Smith's skilful adaptation to steam power of the old and simple mint machinery driven by animal power were referred to in a financial despatch of 16 March 1841 to the court of directors as highly creditable. On 13 Jan. 1846 he visited the Cape of Good Hope on leave of absence, returning to the mint on 28 Dec. 1847. An innovation which Smith introduced of adjusting the weights of the blanks by means of the diameters of the pieces, instead of by their thickness, resulted in his design of a very ingenious and beautiful machine, by which twenty or a hundred blanks could be weighed to half a grain and deposited in a separate cell by a single person with two motions of the hand. After the pieces had been thus sorted they were passed through a set of circular cutters, which removed a certain weight according to the excess of each over the standard. By this means almost the whole of the blanks were obtained of the exact weight without further correction. This machine gained an award at the London International Exhibition of 1851.
Smith was promoted to be major on 2 March 1852, and lieutenant-colonel on 1 Aug. 1854. About this time he made some ingenious inventions, which he proposed to apply to the demolition of Cronstadt; and he also invented a refracting sight for rifles. On 21 Sept. 1855 he was appointed mint-master at Calcutta. The following year he went to England to arrange about copper machinery for the mint, and did not go back, retiring on a pension, with the honorary rank of colonel, on 23 Oct. 1857. After his return to England he devoted himself to currency problems, and favoured the introduction of a gold standard into India. He was deputed to attend the international monetary congress held in Paris in 1865, besides taking active part in the proceedings of many learned societies.
Smith was for a long time consulting engineer to the Madras Irrigation Company; he was also a director of the Delhi bank and of the Madras Railway Company, of which he was for some years chairman. On 17 May 1866 he was appointed a member of the consulting committee, military fund department, at the India office, which post he held until the committee was abolished on 1 April 1880. He died at his residence, 10 Gledhow Gardens, London, on 14 May 1882. Sir Arthur Cotton observes of him: ‘He was one of the most talented, laborious, clear-headed, and sound-judging men I have ever met with, or known of by other means.’ He married, on 27 June 1837, Maria Sarah, daughter of R. Tyser, M.D., by whom he had five sons (for the eldest of whom see below) and eight daughters. A portrait is in possession of his daughter-in-law, Mrs. Percy Smith.
Smith, who was a member of many learned bodies, was author of: 1. ‘Observations on the Management of Mints,’ 8vo, Madras, 1848. 2. ‘Observations on the Duties and Responsibilities involved in the Management of Mints,’ 8vo, London, 1848. 3. ‘Report on the Madras Military Fund, containing New Tables of Mortality, Marriage, &c., deduced from the Fifty Years' Experience, 1808–1858,’ by Smith, in conjunction with S. Brown and P. Hardy. 4. ‘Remarks on a Gold Currency for India, and Proposal of Measures for the Introduction of the British Sovereign,’ 8vo, London, 1868. 5. ‘Silver and the Indian Exchanges,’ 8vo, London, 1880.
Smith initiated the ‘Professional Papers of the Madras Engineers,’ and edited vols. i. ii. and iii. of ‘Reports, Correspondence, and Original Papers on various Professional Subjects connected with the Duties of the Corps of Engineers, Madras Presidency’ (4to, Madras, printed between 1845 and 1855; the third edition of the first four volumes was printed at the American Press, Madras, in 1859). Smith contributed to these volumes many papers, mainly on mintage and lighthouse construction.
The eldest son, Percy Guillemard Llewellin Smith (1838–1893), was born at Madras on 15 June 1838, became a lieutenant in the royal engineers on 28 Feb. 1855, served in South Africa from August 1857 to January 1862, was promoted captain on 31 Dec. 1861, and was employed on the defences of Portland and Weymouth until 1869, and on the construction of Maryhill Barracks, Glasgow, until 1874. On 5 July 1872 he was promoted to be major, and in 1874 was appointed instructor in construction at the School of Military Engineering at Chatham. He was promoted to be lieutenant-colonel on 20 Dec. 1879, in which year he became an assistant director of works under the admiralty at Portsmouth. In October 1882 he succeeded Major-general Charles Pasley [q. v.] as director of works at the admiralty, and during ten years of office carried out many important works, both at home and at Malta, Gibraltar, Bermuda, Halifax, and Newfoundland. He was promoted to be brevet colonel on 20 Dec. 1883. He retired from the military service on 31 Dec. 1887 with the honorary rank of major-general, but retained his admiralty appointment. He died at Bournemouth on 25 April 1893. He was twice married: first to a daughter of Captain Bailey, R.N.; and, secondly, in 1886, to Miss Ethel Parkyns. He was the author of ‘Notes on Building Con-