tinder the River Thames. 37 



With respect to the manner of sinking this machine, I 

 propose that two short ropes of sufficient strength, with 

 loops at each end, should be passed over each frame, and 

 slightly secured to keep them in their places ; that when 

 the machine is floated to its destined situation, (which 

 should be about an hour before low water at the lowest 

 tide,) anchors and cables shall be in readiness to secure it 

 in its place ; and that then a number of boats (suppose 160) 

 shall attend, half on one side and half on the other, each 

 with five tons of ballast conveniently disposed so as im- 

 mediately to hook on to the ends of the short ropes before 

 mentioned, in such a manner that one end of the tunnel 

 shall not sink before the other, but both exactly together. 

 These weights may be so regulated as occasion may re- 

 quire, should there appear any irregularity in its descent; 

 and when it is placed as desired, and water admitted to fill 

 it, they may be removed altogether*. The whole of this 

 operation may, I am persuaded, be effected in two hours, 

 that preceding and that following ebb-tide, if every pre- 

 vious arrangement be properly made. 



This part of the tunnel is then supposed to occupy the 

 space from b to c, fig. 1, and to be placed so as that the 

 upper surface of it shall be nearly equal to, or rather below, 

 the present bottom represented by the waving line. After 

 which, by piling off the tide from low-water mark, the 

 ends may be finished, as on dry land; which may be done 

 cither by a continuation of the same frames, or by arches 

 of masonry or of brickwork, as may be judged best. It 

 will then only remain to open the communication with 

 the middle part, by removing the oak planking at each end, 

 and pumping out the water; when, by laying a sufficient 

 quantity of ballast so as to form a road-way clear above 

 the lower flanches, and restoring the banks to their former 

 state, the tunnel will be immediately ready for use 



In the execution of this project a situation should be 

 selected close to low- water mark, oF nearly 300 vards in 

 length, where it would be necessary to lay down blocks of 

 sufficient strength to support the great weight, and upon 

 which the whole 80 frames may be screwed together, the 

 level of which should be at least 15 feet below that of 

 spring tides to ensure its floating when completed. 



It may be objected to this great machine, that from its 



* Or perhaps the sinking may be conveniently effected by merely ad- 

 mitting from 800 to 1000 tons of water into the tunnel, a pump of suffi- 

 cient power being properly secured in each end frame to pump out 200 or 

 300 tons, should it be found necessary to float the tunnel again. 



C 3 vast 



