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Show i BRIDGE TRIBUTE TO SKILL OF ENGINEER Structure Crossing Firth of Forth a Marvel. The huge bridge which spans the ' firth of Forth In Scotland, and known as the Forth bridge Is a marvel of engineering skill. This wonderful bridge was started In 1882, but was not completed until 1S89. Erected to obviate the detour around the head of the firth, Its total length Is over 8,000 feet. It crosses the flrth at Queensferry, where the channel Is comparatively narrow, and where stands 1a mid-channel the Isle of Inchgarvle. The amount of steel used In Its structure Is somewhat amazing 51,000 tons woven Into this giant bridge, j which is capable of holding aloft two railway tracks so firmly that express trains are able to pass over at a speed of 60 to 70 miles an hour. The manner man-ner in which the workmen dug out the bed of the estuary until they reached the solid rock on which they built the masonry,- working all the time under compressed air conditions, Is amazing and great credit is due to the engineers who had the work In hand, Sir John Fowler and Sir Benjamin Ben-jamin Baker. This bridge is one of the most famous of the "Cantilever" type, sometimes known as a bracket bridge, so called because each end of a span is built out like a bracket, braced on a Ann foundation, and a center portion Is then riveted to the ends, similar to a shelf supported on wall brackets. . As with suspension bridges, cantilever canti-lever bridges can be built In long spans, so these types are chosen where many supports would be a hindrance to navigation. Each year there is 145 acres of surface to be painted, so one can readily conceive the extent of this bridge. The two nkaln spans are 1,710 feet long and formed of two cantilevers, each 680 feet long, united by a girder 850 feet in span. Supporting the cantilevers can-tilevers are steel towers 361 feet high. It will not be surprising that the cost of erecting this bridge amounted to nearly $10,000,000, for from 4,000 to 5,000 men were employed for seven years before the Forth bridge was opened for traffic. |