whose theorems had been employed in the investigation.

The merits of Mayer's tables having been fully established, the Board of Longitude was induced to promote their application to practical purposes, by the annual publication of the Nautical Almanac, which was arranged and conducted entirely under Maskelyne's direction for the remainder of his life. He was also actively employed, without any other motive than the love of science and of his country, in almost every decision which was required of the Board of Longitude; and he had to give his opinion of the merits of an infinite number of fruitless projects which were continually submitted to his judgment. He must of course have made many enemies amongst the weak and illiberal; but the universal impartiality and the general accuracy of his determinations were acknowledged by all candid persons; and it must be admitted that the longitidinary speculators of Great Britain do in general submit to discouraging remarks from persons in authority, with wonderful fortitude and with great personal civility.

During the forty-seven years that he held the situation of astronomer-royal, he acquired the respect of all Europe by the diligence and accuracy of his observations, which he never neglected to conduct in person whenever it was in his power, and he required only one assistant. The French had a handsome building to amuse the public by its exterior magnificence; but the establishment of the observers was never arranged in so methodical a manner as that of the English National Observatory, and the fruits of their labours were never systematically made public, the attempt which was once made by Lemonnier, in his Histoire Celeste, having been interrupted and discontinued. Dr Maskelyne, on the other hand, obtained leave from the British government to have his observations printed at the public expense, under the direction of the Royal Society, who are the legal visitors of the observatory, appointed by the king's sign manual. The early observations of Flamsteed and of Bradley were considered as private property. Flamsteed published his own, and Bradley's were very liberally bought of his family, and afterwards printed by the University of Oxford, who are still as liberal in bestowing them where they are likely to be employed for the benefit of science. Flamsteed was the astronomer-royal from 1690 to 1720, then Halley to 1750, Bradley to 1762, and Bliss to 1765, when Maskelyne was appointed. He took his doctor's degree in the year 1777.

He made several improvements in the arrangement and employment of the instruments, particularly by enlarging the slits through which the light was admitted; by making Maskelyne—the eye-glass of his transit telescope moveable to the place of each of the wires of the micrometer; and, above all, by marking the time to tenths of a second, which had never been attempted before, but which he found it practicable to effect with surprising accuracy, as the comparison of the observations at the different wires sufficiently demonstrated.

The object of his expedition to Shehallien is well known. Bouguer had made an unsuccessful attempt to measure the attraction of a mountain in South America, and had been obliged to conclude that the mountain was hollow, in consequence of the eruption of a volcano, the attraction being too little sensible. Dr Maskelyne's results, on the other hand, as computed by Dr Hutton, made the mountain more dense than could well have been expected; but those who are acquainted with the difficulty of executing astronomical measurements without an error of a single second of space, will be ready to allow that the deviation of 5" or 6", attributed to the effect of the mountain, is liable to a much greater proportional uncertainty than the results obtained by Mr Cavendish with the apparatus invented by Mr Michell. (See Cavendish.) The geodesical operations which were soon afterwards performed with his concurrence and assistance, for determining the relative situations of Greenwich and Paris, were equally creditable to the English artists who constructed the instruments, and to the astronomers and geographers who made the observations with them; and, even by the confession of their rivals, they excelled every thing that had ever been effected in former measurements of the same kind.

As no man had done more for practical astronomy than Dr Maskelyne, so there was none whose merits were more justly appreciated. He made every astronomer his friend, as well by his personal kindness as by his professional labours; and he obtained the rare distinction of being made one of the eight foreign associates of the French Academy of Sciences. His example and encouragement contributed to the establishment of several private observatories, which must always be, if not immediately, at least remotely, beneficial to astronomy, as tending to promote the improvement of instruments, and of the methods of employing them.

He was modest, and somewhat timid, in receiving the visits of strangers; but his usual conversation was cheerful, and often playful, with a fondness for point and for classical allusion. He inherited a good paternal property, and he obtained considerable preferment from his college; he also married, somewhat late in life, the sister and co-heiress of Lady Booth of Northamptonshire. His sister was the wife of Robert Lord Clive, and the mother of the Earl of Powis. He died on the 9th of February 1811, in his seventy-ninth year, leaving a widow and an only daughter.

1. Dr Maskelyne's first communication to the Royal Society is a Proposal for discovering the Annual Parallax of Sirius. (Phil. Trans. li. 1760, p. 889.) It is founded on Lacaille's observations made at the Cape of Good Hope, which appeared to indicate a maximum amounting to 8°.

2. A Theorem for Spherical Aberration (iii. 1761, p. 17), dated from the Prince Henry, St Helen's Roads, the calculation being adapted to the object-glasses of achromatic telescopes.

3. The next article (p. 21) is a letter from La-caille, recommending that he should make observations at St Helena on the lunar parallax, and remain some time in the island for that purpose, and promising, on his own part, to make corresponding observations. It is followed by a letter from Maskelyne, proposing some additional joint observations.

4. Observation of the Transit of 1761 (p. 196). The sun was lower than had been expected, and the instant of contact uncertain, from a tremulous motion in the apparent discs.

5. Observations on a Clock of Shelton, 1762 (p. 434); giving the proportion of -99754 to 1 for the comparative force of gravity at Greenwich and at St Helena.

6. A Letter on the Mode of observing and Marking Lunar Distances (p. 558); dated from St Helena; the first demonstration of the practicability and utility of the method. He found the error of observation not to exceed half a degree of longitude, an error which was very strangely suffered to remain as a fair allowance for the uncertainty of observation, in the acts for encouraging the perfection of the lunar tables, only recently repealed.

7. On the Tides at St Helena (p. 586); observations made in a harbour, for about two months.

8. Note to Lalande (p. 607), on lunar distances and occultations.

9. Rules for correcting Lunar Distances (Phil. Trans. 1764, p. 263); a demonstration of the rules before published in the Transactions and in the British Mariner's Guide.

10. Remarks on the Equation of Time (p. 335); correcting a mistake of Lacaille and an inadvertence of Lalande, and giving a formula, which, though not geometrically perfect, is abundantly accurate for all practical purposes.

11. Astronomical Observations made at St Helena (p. 348). The observations for determining the lunar parallax were too few to afford a satisfactory result. The author suggests that the figure of the earth might be ascertained by repeated and comparative observations of the apparent distance of the moon from neighbouring stars.

12. Observations made at Barbadoes (p. 189), especially on Jupiter's satellites.

13. Introduction to two Papers of Mr Smeaton (lviii. 1768, p. 154); the one on the menstrual parallax, the other on observing stars out of the meridian.

14. Introduction to the Observations of Mason and Dixon (p. 270).

15. Conclusion respecting the Length of a Degree (p. 323, 325). Mr Charles Mason had been sent with Mr Dixon to observe the transit of 1761, at Ben-oolen; but their voyage was interrupted by accidental circumstances, and they made their observations at the Cape of Good Hope, with tolerable success. They then proceeded to join Maskelyne at St Helena, and to assist in his operations there. They were afterwards engaged by Lord Baltimore and Mr Penn, to determine the boundaries between Maryland and Pennsylvania; and having completed their survey, they suggested to the council of the Royal Society the eligibility of measuring a degree in the country bordering on the Delaware and the Chesapeake. Their proposals were readily accepted, and the results of their measurement are here recorded.

Dr Maskelyne afterwards employed Mason in his operations on Stichalien, in computing Bradley's observations, and in improving Mayer's tables, by a comparison with them; but he was so fearful of admitting any empirical corrections, not founded on the most general principles, that he would not allow some of the equations discovered by Mason to be introduced into the computation of the Nautical Almanac, until M. de Laplace had proved their dependence on the theory of gravity. Lalande tells us, that Mason was dissatisfied because he did not receive a public reward for the success of his labours; but he was, in fact, little more than the agent of Maskelyne, and of the Board of Longitude; and he was fairly repaid for the time and labour which his computations had required. Delambre says, that he died in Pennsylvania in 1787. Dixon is said to have been born in a coal mine, and to have died at Durham in 1777.

15. Postscript respecting French and English Measures (p. 325). The result of this comparison agrees admirably well with the later measurement of Pictet, Prony, and Captain Kater.

16. Observation of the Transit of 1769, made at the Royal Observatory (p. 355).

17. Eclipses and Occultations, 1769 (p. 399), chiefly for the longitude of Glasgow.

18. On the Use of Dolland's Micrometer, 1771 (p. 536). On the application of the divided object-glass micrometer to determining differences of right ascension and of declination, especially in the case of transits; a part of the instructions sent with the observers to the South On the Adjustment of Hadley's Quadrant, 1772, p. 99; especially for the back observation, and to insure the parallelism of the glasses. 20. Deluc's Rule for Measuring Heights, 1774 (p. 158); adapted to English measures, and rendered somewhat more convenient. 21. Observations at Greenwich and in America compared (p. 184, 190). 22. Proposal for Measuring the Attraction of a Hill, 1775 (p. 495); read in 1772. 23. Observations made on Shehallien (p. 500); a paper which obtained its author the honour of a Copleian medal. Mason had been sent to examine the hills of Scotland, and had recommended Shehallien; the funds were supplied by the remainder of the royal grant for observing the transit of Venus. Mr Reuben Barrow and Mr Menzies were principally employed in assisting the astronomer-royal in his observations and surveys; and Dr Hutton afterwards made the necessary computations for determining the attraction of the mountain. 24. Description of a Prismatic Micrometer, 1777, (p. 799), consisting of one or more prisms sliding in the axis of the telescope, and resembling in its operation that of Rochon, which has in great measure superseded it. 25. On the Longitude of Cork, 1779 (p. 179); observations for correcting the computed times of the eclipses of Jupiter's satellites. 26. On the Comet expected in 1789 (Phil. Trans., 1786, p. 428); supposing those of 1532 and 1661 to be the same. (See Mechan.) 27. On the Latitude and Longitude of Greenwich, 1787 (p. 151); with Cassini's Memoir on its uncertainty, which he states as amounting to 11° in longitude, and 15° in latitude. Dr Maskelyne, however, shows that it is confined within much narrower limits, though he approves of the object of the memoir in promoting a survey. 28. On a Difficulty in the Theory of Vision, 1789 (p. 256). This paper sufficiently proves that Euler was mistaken in thinking the eye achromatic; and that any appearance of colour which it could produce, according to the common laws of refraction, would be imperceptible in ordinary circumstances. But that there are circumstances under which such appearances may be observed, was afterwards shown by Dr Young and Dr Wollaston. 29. Account of an Appearance of Light on the Dark Part of the Moon, 1793 (p. 429); seen by Mr Wilkins, and by a servant of Sir George Booth, and supposed to have arisen from a volcano. 30. Observations of the Comet of 1793 (Phil. Trans., 1794, p. 55); discovered by the Rev. E. Gregory of Langar, in Nottinghamshire.

The earliest of Maskelyne's separate publications was the British Mariner's Guide, London, 1763, 4to; a small volume, which has become scarce, having been superseded by later works.

32. The Nautical Almanac and Astronomical Ephemeris for 1767 appeared in 1766; and the publication has been regularly continued upon the same plan to the present time, by the computers and comparers whom Dr Maskelyne had trained by his instruction and example. His successor in the observatory, though admirably qualified to equal, and perhaps to excel him in the practical department, had it not in his power to devote so much of his attention to the publication as Dr Maskelyne's paternal affection for a child of his own had induced him to bestow on it; and the Board of Longitude was very liberally furnished by government with the means of obtaining some further assistance to supply his place.

33. Tables requisite to be used with the Nautical Almanac, London, 1766, 1783, 1802, 8vo; now partly superseded by Professor Lax's new edition.

34. The volume of Selections, from the additions that have been occasionally made to the Nautical Almanac, London, 1812, 8vo, contains several papers of Dr Maskelyne; for example, Instructions relating to the Transit of Venus in 1769, N. A. 1769; Elements of Lunar Tables, and Remarks on Hadley's Quadrant, N. A. 1774; Advertisement of the Comet expected in 1788, N. A. 1791; and on the Disappearance of Saturn's Ring in 1780, N. A. 1791.

35. The Astronomical Observations made at Greenwich, from 1765 to 1811, were published annually in folio, making three volumes, and part of a fourth, London, 1774. They are allowed to constitute the most perfect body of astronomy in detail that was ever presented to the public. The first volume contains a variety of useful tables, accompanying the observations for 1772, and principally serving for the correction of the places of the stars, and for facilitating the solution of other astronomical problems. Many of them have been reprinted in Vince's Astronomy, but, in some cases, without the necessary explanations.

(Kelly in Rees's Cyclopaedia, art. Maskelyne. Chalmers, Biographical Dictionary, xxi. 8vo, London, 1815. Delambre, Mem. de l'Inst. des Sc. 1811, H. lix.; and Biographie Universelle, xxvii. 8vo, Par. 1820.)

Maskelyne's Islands, a cluster of small islands in the South Pacific Ocean, lying off the south-east point of Malcollo Island. Long. 167.59. E. Lat. 16.32. S.