90 Mr. Alexander B. Binnie [March 6, 



and from 10 to 15 feet in depth immediately over the part of the 

 tunnel under construction. While the tunnel was being formed 

 beneath the river there was always a very large escape of air which 

 boiled up through the water, and also came up in some places in- 

 land at a distance of 800 feet from the working face. Notwithstand- 

 ing all the precautions taken the air pressure on two occasions blew 

 up the bottom of the river, and once the surface water rose to a height 

 of 25 feet over a diameter of 50 feet. Any water therefore which 

 enters the tunnel between the working face and the air-tight bulk- 

 head, is forced out through pipes which extend from the working face 

 through the air-tight bulkhead to the bottom of shaft No. 4, the supe- 

 rior air pressure within the working part of the tunnel being used 

 for the purpose ; and from the bottom of shaft No. 4 it is raised by 

 steam pumps to the surface. Passing from the bottom of shaft No. 4 

 down the incline to shaft No. 3, the visitor may observe the cast- 

 iron rings of which the tunnel is built up quite uncovered as the inner 

 lining of concrete has not yet been inserted. It will be noticed that 

 the work is lighted by means of incandescent electric lamps which give 

 sufficient light to see that, as fixed, the plates are quite water-tight 

 and, but for appearance sake, require no internal lining. After 

 passing the bottom of shaft No. 3, which is domed over, we enter on 

 the portion of the tunnel below the river, and most probably soon after 

 hear a loud rumbling roaring noise. This is caused by the escape of 

 the compressed air from one of the air-locks as some men or materials 

 are being locked out. Arriving at the air-tight bulkhead we enter 

 the lock, close the outer door, and turn on the compressed air which 

 enters from the working space beyond the bulkhead. The effect of 

 so doing is at once apparent, for the noise of the inrushing air is as 

 loud as that of the steam escaping from some large steam boiler, and 

 quite drowns the voice and renders hearing impossible. At the same 

 time every one feels a more or less acute pain in the ears caused by 

 the increased pressure of the air on the outer surface of the drum of 

 the ear ; this can in most cases be removed by equalising the 

 pressure through the Eustachian tubes which communicate with the 

 middle ear ; this is effected by swallowing, and blowing into the nose 

 when it is pinched with the fingers, but if the pain becomes and 

 continues very acute the person suffering should at once leave the 

 air-lock. 



As the air in the lock becomes more compressed the temperature 

 rises rapidly ; this is due to the compression and only lasts while in 

 the lock, for as soon as equalisation is established and the inner door 

 is opened and you step into the working space you find the tempera- 

 ture falls to about 60° to 65° F. I am often asked what it feels like 

 in compressed air ; this I think must in all cases be a personal matter. 

 But summing up the result of my many weekly visits to the tunnel 

 during the past two years, I should say that I feel no difference from 

 that when under the ordinary atmospheric pressure. There is a very 

 slight feeling of exhilaration if the pressure is over 20 lbs. per square 



