658 EEPORT — 1882. 



class are, however, no-w well in hand, namely the Severn Tunnel at Portskewet, 

 and the Mersey Tunnel at Liverpool. Having reference to this fact, it will be 

 interesting to quote the following passage from a letter addressed to the press by a 

 Mr. Thoroas Deakin on March 6, 1835, that is to say more than forty-seven years 

 a!?o. Mr. Deakin writes: — 'The Great Western railroad from London to Bristol 

 wiU be accomplished no doubt, and why not continue it under the Severn mouth, 

 near Chepstow, Monmouthshire, through Glamorganshire, and to Milford Haven 

 in Pembrokesbire ? It would then traverse the coal-field of South Wales through- 

 out its whole extent — a tract of country possessing also inexhaustible stores of 

 ironstone. A tunnel was once proposed to be formed under the Mersey at Liver- 

 pool, and had it not been for the failure of the Thames Timnel would most 

 prob.iblr have been carried into effect.' It is not a little singular that the two 

 tunnels 'thus foreshadowed by Mr. Deakin should both be in hand at the present 

 moment. 



Undoubtedly the numerous accidents which occurred during the construction of 

 the Thames Tunnel, together with its enormous cost of about 1,500/. per lineal 

 yard, and the eighteen years occupied in its construction, destroyed the chance of 

 any other projected subaqueous timnel for many subsequent years. One lesson 

 enforced bv the Thame.sTunnel was the necessity of lea vine: a reasonable thickness of 

 o-round between the water and the tunnel. In the Severn Tunnel the minimum 

 thiclmess is 40 feet, and in the Mersey Tunnel 22 feet. The width of the river at 

 the point of crossing of the former tunnel is 2^^ miles, and the maximum depth of 

 the rails below high water 163 feet. In the case of the Mersej^ Tunnel the width is 

 nearlv if of a mile and the depth 144 feet. The Thames Tunnel, as almost everyone 

 knows, was carried on by means of a special contrivance termed by Brunei a 'shield.' 

 No special appliances have been adopted in the case either of the Severn or the 

 Mersev tunnel. Both are di-iven in the ordinary way, but of course enormous 

 pumping power is required and has been provided. 



Where no special appliances are used in the construction of a subaqueous tunnel, 

 it will be clear to all that an unknown risk is eneoimtered. All may go well, and 

 the encrineer will then justly receive congratulations from everyone for his boldness 

 and success. But, on the other hand, something may go wrong, even at the last 

 moment, and I fear the engineer then would be abused no less roundly by the 

 unthinkinsr public ibr his temerity and consequent failure. It would be a ' Majuba 

 Hill ' incident over again, and if the accident caused much loss of life the engineer 

 probably would envy the fate of the brave but ill-starred General Colley, who at 

 least fell with the victims of his rashness. 



In manv cases of tunnels under estuaries, special appliances could be used which 

 would obviate all risk and make the successful completion of the work a mathe- 

 matical certainty. A tunnel under the Ilumber, about li mile in length, projected 

 by mvself in 1873, the Bill for which was subsequently passed by the Commons 

 and thrown out by the Lords, was a case in point. The bed of the Humber is of 

 verv fine silt, and I proposed to build the tunnel in lengths of 160 feet, under the 

 protection of rectangular iron caissons 160 feet long, by 42 feet wide, sunk by the 

 pneumatic process. As the pressure of the air in the caissons would alwavs be 

 slio-htlv in excess of that due to the head of water in the river, no interruption 

 from influx of water could ever occur, and the operation of building the tunnel in 

 leno'ths inside this huge diving-bell would be as certain and free from risk as the 

 every-day work of sinking a bridge pier by the pneumatic process. 



A tunnel over a mile in length now in progress under the Hudson River at 

 New York is being driven through a silty stratum by the aid of compressed air, 

 and with a certain amount of success, as only some twenty men have been drowned 

 up to the present time. The principle upon which the compressed air is used is, 

 however, a false one, since it is merely forced into the tunnel with a view to uphold 

 the o-rouud by its pressure, like so much timbering, and not to keep out the water on 

 the principle of a diving-bell. It is clear, therefore, that the completion of the 

 Hudson River Tunnel, if the present system be persevered in, is purely a matter of 

 conjecture, and all we can do is to hope for the best. The same remark applies, 

 of coui-se, to the Severn Tunnel and the Mersey Tunnel, although in those cases the 



