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
