98 RENNIE. 



public works was to build a bridge across the Tweed ! The iron 

 bridges which he executed are, the one at Boston, over the Witham, 

 with a span of 100 feet ; and the noble bridge at Southwark, over 

 the Thames, begun in 1815 and opened in 1819. The latter consists 

 of three circular arches of equal curvature, the centre one having a 

 span of 240, and the other two of 210 feet. The total weight of 

 iron in the structure was 5780 tons, and the entire cost, including 

 approaches, &c., 800,OOOZ. 



The improvement of harbours and the construction of docks 

 occupied much of Mr. Rennie's attention, and in these operations 

 his diving-bell apparatus was of peculiar value. Smeaton was the 

 first who used the diving-bell effectually for building with stone 

 under water; the machine he employed for that purpose was, how- 

 ever, very defective, and could only be used in certain situations. 

 But Rennie, by improvements in the instrument itself, and in the 

 machinery by which its movements could be regulated,* was enabled 

 to carry on masonry, and the foundations of sea-walls, piers, and 

 quays, as well under water as above it. He first emploj-ed his 

 apparatus in 1813, in building the East Pierhead at Ramsgate, the 

 foundations of which were 17 feet below low water at spring tides. 

 It was afterwards used in founding the pierheads and outer walls of 

 the harbours at Holyhead, Howth, and Sheerness, and other works 

 under his direction. Amongst the numerous wet docks introduced 

 at Liverpool in 1710, and since constructed at almost all the prin- 

 cipal sea-ports in the kingdom, Mr. Renriie executed the London 

 Docks, and those at Leith, Dublin, Hull, and Greenock, and also 

 the East and West India Docks, in conjunction with Jessop and 

 Ralph Walker. He also constructed the harbours of Queensferry, 

 Berwick, Howth, Holyhead, and that at Kingston, the largest 

 attempted in this country. At the low water of spring tide, the 

 depth of this harbour was 26 feet, while the area enclosed amounted 

 to 250 acres. The breakwater at Plymouth for protecting the 

 Sound from the swell of the sea was likewise designed by him and 

 Mr. Whitby, and was the first and largest example of a detached 

 breakwater in this country. One of the most useful works executed 

 by Mr. Rennie was the drainage of the great Fen district bordering 

 upon the rivers Trent, Witham, New Welland, and Ouse, and ex- 

 tending 60 miles in length by 25 in breadth. In the carrying out 

 of this great work, by which many hundreds of square miles were 

 rendered productive, and the salubrity of the district improved, he 

 was assisted by Mr. Telford and his son, Sir John Rennie. The 

 chief canals of which he was engineer are the Kennet, Avon, Crinnn, 

 Rochdale, and Lancaster. The naval dockyards at Portsmouth, 

 Plymouth, Chatham, and Sheerness, also attest his skill as an engi- 



* By the invention and employment of what is now well known as the tra- 

 velling-crane. 



