36* Proposal for an Iron Tunnel 



By the section across the river it appears that the depth 

 of the bed at low water (being only about 30 feet) is not 

 sufficient to admit of laying down a tunnel such as I pro- 

 pose upon the bottom, without obstructing the course of 

 the stream, or interfering with the ease of navigation : 

 therefore, the first thing necessary would be, to excavate 

 the bed of the river entirely across to about 1 6 feet deeper, 

 and from 6*0 to 80 feet wide ; and to render it as even as 

 possible throughout; which I conceive may be effected 

 without extraordinary labour or difficulty. This being 

 done as far as from b to c, fig. 1 , about 600 feet or some- 

 thing more, I will next suppose eighty of those frames, 

 previously formed agreeably to the plan and section, figs. 2 

 and 3, to be joined by screwing them strongly together, 

 as represented in figs. 2 and 4, with half-inch sheet-lead 

 between the flanches ; which operation should be per- 

 formed on the bank of the river rather below the level of 

 low water, in a situation where the tide may have free ac- 

 cess to it. 



If then the ends of these 80 tunnel-frames so joined be 

 (when empty) close stopped with strong oak plank, and 

 well secured so as to render them perfectly water-tight, a 

 machine is formed iv hick on the admission of the ijde will 

 float ; as may be proved by the subjoined calculation, 

 which for greater security does not include the convexity 

 of the top. At spring-tide, therefore, the whole may be 

 floated to the required situation, and by additional weights 

 upplied sunk in its proper place. But in case of any irre- 

 gularity in its descent, or unevenness of the bottom pre- 

 pared to receive it, by removing those additional Heights it 

 will again become buoyant, when the necessary remedies 

 may be applied and obstacles removed. When once pro- 

 perly placed, by turning cocks fixed in each end it will 

 soon fill with water and be permanently bedded. 



Calculation of the weight of this tunnel in round num- 

 bers : — 



Cast-iron . . 20,020 cubic feet .... about 4,270 tons. 



Lead 566 178 



Oak 200 * 



Tons . . 4,453 

 Water displaced 1,850,000 cubic feet ... 5,1 62 



This tunnel will require to sink it more than 709 

 Exclusive of the convexity at top estimated at 60 



Total . . 769 



With 



