The external view of " The Novelty," given in the front page of our present Number, will at once satisfy our readers, that it has not been unmeritedly extolled by all who have seen it for its singular lightness, elegance, and compactness. All locomotive engines have been hitherto so constructed, as to require a separate tender to carry the water and fuel necessary for these operations (we canoot es yet except Mr. Gurney's); but "The Novelty" includes within itself every necessary accommodation for these purposes, and is, nevertheless, much lighter than any engine on the old plan. "The Rocket" of Mr. Stephenson, which is one requiring a separate tender, weighs 4 tons 3 cwt., while " The Novelty" weighs only 2 tons 15 cwt.; making a difference in favour of the latter of 1 ton 8 cwt.

There have been people so absurd as to say there can be nothing gained by so great a reduction in the weight of an engine as this; that it is "something like substituting a Scotch galloway tor a good team-horse, because the lighter the engines are the weaker." We do not dispute that there is a limit beyond which there is nothing to be gained by lessening the weight of an engine; but we think the performances of "The Novelty" furnish abundant proof that this engine at least has not approximated to that limit. The plan besides which the judges adopted of requiring that each engine should draw three times its own weight, was calculated to prevent most effectually any delusion on this head.

The advantage gained by such reduction in weight as "The Novelty" exhibits, is one of no small moment. On the Stockton and Darlington Railway, the enormous weight of the engines employed (12 tons, we believe) has been a subject of great complaint. "The speed of the engines," says a writer on rail-roads,* "has been intreased on the Darlington road, by substituting wheels of 4 feet diameter instead of 3; but these working upon the plain bars cannot be case-hardened, for fear they should turn round when they have a hard pull - consequently, they are cast of soft iron, which from the immense weight of the engines, wears into grooves, the width of the rails, and with the heavy drag, bites upon the rails, and twists them sideways, which keeps men incessantly upon the line setting them straight: the proof ie obvious, because where the engines do not work, but the waggons only, the rails keep their position, and want no repairs."

[* A Treatrise on the Utility of a Railway from Leeds to Selby and Hull, &c. By Thomas Hill]

The Directors of the Liverpool and Manchester Railway having the experience of these results before them, very wisely made superior lightness, one of the foremost qualifications which should enable an engine to be ranked as " the most improved" of those competing for the prize. They announced that "the weight of the machine, with its complement of water in the boiler, must at most not exceed 6 tons, and that a machine of less weight will be preferred if it drew after it a proportionate weight."

The means by which the inventors of "The Novelty" have been able to combine so much lightness with great power, will be unfolded as we proceed with our description.

The boiler is made to contain about 45 gallons of water; the diameter of each of the cylinders is 6 inches, and the length of the stroke 12.

The wheels are of the excellent description patented by Messrs. Jones and Co.,* and the choice of them by Messrs. Braithwaite and Ericsson is as strong a tribute as could well have been paid to their merits. From the peculiar manner of their construction they act with the least possible interference from tile weight of the engine, and being perfectly cylindrical, bear equally with their whole breadth on the rails. 'The lightness for which these wheels are famed, is not in this instance so remarkable; "The Novelty" being itself in its main parts so light, as to throw other things in comparison with it into the shade. Of the total weight of 2 tons 15 cwt., we believe 18 cwt. falls to the share of thc wheels.

[*For a particular description of Messrs. Joner and Co.'s wheels, the reader may consult our 245th number.]

[To be continued in our next, when we shall complete our account of "The Novelty," describe one or more of the other engines, and add some general remarks.]

Mechanics Magazine,
MUSEUM, REGISTER, JOURNAL, AND GAZETTE

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No. 324.] SATURDAY, OCTOBER 24TH, 1829 [Price 3d.

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1. THE NOVELTY—(CONCLUDED)

S is the furnace, which is supplied with fuel from the hopper L (see the engraving in our last No.), through the vertical tube in the centre of the steam-chamber A; the heated air from this furnace passes off through a flue, which is made to wind twice or thrice up and down the cylinder EE, and gradually diminishes in diameter till its termination in the escape- pipe Q (called N by mistake in the description in our last Number). The parts shaded in the sketch are those occupied by the water, which, it will be observed, surrounds the boiler as well as the flue.

The extent of surface exposed to the action of the heat by this arrangement is a great deal less than in other engines; and were the heat left to circulate as in other engines, through the agency of what is commonly called atmospheric draught merely, there would probably be nothing gained in respect of the quantity of steam generated. But instead of depending on the atmospheric draught, Messrs. Braithwaite and Ericsson make use of the bellows - sort of apparatus (CK), represented in the front elevation of the engine given in our last Number, to force the heated air through the flue; and by thus supplying a greater quantity of caloric in a given time they obtain an effect precisely analogous to what would result from doubling or quadrupling the size of the furnace, and the extent of the flue. Nor is this all: the quantity of atmospheric air which is introduced under and through the fire by the pipe K, has not only the effect of forcing the heated air onwards through the flue, but is itself a source of heat — equivalent to the employment of so much additional coke. It is in these two circumstances — the acceleration of the draught and the supply of fuel (if we may so speak), derived from the atmosphere — that the great merit of "The Novelty" — the secret of its vast superiority — consists. It makes up by the quickness of its operations for the diminutiveness of its dimensions; by what it borrows from tho air around it for the small supply of coke which it carries.

Neither does the rapidity with which the current of hot air passes through the flue constitute any exception to the efficiency of the process: for such is the aptitude of small circular pipes, like this, to abstract heat from any fluid conveyed through them, and to part with it again to surrounding substances, that little, if any, caloric is suffered to pass unappropriated.

The flue is made to diminish gradually, because the heated air cools in its passage through it, and gradually requires less and less vent. It has also a downward inclination given to it, as represented in the sketch — such, that if a marble ball were dropped in at the furnace end, it would roll rapidly through all the convolutions of the pipe to the other extremity; and the object of so constructing it is, that any dust which may arise from the furnace may have always a descending passage to escape by.

In the specification of the patent which Messrs. Braithwaite and Ericssson have taken out for this mode of generating steam, mention is made of two air-forcing pipes: one by which atmospheric air is forced on to the top of the fuel in the furnace; aud another through which air is forced under the bottom of the fuel. A double supply of air, however, is only considered necessary where coal is the fuel employed, in order to ensure its combustion more effectually; and where fuel of the purity of coke is made use of, as in "The Novelty," the upper pipe is dispensed with.

There are, of course, cocks to regulate the transmission of air through the pipe K; also safety-valves to the boiler and steam-chamber; but these, as well as the feed-pump for supplying the water from the tank, have been left out in our sketches, as being unnecessary to illustrate the principle of the engine.

It is now fitting we should explain more particularly, than has yet been done, the cause of those accidents by which some doubt has been for the moment thrown on the soundness of that principle. The engine, it appears, had been got up in a hurry — having been begun aud finished with in the short space of the six weeks immediately proceeding the competition - and had never been subjected to any sort of proof. It was not to be expected therefore that it should be found perfect at all points. The par which was first observed to perform its office insufficiently, was the pipe of the feed-pump; and the consequence was, that the water, which it is the business of this pump to keep always at the height marked in our sectional sketch, sunk below the level of the flue of the furnace; which flue thus being left exposed to a dry temperature of high elevation gave way near to the flange a. In order to get at this damaged part of the flue, it was necessary to lift off the steam- chamber A, and for this purpose to undo the joints b, c, d, and e. To renovate the flue was an easy matter, but not so to restore the joints all at once to the state in which they previously were. The cement with which they were resecured would have required a week at least to harden properly; but it was as yet scarce twelve hours' old when the engine started to perform the last task assigned to it. As might have been naturally expected, the joints yielded to the high temperature (300º) to which they were exposed; the steam began to escape at all points; and the efficiency of the engine was for the time and occasion, at an end.

The impartial reader will see nothing in any of these mischances tending in the least to discredit the principle on which "The novelty" is constructed. It was not the peculiarity of that principle which caused either the defective feed-pipe tp go wrong, or the unduly-exposed flue to crack, or the green joints to give way. The principle worked admirably, as long as every part of the machinery stood firm and had fair play, nor can a doubt be reasonably entertained, that had the engine been previously proved (as cannon and muskets are proved), and been kept in good working order, it would upon the trial for a continuance have fully realized the expectations which its previous performance had excited. The grand point on which its superiority depends had already been fully established; namely, that it can generate a greater quantity of steam in a given time than was ever before produced bv an apparatus of equal capacity. No further trial was wanted to show that what it could do for one hour in this respect, it would do for any number of hours. There might be errors committed in estimating the quantity of water and fuel requisite for a long journey, but there could be none in assuming that the power of the air forcing pump to augment the heat and accelerate the circulation of the heated air, must of necessity remain the same, whether the journey is short or long. Every thing needful for the manifestation of the master principle of the engine had been done; and all that was left unaccomplished, was but such a practical display as might convince those who, unable to appreciate principles, look only to results.*

[* In mentioning in our last Number the preference which Messrs. Brsithwaite and Ericsson have given to the excellent wheels of Messrs. Jones and Co., we mentioned that they weighed I8 cwt. We have been since assured by the patentees, that their actual weight was only 13 cwt.]