NON-CONDENSING ENGINES.- LEUPOLD'S ENGINE. TREVETHICK AND VIVIAN. EFFECTS OF RAILWAY TRANSPORT.- HISTORY OF THE LOCOMOTIVE ENGINE. BLENKINSOP. MESSRS. CHAPMAN. WALKING ENGINE. MR. STEPHENSON'S ENGINES AT KILLINGWORTH. LIVERPOOL

AND MANCHESTER RAILWAY.-EXPERIMENTAL TRIAL. THE ROCKET. 1 THE SANS PAREIL. THE NOVELTY. SUBSEQUENT IMPROVEMENTS IN THE LOCOMOTIVE ENGINE. LARDNER'S EXPERIMENTS IN 1832. ADOPTION OF BRASS TUBES. MR. BOOTH'S REPORT. - DETAILED DESCRIPTION OF THE MOST IMPROVED LOCOMOTIVE ENGINES. POWER OF LOCOMOTIVE ENGINES. - EVAPORATION OF BOILERS. LARDNER'S EXPERIMENTS IN 1838.-RESISTANCE TO RAILWAY TRAINS. RESTRICTIONS ON GRADIENTS. COMPENSATING EFFECT OF GRADIENTS. EXPERIMENT WITH THE HECLA. METHODS OF SURMOUNTING STEEP INCLINATIONS.

(180.) IN the various modifications of the steam engine which we have hitherto considered, the pressure introduced on one side of the piston derives its efficacy either wholly or partially from the vacuum produced by condensation on the other side. This always requires a condensing apparatus, and a constant and abundant supply of cold water. An engine of this kind must therefore necessarily have considerable dimensions and weight, and is inapplicable to uses in which a small and light machine only is admissible. If the condensing apparatus be dispensed with, the piston will always be resisted by a force equal to the atmospheric

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pressure, and the only part of the steam pressure which will be available as a moving power, is that part by which it exceeds the pressure of the atmosphere. Hence, in engines which do not work by condensation, steam of a much higher pressure than that of the atmosphere is indispensably necessary, and such engines are therefore called high-pressure engines.

We are not, however, to understand that every engine, in which steam is used of a pressure exceeding that of the atmosphere, is what is meant by an high-pressure engine; for in the ordinary engines in common use, constructed on Watt's principle, the safety-valve is loaded with from 3 to 5 lbs. on the square inch; and in Woolf's engines, the steam is produced under a pressure of 40 lbs. on the square inch. These would therefore be more properly called condensing engines than low-pressure engines; a term quite inapplicable to those of Woolf. In fact, by high-pressure engines is meant engines in which no vacuum is produced, and, therefore, in which the piston works against a pressure equal to that of the atmosphere.

In these engines the whole of the condensing apparatus, viz. the cold-water cistern, condenser, air-pump, cold-water pump, &c., are dispensed with, and nothing is retained except the boiler, cylinder, piston, and valves. Consequently, such an engine is small, light, and cheap. It is portable also, and may be moved, if necessary, along with its load, and is therefore well adapted to locomotive purposes.

(181.) High-pressure engines were one of the earliest forms of the steam engine. The contrivance, which is obscurely described in the article already quoted (7.), from the Century of Inventions, is a high-pressure engine; for the power there alluded to is the elastic force of steam working against the atmospheric pressure. Newcomen, in 1705, applied the working-beam, cylinder, and piston to the atmospheric engine; and Leupold, about 1720, combined the working-beam and cylinder with the high-pressure principle, and produced the earliest high-pressure engine worked by a cylinder and piston. The following is a description of Leupold's engine: —

A (fig. 82.) is the boiler, with the furnace beneath it; cc are two cylinders with solid pistons P P', connected with the

working-beams B B', to which are attached the pump-rods R R', of two forcing pumps F F', which communicate with a great force-pipe s; G is a four-way cock (66.) already described. In the position in which it stands in the figure, the steam issues from below the piston P into the atmosphere, and the piston is descending by its own weight; steam from the boiler is at the same time pressing up the piston P', with a force equal to the difference between the pressure of the steam and that of the atmosphere. Thus the piston R of the forcing-pump is being drawn up, and the piston p' is forcing the piston R' down, and thereby driving water into the force

pipe s. On the arrival of the piston P at the bottom of the cylinder c, and P' at the top of the cylinder c', the position of the cock is changed as represented in fig. 83. The steam, which has just pressed up the piston P', is allowed to escape into the atmosphere, while the steam, passing from the boiler below the piston P, presses it up, and thus P ascends by the steam pressure, and P' descends by its own weight. By these means the piston R is forced down, driving before it the water in the pump-cylinder into the force-pipe s, and the piston R' is drawn up to allow the other pump-cylinder to be re-filled; and so the process is continued.

A valve is placed in the bottom of the force-pipes, to prevent the water which has been driven into it from returning. This valve opens upwards; and, consequently, the weight of the water pressing upon it only keeps it more effectually closed. On each descent of the piston, the pressure transmitted to the valve acting upwards being greater than the weight of the water resting upon it, forces it open, and an increased quantity of water is introduced.

(182.) From the date of the improvement of Watt until the commencement of the present century, non-condensing engines were altogether neglected in these countries. In the year 1802, Messrs. Trevethick and Vivian constructed the first non-condensing engine of this kind which was ever brought into extensive practical use in this kingdom. A section of this machine, made by a vertical plane, is represented in fig. 84.

The boiler A B is a cylinder with flat circular ends. The fire-place is constructed in the following manner: - A tube enters the cylindrical boiler at one end; and, proceeding onwards near the other extremity, is turned and recurved, so as to be carried back parallel to the direction in which it entered. It is thus conducted out of the boiler, at another part of the same end at which it entered. One of the ends of this tube communicates with the chimney E, which is carried upwards as represented in the figure. The other mouth is furnished

with a door; and in it is placed the grate, which is formed of horizontal bars, dividing the tube into two parts; the upper

part forming the fire-place, and the lower the ash-pit. The fuel is maintained in a state of combustion, on the bars, in that part of the tube represented at c D; and the flame is carried by the draught of the chimney round the curved flue, and issues at E into the chimney. The flame is thus conducted through the water, so as to expose the latter to as much heat as possible.

A section of the cylinder is represented at F, immersed in the boiler, except a few inches of the upper end, where the four-way cock G is placed for regulating the admission of the steam. A tube is represented at н, which leads from this four-way cock into the chimney; so that the waste steam, after working the piston, is carried off through this tube, and passes into the chimney. The upper end of the piston-rod is furnished with a cross-bar, which is placed in a direction at right angles to the length of the boiler, and also to the