A Letter to the Kensington Canal Company on the Substitution of the Pneumatic Railway for the Common Railway by Which They Contemplate Extending Their Line of Conveyance

by John Vallance

Blast apparatus being as indispensable appendages to smelting furnaces, as the flux is to the ironstone which is to be smelted in those furnaces, it follows, that (with the possibility of exception where one blast apparatus may be made to serve more than one furnace) there must, seven years ago, have been 284 sets of pneumatic apparatus for urging the fires of these furnaces to the necessary intensity, by forcing currents of air into them. These apparatus formerly varied in form, from common bellows on a large scale, to the diversities of the “water blast.” But the whole of these varieties of blast apparatus are now found so inferior to what are termed “blowing cylinders” that no one who erects a smelting furnace ever thinks of applying to it any other means for urging its fire than this latter description of apparatus.

These “blowing cylinders” are all air-pumps on a large scale; differing from the common air-pump only in being of iron instead of brass; in having their valves so arranged as to cause them, instead of exhausting air from the vessel they operate on, to blow into it; and in their being as much larger than a common air-pump as the “monster mortar” used at the late reduction of the citadel of Antwerp is than a boy’s sixpenny cannon.

The largest of this kind of air-pumps that I have seen was nine feet in diameter, by an equal or rather superior height; though an iron-founder has informed me that he once cast one of eleven feet in diameter. And it is unquestionable, that it will require only the preparation of the necessary moulding and boring, &c. &c. apparatus, to make any number, of any diameter we please, not exceeding (say) twelve feet. Supposing them to be 11.3 feet in diameter, their area would be equal to 100 square feet; and, supposing the velocity with which their pistons moved, to be only half that of the average velocity of the pistons of steam-engines, each of these air-pumps would cause 11,000 cubic feet (i.e. about 70,000 gallons) of air, to pass through each of them per minute; which air would be drawn out of, or forced into, any thing, according as the valves were arranged.

Every one of such pumps that was used to exhaust air from a tunnel of eight feet in diameter would produce a current in it, moving at the rate of two miles and a half an hour; while, supposing that its piston moved at the same velocity whereat the pistons of steam-engines in general move, this current would pass through the tunnel at the rate of five miles an hour.

It being evident, then, that it is necessary only properly to arrange the size and number of the pumps, to cause the atmosphere to rush along the tunnel at any rate we desire; and it being a fact that we have, in daily operation, about 300 such air-pumps as these (though not quite so large) there is only one remaining shelter behind which these “impossibleists” can pretend to screen themselves.

The first steam-engine which Boulton and Watt erected in their manufactory of Soho as a specimen for the examination of those who wanted such machines, was about the year 1780. The exact number we now have among us there are no means of ascertaining. But the authority which I have quoted for the existence of 15,000 steam-engines in Great Britain, states them to be of the average power of twenty-five horses.

If this may be received, the whole amount of “horse power” in operation among us in 1831 was equal to that of 375,000 horses. And even though it should be necessary to lower this down to M. Dupin’s estimate of 200,000 horses in 1824, there would remain an aggregate ample for our purpose. Since, if there was not in 1790 one steam-engine in Manchester, while there are now nearly 300 there, it may safely be assumed that so much the larger proportion of the thousands of them which are now spread over the kingdom have been made within the last thirty years, as to admit of its being fairly inferred that we have, for many years past, constructed them at a rate equal to ten thousand horses’ power per annum.

Yet, with these facts almost as easily verified as it would be to obtain copies of all the newspapers published in the kingdom, and with some of these engines so large as to be equal to 300, or 500, or (as quoted in page [46]) even 1000 horses’ power, do these “impossibleists” say we cannot obtain power enough to work the air-pumps we should require to pump the air out of the tunnel. Just as, twenty years ago, they said we could not use steam to carry us across the seas, nor gas to light our streets.

In reply to a demand of the great Lord Chatham that a certain naval force should be ready by a certain day for an expedition be contemplated; and which, the nature of the service rendered it necessary should be despatched as promptly as it was determined on, the then first lord of the admiralty stated, as an intended conclusion to several notes (or messages) which had passed between the two departments on the subject, that “it could not be done, because it was impossible.” “Inform the first lord from me,” said the minister, “that the service of the state requires the immediate despatch of the expedition: and that if he, with the military marine of the kingdom at his order by virtue of his office, and the commercial marine at his command by the course of hiring transports, delays the departure of the expedition because he deems it impossible, I will impeach him.” Under this alternative, the “impossibility” vanished, and the expedition sailed.

Now as the facts which I have adduced relative to the existence of all the necessary means for rendering importantly available to general use the principle here described, prove that the gentlemen of that profession which is devoted to the practical application of mechanical science to the public service have, for these seven years, proclaimed to be “impossible” that which is as easily practicable as it was for the first lord of the admiralty to prepare the naval part of the expedition referred to, I leave it to themselves to make evident why they should not be impeached, as equally traitors to the cause of practical science, as the first lord of the admiralty would have been to the state, had the expedition not sailed at the period the minister required.