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 the degree of 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 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 Irvine'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 Maskelyne, 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 longitudinal speculators of Great Britain in those days submitted 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 Céleste 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 royal 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 by 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 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 Schelliken 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 Maskelyne 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 everything 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.

Dr Maskelyne's first communication to the Royal Society is, A Proposal for discovering the Annual Parallax of Sirius. (Phil. Trans. II, 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-glass of achromatic telescopes. 3. An article (p. 21) is a letter from Lacaille recommending that he should make observations at St Helena for 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. 190). The sun was lower than had been expected, and the instant of contact uncertain, from a tremendous 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 Means of Observing and Calculating Lunar Distances (p. 558), dated from St Helena; the first demonstration of the practicability and utility of the method. He found the mean variation not to exceed half a degree of longitude, an error which was very largely suffered to remain as a fair allowance for the uncertainty of observation in the acts for encouraging the perfection of the lunar tables, subsequently repealed. 7. On the Tides at St Helena (p. 556); observations made in a harbour for about two months. 8. Note to La Lande (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 Astronomer's Guide. 10. Remarks on the Equation of Time (p. 336); correction of mistake of Lacaille and an inadvertence of La Lande, 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 observa- Maskelyne's separate publications was the *British Mariner's Guide*, London, 1733, 4to—a small volume, which has become scarce, having been superseded by later works. 32. The *Nautical Almanac* and *Astronomical Ephemeris* for 1765 appeared in 1765; and the observations regularly continued under the same plan for some time, by the computists 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, 1763, 1783, 1802, Svo.—These papers were compiled by Professor Lex's aid. 34. The volume of Selections, from the additions that have been occasionally made to the *Nautical Almanac*, London, 1812, Svo, 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 Bradley'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 3 vols., and part of a fourth, London, 1774. They are also given to constitute the most perfect body of astronomy that was ever prepared for future use. 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, Svo, London, 1815; Delambre, Mém. de l'Inst. des Sc., 1811, H. lix.; et Biographie Universelle, xxvii, Svo, Paris, 1820.)