JOHN RENNIE, (1761-1821), engineer and architect, was the son of a farmer, and was born at Phantassie, East Lothian, 7th June 1761. While attending the parish school of East Linton he had to pass the workshop of Andrew Meikle, the inventor of the thrashing machine, and evinced such a strong interest in the operations there in progress that the workmen were in the habit of lending him their tools and teaching him their various uses. In his twelfth year he left school and placed himself under Meikle, but at the end of two years he went to a school at Dunbar, in order to obtain a more thorough knowledge of mathematics and mechanical drawing. Afterwards he occasionally assisted Meikle, but before his eighteenth year he had erected several corn mills, on his own account, while in the winter months he visited Edinburgh to attend the classes of physical science at the university. By Prof. Robison of Edinburgh he was introduced to Messrs Boulton & Watt of Soho near Birmingham, for whom in 1786 he superintended the construction of the Albion flour mills near Blackfriars Bridge, London. It is believed that the difficulties which occurred at the Albion mills in regard to the ebb and flow of the tide first led Rennie to the study of that branch of civil engineering connected with hydraulics and hydrodynamics, in which he became so celebrated as to have no rival after the death of Smeaton. Immediately after the completion of the Albion mills Rennie's reputation was so firmly established in everything connected with mill work that he found himself in a very extensive line of business. In the construction of sugar mills in Jamaica and the other West Indian Islands he soon had almost a monopoly, and among other mills constructed by him in England mention may be made of the powder mill at Tunbridge, the great flour mill at Wandsworth, and the rolling and triturating mills at the Mint on Tower Hill. Wherever the machinery of his mills was impelled by steam, the engines of his friends Messrs Boulton & Watt supplied the motive power. It is, however, on his achievements as an architect and civil engineer that the fame of Rennie chiefly rests. Of the bridges connecting the banks of the Thames at London, three have been built from his designs,Southwark Bridge, in the construction of which he introduced a method of employing cast iron which formed a new epoch in the history of bridge-building; Waterloo Bridge,, which then had no parallel for its magnitude, elegance, and solidity; and London Bridge, on the model of Waterloo Bridge. Bridges at Leeds, Musselburgh, Kelso, Newton-Stewart, Boston, New Galloway, and numerous other places bear similar testimony to his skill and taste. His earliest canal project was that of the Crinan Canal, and following it was the Lancaster Canal, which besides other difficulties presented that of an aqueduct over the Lune. His execution of these works so established his reputation that his opinion and assistance were required from all quarters in regard to similar undertakings, among others the construction of the Great Western Canal in Somersetshire, the Polbrook Canal in Cornwall, the Portsmouth Canal, and the Avon and Kennet Canal. But more important than these were his works in connexion with docks and harbours, his designs embracing the London Docks, the East and West India Docks at Blackwall, and docks at Hull, Greenock, Leith, Liverpool, and Dublin. The harbours of Queensferry, Berwick, Howth, Holyhead, Kingstown, Newhaven, and several others owe their security and convenience to his labours. But even these works must yield to what he executed in connexion with the Government dockyards at Portsmouth, Chatham, Sheerness, and Plymouth. One other effort of his genius falls to be mentioned, the drainage of that vast tract of marshland bordering upon the rivers Trent, Witham, Welland, and Ouse which for centuries had baffled the skill of some of the ablest men in that department of civil engineering. Rennie's industry was very extraordinary; though fond of the society of his select friends and of rational conversation, he never suffered amusement of any kind to interfere with his business,, which seldom engaged him less than twelve hours and frequently fifteen in the day. His conversation was. always amusing and instructive. In person he was of great stature and strength; and his noble bust by Chantrey, when exhibited in Somerset House, obtained the name of Jupiter Tonans. He died 16th October 1821.
His son SIR JOHN RENNIE (born August SO, 1794, died Sept. 1874) succeeded him as engineer to the Admiralty, and acquired a high reputation in the same line of business as his father. On the completion of the London Bridge from his father's designs in 1831, he received the honour of knighthood. He was the author of The Theory, Formation, and Construction of British and Foreign Harbours, 4 vols., 1851-54.