Ferguson — On a Mode of Suh-aqueous Tunnelling. 81 



to exist only in theory, we may easily conceive of arrangements by 

 which the under margins of such a flooring could be made to bite 

 into such a bottom to a sufficient depth to break the continuity of the 

 water pressure from above, as well as to resist the sliding action of 

 currents. 



I submit that the Academy might advantageously employ a portion 

 of the fund for aiding Scientific Research in investigating experimen- 

 tally the force of adhesion under varying heights of water pressure, 

 and defining the point at which the dynamical action of water is 

 arrested by the interposition of non-fluid matter. 



Since I put the foregoing Paper into the hands of the Secretary, 

 I have learned — what indeed I might have foreseen to be highly 

 probable — that one leading thought in it has already occurred to 

 other minds. Our brother Academician, Mr. Thomas F. Pigot, Pro- 

 fessor of Engineering in the Royal College of Science, informs me 

 that, "When the scheme for the Channel Tunnel was proposed, one 

 of the suggestions was to construct a water-tight metal tube immersed 

 on the bed of the straits " ; and that the deposit of an iron syphon of 

 three feet in diameter under a waterway of eighty feet wide, at 

 Dantzig, was effected by excavating a sub-aqueous trench for its re- 

 ception. I assure the Academy, however, that it was from no desire 

 to seek credit for priority of invention I ventured into this region of 

 speculation, or presumed to invite, as I have done, the attention of 

 our leading Civil Engineers to the subject. The primary motive in- 

 ducing me has been, I confess, a wish to bring the Engineering intel- 

 ligence of the country to consider whether a way may not be found 

 for preserving our city from the necessity of a high-level railway bridge 

 over the Liffey. If, in prosecuting this purpose, I have put forward 

 the rudimentary outlines of a method of more general application, by 

 which unbroken traffic might, pass from bank to bank of the Suir at 

 Waterford, or of the Rhine at Cologne, without impediment to naviga- 

 tion, and without the necessity of having to seek a rock stratum en- 

 tailing lengthened approaches, it will not commend itself the less to 

 practical minds because it has originated in a desire that the architec- 

 tural beauties bequeathed us by that splendid race of men who once 

 inhabited Dublin may be preserved unimpaired for the enjoyment of 

 future generations. I have not been unmindful of the maxim ne sutor, 

 and have not presumed to bring my crude conceptions before this 

 assembly without having had the assurance from a competent autho- 

 rity, as regards the tunnel of 400 feet above described, that, subject 

 to some alterations of detail in execution, "the project is one well 

 within the range of practical application." 



