1884.] on London {helow bridge) No-rth, and South Communication. 499 



water was then to be admitted into the float so that the vessel would 

 gradually sink, until the edges of its open bottom cut their way into 

 the soil ; then air was to be driven into the open vessel, expelling the 

 water, and enabling the workmen to descend through shafts provided 

 with air locks, and to carry on the work of excavation within this 

 chamber of 160 feet long, 42 feet wide, and 12 feet deep. As the 

 excavation was continued, the vessel sank lower and lower, until the 

 desired depth was attained, the sinking being guided by the screw piles. 

 At this, the lowest point, the working stage was still sufficiently raised 

 above high water. When the lowest point was reached, the work of 

 building the tunnel proper was begun, and was carried on till the 

 lower half was finished, thereby nearly filling the chamber to the 

 top. Then the water was pumped out of the float, allowing the 

 whole apparatus to rise to a certain distance, admitting the water to 

 flow over the lower part of the finished work, but permitting this to 

 be added to ; and in this way it is possible to build a timnel of some 

 23 feet total depth by the aid of an air chamber of but little more 

 than half that depth. The 160 feet length having been finished, the 

 float was entirely emptied of water so as to come up to the surface, 

 the screw piles were withdrawn, and the apparatus was moved forward 

 to make the next length of the tunnel. There was an extremely 

 ingenious provision by which the junctions of the successive lengths 

 were effected, but time will not admit of my going into that detail. 



Last year Mr. Law, whom we have already had to thank this 

 evening for the diagi-am of the Tunnel, exhibited to a Parliamentary 

 Committee the model which he has kindly lent me to-night, showing 

 how " cut-and-cover " could be executed by a compressed-air appa- 

 ratus. This model represents the manner in which it is intended to 

 construct, under the Thames, the tunnel of the Charing Cross and 

 "Whitehall Electric E ail way, and here also for the pui-pose of saving 

 depth " cut-and-cover " is resorted to. The tunnel has its sides and 

 roof made of wrought iron, lined with concrete. On a staging prepared 

 in the river, a 50-feet length of the tunnel is riveted up and lined, 

 and then from this staging, it is lowered on to the bed of the river 

 by hydraulic api3aratus ; the ends of the length are first temporarily 

 closed, but the bottom is left open, and thus the length becomes a 

 diving-bell ; air is pumped into it, and air shafts and air locks being 

 provided, men descend and carry out the excavation. As this is 

 done the length sinks further and further, until the desired depth is 

 reached ; recesses in the ends of the length contain flexible tubes, 

 into which a water pressure can be put, so as to expand the tubes, 

 and thus make a provisional joint against the length already com- 

 pleted. The temporary closing of the end is then removed, and the 

 permanent attachment of the one length to the other is made. 



In any one of these ways the tunnel may be made, but when made, 

 people have a sort of feeling that after all a tunnel is an ill- 

 lighted, ill-ventilated, damp, unpleasant sort of a place. There is 

 not the slightest reason why this should be; and I will undertake to 



