Leonard Horner 1785 – 1864, was a Scottish geologist, and the brother of Francis Horner, Fellow of the Royal Society, one of the founders of the Edinburgh Academy, Warden of London University (now University College London),
Leonard Horner was an advocate of homeopathy (though Charles Lyell implied that homeopathy ‘… did him harm…’ (Charles Darwin, The Correspondence of Charles Darwin:, Volume 12; Volume 1864, (Cambridge University Press, 12 Jul 2001). Page 43.)). Leonard Horner was the father in law of Charles Lyell, and a friend of Charles Darwin, and in 1826, Leonard Horner took Charles Darwin to the opening session of the Royal Society of Edinburgh.
An expert on the mineral waters of Great Malvern, it is possible that Leonard Horner knew James Manby Gully. His daughters were close to Florence Nightingale, herself a patient of James Manby Gully, and his eldest daughter married Charles Lyell, who was related by marriage in the next generation to the family of James John Garth Wilkinson. Cecilia Helena Payne Gaposchkin, the great grand daughter of James John Garth Wilkinson was related to Charles Lyell through her Aunt Katherine Lyell, Charles Lyell‘s sister in law, and through Leonard Lyell 1st Baron Lyell (1850-1926) Charles Lyell’s nephew. Leonard Horner and Francis Horner were also related by marriage to James John Garth Wilkinson via his Pertz granddaughters:
‘… [letter 3.12.1894] My granddaughters E & F Pertz, are also great granddaughters by marriage of Leonard Horner, & so of Francis Horner; so I have some touch of Scotland: also by my first cousins, the Horsburghs. The cousin of my girls by marriage is Leonard Lyell, MP for Orkney and Shetland. He is I am sorry to say a Gladstone Baronet… (Cecilia Helena Payne Gaposchkin, Katherine Haramundanis (Ed.), Cecilia Payne Gaposchkin: An Autobiography and Other Recollections, (Cambridge University Press, 21 Mar 1996). Pages 79-80. See also Swedenborg Archives K125  letter dated 3.12.1894 from Garth Wilkinson to John Thomson)…’
Horner was a ‘radical educational reformer’ who was involved in the establishment of University College School was born in Edinburgh.
His father, John Horner, was a linen merchant in Edinburgh, and Leonard, the third and youngest son, attended the Royal High School and entered the University of Edinburgh in 1799. There in the course of the next four years he studied chemistry and mineralogy, and gained a love of geology from Playfairs Illustrations of the Huttonian Theory.
At the age of nineteen he became a partner in a branch of his father’s business, and went to London.
In 1808 he joined the newly formed Geological Society of London and two years later was elected one of the secretaries. Throughout his long life he was ardently devoted to the welfare of the society; he was elected president in 1846 and again in 1860.
In 1811 he read his first paper On the Mineralogy of the Malvern Hills (Trans. Geol. Soc. vol. i.) and subsequently communicated other papers on the Brine-springs at Droitwich, and the Geology of the S.W. part of Somersetshire.
He was elected Fellow of the Royal Society in 1813. In 1815 he returned to Edinburgh to take personal superintendence of his business, and while there (1821) he was instrumental in founding the Edinburgh School of Arts 101 the instruction of mechanics, and he was one of the founders of the Edinburgh Academy.
In 1827 he was invited to London to become warden of London University (now University College London), an office which he held for four years; he then resided at Bonn for two years and pursued the study of minerals and rocks, communicating to the Geological Society on his return a paper on the Geology of the Environs of Bonn, and another On the Quantity of Solic Matter suspended in the Water of the Rhine.
In 1833 he was appointed one of the commissioners to inquire into the employment of children in the factories of Great Britain, and he was subsequently selected as one of the inspectors.
In later years he devoted much attention to the geological history of the alluvial lands of Egypt; and in 1843 he published his Life of his brother Francis Horner.
He died in London on the 5th of March 1864.