« السابقةمتابعة »
The steam is collected in a vessel on the highest part of the body, and enters the steam-pipe at the top of this vessel; it then passes to the bottom, traversing in the pipe the whole length of the carriage, to the seat of the conductor; it then turns directly upwards to the head of the direction, and then directly down again to the under part of the carriage; it now passes back under the carriage and turns down to undergo in the valves two or three additional distortions. Well may Mr. Gurney say that his steam is wiredrawn! After undergoing eight right angled turns, it must, indeed, be sufficiently attenuated and enfeebled. To a practical man the statement appears to be absolutely incredible, and to involve the most inconceivable infatuation. Here we have a boiler wasting with a high temperature, and bursting with a fearful force, while not a fourth part of it is available to use in the engine. The result we shall give in his own words, as elicited by the examination of the Committee of the House of Commons on Steam-Carriages.
“ During the experiments you have been making, have you frequently had your tubes burst?-Very often.
“What is the average pressure on the boiler per square inch in your ordinary rate of travelling ?-About 70 pounds-never more than 130 pounds. I do not think that the pressure is more than 20 pounds to an inch on the piston.”—p. 21.
What a strange acknowledgment! Had Mr. Gurney been devising the most certain method of rendering his engine at once ineffective and dangerous, he could not have hit upon any one better calculated to serve his purpose than the extraordinary dance he has led his steam. Does he not know that even a circuit around the outside of a cylinder is condemned as injurious to the power of an ordinary engine? Where was Dr. Lardner's acumen and sagacity when he omitted to notice this fact? Shall we suppose that he was only unwilling to express an unfavourable opinion of his friend's invention? Or shall we suppose him entirely ignorant of the effect and the manner in which it is produced?
In regard to Mr. Gurney's cylinders and other working apparatus, we must do him the justice to say, that they have of late been much improved. Originally, their diameter was ridiculously small; dear experience has at last brought them up to tolerable dimensions. The piston rods act through connecting rods upon cranks in the hind axle, by which one or both wheels may be turned round and the carriage propelled. Mr. Gurney complains that his axles broke in a most unaccountable manner. We, on the other hand, think that the fracture was the natural consequence of their position, and the double strain to which they are subject; and the only wonder is, how they ever stand any impulsive force at all!
The next matter of attention is the manner in which the hanging of Mr. Gurney's engine upon springs is accomplished. We have seen how absolutely necessary, even to engines on railroads, is a perfectly easy and entire suspension on flexible springs. Much more are they indispensable to machinery which is to be subjected at a high velocity to the irregular impulses of a pebbled road. Mr. Gurney's language on this point is, we think, calculated to mislead, perhaps without his intending it. In his examination before the Commons' Committee, his answer to the question—" Is the chief weight supported on springs?"—was most unqualified." The whole is on springs.” It is quite true that the boiler and body of the vehicle are upon springs, but it is not less true that the engine and machinery, the most important part, are not. The most simple inspection of any drawing of it will show, what we first noticed in the reality, that the machinery being placed beneath the body of the carriage, resting on the perches, communicates with and terminates in the hinder axle, and receives from the road an unbroken jolt from every stone over which the binder wheels are driven. This is, indeed, what Dr. Lardner should have called the “ cardinal defect" of Mr. Gurney's and almost every other steam-carriage. Of the obstacles which the ignorance or apprehensions of interested parties would interpose to prevent the general introduction of steam-carriages on roads, Mr. Gurney, who has had some experience in them, complains, naturally enough, with some degree of bitterness. Such things however can excite no surprise; they have been the invariable concomitants of every great improvement in our machinery and manufactures, on their first introduction. A very short time will be sufficient to dispel all the absurd notions which have been so industriously propagated on the subject, some of which, it was painful to observe in a recent instance, have been taken up by the dispensers of justice. The information contained in the late Report of the Commons' Committee, and the Evidence which accompanies it, cannot fail, when generally diffused, to enlighten the public mind on all the points connected with it.
Only one point of enquiry remains, as to the qualifications and powers of Mr. Gurney's engine, according to our code of esamination. Has Mr. Gurney made any provision for the ascent of hills, or for the exertion of a greater or less power in propelling greater or less weights? We shall amuse our readers by the two methods which he either uses or proposes. When a hill or obstacle is to be conquered, Mr. Gurney uses what he calls preparation. This seems rather a vague term, but we shall explain it: before arriving at the ascent, the carriage is either stopped, or its motion retarded to the slowest rate; the steam is then allowed
to accumulate within the boiler till it is ready to burst, and then, being taken at its greatest strength, the carriage is set agoing, and the accumulated steam will just carry it up a slight ascent. Dr. Lardner speaks of another mode, which he calls “ opening the throttle valve ;" the doctor ought to have known that this can do nothing more than merely let off a previous accumulation of steam when there is an excessive supply; but the supply in Mr. Gurney's engine is well known to be scanty enough for the most ordinary purposes, much less to accumulate a sinking fund for exigencies. Mr. Gurney knew the inexpediency of the doctor's cure, and therefore he gives us a third mode of gaining a permanent increase of power, which is so rich that we must give it in his own words. That power being equally requisite for dragging a greater weight on the level, or the same weight up hill.
“What diameter do you propose to make the propelling wheels of your new carriages?" "I propose to have them about five feet. I would observe that by taking a wheel of five feet diameter off the axle, and putting on one of two feet six, the engine would be multiplied double its power, and lose of course one half in speed; in some cases it may be desirable to do so if the carriages are used for general purposes; for speed and dragging of heavy weights alternately, larger or smaller wheels may be put, to meet circumstances as they occur."— Report, p. 19.
So when we start one of Mr. Gurney's coaches, we are also to be provided with sundry spare sets of wheels of various sizes, from the “ ten feet ten" of a timber yard to the “ two feet two" of a poney phaeton. Starting light, we are to use the ordinary five feet wheel, but picking up a load by the way, we are forthwith to unscrew our caps, pull out our linch pins, remove these wheels, and lower the hinder parts of the vehicle to the moderate level of fifteen inches above the ground! Precious manæuvre; valuable travelling accommodation in the nineteenth century! We are to carry with us, either in our great coat pockets, or in the fore boot, or hung around the carriage, where best we can find accommodation for such bulky passengers, sets of coachwheels of various sizes, to be substituted for each other in order to " meet circumstances as they occur!” We hope Dr. Lardner will not omit this “ cardinal'excellence" in his next edition.
Still we do not altogether despair of Mr. Gurney's final success. He has not shown himself averse to improvements, or doggedly prepossessed in favour of one peculiar system. Already he has adopted three different ones. First, he used propelling feet like those of a horse; then abandoning them he adopted wheels; and now, in his third system, he has removed the steam machinery from the carriage with the passengers, and places it as a steam horse in front of the carriage, to drag it along the road. Let him make one change more--a radical one certainly—and we promise him success. Let him construct a more efficient boiler, use shorter passages, larger cylinders, and simpler gear; let him set the whole
upon elastic springs, and invent a more commodious mode of varying power. Until he does this, we shall express the same opinion of Mr. Gurney's engine that a Scotchman once gave of his own fowling-piece, that the gun was a very good gun, but only wanted a new stock, lock and barrel.
Mr. Walter Hancock has invented another steam carriage, which has been run for some time on the Harrow Road, as an omnibus, with some measure of success. Mr. Hancock has invented a powerful boiler, a strong engine, and has suspended it upon springs in a much better way than hitherto adopted. But his engine does not seem adapted for rapid motion, and only aspires to the sober pace of eight miles an hour. It is clumsy and heavy, and has, we think, already attained all that it ever can attain. It resembles very much the cumbrous diligences of the French, and only wants the exalted cabriolet on the top to present a perfect likeness of one of these tardy vehicles. In looking at it, one is induced to suppose that coach building has gone back half a century. We give the inventor's own description of his vehicle from the Report of the House of Commons' Committee.
“Will you state the progress you have made in the improvement of your steam-carriage ?— The principal improvement I consider is in the boiler, that of constructing the boiler much lighter than any now in use. There are flat chambers which are placed side by side, the chambers being about two inches thick, and there is a space between each two inches; there are ten chambers and there are ten flues, and under the Aues there is six square feet of fire, which is the dimension of the boiler, top and bottom; the chambers are filled from half to two-thirds full of water, and the other third is left for steam, there is a communication quite through the series of chambers, top and bottom; this communication is formed by means of two large bolts which screw all the chambers together, the bottom bolts the bottom part of the chambers and the top bolts the top part of the chambers, and by releasing these bolts at any time all the chambers fall apart, and by screwing them they are all made tight again; we bave braces to fasten them; the steam is driven out through the centre of one of the flues, and the water is ejected from the pump at the bottom communication for the supply of water. The boiler is placed behind the carriage; there is an engine-house between the boiler and the carriage; the engines are placed perpendicular between the passengers and the boiler, and the fore part of the vehicle is for the passengers; so that all the machinery is quite behind the carriage and the fore part of the carriage entirely for the convenience of passengers.' • What is the weight of your vehicle?" "I should imagine about three tons and a half.' * To how many of your wheels do you apply your power?' ' To two, occasionally one. The axletree of the present car
riage is made precisely the same as the common axles now in use, straight and merely bent at the end, and I have a chain which I put on the nave of the wheel, and that communicates with a corresponding chain wheel on the crank shaft of the engines. There are two engines working on two cranks, exactly on the same principle as used in common for steam *coaches; I take the chains; I place the engines four feet from the axletree of the hind wheels, and the communication of the chain is to allow me to put my work on the springs, and the play of the carriage up and down is accommodated by the springs.' • Has your engine met with accidents.' No, except once I broke my chain.””—p. 32.
This accident of the chain, and another in which his boiler burst, without injury to the passengers, are the only circumstances of further importance in his examination.
Another carriage has been lately started by Messrs. Ogle and Summers, and had a few trials; it has run on an average eight or ten miles an hour. But its machinery is not upon springs, and its weight and bulk are so enormous as to leave to us no hope of its success. The only circumstance in this carriage that offers any novelty, is its boiler, which seems calculated to generate steam of an enormous pressure. But till it accomplish something more promising than its performances have yet realised, we do not think the detail of its parts sufficiently interesting to reward the trouble of going deeply into them. It is sufficient to say, that the general principles of its construction do not fulfil the conditions we have already shown to be essential to success.
We had looked to gain some information or useful hints on the subject from our neighbours across the Channel, but have been disappointed. The two books placed at the head of this article are almost the only ones we have found in which the subject is professedly treated, and one of these, it will be observed, is a translation from the English. A rail-road has been lately forming, and is now nearly completed between Roanne and SaintEtienne, and the proprietors have procured two English engines, one of Mr. Stephenson's, and one of Messrs. Fenlow and Murray's, of Leeds, to be applied to the same purposes as on the Liverpool rail-road. The following is the account given of a partial trial given to the first of these. Our sprightly neighbours are, as may be expected, prodigiously delighted at the idea of travelling forty miles an hour, a rate of speed so different from any to which they have been hitherto accustomed, and also of being no longer compelled to cross the Channel in order to be witnesses of this « étonnante decouverte.”
“Le 1 Juillet, la première de ces machines a été mise en experience, avec le concours du préfet de la Loire, des autorités du département, et d'un grand nombre de curieux et de dames. Le convoi était composé de douze voitures, renfermant 400 personnes ; l'une de ces
VOL. X. NO. XX.