In addition to these things, the line I propose would save five per cent. on the whole cost; owing to its being in that proportion shorter than the line pointed out on the plan for the railway which was laid before the meeting.
The course I propose is as follows. 1st. Along the road on the east of your basin, to the turnpike road; in which length I should sink it so as to go under the turnpike. 2nd. Diagonally across the turnpike to the bottom of Addison Road; up and underneath which it would be continued to the Uxbridge Road. 3rd. Under that road, and the farm yard and ground opposite Addison Road, to the Green lane which runs upwards by the side of Morland Hall; where would be the only cultivated ground (and that only two or three furlongs) which it might be necessary to purchase.
From this point it would go under the track to Notting Barn Farm; and from thence under that farm yard up the track to the bridge now crossing the Grand Junction Canal; where I propose obviating any opposition of the Grand Junction company, by fixing the bridge which must be thrown across to carry the tunnel, close to that bridge; so that there would still be, as it were, but one bridge for their barges to pass under.
From this point it might be carried under the short piece of road leading to the Harrow Road; and thence, under and across that road, up (though under) Kilburn Lane, to the line of the London and Birmingham Railway.
There being only between three and four furlongs, which are cultivatible throughout this route; and as the tunnel (being carried under them) would be no impediment to the usual operations of agriculture (unless some repair should, by chance, be necessary, while the crops were on the ground) the expense of the ground line, would, comparatively, be not worth speaking of; instead of proving the costly matter it would be, as relates to a canal or railway.
And the foundation which the width of the “lengths” of the tunnel would give for the railway inside it, being thirty times greater than those of the bases on which the rails of the Liverpool and Manchester Railway are laid (those bases too, being of an extra and unusual size) the tunnel would be less likely to need repair as relates to its foundation, than the Liverpool and Manchester Railway is, by thirty times. Indeed, owing to the less weight there will be on each “length” of the tunnel, in comparison with that thrown on the railway bases, the probability of repair proving necessary will be less than this.
The stone blocks, or bases, which carry the rails of the Liverpool and Manchester Railway are two feet square. The weight of the large locomotive engines on that railway, is above ten tons; more than half of which, being thrown on two of the wheels, each block has three tons weight on it when those wheels pass over it. The pressure on every square inch of the foundations of the Liverpool and Manchester Railway, is, consequently, above four times as much as on the boilers of Boulton and Watt’s steam-engines; from which result the sinkings, “drivings into the ground,” and the twenty-fold more expensive repairs than were originally calculated on, alluded to in the extract from the Foreign Quarterly Review, given at page [11].
Now as the construction of the carriages which would go in the tunnel, would prevent more than three tons being thrown on a “length” of the tunnel; and as each of these “lengths” would expose a base of 120 square feet to the ground, the pressure on each square inch of the foundation of the tunnel, would not be one-thirtieth of what it is on the bases of the Manchester and Liverpool Railway; which, taken in conjunction with the superior bases exposed by the tunnel, would, perhaps, render the probability of sinking less than one hundredth. It may, therefore, be presumed that after the tunnel was once fairly set in its place, it never would be necessary to disturb the ground over it.
Neither will the height to be surmounted by your extension, prove an at all serious impediment to the effect of the principle which the tunnel will enable us to put in operation.
As the pressure of the atmosphere, acting in all directions, admits of a tunnel being effective even were it fixed vertically, all gradations of ascent, fall, necessarily, within in its range; with varieties of effect, increasing in proportion as their angles approach the horizon. In consequence of this, the height to be surmounted in the course of your extension, is merely an impediment of degree; while the following circumstance will render that degree comparatively unimportant.