Engineering Wonders of the World
Volume I

THE BRIDGES OF THE MENAI STRAITS. 149 with its load of timber for the scaffoldings or of stone for the masonry. The building of the towers and abutments was in itself a great work. The 230-foot Bri- tannia Tower alone consumed 150,000 cubic feet of Anglesey marble and as many feet of limestone ; and even greater quantities were Riveters and Rivets. bers of the main spans. No fewer than two million rivets, each four inches long and seven-eighths of an inch in diameter, and totalling nine hundred tons in weight, were used to hold the tube plates together. When the first of the tubes approached com- CONSTRUCTING THE CELLULAR ROOF OF A TUBE. Observe the rivet boys throwing up heated rivets to the “ catcher ” on the tube. (From an Old Print, by Permission of the London and North-Western Railway Company.) needed for the two land towers, each 160 feet j high. To render the elevation of the large tubes possible, vertical open- material ings were left in the masonry needed three towers, in which for the Towers the ends of the tubes would move upwards to their berths like the frame of a window in its sash. While the towers and land spans were in progress, gangs of riveters working on the shore platforms joined up the plates and other mem- pletion, a portion of tue wooden platform Tinder each of its ends was removed, and the rock beneath excavated to form a dock large enough to accom- Preparations modate four pontoons, each 98 ,, .. r # floating the feet long, 25 feet wide, and 11 pjrst Tube. feet deep. All eight pontoons were furnished with large valves, through which the water passed in and out as the tides rose or ebbed. The combined buoyancy of the pon- toons—3,200 tons—exceeded the weight of