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Nevil Maskelyne (1732-1811)
Fifth Astronomer Royal

Nevil Maskelyne, Astronomer Royal

Nevil Maskelyne, Fifth Astronomer Royal was grandfather by marriage to B-P’s Uncle Sir Warington Wilkinson Smyth, brother of Henrietta Grace Smyth Baden-Powell.

From: Encyclopaedia Britannica, 11th Edition, 1910.

MASKELYNE, NEVIL (1732-1811), English astronomer-royal, was born in London on the 6th of October 1732. The solar eclipse of 1748 made a deep impression upon him; and having graduated as seventh wrangler from Trinity College, Cambridge, in 1754, he determined to devote himself wholly to astronomy. He became intimate with James Bradley in 1755, and in 1761 was deputed by the Royal Society to make observations of the transit of Venus at St Helena. During the voyage he experimented upon the determination of longitude by lunar distances, and ultimately effected the introduction of the method into navigation (q.v.). In 1765 he succeeded Nathaniel Bliss as astronomer-royal. Having energetically discharged the duties of his office during forty-six years, he died on the 9th of February 1811.

Maskelyne’s first contribution to astronomical literature was “A Proposal for Discovering the Annual Parallax of Sirius,” published in 1760 (Phil. Trans. li. 889). Subsequent volumes of the same series contained his observations of the transits of Venus (1761 and 1769), on the tides at St Helena (1762), and on various astronomical phenomena at St Helena (1764) and at Barbados (1764). In 1763 he published the “British Mariner’s Guide,” which includes the suggestion that in order 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 important proposal, the germ of the “Nautical Almanac,” was approved of by the government, and under the care of Maskelyne the “Nautical Almanac for 1767” was published in 1766. He continued during the remainder of his life the superintendence of this invaluable annual. He further induced the government to print his observations annually, thereby securing the prompt dissemination of a large mass of data inestimable from their continuity and accuracy. Maskelyne had but one assistant, yet the work of the observatory was perfectly organized and methodically executed. He introduced several practical improvements, such as the measurement of time to tenths of a second; and he prevailed upon the government to replace Bird’s mural quadrant by a repeating circle 6 ft. in diameter. The new instrument was constructed by E. Troughton; but Maskelyne did not live to see it completed. In 1772 he suggested to the Royal Society the famous Schehallion experiment for the determination of the earth’s density and carried out his plan in 1774 (Phil. Trans. 1. 495), the apparent difference of latitude between two stations on opposite sides of the mountain being 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 (ib. lxviii. 782). Maskelyne also took a great interest in various geodetical operations, notably the measurement of the length of a degree of latitude in Maryland and Pennsylvania (ibid. lviii. 323), executed by Mason and Dixon in 1766-1768, and later the determination of the relative longitude of Greenwich and Paris (ib. lxxvii. 151). On the French side the work was conducted by Count Cassini, Legendre, and Mechain; on the English side by General Roy. This triangulation was the beginning of the great trigonometrical survey which has since been extended all over the country. His observations appeared in four large folio volumes (1776-1811). Some of them were reprinted in S. Vince’s Astronomy (vol. iii.).

Biography of Nevil Maskelyne
From the National Dictionary of Biography, Oxford, 1893.

Nevil Maskelyne (1732-1811), astronomer royal, was the third son of Edmund Maskelyne of Purton in Wiltshire, by his wife Elizabeth Booth, and was born in London on 6 Oct. 1732. From Westminster School he entered in 1749 Catharine Hall, Cambridge, but migrated to Trinity College, whence he graduated in 1754 as seventh wrangler, taking degrees of M.A., B.D., and D.D. successively in 1757, 1768, and 1777. He was elected a fellow of his college in 1757, and admitted to the Royal Society in 1758. Having been ordained to the curacy of Barnet in Hertfordshire in 1755, he was presented by his nephew, Lord Clive, in 1775 to the living of Shrawardine in Shropshire, and by his college in 1782 to the rectory of North Runcton, Norfolk. The solar eclipse of 25 July made an astronomer of him, as it did of Lalande and Messier; he studied mathematics assiduously, and about 1755 established close relations with Bradley. He learned his methods, and assisted in preparing his table of refractions, first published by Maskelyne in the Nautical Almanac for 1767, the rule upon which it was founded having been already communicated to the Royal Society (Phil. Trans. liv. 265).

Through Bradley’s influence he was sent by the Royal Society to observe the transit of Venus of 6 June 1761, in the island of St. Helena. He proposed besides to determine the parallaxes of Sirius and the moon (ib. li. 889, lii. 21), but met disappointment everywhere. The transit was concealed by clouds; a defective mode of suspension rendered his zenith-sector practically useless (ib. liv. 348). An improvement on this point, however, which he was thus led to devise, was soon after universally adopted; and during a stay in the island of ten months he kept tidal records, and determined the altered rate of one of Shelton’s clocks (ib. pp. 441, 586). On the voyage out and home he experimented in taking longitudes by lunar distances, and published on his return The British Mariner’s Guide, London, 1763, containing easy precepts for this method, which he was the means of introducing into navigation. Deputed by the board of longitude in 1763 to try Harrison’s fourth time-keeper (Observatory, No. 173, p. 122), he went out to Barbados as chaplain to her majesty’s ship Louisa, accompanied by Mr. Charles Green. His astronomical observations there were presented to the Royal Society on 20 Dec. 1764 (Phil. Trans. liv. 389).

Maskelyne succeeded Nathaniel Bliss [q.v.] as astronomer royal on 26 Feb. 1765, and promptly obtained the establishment of the Nautical Almanac. The first number, that for 1767, was issued in 1766, and he continued for forty-five years to superintend its publication. Of the Tables requisite to be used with the Nautical Ephemeris, compiled by him in 1766 for the convenience of seamen, ten thousand copies were at once sold, and they were reprinted in 1781 and 1802. Maskelyne’s administration of the Royal Observatory lasted forty-six years, and was marked by several improvements. The observations made were, on his appointment, first declared to be public property, and he procured from the Royal Society a special fund for printing them. They appeared accordingly in four folio volumes, 1776-1811, and were at once made use of abroad, Delambre’s solar and Burg’s lunar tables being founded upon them in 1806. They numbered about ninety thousand, yet Maskelyne had but one assistant. Their scope was limited to the sun, moon, planets, and thirty-six fundamental stars, formed into a reference catalogue (for 1790) of careful accuracy. The proper motions assigned to them were employed in Herschel’s second determination of the solar translation (ib. xcv. 233). Maskelyne perfected in 1772 the method of transit-observation by noting, in tenths of a second, the passages of stars over the five vertical wires of his telescope. He obviated effects of parallax by using a movable eyepiece. In 1772 he had achromatic lenses fitted to Bradley’s instruments, and he procured about the same time a forty-six inch telescope, with triple object-glass by Dollond. The value of his later observations was impaired by the growing deformation of Bird’s quadrant; and a mural circle, six feet in diameter, which he ordered from Troughton, was only mounted after his death.

Maskelyne published in the Nautical Almanac for 1769 Instructions relative to the Observation of the ensuing Transit of Venus, and observed the phenomenon himself on 3 June at Greenwich with a two-foot Short’s reflector (ib. lviii. 233). From observations of it made at Wardhus and Otaheite he deduced a solar parallax of 8Ó×723 (VINCE, Astronomy, i. 398, 1797). He discussed the geodetical data furnished by Charles Mason (1730-1787) [q.v.] and Dixon from Maryland (Phil. Trans. lviii. 323), explained a method of making differential measures in declination and right ascension with Dollond’s divided object-glass micrometer (ib. lxi. 536), and facilitated the use of Hadley’s quadrant (ib. p. 99). His invention of the prismatic micrometer (ib. lxvii. 799) had been in part anticipated by the Abbé Rochon. The discharge of his onerous task of testing timepieces exposed him to unfair attacks, especially from Mudge and Harrison, against which he defended himself with dignity. In 1772 he proposed to the Royal Society a mode of determining the attraction of mountains by deviations of the plumb-line (ib. lv. 495), and Schiehallion in Perthshire was fixed upon as the subject of experiments, skilfully conducted by Maskelyne from June to October 1774. Their upshot was to give 11Ó×6 as the sum of contrary deflections east and west of the hill, whence Hutton deduced for the earth a mean density of 4×5 (ib. lxviii. 782). The Copley medal was in 1775 awarded to Maskelyne for his curious and laborious observations on the attraction of mountains.

In the dissensions of the Royal Society in 1784 Maskelyne strongly supported Dr. Charles Hutton [q.v.] against the president, Sir Joseph Banks. He advertised astronomers in 1786 of the vainly expected return of the comet of 1532 and 1661 (ib. lxxvi. 426), and discussed in 1787 the relative latitude and longitude of the observatories of Greenwich and Paris (ib. lxxvii. 151). Always attentive to the needs of nautical astronomy, he directed Mason’s correction of Mayer’s Lunar Tables, and edited the completed work in 1787. His essay on the Equation of Time (ib. liv. 336) was translated in Bernouilli’s Recueil pour les astronomes (t. i. 1771); his observations of the transit of 1769 were communicated to the American Philosophical Society at Philadelphia in 1770 (Trans. i. 100, 2nd edit. 1789); he edited in 1792 Taylor’s Tables of Logarithms, and in 1806 Earnshaw’s Explanations of Time-keepers.

Maskelyne was elected in 1802 one of eight foreign members of the French Institute. Indefatigable in the duties of his office, he died at the observatory on 9 Feb. 1811, aged 79. He married about 1785 Sophia, daughter and co-heir of John Pate Rose of Cotterstock, Northamptonshire, sister of Laetitia, wife of the Rev. Sir George Booth, Bart. Their only child, Margaret (b. 1786), married in 1819 Anthony Mervyn Story, to whom she brought the family estates in Wiltshire, inherited by her father. She showed much ability; she died in 1858. Her son Nevil Story-Maskelyne (b. 1823) was professor of mineralogy at Oxford (1856-95). Maskelyne was of a mild and genial temper and estimable character. Herschel’s remark, That is a devil of a fellow! after their first interview in 1782, was probably meant as a compliment (Memoirs of Caroline Herschel, p. 41). His sister Margaret, Lady Clive, survived him until 1817. A portrait of him by Vanderburgh is in the possession of the Royal Society. His manuscripts were after his death consigned to the care of Samuel Vince, F.R.S., but no publication resulted.

The Royal Observatory Greenwich: A Glance At Its History and Work.
by E. Walter Maunder, F.R.A.S. (1900)

From Chapter III.
Halley and His Successors.

Nevil Maskelyne, the fifth Astronomer Royal, was, like Bliss, a close friend of Bradley’s. He was the third son of a wealthy country gentleman, Edmund Maskelyne, of Purton, in Wiltshire. Maskelyne was born in London, October 6, 1732, and was educated at Westminster School. Thence he proceeded to Cambridge, where he graduated seventh Wrangler in 1754. He was ordained to the curacy of Barnet in 1755, and, twenty years later, was presented by his nephew, Lord Clive, to the living of Shrawardine, in Shropshire. In 1782 he was presented by his college to the Rectory of North Runcton, Norfolk.

The event which turned his thoughts in the direction of astronomy was the solar eclipse of July 25, 1748; and about the time that he was appointed to the curacy of Barnet he became acquainted with Bradley, then the Astronomer Royal, to whom he gave great assistance in the preparation of his table of refractions.

Like Halley before him, he made an astronomical expedition to the island of St. Helena. This was for the special purpose of observing the transit of Venus of June 6, 1761, Bradley having induced the Royal Society to send him out for that purpose. Here he stayed ten months, and made many observations. But though the transit of Venus was his special object, it was not the chief result of the expedition: not because clouds hindered his observations, but because the voyage gave him the especial bent of his life.

Halley had actually held a captain’s commission in the Royal Navy, and commanded a ship; Maskelyne, more than any of the Astronomers Royal before or since, made the improvement of the practical business of navigation his chief aim. None of all the incumbents of the office kept its original charter — "To find the so much desired Longitude at Sea, for the perfecting the Art of Navigation," so closely before him.

The solution of the problem was at hand at this time — its solution in two different ways. On the one hand, the offer by the Government of a reward of £20,000 for a clock or watch which should go so perfectly at sea, notwithstanding the tossing of the ship and the wide changes of temperature to which it might be exposed, that the navigator might at any moment learn the true Greenwich time from it, had brought out the invention of Harrison’s time-keeper; on the other hand, the great improvement that had now taken place in the computation of tables of the moon’s motion, and the more accurate star-catalogues now procurable, had made the method of "lunars," suggested a hundred and thirty years before by the Frenchman, Morin, and others, a practicable one.

In principle, the method of finding the longitude from "lunars," that is to say, from measurements of the distances between the moon and certain stars, is an exceedingly simple one. In actual practice, it involves a very toilsome calculation, beside exact and careful observation. The principle, as already mentioned, is simply this: The moon travels round the sky, making a complete circuit of the heavens in between twenty-seven and twenty-eight days. It thus moves amongst the stars, roughly speaking, its own diameter, in about an hour. When once its movements were sufficiently well known to be exactly predicted, almanacs could be drawn up in which the Greenwich time of its reaching any definite point of the sky could be predicted long beforehand; or, what comes to the same thing, its distances from a number of suitable stars could be given for definite intervals of Greenwich time. It is only necessary, then, to measure the distances between the moon and some of these stars, and by comparing them with the distances given in the almanac, the exact time at Greenwich can be inferred. As has been already pointed out, the determination of the latitude of the ship and of the local time at any place where the ship is, is not by any means so difficult a matter ; but the local time being known and the Greenwich time, the difference between these gives the longitude; and the latitude having been also ascertained, the exact position of the ship is known.

There are, of course, difficulties in the way of working out this method. One is, that whilst it takes the sun but twenty-four hours to move round the sky from one noon to the next, and consequently its movements, from which the local time is inferred, are fairly rapid, the moon takes nearly twenty-eight days to move amongst the stars from the neighbourhood of one particular star round to that particular star again. Consequently, it is much easier to determine the local time with a given degree of exactness than the Greenwich time; it is something like the difference of reading a clock from both hands and from the hour hand alone.

There are other difficulties in the case which make the computation a long and laborious one, and difficult in that sense; but they do not otherwise affect its practicability.

During this voyage to St. Helena, both when outward bound and when returning, Maskelyne gave the method of "lunars" a very thorough testing, and convinced himself that it was capable of giving the information required. For by this time the improvement of the sextant, or quadrant as it then was, by the introduction of a second mirror, by Hadley, had rendered the actual observation at sea of lunar distances, and of altitudes generally, a much more exact operation.

This conclusion he put at once to practical effect, and, in 1763, he published the British Mariner’s Guide, a handbook for the determination of the longitude at sea by the method of lunars.

At the same time, the other method, that by the time-keeper or chronometer, was practically tested by him. The time-keeper constructed by John Harrison had been tested by a voyage to Jamaica in 1761, and now, in 1763, another time-keeper was tested in a voyage to Barbados. Charles Green, the assistant at Greenwich Observatory, was sent in charge of the chronometer, and Maskelyne went with him to test its performance, in the capacity of chaplain to his Majesty’s ship Louisa.

The position which Maskelyne had already won for himself as a practical astronomer, and the intimate relations into which he had entered with Bradley and Bliss, made his appointment to the Astronomer Royalship, on the death of the latter, most suitable.

At once he bent his mind to the completion of the revolution in nautical astronomy which his British Mariner’s Guide had inaugurated, and in the year after his appointment he published the first number of the Nautical Almanac, together with a volume entitled, Tables Requisite to be Used with the Nautical Ephemeris, the value of which was so instantly appreciated, that 10,000 copies were sold at once.

The Nautical Almanac was Maskelyne’s greatest work, and it must be remembered that he carried it on from this time up to the day of his death — truly a formidable addition to the routine labours of an Astronomer Royal who had but a single assistant on his staff. The Nautical Almanac was, however, in the main not computed at the Observatory; the calculations were effected by computers living in different parts of the country, the work being done in duplicate, on the principle which Flamsteed had inaugurated in the preparation of his Historia Coelestis.

Maskelyne’s next service to science was almost as important. He arranged that the regular and systematic publication of the observations made at Greenwich should be a distinct part of the duties of an Astronomer Royal, and he procured an arrangement by which a special fund was set apart by the Royal Society for printing them. His observations covering the years 1776 to 1811 fill four large folio volumes, and though, as already stated, he had but one assistant, they are 90,000 in number. Thus it was Maskelyne who first rendered effective the design which Charles II. had in the establishment of the Observatory. Flamsteed and Halley had been too jealous of their own observations to publish; Bradley’s observations — though he himself was entirely free from this jealousy — were made, after his death, the subject of litigation by his heirs and representatives, who claimed an absolute property in them, a claim which the Government finally allowed. None of the three, however much their work ultimately tended to the improvement of the art of navigation, made that their first object. Whereas Maskelyne set this most eminently practical object in the forefront, and so gave to the Royal Observatory, which under his predecessors somewhat resembled a private observatory, its distinctive characteristics of a public institution.

It fell to Maskelyne to have to advise the Government as to the assignment of their great reward of £20,000 for the discovery of the longitude at sea. Maskelyne, while reporting favourably of the behaviour of Harrison’s time-keeper, considered that the method of ‘lunars’ was far too important to be ignored, and he therefore recommended that half the sum should be given to Harrison for his watch, whilst the other half was awarded for the lunar tables which Mayer, before his death, had sent to the Board of Longitude. This decision, though there can be no doubt it was the right one, led to much dissatisfaction on the part of Harrison, who urged his claim for the whole grant very vigorously; and eventually the whole £20,000 was paid him. The whole question of rewards to chronometer-makers must have been one which caused Maskelyne much vexation. He was made the subject of a bitter and most voluminous attack by Thomas Mudge, for having preferred the work of Arnold and Earnshaw to his own.

Otherwise his reign at the Observatory seems to have been a singularly peaceful one, and there is little to record about it beyond the patient prosecution, year by year, of an immense amount of sober, practical work. To Maskelyne, however, we owe the practice of taking a transit of a star over five wires instead of over one, and he provided the transit instrument with a sliding eye-piece, to get over the difficulty of the displacement which might ensue if the star were observed askew when out of the centre of the field. To Maskelyne, too, we owe in a pre-eminent degree the orderly form of recording, reducing, and printing the observations. Much of the work in this direction which is generally ascribed to Airy was really due to Maskelyne. Indeed, without a wonderful gift of organization, it would have been impossible to plan and to carry the Nautical Almanac.

Beside the editing of various works intended for use in nautical astronomy or in general computation, the chief events of his long reign at Greenwich were the transit of Venus in 1769, which he himself observed, and for which he issued instructions in the Nautical Almanac; and his expedition in 1774 to Scotland, where he measured the deviation of the plumb-line from the vertical caused by the attraction of the mountain Schiehallion, deducing therefrom the mean density of the earth to be four and a half times that of water.

He died at the Observatory, February 9, 1811, aged 79, leaving but one child, a daughter, who married Mr. Anthony Mervin Story, to whom she brought the family estates in Wiltshire, inherited by Maskelyne on the deaths of his elder brothers, and, in consequence, Mr. Story added the name of Maskelyne to his own.

Maskelyne’s character and policy as Astronomer Royal have been sufficiently dwelt upon. His private character was mild, amiable, and generous. ‘Every astronomer, every man of learning, found in him a brother;’ and, in particular, when the French Revolution drove some French astronomers to this country to find a refuge, they received from the Astronomer Royal the kindest reception and most delicate assistance.

Maskelyne added no instrument to the Observatory during his reign, though he improved Bradley’s transit materially. He designed the mural circle, but it was not completed until after his death. His additions to the Observatory buildings consisted of three new rooms in the Astronomer Royal’s house, and the present transit circle room.

		Nevil Maskelyne is buried in an elaborate vault with several elegant memorial plaques in St. Mary’s, Purton in Wiltshire. His wife, Sophia,his daughter, Margaret and her husband Anthony Mervin Storey-Maskelyne are also buried and commemorated there.
		The Royal Observatory Greenwich by E. Walter Maunder, F.R.A.S. (1900). Contains a history of Greenwich with biographies of the Astronomers Royal and a description of the resources and facilities of the Observatory.
		Baden-Powell Family History. A series of links starting with the research of Robin Baden Clay, a grandson of Baden-Powell. These links are focused on the genealogy of the Powell family. The author is extremely grateful to Mr. Clay for sharing the results of his labors with the Scouting community. Links are provided to pages for three of B-P’s brothers: Baden, Warington and Sir George Baden-Powell, to members of his extended family, and to the genealogy of the Smyth and Warington families.
		Baden-Powell Home Page

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