The Mirror Of Literature, Amusement, And Instruction. Volume 14, No. 391, September 26, 1829. VariousЧитать онлайн книгу.

      MR. GURNEY'S IMPROVED STEAM CARRIAGE

      Mr. Gurney, in perfecting this invention, has followed Dr. Franklin's advice—to tire and begin again. It is now four years since he first commenced his ingenious enterprise; and nearly two years since we reported and illustrated the progress he had made. (See MIRROR, vol. x. page 393, or No. 287.) He began with a large boiler, but public prejudice was too strong for it; and knowing people talked of high pressure accidents; the steam, could not, of course, be altogether got rid of, so to divide the danger, Mr. Gurney made his boiler in forty welded iron pipes; still the steam ran in a main pipe beneath the whole of the carriage, and the evil was but modified. At length the inventer has detached the engine and boiler, or locomotive part of the apparatus, which is now to be fastened to the carriage, and may be considered as a STEAM-HORSE, with no more danger than we should apprehend from a restive animal, in whose veins the steam or mettle circulates with too high a pressure. Fair trials have been made of the Improved Carriage on our common roads, the Premier has decided the machine "to be of great national importance," from sundry experiments witnessed by his grace, at Hounslow Barracks; and the coach is announced "really to start next month (the 1st) in working—not experimental journeys—for travellers between London and Bath."1 Crack upon crack will follow joke upon joke; the Omnibus, with its phaeton-like coursers will be eclipsed; and a journey to Bath and the Hot Wells by steam will soon be an everyday event.

      Descriptions of Mr. Gurney's carriage have been so often before the public, that extended detail is unnecessary. Besides, all our liege subscribers will turn to the account in our No. 287. The recent improvements have been perspicuously stated by Mr. Herapath, of Cranford, in a letter in the Times newspaper, and we cannot do better than adopt and abridge a portion of his communication.

      "The present differs from the earlier carriage, in several improvements in the machinery, suggested by experiment; also in having no propellers;2 and in having only four wheels instead of six; the apparatus for guiding being applied immediately to the two fore-wheels, bearing a part of the weight, instead of two extra leading wheels bearing little or none. No person can conceive the absolute control this apparatus gives to the director of the carriage, unless he has had the same opportunities of observing it which I had in a ride with Mr. Gurney. Whilst the wheels obey the slightest motions of the hand, a trifling pressure of the foot keeps them inflexibly steady, however rough the ground. To the hind axle, which is very strong, and bent into two cranks of nine inches radius, at right angles to each other, is applied the propelling power by means of pistons from two horizontal cylinders. By this contrivance, and a peculiar mode of admitting the steam to the cylinders, Mr. Gurney has very ingeniously avoided that cumbersome appendage to steam-engines, the fly-wheel, and preserves uniformity of action by constantly having one cylinder on full pressure, whilst the other is on the reduced expansive. The dead points—that is, those in which a piston has no effect from being in the same right line with its crank,—are also cleared by the same means. For as the cranks are at right angles, when one piston is at a dead point, the other has a position of maximum effect, and is then urged by full steam power; but no sooner has the former passed the dead point, than an expansion valve opens on it with full steam, and closes on the latter. Firmly fixed to the extremities of the axle, and at right angles to it, are the two 'carriers'—(two strong irons extending each way to the felloes of the wheels.) These irons may be bolted to the felloes of the wheels or not, or to the felloes of one wheel only. Thus the power applied to the axle is carried at once to the parts of the wheels of least stress—the circumferences. By this artifice the wheels are required to be of no greater strength and weight than ordinary carriage-wheels; and, like them, they turn freely and independently on the axle; but one or both may be secured as part and parcel of the axle, as circumstances require. The carriage is consequently propelled by the friction or hold which either or both hind-wheels, according as the power is applied to them jointly or separately, have on the ground. Beneath the hind part drop two irons, with flat feet, called 'shoe-drags.' A well-contrived apparatus, with a spindle passing up through a hollow cylinder, to which the guiding handle is affixed, enables the director to force one or both drags tight on the road, so as to retard the progress in a descent, or if he please, to raise the wheels off the ground. The propulsive power of the wheels being by this means destroyed, the carriage is arrested in a yard or two, though going at the rate of eighteen or twenty miles an hour. On the right hand of the director lies the handle of the throttle-valve, by which he has the power of increasing or diminishing the supply of steam ad libitum, and hence of retarding or accelerating the carriage's velocity. The whole carriage and machinery weigh about 16 cwt., and with the full complement of water and coke 20 or 22 cwt., of which, I am informed, about 16 cwt. lie on the hind-wheels."

      Mr. H. then enumerates the principle of the improvements:—"That troublesome appendage the fly-wheel, as I have observed, Mr. Gurney has rendered unnecessary. The danger to be apprehended in going over rough pitching, from too rapid a generation of steam, he avoids by a curious application of springs; and should these be insufficient, one or two safety valves afford the ultimatum of security. He ensures an easy descent down the steepest declivity by his 'shoe-drags,' and the power of reversing the action of the engines. His hands direct, and his foot literally pinches obedience to the course over the roughest and most refractory ground. The dreadful consequences of boiler-bursting are annihilated by a judicious application of tubular boilers. Should, indeed, a tube burst, a hiss about equal to that of a hot nail plunged into water, contains the sum total of alarm, while a few strokes with a hammer will set all to rights again. Lastly, he has so contrived his 'carriers,' that they shall act without confining the wheels, by which means there is none of that sliding and consequent cutting up of the road, which, in sharp turnings, would result from inflexible constraint.

      "Hills and loose, slippery ground are well known to be the res adversæ of steam-carriages; on ordinary level roads they roll along with rapid facility. In every ascent there are two additional circumstances inimical to progressive motion. One is, that carriages press less on the ground of a hill than on that of a plain, thus giving the wheels a less forcible grasp or bite. But this may be easily remedied in the structure of a carriage, and is not of very material consequence in the steepest hills that we have. The other is more serious. When a carriage ascends a hill, the weight or gravity of the whole is decomposable into two—one perpendicular, and the other parallel to the road. The former constitutes the pressure on the road, the latter the additional work the engine has to perform. Universally this is the same part of the whole carriage and its load together, which the perpendicular ascent of the hill is of its length. With these principles, if we knew the bite of the wheels on the road, we could at once subject the powers of Mr. Gurney's carriage to calculation.

      "Now, from one of the experiments made in the barrack-yard, at Hounslow, I find we can approximate towards it. For instance, with one wheel only fixed to the 'carriers,' the carriage drew itself and load of water and coke (about 1 ton), with three men on it, and a wagon behind of 16 cwt. containing 27 soldiers. This, at the rate of 1-1/2 cwt. to a man, in round numbers is 4 tons. Estimating the force of traction of spring carriages at a twelfth of the total weight, it consequently gives a hold or bite on the road of 1-12 of 4 tons, or 6 2-3rds cwt. per wheel, or 13 1-3rd cwt. for the two wheels. This is likewise the propelling force of the carriage. Supposing, therefore, we were ascending a hill of 1 foot rise in 8, which I am assured exceeds in steepness any hill we have, we should be able to draw a load behind of 2 tons 2 cwt., or between 3 and 4 tons altogether....

      "On a good level road I think it not improbable it might draw, instead of 7 tons which our experiment would give, from 10 to 11, besides its own weight, or 100 ordinary men, exclusive of 2 or 3 tons for carriages; and up one of our steepest hills, 3 tons besides itself, or 25 men besides a ton for a carriage. This it would do at a rate of 8, 9, or 10 miles an hour. For it is a singular feature in this carriage, and which was remarked by many at the time, that it maintained very nearly the same speed with a wagon and 27 men, that it did with the carriage and only 5 or 6 persons. But there is a fact connected with this machine