Maskelyne’s first contribution to astronomical literature was “A Proposal for Discovering the Annual Parallax of Sirius,” published in 1760 in the Philosophical Transactions, in which also most of his later original memoirs appeared— e.g., his observations of the transit of Venus (1761 and 1769), observations on the tides at St Helena (1762), astronomical observations at St Helena (1764) and at Barbados (1764). In 1763 he published a small octavo, The British Mariner’s Guide, which contains the valuable 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 suggestion, 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. During the remainder of his life Maskelyne continued to superintend the publication of this invaluable annual, the Nautical Almanac for 1815 being the last which he prepared. Another valuable service which he rendered astronomy was his inducing the Government to print his observations annually. Flamsteed’s and Bradley’s observations had been private property, and were published as such. The result of Maskelyne’s action was the accumulation and rapid dissemination of a long series of observations which from their continuity and accuracy have been of inestimable value to astronomers, and form along with the Nautical Almanac his most lasting monument. The whole work of the observatory was carried on by him and his one assistant in a most methodical manner, Greenwich being in point of organization second to none amongst the observatories of the day. He introduced several improvements in the use of the instruments, being, for example, the first astronomer who measured to tenths of a second; and he prevailed upon the Government to replace Bird’s mural quadrant, which had become untrustworthy, by a repeating circle of 6 feet in diameter. The new instrument was constructed by 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. Forty years previously Bouguer had demonstrated by experiment that Chimborazo in South America affected the direction of the plumb-line quite appreciably; but his observations were not made with sufficient care to deduce therefrom any trustworthy result. Maskelyne’s experiments were made in 1774 (see Philosophical Transactions for 1775), 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 Hutton deduced by laborious calculations that tħe density of the earth was 4’5 times that of pure water. Playfair subsequently estimated with greater accuracy the mass of Schehallion, and obtained 4 - 7 for the earth’s mean density. Maskelyne also took a great interest in various geodesical operations, notably the measurement of the length of a degree of latitude in Maryland and Pennsylvania (Philosophical Transactions, 1769), which was carried out by Mason and Dixon in 1766-68, and later the determination of the relative longitude of Greenwich and Paris (Philosophical Transactions, 1787). Cassini, Legendre, and Μéchain conducted the triangulation on the French side; on the English side the work was carried on under the superintendence of General Roy. This triangulation was the beginning of the great trigonometrical survey which has since been extended all over the country. A volume of Selections (London, 1812) contains several papers that were published, by Maskelyne as additions to the Nautical Almanac. His observations fill three large folio volumes, and many of them were reprinted in Vince’s Astronomy.