THE TOWER BRIDGE across the River Thames, in the heart of London, is one of the most famous examples of the bascule type of bridge. The bridge is built of steel, a fact disguised by the facing of masonry over the completed structure. Work was started in 1886 and the bridge was opened in 1894, having cost about £1,000,000. At high water the footways at the top of the bridge are 140 feet above the river. The central opening span is 200 feet long and each of the fixed suspension spans at the landward ends is 270 feet long.