|Activity||Brother of Francis Horner, was born in Edinburgh, 17 Jan. 1785, and educated at the Edinburgh High School. In 1802 Horner studied chemistry at the university of Edinburgh under Thomas Charles Hope, having already shown a strong bias towards scientific pursuits, and about the same time began to collect mineralogical specimens. Becoming partner in his father's linen factory, he went to London in 1804, and settled there in his twenty-first year, after marrying a Miss Lloyd. From his brother's influence and his own acquirements as mineralogist and geologist Horner was soon well known among scientific and literary men of the day. In 1808 he was elected fellow of the Geological Society, and throughout his life remained intimately associated with that body being appointed one of the secretaries, in 1828 vice-president, and in 1846 president. In 1813 he was admitted a fellow of the Royal Society.|
Horner's business duties recalled him to Edinburgh in 1817, where he settled, after accompanying his brother Francis to Italy, and became prominent as a Whig politician and educational reformer. In 1821 he founded the School of Arts there for the instruction of mechanics, and according to Lord Cockburn, was ‘indirectly the founder of all such institutions.’ From 1821 to 1826 a series of annual political meetings, ‘by far the most effective of all the popular movements in Scotland at that time’ (Cockburn), were organised chiefly by Horner. In 1825 he was corresponding with Peel, Home Secretary, respecting workmen's combinations (Parker, Sir R. Peel, 1891, p. 379).
Horner was one of the founders of the Edinburgh Academy. In 1827 Horner was invited to London to assist in organising the London Institution, and in the following year became warden of the London University at its opening. In 1831 he resigned the latter office, partly on account of ill-health, and went with his family to live at Bonn on the Rhine. While there Horner occupied himself in studying mineralogy, and in 1833 read a paper (Geol. Soc. Proc. Trans. ut infra) on the geology of the environs of Bonn. During that year he was appointed one of the commissioners to inquire into the employment of children in factories, and was until 1856 one of the chief inspectors under the Factories Act, performing his duties with remarkable energy.
After 1856 Horner mainly devoted his attention to geology, and drew up catalogues of the Geological Society's collections. After a sojourn at Florence in 1861 in search of health, Horner died on 5 March 1864, at Montagu Square, London.