5 



It is computed that the Severn tunnel cost almost £1 ,000,000 

 per mile of breadth of river to be tunnelled, and at the present 

 time 1,000,000 gallons of water have to be pumped out per hour 

 in order to keep the finished tunnel dry. 



The St. Clair tunnel is another example of what one may 

 expect in constructing subaqueous tunnels. It is only to be 

 2,300 yards long, with 770 yards subaqueous, for a single line ; 

 and, owing to the favourable material of the river-bed, the 

 shallowness of the water, etc., the estimate was moderate, being 

 ^"517,000, or about £7$ per foot run ; yet this modest estimate 

 has already been exceeded, and the tunnel is still incomplete. 



The Mersey tunnel, constructed under the most modern 

 system, and under the most favourable conditions, cost about 

 £76 per foot run. 



Taking, then, these very favourable costs as data from which 

 to approximately estimate the cost of the proposed North 

 Channel tunnel, we have as the necessary sum ^"9,900,000, and, 

 under favourable conditions, 16 to 20 years for its construction. 



Again, assuming that the proposed tunnel would discharge 

 the same quantity of water as the Severn, although the former 

 would be nine times the subaqueous length of the latter, then it 

 would require pumping engines developing 10,000 horse-power 

 constantly working to keep the tunnel dry when complete. This 

 would be one small item in the working expense. I have 

 merely touched upon these points, lest the public should be- 

 come too enthusiastic over a scheme founded principally upon 

 assumptions that can never be verified until after the tunnel is 

 complete. 



It was after much deliberation that I decided upon the title for 

 this paper, as the design of the proposed bridge contains some 

 of the essentials of a bridge, of a viaduct, and of a tunnel (as will be 

 readily understood by referring to their definitions), and the title, 

 " Submerged Buoyant Bridge " is, perhaps, the most descriptive 

 of the character and peculiarities of the structure. In order 

 to compare it with existing bridges, I have procured a 

 number of lantern slides illustrating different types of aerial 



