6o Discussion on the Proposed Channel Tunnel. 



the bridge floats, the effect of its motion and other actions, and 

 we can calculate from known strength of materials the proper 

 proportions to suit these known conditions. But in the case of 

 the subaqueous tunnels we can have no idea, for instance, of the 

 amount of water to be pumped out. The nature of the rock is 

 also practically an unknown quantity, and I think the geologist 

 is perhaps too sanguine as to his power of estimating its nature. 

 I should say the geologist's habitual methods conduce towards 

 an attitude of mind not suitable for an undertaking of this 

 kind. In the ordinary pursuit of his science he allows his 

 scientific imagination to roam over remote ages of the past 

 where no one can contradict him and no one can gainsay his 

 conclusions. And when he goes to the top of the Gobbins or 

 Black Head and gazes over the inscrutable expanse of ocean 

 before him, his mind is tempted, I fear, to assume the same 

 attitude as in contemplating these remote inscrutable ages. 



I should doubt the feasibility of Mr. M'Cullough's proposal 

 to keep water out of the workings by air pressure, because the 

 pressure required, corresponding to the depth of water, would 

 be say 300 lbs. per square inch, and no one could live, I think, 

 in air at anything near that pressure. 



In a recent publication the difficulty of mooring the bridge 

 has been compared to the difficulty of mooring a ship. A ship 

 is no doubt very difficult to moor under certain circumstances, 

 but it does not form a parallel case. A ship is not designed 

 principally for being moored, but for motion. It is moored by 

 one end only, and is acted on not only by current but by wind 

 and waves. The bridge, on the contrary, is designed for 

 mooring, is not acted on by wind and waves, and is moored 

 at many points. 



Professor Everett said : — As regards the great heat ex- 

 perienced in the Mont Cenis tunnel, it is simply the natural 

 heat of the ground at that depth. Nothing of the kind would 

 be encountered in a channel tunnel, for the temperature of the 

 ground 50 feet beneath the bed of the channel would be only 

 about 1° higher than the temperature of the bottom water. But 



