Engineering Wonders of the World
Volume I

150 ENGINEERING WONDERS OF THE WORLD. Elevation of the Britannia Tower, showing position of Hydraulic Press, Chains, and Tube. the tube and its apparatus by about 1,400 tons. By the middle of June 1849 tube No. 1 was ready for moving. In the upper part of each of the towers for which it was destined had been placed iron beams, 40 feet above the rectangular tube openings, to support a hydraulic press of 2,620 tons lifting power. Each of the two cylinders of a press was 9| feet long, nearly 5 feet in diameter, and weighed 16 tons. Its piston had a diam- eter of 20 inches and a stroke of 6 feet, and moved in a ver- tical direction. To its upper end was attached a cross- beam, from which depended two chains, composed of series of eight or nine flat plates bolted firmly together. The links were 6 feet long, and “ stepped ” near the eyes, so that when the press had made its full stroke the chain could be gripped by a huge clamp, The and sustained while the piston Hydraulic r Presses. was withdrawn for the next lift and given a fresh grip in the chain. Each chain was 145 feet long and weighed 25 tons. The floating of a tube to the bottom of the towers was no easy matter, owing to the strength of the current running through the straits. Elaborate precautions, including the provision of guide-ropes and capstans, were The Tube afloat. mighty load. But A Mishap and a Rescue. taken for controlling the pontoons and their freight, and swinging them gradually across the channel as they neared the towers. On the evening of June 19 a huge crowd began to gather from far and near. Specta- tors knew that they would behold such a sight as most of them were never likely to see again. As the tide came in, the pontoons, of which the valves had been closed, lifted slowly, shouldering their Presently the shout arose, “ She floats ! a slight accident prevented operations being continued till the following evening, when the pontoons swung out into the channel, one end of the tube describing part of a circle. Guided by its hawsers, this strange craft moved slowly down towards the bases of the towers, in which recesses had been prepared for the tube. As it got broadside on to the current the pull on one of the controlling capstans became so vio- lent as to drag the mechanism bodily from its foundations. For a few mo- ments it looked as if this first launch were to end in disaster. Fortunately, Mr. Charles Rolfe, who was in command of the capstan, had the presence of mind to shout to the spectators to seize hold and check the progress of the tube. A crowd of men, women, and children flung themselves upon the rope. There ensued a tug-of-war in which human muscles bested the pull of the tide, and the tube was brought up safely with its ends over the recesses cut in the towers. As the tide sank the ironwork came to rest in the exact position required by its designer. So accurately had all calculations been made that, though the tube was 460 feet long, there remained between the ends of the iron plates and the walls of the recesses a space somewhat less than an inch ! The first act of the play was finished. Little time was lost in proceeding with the second. The chains of the hydraulic presses were made fast to the lifting cradles attached to the tube