HISTORY OF CIVIL ENGINEERING IN NEW SOUTH WALES. 615 



The bi'idge over tlie Peel River at Tarn worth consists of two hittice 

 main girders forming a clear span of one hundred and fifty feet. 

 The main girders are each one hundred and sixty-one feet nine 

 inches over all, and placed foui'teen feet apart in the clear. 

 Between tlieni transvei'se or roadway girders are placed at a 

 distance of three feetceiatre to centre. There are two piers, each 

 of which consists of cast-iron cylinders nine feet in diameter, 

 tilled with cement concrete, and braced together with wrought-iron 

 diagonals and ties. The calculations show that with a live load of 

 1.4 ton per foot run on the bridge, the booms are subjected to a 

 stressor 3.72 tons per square inch in compression, and 4.37 tons 

 per square inch in tension. The maximum deflection observed 

 with a live load equivalent to 1.4 ton per foot run was -9 inch. 

 There are timber approaches on each side similar to those of the 

 Wagga Wagga iron bridge. The bridge over Peel-street, at Tam- 

 worth, consists of one span sixty feet in the clear, formed of two 

 plate web main girders, each sixty-five feet nine and a-half inches 

 long over all, spaced fourteen feet eight inches apart in the clear, 

 and fifteen feet ten and a-half inches centre to centre. The piers 

 are built of brickwork, with stone caps. The maximum sti'esses 

 developed with a live load of 1.5 tons per foot run are 3.5 tons per 

 square inch in tension and 4.42 tons per square inch in compression. 

 The maximum deflection observed with this load was .29 inch. 



The bridge over the Macdonald River is similar in design to the 

 bridge over the Peel River at Tamworth, except the piers are of 

 brick in cement. The maximum stresses and deflections observed 

 are about the same as those obtained in the Peel River Bridge. 



From Sydney to Kiama, on the Illawarra Railway, the first im- 

 portant work occurs four and a-half miles from Sydney, viz., the 

 bridge o\er Cook's River, which is constructed for a double line of 

 railway. It consists of three openings, each sixty feet in the 

 clear, formed with two plate web girders, each continuous over 

 two piers. The piers and abutments consist of cast-iron cylinders 

 six feet in diameter. The details of this bridge are similar to 

 those erected over Orimbah and other creeks on the Strath field to 

 Waratah line already referred to, and the deflections under the 

 test load showed similar stiffness. There are ten tunnels, the first 

 of which occurs aljout five and a-quarter miles from Sydney, con- 

 structed for a double line Of railway. The remaining nine tunnels 

 are constructed for a single line. The form and dimensions of the 

 double line tunnel are similar to those constructed on the Strath- 

 field and Waratah line. The single line tunnels are elliptical in 

 section, seventeen feet high from rail level to sotfit of arch, and 

 fifteen feet wide. At a height of five feet above the rails the 

 curve of the tunnel is struck with four centres, with the followino- 

 radii : seven feet six inches, thirteen feet six inches, nineteen feet 



