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MELVILL, THOMAS (1726–1753), experimental philosopher, was a student of divinity in 1748–9 at the university of Glasgow, where he became intimate with Dr. Alexander Wilson [q. v.] They discussed many philosophic schemes, and experimented together, by means of kites, on the temperature of the air at various altitudes. Melvill then studied optics with the view of verifying Newton's theories. His ‘Observations on Light and Colours,’ read before the Medical Society of Edinburgh on 3 Jan. and 7 Feb. 1752, showed him to be familiar with the use of the prism for examining coloured flames, and contained a remarkable notice of the peculiar yellow light of burning sodium (Edinburgh Physical and Literary Essays, ii. 34). These fundamental experiments in spectrum analysis were not repeated until after seventy years.

In a communication to Dr. Bradley on the ‘Cause of the different Refrangibility of the Rays of Light,’ dated from Geneva 2 Feb. 1753, and read before the Royal Society on 8 March, Melvill threw out the idea of employing the eclipses of Jupiter's satellites to test possible variations with colour in the velocity of light (Phil. Trans. xlviii. 261). A second letter to Bradley of 2 June suggested that the rate of light-travel concerned in aberration might be that in the humours of the eye itself. Melvill died at Geneva in December 1753, at the early age of twenty-seven.

[Edinburgh Phys. and Lit. Essays, ii. 12; Brewster's Edinburgh Journal of Science, x. 5, 1829; Chemical News, v. 251 (Jevons); Priestley's Hist. of Optics, i. 359; Clerke's Popular Hist. of Astronomy, p. 165, 2nd ed.]

A. M. C.