MELVILL, THOMAS

(b. Glasgow [?], Scotland, 1726; d. Geneva, Switzerland, December 1753)

astronomy, physics.

Thomas Melvill noted the yellow spectrum of sodium and considered a means of testing a suggested relation between the velocity of light and its color.

Melvill’s origins are obscure, but at a relatively late age, in 1748 and 1749, he studied divinity at the University of Glasgow, where he acquired a taste for experimental philosophy from Alexander Wilson. Together they used kites to investigate the change in atmospheric temperature with altitude. Melvill studied Newton’s Opticks closely. In a paper “Observations on Light and Colours,” given to the Medical Society of Edinburgh on 3 January and 7 February 1752, he wrote of his use of a prism for examining color in flames (Edinburgh Physical and Literary Essays, II [Edinburgh, 1752], 35). The property of common salt, whereby it turns a flame yellow, was probably well recognized, but Melvill was seemingly the first to treat the coloration in any way quantitatively. He studied the spectrum of burning alcohol into which he introduced in turn sal ammoniac, potash, alum, niter, and sea salt, noting the persistence of the yellow component of the spectrum, and he remarked that this yellow color was of a definite degree of refrangibility. His work appears to have had little influence, and the origins of spectrum analysis are not usually traced back before W. H. Wollaston’s discovery of dark solar lines (1802).

As an explanation of the different refrangibilities of light of different colors, in terms of the corpuscular theory, Melvill suggested that the several colored rays were projected with various velocities from the luminous body—the violet with the least. A letter to Bradley, written from Geneva, dated 2 February 1753, and read to the Royal Society on 8 March 1753, pointed out an interesting consequence regarding aberration. Depending on velocity, the aberration would be different for different colors, and the satellites of Jupiter would gradually change color in one way (white to violet) on entering the planet’s shadow, and another way (red to white) on leaving the shadow. This effect was not observed, and the suggestion was soon forgotten. Its originality is in some doubt, since Courtivron’s Traité d’optique, published in 1752 and readily available to Melvill in Geneva, contained not only the fundamental hypothesis but its consequences for the appearance of Jupiter.

Melvill developed the idea further in a letter of 2 June 1753, and suggested that Bradley’s observations of aberration revealed the ratio of the velocities of light, not in space and air, but in space and in the humors of the eye. He believed that it would be necessary to reject what he called “Sir Isaac Newton’s whole doctrine of refraction by an accelerating or retarding power,” if the consequences of his new hypothesis were not confirmed. Dying at the age of twenty-seven, he scarcely lived long enough to be disappointed at the neglect of his letter, which contains essentially the same idea as that adopted by Alexander Wilson’s son, Patrick, who long afterwards discussed the consequences for an observer with a water-filled telescope. Conclusions drawn by Wilson and Robison (Philosophical Transactions of the Royal Society, 74 [1784), 35) were put to the test by Arago and communicated to the Institut de France in 1810 (Complexrendus hebdomadaires des séances de l’Académie des science, 8 [l839], 326, and 36 [1853], 38).

At the close of his second letter to Bradley, Melvill stated that he had designed and had made in Geneva a timepiece with a conical pendulum, the virtues of which he extolled. His early death deprived physics of a gifted and ingenious experimenter.

BIBLIOGRAPHY

I. Original Works. Melvill published only the papers cited above. The letter of 2 June 1753 was unpublished until it was printed by S. P. Rigaud in Miscellaneous Works and Correspondence of the Rev. James Bradley (Oxford, 1832), 483–487. The letter is now at Oxford, Bodleian Library, MS Bradley 44, f. 112.

II. Secondary Literature. On Melvill and his work see Brewster’s Edinburgh Journal of Science, Technology and Photographic Art,10 (1829), 5; A. M. Clerke, History of Astronomy During the Nineteenth Century, 3rd ed. (London, 1893), 165; and E. T. Whittaker, History of the Theories of Aether and Electricity, 2nd ed., I (Edinburgh, 1951), 99, 367.

J. D. North