RENNIE, JOHN (1761-1821), British engineer, was the youngest son of James Rennie, a farmer at Phantassie, Haddingtonshire, where he was born on the 7th of June 1761. On his way to the parish school at East Linton he used to pass the workshop of Andrew Meikle (1719-1800), the inventor of the threshing machine, and its attractions were such that he spent there much of the time that was supposed to be spent at school. In his twelfth year he was placed under Meikle, but after two years he was sent to Dunbar High School, where he showed marked aptitude for mathematics. On his return to Phantassie he occasionally assisted Meikle, and soon began to erect corn mills on his own account. In 1780, while continuing his millwright's business, he began to attend the classes on physical science at Edinburgh University. Four years later he was commissioned by Boulton and Watt, to whom he was introduced by Professor John Robison (1739-1805), his teacher at Edinburgh, to superintend the construction of the machinery for the Albion flour mills, which they were building at the south end of Blackfriars Bridge, London, and a feature of his work there was the use of iron for many portions of the machines which had formerly been made of wood. The completion of these mills established his reputation as a mechanical engineer, and soon secured him a large business as a maker of millwork of all descriptions. But his fame chiefly rests on his achievements in civil engineering. As a canal engineer his services began to be in request about 1790, and the Avon and Kennet, the Rochdale and the Lancaster canals may be mentioned among his numerous works in England. His skill solved the problem of draining and reclaiming extensive tracts of marsh in the eastern counties and on the Solway Firth. As a bridge engineer he was responsible for many structures in England and Scotland, among the most conspicuous being three over the Thames—Waterloo Bridge, Southwark Bridge and London Bridge—the last of which he did not live to see completed. A noteworthy feature in many of his designs was the flat roadway. Among the harbours and docks in the construction of which he was concerned may be mentioned those at Wick, Torquay, Grimsby, Holyhead, Howth, Kingstown and Hull, together with the London dock and the East India dock on the Thames, and he was consulted by the government in respect of improvements at the dockyards of Portsmouth, Sheerness, Chatham and Plymouth, where the breakwater was built from his plans. He died in London on the 4th of October 1821, and was buried in St Paul's. In person he was of great stature and strength, and a bust of him by Chantrey (now in the National Gallery), when exhibited at Somerset House, obtained the name of Jupiter Tonans. Of his family, the eldest son George, who was born in London on the 3rd of September 1791 and died there on the 30th of March 1866, carried on his father's business in partnership with the second son John, who was born in London on the 30th of August 1794 and died near Hertford on the 3rd of September 1874. George devoted himself especially to the mechanical side of the business. John completed the construction of London Bridge, and at its opening in 1831 was made a knight. He succeeded his father as engineer to the Admiralty, and finished the Plymouth breakwater, of which he published an account in 1848. He was also the author of a book on the Theory, Formation and Construction of British and Foreign Harbours (1851-54), and his Autobiography appeared in 1875. He was elected president of the Institution of Civil Engineers in 1845, and held the office for three years.