342 THE POPULAR SCIENCE MONTHLY 



over to Scotland would lead in a northwesterly direction, the present 

 water route to England and London would be shorter and quicker, and 

 it is doubtful if the causeway would be practicable. 



Investigations show that the best way of establishing a channel 

 railway to Ireland is either by means of a submarine tunnel or a floating 

 tube, the cost in both cases being much less than a bridge or causeway. 

 The deep water of Beaufort's Dyke could be avoided by selecting a 

 location from Laggan Head to Maiden Island and thence over to 

 Antrim, or by bending the tunnel to the north around the end of this 

 depression, and thereby increasing the tunnel length under the water 

 to twenty-five miles, with a total length of thirty-five miles, including 

 the approaches. A two-track bore, 150 feet below sea bottom, under 

 water 500 feet deep, would probably cost $50,000,000 to $60,000,000 

 and the possibility of building it would depend wholly upon finding 

 rock strata absolutely water-tight and impervious. Tunneling with 

 compressed air to exclude water is possible only at depths not exceeding 

 about 150 feet below the surface of the water, for then the atmospheric 

 pressure reaches 75 pounds per square inch, and pressures and depths 

 not exceeding half these amounts are usually enough for effective work. 

 It is evident, therefore, that water could not be excluded by means of 

 compressed air at the depth which would be necessary beneath the 

 Irish Channel, and, as previously stated, the possibility of carrying on 

 such work would depend entirely on finding impervious strata, the 

 presence of which could not be definitely determined until the bore 

 was made. The overhead thickness of rock in the Mersey tunnel is 

 30 feet, and in the Severn tunnel it is 40 feet. 



It appears, therefore, that a tunnel would cost from $35,000,000 to 

 $50,000,000, according to its location and other conditions, and would 

 require from ten to twelve years for its construction. 



Another method of crossing the channel is by means of floating 

 tubes, lying either on the surface of the water or anchored far enough 

 beneath the surface to allow ships to pass over out. While no structure 

 of this kind has been built, somewhat similar submerged floating piers 

 have occasionally been used, such as those under two swing bridges at 

 Dublin, and the later one at Norwich, England. Very interesting 

 designs for floating piers also appeared in a recent competition for a 

 new bridge over the Hooghly Eiver at Calcutta. The type is probably 

 the most practical of all methods for crossing a navigable channel of 

 so great a depth. 



If the tubes were to float xipon the surface, openings must be left 

 for water travel, and this can be done by depressing occasional sections, 

 four to five miles apart, leaving openings of 1,000 feet, the presence of 

 the openings being indicated by signals. The depressed sections would 

 connect with those on the surface by means of suitable grades. As the 



