Page:Dictionary of National Biography volume 16.djvu/242

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He was possessed also of considerable mathematical and mechanical ingenuity, and was highly esteemed by all who knew him. He painted landscapes on his own account, and contributed to the Royal Academy exhibitions from 1827 to 1832, and occasionally to the British Institution. In 1832, however, he suffered from disease of the heart, which caused his death early in November of that year at East Bergholt, where he was buried. There were also two artists of the name of John Dunthorne, father and son, who lived at Colchester, and contributed small genre pictures to the Royal Academy exhibitions from 1783 to 1792. Some of these were engraved in stipple by E. Scott and others. The younger Dunthorne is said to have died young, and to have shown much ability.

[Redgrave's Dict. of Artists; Graves's Dict. of Artists, 1760–1880; Leslie's Life of Constable; Registers of East Bergholt, per Rev. J. Woolley.]

L. C.

DUNTHORNE, RICHARD (1711–1775), astronomer, was born in 1711 at Ramsey in Huntingdonshire. His father was a gardener, and his innate love of learning received its earliest stimulus from poring over the torn pages of old magazines used for wrapping up seeds. At the free grammar school of Ramsey he was distinguished for his talents by Dr. Long [q. v.], master of Pembroke Hall, Cambridge, who after a time removed him thither as his footboy. Diligently pursuing mathematical and other studies, he was qualified, on reaching maturity, to undertake the management of a preparatory school for the university at Coggeshall in Essex, but was soon recalled to Cambridge by Dr. Long in the capacities of butler of his college and scientific assistant to himself. He aided him in the construction of a hollow sphere, eighteen feet in diameter, representing the movements of the heavenly bodies, and is said to have printed the greater part of his ‘Astronomy.’ On his death in 1770, Dunthorne found himself charged with the task of completing the work, but achieved only a rough draft of the concluding historical section. He was then, and had been for many years, closely occupied as superintendent of the works of the Bedford Level Corporation. He conducted a survey of the fens; the locks on the Cam, near Chesterton, were built under his direction, and he left a volume of observations for a map of Cambridgeshire which, if executed, was probably burnt after his death as waste paper, with a quantity of his other valuable drawings and manuscripts. He was also comparer of the Nautical Almanac, and retained his butlership until his death, which occurred at Cambridge on 10 March 1775. Notwithstanding the inferiority of his position, he was admitted to the intimacy of many men distinguished in science, and Dr. Long testified his unbroken regard by appointing him one of the executors to his will. Dunthorne was esteemed not only for his astronomical requirements, but for his integrity and kindliness. He never forgot his humble relatives, and procured a settlement in life for some of the younger ones.

He published in 1739 at Cambridge, with a dedication to Dr. Long, ‘The Practical Astronomy of the Moon, or New Tables of the Moon's Motions, exactly constructed by Sir Isaac Newton's Theory as published by Dr. Gregory in his Astronomy. With precepts for computing the place of the Moon and Eclipses of the Luminaries.’ The satisfactory result of a comparison with observation of a hundred longitudes computed from these tables was embodied by him in ‘A Letter concerning the Moon's Motion,’ addressed to Charles Mason, F.R.S., and read before the Royal Society on 5 Feb. 1747 (Phil. Trans. xliv. 412). This was followed after two years by ‘A Letter concerning the Acceleration of the Moon’ (ib. xlvi. 162), in which Halley's assertion of the fact was, for the first time, examined and confirmed. Computing from his tables eclipses observed by Ibn Jounis at Cairo in the tenth century, as well as earlier ones recorded by Theon and Ptolemy, he found that their retarded occurrence could be explained by supposing the moon's mean motion accelerated at the secular rate of 10″. This earliest value of the correction was almost precisely that arrived at by Laplace, and is probably very near to absolute accuracy.

Dunthorne's ‘Letter concerning Comets,’ addressed to Dr. Long, was communicated to the Royal Society on 14 Nov. 1751 (ib. xlvii. 281). It contained the first elements computed for the comet of 1264, founded chiefly on a manuscript account of its appearance by Frater Egidius, discovered by Dunthorne in the college library. Their striking resemblance to those assigned by Halley to the comet of 1556 suggested to him that the two apparitions were of one and the same body, revolving in 292 years, and again due at perihelion in 1848. The prediction indeed failed of realisation, but the similarity of orbits was fully established by the researches of Mr. Hind. Dunthorne concluded his ‘Letter’ with some extracts from an unpublished treatise ‘De significatione cometarum’ relating to the great comet of 1106, tending to invalidate Halley's arguments in favour of its identity with the comet of 1680.

His ‘Elements of New Tables of the Motions