HISTORY OF CIVIL EXGINEERING IN NEW SOUTH WALES. 611 



wrought iron cylindex's braced together (the average depth of the 

 cylinder piers is seventy-six feet), and the clear headway under 

 the bridge is forty-seven feet six inches above the summer level. 

 The cross girders are two feet two inches deep, spaced seven feet 

 four inches centre to centre, with longicudinal rolled iron girders 

 under rails eight inches deep. The unit stresses developed in this 

 bridge with a live load of l"4r ton per foot run are similar to those 

 of the Bathurst Bridge, but the deflections prove the bridge to be 

 somewhat stitier. 



On the Northern line from Strathtield the first important 

 work is the bridge over the Parramatta River, which is con- 

 structed for a double line of railway : it consists of six spans, 

 each one hundred and fifty feet in the clear. There are 

 four main lattice girders, each continuous over two piers, the 

 aggregate length of which is nine hundred and fifty -six feet eleven 

 inches over all, and seventeen feet eight and three-quarter inches 

 deep. The details of the main girders, the dimensions and 

 arrangement of the cross girders, rail bearers, ifec, are similar to 

 those of the Albury Bridge. The piers consist of cast and wrought 

 iron cylinders braced together and sunk to an average depth of 

 eighty-five feet, giving a clear headway of thirty-five feet above 

 high water. The unit stresses developed in this bridge with a live 

 load of 1.4 ton per foot run are similar to the Albury Bridge, 

 but the deflections observed under test loads proved it to be stifler, 

 The bridge was tested by Mr. Whitton in various ways, and the 

 maximum deflection observed with three engines on each pair of 

 rails, of a total weight of four hundred tons, or equivalent to 

 1.4 ton per foot run, was "8 inches. Six tunnels occur in the 

 descent to Peat's Ferry, the total length of which is one thousand 

 seven hundred and sixty-two yards. They are twenty feet high 

 from rail level to sofiit of arch, and twenty-five feet wide at a 

 height of seven feet six inches above the rail level, with a semi- 

 circular arch of twelve feet six inches radius. The sides of the 

 tunnel consist of curves struck with arcs of circles of thirty feet 

 r<idius, and where inverts occur the radius is one hundred feet. 

 These tunnels, like all the railway tunnels on this line, are lined 

 throughout with brickwork or concrete eighteen inches thick. At 

 thirty-six miles 15.44 chains from Sydney occurs the most 

 important bridge in Australia. 



THE HAWKESBURY BRIDGE. 



The bridge now in course of construction across the Hawkes- 

 bury River presents many features of interest. Instead of being 

 designed by the Engineer-in-Chief, as in other cases, tenders and 

 designs were invited by the Agent-General, Sir Saul Samuel, in 

 England. In response to this invitation, fourteen ofters to con- 

 struct the bridge were received from the leading bridije constructors 



