MECHANICS AND USEFUL ARTS. 21 



places ; and in order to obtain a firm footing upon the bottom of 

 tlie sea, the tube will be weighted by a lining of brick in cement, 

 and for further protection will be tied to the ground by screw 

 piles, which will pass through stuflSng-boxes in the bottom of 

 the tube. These piles will, during the construction of the tube 

 within the bell-chamber, be introduced in the annular space be- 

 tween the outside of the tube and the inside of the bell, and will 

 be screwed into the ground as they are left behind by the pro- 

 gression of the bell. The hydraulic presses, and the other h}- 

 draulic machinery which will be employed for lifting and fixing 

 the various segments of the tube, will be supplied with the power 

 required for working them from accumulators on shore, on Sir 

 William Armstrong's system, and the supply of fresh air re- 

 quired for the sustenance of the workmen employed within the 

 bell and within the tube will be insured also by steam power on 

 shore. As the tube is completed, the rails will be laid within it 

 for the trains of wagons to be employed in bringing up segments 

 of the rings as they may be required for the construction of the 

 tube, and for taking back the waste water from the hydraulic 

 presses, or any water from leakage during the construction. Tiie 

 tube will be formed of rings of 10 feet in length, each ring con- 

 sisting of 6 segments, all precisely alike, turned and faced at 

 the flanges or joints, and fitted together on shore previously to 

 beins: taken into the bell, so that on their arrival the soo-ments 

 may, with perfect certainty and precision, be attached to eacli 

 other. The tube when laid will be secure from all dangers aris- 

 ing from anchors, or wrecks, or submarine currents. The build- 

 ing of the tube will be commenced on dry land above the level 

 of the sea, and will be gradually submerged as the tube length- 

 ens. The first half mile will test the feasibility of construction, 

 for that will have to be built both above and under water. 

 When once fairly under water, the progress should be rapid, and 

 it is estimated that the whole undertaking may be easily com- 

 pleted in 5 years. The precise line to be taken will probably 

 be between a point in close proximity to Dover, and a point in 

 close proximity to Cape Grisnez, on the French coast, where the 

 sea bed on this line appears to be the most uniform in level, and, 

 while free from hard rocks and broken ground, to consist of 

 coarse sand, gravel, and clay. Tiie average depth of water is 

 about 110 feet, the maximum about 200 feet. On the line sug- 

 gested the water increases in depth on both sides more rapidly 

 than elsewhere, although in no instance will the gradient be more 

 than about one in 100. The tube, when completed, will occupy 

 about 16 feet in depth above the present bottom of the sea. Up 

 to the point on each shore at which the depth of water above the 

 depth of the tube would reach, say 30 feet at low water, an open 

 pier, or other protection, would have to be constructed for the 

 purpose of pointing out its position, and of preventing vessels 

 striking against the tube. The tube at each end would gradually 

 emerge from the water, and on arrivino; above the level of the 

 sea would be connected with the existing railway systems. The 

 distance across the Channel on the line chosen is about 22 miles. 



