Page:Dictionary of National Biography volume 26.djvu/270

 ii. 487), in observations of the second comet of 1825, and of the Andromeda nebula (ib. pp. 486, 495). His great review of the nebulæ visible in the northern hemisphere was carried out at Slough with its aid during 1825–33, and the results embodied in a catalogue of 2,307 nebulæ, of which 525 were discovered by himself, presented to the Royal Society on 1 July 1833 (''Phil. Trans''. cxxiii. 359). The memoir was accompanied by nearly one hundred elaborate drawings, and contained many valuable suggestions. Its importance was recognised in 1836 by medals from the Royal and Astronomical Societies.

In a paper read before the Royal Society on 9 March 1826 Herschel gave the first discussion of the changes of position-angle between two adjacent stars as a means of detecting annual parallax (ib. cxvi. 266). He was elected president of the Royal Astronomical Society in February 1827, and for two subsequent biennial periods. His discoveries of double stars meanwhile, which in 1832 numbered 3,346, were progressively communicated in six catalogues to the Royal Astronomical Society (Memoirs, vols. ii–ix.), besides two extensive lists of measures of known pairs. These were after 1828 executed with a refractor of five inches aperture and seven feet focal length, which had been the chief instrument in the Blackman Street observatory. A graphical method of investigating stellar orbits, described by him before the Royal Astronomical Society on 13 Jan. 1832 (ib. v. 171), was a contribution of primary importance to a new branch of gravitational astronomy, recognised by a medal from the Royal Society on 30 Nov. 1833.

In a memoir ‘On the Aberration of Compound Lenses and Object-Glasses,’ read before the Royal Society on 22 March 1821 (Phil. Trans. cxi. 222), Herschel presented a complete analytical theory of spherical aberration, deducing practical rules of easy application for the construction of lenses, a popular abstract of which appeared in the ‘Edinburgh Philosophical Journal’ (1822, vi. 361). He still accepted the emission theory of light, but the results of Young and Fresnel soon afterwards engaged his eager study and acquiescence, and were brilliantly expounded in his article on light, written in 1827 for the ‘Encyclopædia Metropolitana.’ This admirable treatise, translated into French by Quetelet, besides including many original discoveries, gave European currency to the undulatory theory of light. Lucidity and power were no less conspicuous in Herschel's treatment of the subjects sound, heat, and physical astronomy, in the same publication. His ‘Preliminary Discourse on the Study of Natural Philosophy,’ published in 1830 as the opening volume of Lardner's ‘Cabinet Cyclopædia,’ and styled by Whewell an ‘admirable comment on the “Novum Organum”’ (Quarterly Review, July 1831), captivated readers of all classes by the quiet charm of its style, and the justice and breadth of its views. It was translated into French, German, and Italian, and reprinted in English in 1851. To the same repertory in 1833 Herschel contributed ‘A Treatise on Astronomy,’ enlarged in 1849 into the deservedly famous ‘Outlines of Astronomy,’ perhaps the most completely satisfactory general exposition of a science ever penned. A twelfth edition appeared in 1873, and it was translated into Russian, Chinese, and Arabic, besides other languages.

Herschel married, on 3 March 1829, Margaret Brodie, second daughter of the Rev. Dr. Alexander Stewart of Dingwall, Ross-shire. The union was of unclouded happiness. Put forward in 1830 against the Duke of Sussex as the ‘scientific candidate’ for the presidency of the Royal Society, he was defeated by a narrow majority. In 1831 he was created by William IV a knight of the royal Hanoverian Guelphic order, and during a visit to his aunt at Hanover in June 1832 attended the Waterloo banquet in the Herrenhausen Palace. A project long cherished of completing his survey of the heavens in the southern hemisphere became feasible after his mother's death in January 1832; and on 13 Nov. 1833, having declined a free passage in a ship of war (as he subsequently declined the reimbursement by government of his expenses), he embarked with his family and instruments on board the Mountstuart Elphinstone for the Cape of Good Hope, and reached Table Bay on 15 Jan. A house was secured at Feldhausen, six miles from Cape Town, in ‘one of the most magnificent sites’ (Herschel wrote to Baily) ‘I ever saw.’ On 22 Feb. 1834 he observed the Argo nebula with his great reflector, and the equatorial (the seven-foot Slough refractor) was ready for work before June. Both were employed with extraordinary vigour and perseverance during the ensuing four years; commonly under highly advantageous circumstances as to definition, although in the hot season he found the stars to ‘tremble, swell, and waver most formidably.’ The rapid tarnishing of his mirrors would have rendered them useless in three months but for the provident exportation of a polishing machine.

Herschel's work at Feldhausen marked the commencement in a wide sense of southern