AMONG the recently published abstracts of papers to be discussed by the Institution of Civil Engineers are four relating to the design, construction and calculations of the great arch bridge over the harbour at Sydney, New South Wales. The papers, Nos. 4904, 4922, 4923 and 4946, are by Mr. R. Freeman, Mr. L. Ennis, Mr. J. F. Pain, Mr. G. Roberts and Dr. J. J. C. Bradfield, and the discussion will be held on April 10.The bridge, which took a little more than eight years to complete, cost £4,248,000. It consists of a main span of 1,650 ft. with a clearance of 170 ft. over the central 300 ft. of span, and ten approach spans. It accommodates a roadway 57 ft. wide, four railway tracks and two footways. The principal parts of the main-span truss are of silicon steel With a modulus of elasticity of 30,500,000 Ib. per sq. in. Analytical methods of calculation were used, arithmetical processes being carried out by calculating machines. Calculations were required for the following combinations of loads: dead load, live load and impact, horizontal force, centrifugal force, wind loads and temperature variation. Of the total weight of the main truss material, the proportions attributable to various loads are as follows: dead weight of arch, 35 per cent; dead weight of deck, 23 per cent; live load and impact, 26 per cent; wind, 8 per cent; horizontal force, 2 per cent; and temperature, 6 per cent. Tests on model members were made by means of a testing machine of 1,250 tons capacity, capable of dealing with tension and compression specimens up to 50 ft. long and bend test specimens 20 ft. long. Tests of the arch after completion indicated a span | in. in excess of 1,650 ft., a difference partly due to unavoidable errors of survey and possibly partly caused by shrinkage of the concrete below the bearings. The bridge was erected by Messrs. Dorman, Long and Co., of Middlesborough.