Part 10
Bodies moving on levels at the under Have moments, which mentioned velocities, the motions of which (friction being are changed from horizontal to ascending, by counteracted) will means, either of angular or circular ascents. cause them to rise to the under-mentioned heights above the level where those velocities were attained, let the rate of rise, or angle of ascent, be what it may. MILES PER HOUR. FEET. INCHES. 3 0 3½ 4 0 6⅜ 5 0 10 6 1 2⅜ 7 1 7⅝ 8 2 1⅝ 9 2 8½ 10 3 4 11 4 0 12 4 9⅝ 13 5 7¾ 14 6 6⅝ 15 7 6¼ 16 8 6⅝ 17 9 7⅞ 18 10 9⅞ 19 12 0⅝ 20 13 4½
A velocity of six miles an hour being thus capable of giving momentum sufficient to enable any vehicle to surmount an ascent of above one foot in perpendicular height, let the angle of ascent or rate of rise, be what it might, it has been necessary only to lay out our turnpike-roads in alternate short levels, with sharp rises of one foot in height between them, similar to the line below, to render all our roads level, in point of effect, to every vehicle which went at the rate of six miles an hour; since, as the _continued_ draught of the horse would overcome, neutralise, and (as relates to its counteractive effect) annihilate the friction of the wheels and axes during the ascent, the momentum imparted by that velocity would enable the vehicle _of itself_ to rise up, and surmount the ascent, without any _extra_ effort on the part of the horse: while, supposing that the practice of stage-coachmen were to be imitated, and the horses of these six-miles-an-hour vehicles pushed to a pace of twelve miles an hour for a few yards before the wheels actually touched these rises, so as to give the vehicle a velocity of 12 miles an hour at the moment of its _beginning_ to ascend them, the momentum imparted by this velocity would carry the vehicle up four feet nine inches perpendicular, instead of one; so that the road might be laid out in alternate levels and rises of four feet.
It is true that, supposing this principle to be acted on, half the width of the road must be left in the usual manner, in order to enable waggons, which do not move faster than two or three miles an hour, to pass over it. But as the slow rate of two miles an hour will give momentum enough to admit of a rise of 1⅝ inches being surmounted, the principle might be taken some advantage of, even on the half of the road appropriated to waggons; since rises not exceeding 1½ inches each, could be surmounted by vehicles which did not move faster than two miles an hour.
However, leaving the waggon-half of the road to the usual arrangement, the advantage of, as it were, doing away with all hills and rises, and rendering all our roads level (in point of effect) to all vehicles travelling at the rate of six miles an hour, might have amply repaid the expense of this suggested alteration in the _form_ of the roads, had the engineers under whose direction they were cut, but laid them out in that manner: while, supposing that a rate of 16 miles an hour could be attained by pushing the horse to a gallop _just before_ reaching the ascent, the levels and rises might be laid out in gradations of eight feet each instead of four feet.
But let the heights of these proposed elevations be what they might, the advantage of (in effect) doing away with all hills and rises, and of rendering our roads level to us all over the kingdom would be attained; which might prove ample reward for varying the mere form of the roads; and would not, I think, have been unworthy the notice even of our omniscient engineers; notwithstanding that the way in, and degree to which they have neglected and slighted this law of motion, with respect to its application to railways as well as to turnpike-roads, proves them, one and all, to have been equally percipient of its advantages, as they were of the practicability of rapid conveyance on canals; and as they _are_ of the merits of the method of transmission which the individual who has now the honour of addressing you is presumptuous enough to think deserving even of THEIR attention: omniscient as they deem themselves relative to it; and omnipotent as they have, hitherto, proved, with respect to its condemnation and rejection.
Should I, however, be fortunate enough to meet with any who will measure the competence of these gentlemen thus to condemn, by the following standards, I cannot but trust that my appeal from their decision will be favourably received.
The question, divested of technicalities, resolves itself into the three following considerations.
First, can we construct iron (or any other kind of) tunnels, such as would be requisite for the operation of the principle? Secondly, can we construct air-pumps large enough to exhaust from the said tunnels with the necessary rapidity? And, thirdly, can we make steam-engines powerful enough to work these air-pumps?
Now as there is no one who denies that we have the power of making tunnels of any size, not exceeding (say) twelve feet in diameter, nor that we can form the separate segments, or pieces, in which such tunnels might be cast, into cylindrical “lengths,” of from ten to fifteen feet each, so as to lay them down and connect them as (suppose for the present) gas mains are laid down and united—as no one denies this, the second question, relating to the air-pumps, is the first to be replied to.
In 1827 there were, in Great Britain, 284 smelting furnaces; the quantity of iron made during that year by which, was 690,000 tons.
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.
Those who will give themselves the trouble of the calculations necessary to establish the truth of the preceding statements relative to the effect of momentum, it will be unnecessary to remind of any of the occurrences which prove it. But those who do not choose to take that trouble, may be reminded, that a circumstance often witnessed, gives practical demonstration of the accuracy of these statements.
During certain adhesive states of the crust of the road, it is frequently seen when travelling, that the pressure of the wheels causes particles of earth to adhere to, and rise from the ground, sticking to the tire of the wheel.
The adhesion of these particles of earth being, however, soon destroyed by the centrifugal force imparted by the revolution of the wheel, they become, the moment _it_ loosens them from the wheel, and allows the other influence to operate, projected in directions varying according to the position of the part of the wheel to which they adhered, at the moment of their quitting it.
Some of them, being carried to the top of the wheel, fly forward; but the majority, leaving the wheel at about the height of the axle-tree, become projected vertically, and are seen bobbing up and down by the windows of the carriage, somewhat like motes in the sunbeam.
Their thus rising and falling may, perhaps, hitherto have been observed, without being regarded as demonstrative of any principle which may be rendered subservient to our purposes. But as they are, in point of fact, evidences, that the momentum imparted by the velocity at which the tire of the wheels is revolving, will cause bodies to rise to the height of three or four feet perpendicular, above the point of the wheel from which they fly; and as this velocity is exactly commensurate with that at which the carriage goes over the ground, they are unquestionable proofs, that, provided friction be annihilated as relates to counteractive effect, by the continued operation of the moving power, the vehicle itself would ascend an inclined plane of _any_ rate of ascent, to the same height to which they rise above the position of the part of the wheel they adhered to, at the moment of their flying from it.
But, to leave this question relative to momentum, and return to that of the steam-engines and air-pumps.
It being the property of air to neutralise, or absorb, a smaller portion of whatever impulse may be imparted to it, than, perhaps, any other ponderable medium nature offers us, the power of the steam-engines which operated on the air-pumps that exhausted air from the tunnel, might be brought to bear,—and that too, without their energy being so diminished as even to _approach_ an insuperable objection—on the vehicles in it; and an effect in consequence produced, which we cannot, at first, conceive to be possible.
It is evident, that it will not require the power of the engines (each equal to several hundred horses’ power), by which the air-pumps would be worked, to move one, or even many vehicles. What then will become of the surplus power? Will it be lost in overcoming the friction of the air, as adverted to at page 41; or, rather, may it not operate to increase the rate at which the vehicles will move? And if so, how many times will the rate at which we may be conveyed, exceed that at which we now travel, and what is the limit that will be attained in this particular?
It is well known that air will rush into a vacuum at the rate of nearly a thousand miles an hour. Now although it is no more expected we should be conveyed at any such rate as that, than it is intended we should be placed in a vacuum, yet are, both this almost inconceivable velocity, and what is generally expressed by the term “vacuum,” so connected with the subject of consideration, that it becomes unavoidable to advert to them, injurious as they must prove, and strongly as they will array our preconceived notions and prejudices against the proposition.
It cannot be denied that we have the power of laying down a tunnel, such as has been referred to, and of adapting a railway to the inside of it, for any distance we please: and, though it may not be in our power so to connect the separate “lengths” or cylinders which compose it, as to render the joints perfectly air-tight against a vacuum, yet, with reference to the trivial degrees of exhaustion necessary for the purpose here contemplated, every joint may most easily be made “air-tight”: since, supposing the degree of exhaustion to be equal to the pressure at which gas is forced through the mains of a public company whose works I know, a load of above 100 tons would be carried along a tunnel of eight feet in diameter, at whatever rate the air was pumped out of it. Equally certain, as it therefore becomes, that we have the power of extending this tunnel at pleasure, is it, that the power of making and working any number of air-pumps, such as have been referred to, will enable us to exhaust from, and consequently cause air to rush through it, at rates so vastly exceeding any at which we now travel, that our preconceived notions and prejudices cause us to look on the proposition as both impossible and absurd.
One of the circumstances which at first strikes us as fatal to the proposition, is the inability to respire, which we all feel we should be liable to, if conveyed rapidly _through_ the air. A moment’s reflection will, however, enable us to see that this objection has no application whatever to the case. It is not proposed that we shall be conveyed rapidly _through_ the air, but that we shall cause air, which we have first set in rapid motion, _to convey us along with it_, _as fast as itself goes_: a state of things so different from going through, or against, and meeting the air, that our supposed objection does not apply to the case.
Stating facts will, however, be the best way of settling this question; and for this purpose the experience of our aeronauts is referred to. Much as they have sometimes been inconvenienced from the rarity of the air, at the heights to which they have ascended, yet have we never heard them complain of being unable to breathe freely, owing to the velocity with which they were carried along over the earth’s surface, notwithstanding that they have been conveyed at rates of 70, 80, and, in one instance, 160 miles an hour. And why? because that which was the cause of motion went with them.—“I had not,” says Lunardi, in his account of the first ascent ever made in England, “the slightest sense of motion from the machine. I knew not whether I went swiftly or slowly—whether it ascended or descended—whether it was agitated or tranquil, but by the appearance or disappearance of objects on the earth.” Rapidly, therefore, as they have moved, yet have they felt as if in a calm. Now exactly similar in point of respiration, would be the feeling of those who might be conveyed in the proposed tunnel. The air, being the cause of motion, must go, _at least_, equally fast as it drove them, and necessarily be wherever they were. Let the rate of motion therefore, be what it might, the feeling of those who experienced it, must prove that of being in a perfect calm.
Nor are the objections we at first conceive, relative to the effect which pumping air from the tunnel, and producing what only the word vacuum (inapplicable as it is) will enable us to convey the idea of, at all more tenable. The degree to which air would be exhausted from the tunnel might scarcely ever be sufficient to sink a barometer two inches lower than one exposed to the atmosphere stood at; so that even were we exposed to it no inconvenience would be felt. {69} But we never shall be exposed to it, any more than those who witness the cruel experiment of putting a mouse under the receiver of an air-pump, and then exhausting it, are exposed to what the little animal suffers. Between those who _see_ and the poor creature which _feels_ the effect of the apparatus, is the side of the receiver. And between the part of the tunnel in which the exhaustion, or rather the difference of density is, and the passengers in the vehicle, would be the _end_ of the vehicle; so that though _close to them_ would be an atmosphere rarer than (we will suppose) it might prove pleasant to be in, yet would the atmosphere _they actually were in_ be the same as that of the air at large. No inconvenience, therefore, can be experienced in this particular.
Equally untenable is the idea we take up, that it will be impossible so to adapt the ends of the vehicles to the inside of the tunnel, as to cause them to act as pistons in preventing the passage of the air by them, without occasioning friction to a degree which should deprive us of all the advantages the air would otherwise give, as a mean of communicating motion.
In the last carriage which I had for the tunnel I constructed at Brighton, there was a space of above an inch and a half in width left all round between the _piston_ part of the carriage and the tunnel, through which air rushed unimpeded. Yet did not this “windage,” or leak, though equal in the aggregate, to an aperture of three square feet, prevent the carriage from springing forward to the impulse of the air-pumps, with a readiness I was surprised at. Nor did it ever cause the least _perceptible_ diminution in their effect; owing to the small quantity of air that passed through it, in comparison with the immense quantity exhausted by the pumps.
When the Brighton Committee rode in that tunnel, one of them brought with him a mountain barometer, that he might ascertain the degree of “vacuum” or exhaustion necessary to move the carriage. This barometer was accordingly suspended in the part where the “vacuum” was to be produced, and the vernier adjusted with the greatest accuracy. But to his surprise the degree of exhaustion was not sufficient to lower the barometer in the _least_ degree. Being aware of this, I had spirit gauges previously prepared, one of which was fixed in the end of the carriage. But even this gauge, though nearly fifteen times more sensitive than the barometer, was affected hardly enough to be visible, the amount of “vacuum” indicated by it, being only about ten grains per square inch, or _less_ than the ten-thousandth part of a vacuum.