Open main menu

Page:Dictionary of National Biography volume 46.djvu/83

This page has been proofread, but needs to be validated.

Troughton was his intimate friend, and Pond superintended, in his workshop, the construction of several instruments of unprecedented perfection. Dr. Nevil Maskelyne [q. v.], the fifth astronomer-royal, recommended him as his successor to the council of the Royal Society; and Sir Humphry Davy, who had visited him at Westbury in 1800, brought his merits to the notice of the prince-regent. As the result he was appointed astronomer-royal in February 1811, with an augmented salary of 600l. The six-foot mural circle, ordered from Troughton by Maskelyne, was mounted in June 1812; and Pond presented to the Royal Society, on 8 July 1813, a catalogue of the north polar distances of eighty-four stars determined with it (ib. ciii. 280), which Bessel pronounced to be ‘the ne plus ultra of modern astronomy’ (Briefwechsel mit Olbers, 30 Dec. 1813). In 1816 a transit instrument, by Troughton, of five inches aperture and ten feet focal length, was set up at the Royal Observatory. A Ramsden telescope presented by Lord Liverpool in 1811 proved of little use. In a paper on the construction of star-catalogues read before the Royal Society on 21 May 1818 Pond described his method of treating ‘every star in its turn as a point of reference for the rest’ (ib. cviii. 405). He substituted in 1821 a mercury-horizon for the plumb-line and spirit-level (ib. cxiii. 35), and introduced in 1825 the system of observing the same objects alternately by direct and reflected vision, which, improved by Airy, is still employed (Memoirs Roy. Astr. Society, ii. 499). The combination for this purpose of two instruments was suggested to Pond by the possession of a circle by Jones, destined for the Cape, but sent on trial to Greenwich. Pond obtained permission to retain it, and it was transferred in 1851 to the observatory of Queen's College, Belfast. Among his other inventions for securing accuracy were the multiplication, and a peculiar mode of grouping observations.

He showed in 1817, by means of determinations executed in 1813–14 with the Greenwich circle, the unreality of Brinkley's ostensible parallaxes for α Lyræ, α Aquilæ, and α Cygni (Phil. Trans. cvii. 158). As a further test he caused to be erected in 1816 two fixed telescopes of four inches aperture and ten feet focal length, directed respectively towards α Aquilæ and α Cygni, and sedulously investigated their differences of right ascension from suitable comparison-stars. But neither thus nor by the aid of transit observations could any effects of parallax be detected (ib. cvii. 353, cviii. 477, cxiii. 53). Pond's conclusion that they were insensible with the instruments then in use has since been fully ratified. Dr. C. A. F. Peters nevertheless criticised his methods severely in 1853 (Mémoires de Saint-Pétersbourg, tom. vii. p. 47). Against attacks made in this country upon his general accuracy, and even upon his probity as an observer, Bessel vigorously defended him (Astr. Nach. No. 84). From a comparison of his own with Bradley's star-places, Pond deduced the influence upon them of a southerly drift due ‘to some variation, either continued or periodical, in the sidereal system’ (Phil. Trans. cxiii. 34, 529). Herschel's discovery of the solar advance through space appears to have escaped his notice. Airy, however, gave him credit for having had the first inkling of disturbed proper motions (Astr. Nach. No. 590). A discussion on the subject with Brinkley was carried on with dignity and good temper.

Pond received in 1817 the Lalande prize from the Paris Academy of Sciences, of which he was a corresponding member; and the Copley medal in 1823 for his various astronomical papers. He joined the Astronomical Society immediately after its foundation. Directed by the House of Commons in 1816 to determine the length of the seconds pendulum, he requested and obtained the cooperation of a committee of the Royal Society. He was a member of the board of longitude, and attended diligently at the sittings in 1829–30 of the Astronomical Society's committee on the ‘Nautical Almanac,’ of which publication he superintended the issues for 1832 and 1833. The new board of visitors, appointed in 1830, caused him no small vexation. They took exception to his neglect of the planets for the stars, and to the rigidity of mechanical routine imposed upon his assistants. His own mathematical knowledge was very slight. The publication in 1833 of a catalogue of 1113 stars, determined with unexampled accuracy, was his crowning achievement. It embodied several smaller catalogues, inserted from time to time in the ‘Nautical Almanac’ and the ‘Greenwich Observations,’ of which he printed eight folio volumes. In his last communication to the Royal Society he described his mode of observing with a twenty-five-foot zenith telescope, mounted by Troughton and Simms in 1833 (Phil. Trans. cxxiv. 209, cxxv. 145). Harassed by many infirmities, he retired from the Royal Observatory in the summer of 1835 with a pension of 600l. a year, and died at his residence at Blackheath on 7 Sept. 1836. He was buried in the tomb of Halley in the neighbouring churchyard of Lee.

Of a mild and unassuming character, Pond neither sought nor attained a popular reputa-