# Dictionary of National Biography, 1885-1900/Stevenson, Thomas

​STEVENSON, THOMAS (1818–1887), engineer and meteorologist, born in Edinburgh on 22 July 1818, was youngest son of Robert Stevenson [q. v.], and was brother of Alan Stevenson [q. v.], and of David Stevenson [q. v.] He was educated at the high school of Edinburgh where he showed an incapacity for arithmetical calculation which remained with him through life. His mathematical faculty was, however, above the average, and he acquired a knowledge of Latin which he cultivated in later years, Lactantius, Lucan, Vossius, and Cardinal Bona becoming favourite authors. In youth he formed an ardent love of the English classics, and soon developed the habits of a book collector and the faculty of writing English with grace, vigour, and distinction.
In his seventeenth year Stevenson entered his father's office with a view to becoming an engineer. When his apprenticeship was over he in 1842 wrote a paper on the defects of the rain-gauges then in use, with a description of one of an improved form. This was published in the ‘Edinburgh New Philosophical Journal,’ 1842, xxxiii. 12–21, and was the first of a series of numerous contributions to scientific journals on such subjects as lighthouse and harbour engineering, lighthouse optics, experiments on the force of waves, and meteorology. By 1883 these papers had reached a total of forty-four (see Royal Society's Cat. of Scientific Papers, 1800–63 p. 829, 1864–73 pp. 1014–15, and 1874–83 pp. 495–6). In 1843 Stevenson superintended the construction of the lighthouse on Little Ross Island on the Solway, and wrote a paper on the geology of the island (Edinb. New Phil. Journ. xxxv. 83–8). In 1846 he became a partner in his father's firm, and in 1853 he and his brother David were appointed engineers to the board of northern lighthouses. This position he held till his health failed in 1885.
Stevenson won his chief reputation by his successful pursuit of the experiments in lighthouse illumination, which his brother, Alan Stevenson, began. By his efforts ‘the great sea lights in every quarter of the world now shine more brightly.’ His crowning invention was his ‘azimuthal condensing system of lighthouse illumination.’ No attempt had previously been made to allocate the auxiliary light in proportion to the varying lengths of the different ranges and the amplitudes of the arcs to be illuminated, or, where a light had to show all round the horizon, to weaken its intensity in one arc, and with the rays so abstracted to strengthen some other arc, which from its range being longer required to be of greater power. To perfecting this invention he devoted the greater part of his time from 1855 to 1885. Other inventions and improvements he described in his ‘Lighthouse Illumination,’ 1859 (2nd ed. 1871, expanded into ‘Lighthouse Construction and Illumination,’ 1881; see Sir David Brewster, Reply to Messrs. D. and T. Stevenson's Pamphlet on Lighthouses, 1860), and in his article ‘Lighthouse’ in the ninth edition of the ‘Encyclopædia Britannica.’
Other separately issued works were: ‘Design and Construction of Harbours,’ 1864, Edinburgh (2nd ed. 1874; 3rd ed. 1886), a ​reprint of the article in the eighth edition of the ‘Encyclopædia Britannica,’ and ‘Proposal for the Illumination of Beacons and Buoys,’ 1870.
Stevenson was elected a fellow of the Royal Society of Edinburgh in 1848, served frequently on its council, and became its president in 1885. He was elected a member of the Institution of Civil Engineers in 1864, and president of the Royal Scottish Society of Arts in 1859–60. His contributions to the transactions of these and other societies were many and varied. Outside his profession his interests were mainly concentrated on meteorology. He was one of the originators of the Scottish Meteorological Society in 1855, was member of council from the commencement, and, on the death of Dr. Keith Johnstone [q. v.] in 1871, was elected its honorary secretary. Among the original and permanent contributions he made to meteorology were the Stevenson screen for the protection of thermometers, designed in 1864, and now in universal use; the introduction in 1867 into meteorological investigations of the term ‘barometric gradient,’ which is now commonly employed in the science; and the means of ascertaining, by high and low level observations, the vertical gradients for atmospheric pressure, temperature, and humidity which are fundamental data in meteorology.
In later years Stevenson published ‘Christianity confirmed by Jewish and Heathen Testimony, and the Deductions from Physical Science,’ Edinburgh, 1877, 2nd edit. 1879. He died at his house, 17 Heriot Row, Edinburgh, on 8 May 1887. By his wife, Margaret Isabella, daughter of the Rev. James Balfour, minister of Colinton, he was father of Robert Louis Stevenson [q. v.] His widow died on 14 May 1897.
[Personal knowledge; Works in Brit. Mus. Libr.; Scotsman, 9 May 1887; Times, 9 May 1887 and 16 May 1897; Proc. Royal Society of Edinburgh, vol. xx. pp. lxi–lxxviii; R. L. Stevenson's Memoirs and Portraits, p. 132.]
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