Dawes, William Rutter (DNB00)
DAWES, WILLIAM RUTTER (1799–1868), astronomer, was born on 19 March 1799 at Christ's Hospital, where his father was mathematical master. He lost his mother at an early age, and on his father's appointment as governor of Sierra Leone, he was sent to live with his grandfather at Portsmouth, and thence transferred in 1807 to the care of Thomas Scott [q. v.], author of the ‘Commentary.’ His residence with him at Aston-Sandford, Buckinghamshire, interrupted by two years (1811–13) spent at Charterhouse School, terminated only with Mr. Scott's death in 1821. A profession had now to be chosen, and the dissatisfaction felt by young Dawes with certain tenets of the church of England induced him to substitute that of medicine for the ecclesiastical career designed for him by his father. He accordingly passed through the usual course at St. Bartholomew's Hospital, and settled as a medical practitioner at Haddenham in Buckinghamshire, there marrying Mrs. Scott, the widow of his late tutor. At Liverpool, whither he removed in 1826, he again contemplated entering the clerical profession; but his former scruples revived. Finally Dr. Raffles prevailed upon him to take charge of a small independent congregation at Ormskirk in Lancashire.
Here he erected his first observatory, the chief instrument in which was a 5-foot Dollond, of 33/4 inches aperture (Mem. R. Astr. Soc. v. 135). Already, however, a little achromatic of 1.6 inches, mounted at an open window of his house in Liverpool, had enabled him (as he related in a letter to Sir J. Herschel on 17 Dec. 1867) to distinguish a number of double stars belonging to Sir W. Herschel's second and third classes, such as Castor, Rigel, Polaris, γ Virginis, &c. His first published observation was of an occultation of Aldebaran, made at Ormskirk on 9 Dec. 1829 (Monthly Notices, i. 147), and he communicated on 23 April 1831 his measurements of the triple star ζ Cancri (ib. ii. 34). Thenceforward the observation and measurement of double stars constituted Dawes's special line of work, for which his extraordinarily keen vision and attentive habits of accuracy peculiarly fitted him. His ‘Micrometrical Measurements of 121 Double Stars, taken at Ormskirk during the years 1830, 1831, 1832, and 1833,’ were inserted in the eighth volume, and similar results for a hundred stars obtained from 1834 to 1839 in the nineteenth volume of the ‘Memoirs’ of the Royal Astronomical Society. He was admitted a member of that body on 14 May 1830.
Ill-health obliged him to resign his ministerial duties at Ormskirk, and he accepted in the autumn of 1839 the charge of the observatory at South Villa, Regent's Park, belonging to George Bishop [q. v.] Continuing to devote his principal attention to double stars, the results of his measurements, between 1839 and 1844, of about two hundred and fifty such objects, several of them very close pairs, were published in Mr. Bishop's ‘Astronomical Observations at South Villa’ (London, 1852). They included his detection of orbital movement in ε Hydræ, as well as of the faint third components of Σ 3022, and, independently of the Pulkowa observations, of γ Andromedæ. His engagement with Mr. Bishop terminated in the spring of 1844, when he removed his residence from St. John's Wood to Camden Lodge, near Cranbrook, Kent. The observatory fitted up by him there in 1845 was described in the ‘Memoirs’ of the Royal Astronomical Society (xvi. 323). Its instrumental equipment consisted mainly in a transit-circle by Simms two feet in diameter, and an equatoreal by Merz & Mahler of 6½ inches aperture and 8½ feet focus, capable of disclosing the fifth and sixth stars in the Orion trapezium. With these he worked indefatigably until driven, by deplorable suffering from headaches and asthma, to resort to Torquay. He even contemplated the necessity of finally abandoning his astronomical pursuits; but a favourable change enabled him in 1850 to resume them at Wateringbury, near Maidstone, where, unconscious of Bond's discovery in America, he perceived Saturn's dusky ring on 25 and 29 Nov. of the same year. His services to astronomy were recognised by the bestowal on 9 Feb. 1855 of the Astronomical Society's gold medal, in presenting which Sir George Airy dwelt upon his high merits as an accurate, skilled, and keen observer. His last change of residence was in 1857 to Hopefield, Haddenham. His instrumental resources were there reinforced in May 1859 with a fine equatoreal of 81/4 in. aperture, by Alvan Clark of Boston, capable of clearly dividing γ2 Andromedæ, and six years later with an 8-inch Cooke's achromatic.
Dawes married for the second time in 1842 the widow of Mr. John Welsby, solicitor, of Ormskirk. After her death in December 1860 his health rapidly declined. Heart disease was superadded to his other troubles, yet he continued to observe at intervals down to the end of 1867. He lived to see his final results in double-star measurements printed by the Royal Astronomical Society. Just a month before entering on his seventieth year, 15 Feb. 1868, he died, and was buried in Haddenham churchyard. He was a noted benefactor to the poor of his neighbourhood, ever ready to give gratuitous medical advice, and was much esteemed for his amiable and honourable character.
Several valuable improvements in practical astronomy attested his ingenuity. In 1851 and 1852 he described before the Royal Astronomical Society a new kind of solar eyepiece, provided with a sliding diaphragm-plate pierced with apertures varying from 0.5 to 0.0075 inch in diameter (Memoirs R. Astr. Soc. xxi. 157). The advantage of excluding all light external to the minute portion of the surface under scrutiny was proved by his discovery of the ‘black opening,’ constituting the true nucleus of sun spots. Some remarkable instances of rotatory movements in spots were noted by him about the same time, and he made on 22 Jan. 1852 the novel observation of a facula projecting ‘beyond the smooth outlines of the sun's limb in the manner of a mountain ridge nearly parallel to the sun's equator’ (ib. p. 161). His apposite comparison of the inner jagged edge of the penumbra to ‘a piece of coarse thatching with straw, the edge of which has been left untrimmed,’ has often been quoted. The view it described was obtained with a magnifying power of 460 applied to his Merz refractor. Mr. Nasmyth's supposed discovery of solar ‘willow-leaves’ was eagerly controverted by him (Monthly Notices, xxiv. 33, 54, 161). He regarded the phrase as altogether inapplicable to the mottlings visible on the sun's surface, and as misleading, in so far as it tended to substitute the idea of separate ‘entities’ for mere varying conditions of elevation and brightness in the luminous photospheric clouds.
The long-felt want of a fixed standard of stellar magnitude incited Dawes to propose in 1851 a simple and effective method of photometric comparison, depending upon the principle of equalisation by limiting apertures (ib. xi. 187). The magnitudes of his double-stars from 1848 onwards were determined according to the uniform scale thus obtained. The invention of the ‘wedge photometer,’ lately employed to such good purpose by Professor Pritchard, originated with Dawes (Mem. R. Astr. Soc. xlvii, 377, 380). He exhibited before the Royal Astronomical Society in June 1865 a photometric arrangement, brought into use some five years previously, consisting in the application to his solar eye-piece of one or more sliding and carefully graduated wedges of neutral-tint glass (Monthly Notices, xxv. 229). A similar but modified combination was soon afterwards adopted by Dr. Huggins in his measurements of the intensity of nebular light (Phil. Trans'. clvi. 394).
The observations made by Dawes on the physical appearances presented by Saturn were of great interest. They placed beyond doubt in 1843 the reality of Encke's division in the outer ring, suggested discontinuity in the inner bright and dusky rings, and confirmed the semi-transparency of the latter. The phenomena attending the disappearance of the ring system in 1848 were attentively studied by him (Monthly Notices, x. 46; Grant, Hist. of Astronomy, p. 265). He inferred in 1865, from the deepening towards the centre of the disc of the ruddy tint of Mars, its non-atmospheric origin, and detected, 20 Jan. 1865, the ‘ice-island’ in the northern hemisphere of that planet known by his name (ib. xxv. 227). From his drawings Mr. Proctor constructed his map of Mars in 1869; and their value was enhanced by the unconscious delineation in them of some of the ‘canals’ discovered by Schiaparelli in 1877. One of Dawes's latest observations, ‘On Jupiter without a visible Satellite’ (ib. xxviii. 10), included some noteworthy remarks on the appearance of the third and fourth satellites projected on the disc.
He was among the astronomers attracted to Sweden by the total solar eclipse of 28 July 1851. His station was with Mr. Hind near Engelholm, and his vivid description of the prominences seen with his little 1.6-inch Dollond was printed in the ‘Memoirs’ of the Royal Astronomical Society (xxi. 85). He observed the eclipse of 15 May 1836 at Ormskirk, and that of 18 July 1860 at Hopefield, particular attention being paid to the occultation of spots by the moon. Of comets he observed Bremiker's in 1840, Biela's in 1845, De Vico's in 1847, Donati's in 1858; and on 11 Oct. 1847 distinctly saw a tenth-magnitude star right across the centre of Miss Mitchell's comet. A comparison, somewhat to the advantage of the earlier display, of the star-shower of 13 Nov. 1866, with that witnessed by him at Ormskirk on 12 Nov. 1832, formed his sole contribution to meteoric astronomy (Monthly Notices, xxvii. 46). Dawes was the first to point out the exceptional qualities of Alvan Clark's object-glasses. His high opinion was originally founded on the excellent performance of one 7½ inches in diameter, procured from him in 1854. His ‘Catalogue of Micrometrical Measures of Double Stars,’ chiefly afforded by observations from 1839 to 1854, with an appendix giving the scantier results down to 1867, formed part of the thirty-fifth volume of the Astronomical Society's ‘Memoirs.’ A description of the different kinds of micrometer used in the compilation, and ‘Remarks on the Use of various Telescopic Apertures,’ were prefixed; and its value was increased by the addition of notes and the record of previous measures. A list of fifteen new double stars discovered by him 1840–59 was published in 1864 (ib. xxiv. 117). The Royal Society elected him a fellow in 1865.[Monthly Notices, xxix. 116; Astr. Register, vi. 73; Royal Soc. Cat. of Scientific Papers.]