The metallic part of the question being, however, that which concerns the iron trade, I will keep to that.
One of my early views of this method of conveyance, was, that it might prove important to the iron trade, from the much greater quantity of their production which it would consume, than railways require: and it has, for these seven years, been an object with me, to awaken the attention of the iron masters to (as I conceived) its importance to them, and to endeavour to convince them of the propriety of giving to a plan, which would consume tons of their article, where railways consume only hundred weights, the same fostering and support which they gave to bringing forward railways.
But it has not pleased the iron masters to see the case in the same light in which it presented itself to me.
It is well known to them, that in the year 1810 we had neither a steam-vessel nor a gas-work in the kingdom: the propositions to adopt both those important inventions being then termed and treated, just as this proposition of mine is now termed and treated, i.e. as “impossible, absurd, and madness to think of.” Yet have they seen that a sum of (roundly speaking) ten millions, has, since that period, been sunk in the construction of gas-works and steam-vessels.
With proofs such as these before them (and which have led to the consumption of so much of their production as gas-works and mains require), that, what they, a few years ago, deemed utterly impossible, may, nevertheless, be quite the reverse—it might have been supposed that the iron masters would not prove, either incredulous to, or bigoted against, the belief that a still more important extension of the use of their article was about to open to them.
But, to my great surprise, I have found, that of all unbelievers, the iron masters have proved the most unbelieving.
Other people doubted only because the want of knowledge on the subject, which they openly avowed, left them no alternative. But, in the iron masters, I have had “to contend with the pride of false knowledge.” The world at large said, “We cannot believe, because we cannot understand.” But the iron masters say, “We do not believe, because we know better.”
On asking them how and why they “knew better,” I found that it was not, as some might suppose, from any doubt or difficulty as to the tunnel itself; which they admitted could be cast and laid down, of any size or dimensions that might be required. Neither was it from any doubt as to steam-engines or air-pumps being large and powerful enough to do what was necessary;—the tens of thousands of gallons of air ejected per minute, from the air-pumps which they use to blow the fires of their smelting-furnaces, and the hundreds of horses power they know steam-engines are made equal to, removing all question on these points. [46] But their incredulity arose from a difficulty which one of them had met with, in forcing air through a pipe; and of which they supposed me ignorant; but to which I had adverted, in a publication years before, in the following words:
“It is too well known, to be at all affected in point of veracity, by an inability to mention either the exact time or place, that the proprietor of an iron work in Wales had, some years ago, occasion to erect an additional furnace, at the distance (recollection states) of about three-quarters of a mile from his old ones. The blast apparatus of these old works being large enough to supply this new furnace in addition to the old ones, he conceived it would prove much cheaper, if, instead of having power and blast cylinders erected at the new work, he were to lay a pipe from the old ones, to convey to the new one the superfluous blast. This he accordingly did; and as soon as the pipe was completed, set the apparatus going, to ascertain the strength of the blast he could thus apply to the new furnace. To his great surprise, however, no blast was produced; a gentle current, which would hardly blow a candle out, being all that was perceptible. For a result so adverse to his expectation, he could account in no way but by supposing that, from accident or design, the pipe was stopped up. As the readiest way to ascertain whether it was so, he put a cat in at one end, and blocked it up, leaving her to find her way to the other.
“Thus situated, puss had no alternative but that of seeking an exit at the other end: this she accordingly did, and, contrary to his expectations, soon made her appearance there. Convinced by this that the pipe was not stopped up, he concluded that the disappointment he had experienced arose from the friction of the air against it; and finding that he could in no way obviate this difficulty, he was obliged to abandon the design, and be at the additional expense of blast apparatus for his new furnace.
“Now, had the proposition this treatise submits, been, that we should convey ourselves through a tunnel such as has been adverted to, by employing apparatus on the principle of blast furnaces, to blow us through, by forcing air in behind us, the circumstance which has just been stated would be fatal to that proposition. But when, instead of being blown through, by air forced in behind us, it is proposed to cause the air which is behind the vehicle to operate to push it forward, in consequence of some being taken from before it, the case is widely different. Air which is forced to move in a pipe, in consequence of other air being driven into that pipe behind it, operates (in degree) as a wedge, and opposes to the power which moves it, resistance, arising from becoming, as it were, wedged against the pipe, through its whole length. But air which, instead of being forced to move by an impulse from behind, that, as it were, wedges it against even the very end of the pipe it enters at, is allowed to move, owing to some being taken out from before it instead of being forced in behind it, becomes affected as any thing from which a wedge is withdrawn is affected; that is, freedom of motion is allowed, and its parts play so much more freely, that friction is diminished instead of increased. The impediment would prove, therefore, less important in this case than in the other, even were there no method of altogether obviating it; happily, however, the means of doing this are in our power. Between driving a vehicle through the proposed tunnel by forcing air in behind it, and according to the method which has been stated, there is this difference,—that in the former case the impulse can be given only from the end where the moving power operates; while, in the latter, arranging valves, which should be opened by the vehicle as it passed over them, would admit of that impulse being renewed at every hundred yards, could it be necessary to do it so frequently. Let the friction of the air against the pipe be what it may, therefore, a valve at every mile, or at every half or quarter of a mile, which (as may be done) should be opened by the vehicle as it passed along, and caused to remain open till it (the vehicle) had arrived at the next valve, would prevent any diminution of the velocity at which we might be conveyed, that would prove important.
“This reasoning may be illustrated by a figure relating to an experiment. Air was forced through a pipe 56 feet long, at the rate of 20 miles an hour, under a pressure which is equal to 2.2 inches of water; and as it required a pressure which is equal to 0.6 inches of water to make air move at that rate through a hole in the side of a vessel, there was consequently 1.6 inches greater pressure at that end of the pipe at which the air entered, than at the end from whence it issued.
“Now if the length of the pipe—the tenths of pressure at the entering—and those at the issuing end, be expressed by two lines approximating each other, as shewn below, it may be conceived how ‘air which is forced to move in a pipe in consequence of other air being driven into that pipe behind it, operates as a wedge; and opposes to the power which moves it, resistance, arising from becoming as it were wedged against the pipe, through its whole length.’”
