month by month from the factory was an improvement on its predecessors, and the fourteen and twenty miles of the 'Rocket' were raised to sixty and seventy miles; and the Newcastle factory became the largest and most famous in the world." Other manufacturers entered the field of competition, and the vast amount of ingenuity and practical experience brought

i

fig. 144.

to bear on the mechanism of the locomotive by such eminent firms as those of Hawthorn and Company; Sharp, Roberts, and Company; Bury, Curtis, and Kennedy; and last, though not by any means least, of Timothy Hackworth, soon resulted in bringing the locomotive engine to its present high state of perfection.

We now proceed to give illustrations of locomotive engines, showing the majority of the improved arrangements as now introduced. It is impossible to notice the whole details so fully as we should wish in a short treatise like the present; we hope, however, that the illustrations we give will enable the reader pretty closely to understand the arrangements and operation of this beautiful machine.

For the purposes of description, we shall divide the locomotive into two parts: the fire-box, smoke-box, and boiler; and the moving parts of the engine which give motion to the whole.

The fire-box, as may be seen by inspection of the longitudinal sections of engines hereafter given, at cccc, fig. 147, is enclosed on all sides except the bottom; at this part the fire-bars are placed on which the fuel rests; and at the side next the funnel or chimney, this side is pierced with holes, into which are passed the smoke-tubes dd. To prevent the dispersion of the red-hot ashes from the fire, a plate-iron tray or receptacle is placed beneath the fire-bars. Fire-boxes are of two kinds, square and round, as in figs. 153, 155. The round top is recommended by some, as being best calculated to withstand the pressure of the steam. In both methods of construction, however, it is imperatively essential to strengthen the parts by numerous stays or bolts. The fire-box door (see longitudinal sections) is double, to prevent loss of heat; and the outer and inner boxes, between which the water of the boiler is allowed to flow, are here joined. The fire-bars are placed loosely in a frame, so as easily to be lifted out when

required to be renewed. In some instances the fire-bar frame is suspended by catches; when these are withdrawn, the fire-bars and fuel above them are precipitated into the ash-tray.

The smoke-tubes are generally made of brass, but malleable iron ones are now becoming largely used. The number of tubes in each engine varies from 96 or thereabouts to 134. Great care is necessary to fit the tubes into the fire-box end, and also that of the smoke-box. They must be fitted water-tight. The diameter of the tubes is generally about one inch and a half. The communication between the fire-box at one end and the smokebox ss, figs. 153, 155, is kept up entirely by means of the smoke-tubes dd. This is formed of plates of iron of the same shape externally as the fire-box. Access is had to the interior of the smoke-box by a door at the front of the engine; this is made in various ways: in some instances it is hinged at bottom and opens downwards; in others it is in two leaves, like ordinary folding-doors. The smoke-tubes pass through the side of the smoke-box nearest the fire-box. The cylinders are in many instances placed inside the smoke-box; by this arrangement, the loss by radiation and condensation of steam is avoided. The steam, after working the cylinder, is ejected up the chimney through the blast-pipe h fig. 153, and ee fig. 155. The diameter of chimney is about 13 inches, and the height is limited to about 7 feet above the boiler, to allow it to pass under the railway bridges.

The fire is moderated by a damper placed in the chimney; this is generally made of the "throttle-valve" species, being a plain disc, aa fig. 145, turning on an axis d somewhat out of the centre; it is provided with

an aperture through which the end of the blast-pipe passes, when the damper is wholly shut, the end of the blast-pipe projecting above it; the damper is moved by the lever e, actuated on by a long lever under the control of the engine-man. This lever is furnished with three slots, which take into a rest; according as the lever rests on either of the slots, so is the opening of the damper regulated. The upper orifice of the chimney is sometimes covered with a wire-netting; this is in order to arrest the sparks. This contrivance is, however, fast falling into disuse, and a perforated iron plate is placed below the blast in the smoke-box. In American locomotives, where wood is extensively used for firing, a "spark-arrester" is adopted; this gives a degree of size to the chimney unusual in locomotives in this country. This will be described hereafter.

The water is supplied to the boiler by means of a small force-pump,

placed under the boiler and near the fire-box; this pump is worked by a lever from one of the engine eccentrics; in some instances the pump is worked from the piston cross-head. The water is drawn from the tank in the tender through a pipe properly coupled, by a ball-and-socket joint, at the part where the engine is attached to the tender; and the water is delivered to the boiler in some instances at the smoke-box end, a little below the water-level; at others near the fire-box, and in others again near the centre part of the boiler.

There are various appliances connected with the boiler. The safetyvalve is generally placed above the fire-box, as in figs. 153-155, and is pressed down by a lever, the pressure being regulated by a spring balance. The nature of the arrangements of this kind of valve is explained at p. 45, fig. 66, Mechanics and Mechanism.

Lock-up safety-valves are falling into disuse, as, from not being easily

got at, they are apt to stick in the seat and become inoperative. In some engines a valve, as shown in fig. 146, is used. This is loaded a little above the usual pressure; this being obtained by the bent springs forcing down the valve into its seat.

The contrivance known as the steam-whistle is placed on the dome or top of the fire-box; this is shown at b, fig. 147. The peculiar noise elicited is caused by the steam rushing up the tube bb connected with the boiler; and the admission to which is regulated by a cock actuated upon by a handle or lever within reach of the engine-man. The steam passes through the apertures cc and out at dd, and strikes the thin edge ee of the circular cup f, producing the sound so well known now-a-days in almost every district of the kingdom.

The level of the water in the boiler is ascertained by gauge-cocks, which are placed at different heights to indicate different levels at which the water stands. In addition, a glass water-gauge is attached to the front casing; the arrangement of this apparatus is shown in fig. 148. The tubes cc are in communication with the interior of the boiler; a strong

glass tube bb connects the two tubes cc; the upper tube c communicates with the part of the boiler which should contain steam, the lower with that containing water. On opening the upper and lower handles a a, the water rises in the glass-tube to the same height as in the inside of the boiler. The oscillations of the water which would take place in the tube bb, from the rapid movement of the engine, is in some measure prevented by making the communication between the boiler and tube of a small size. A small cock, as f, is placed at the bottom tube, to clear the tube of its accumulated water. Entrance is obtained to the interior of the boiler by means of a man-hole door of similar construction to that described in another and preceding chapter.

The cylinders of locomotive engines are always of the three-ported species, as in the diagram, fig. 149. aa the piston; b the piston-rod; c the stuffing-box; d the exhaust-port, leading to the exhaust-pipe i; g the valve; h valve-rod; e port to upper side of piston; fport to under side; k cleansing and greasing-cock. Cocks are supplied to cylinders in some instances at top and bottom of cylinder: these are opened when required by levers within reach of the engine-man, to allow

the water collected in the cylinders from priming and condensation. The steam is passed from the boiler to the cylinders by a pipe, the entrance to which is at the upper part of a cylindrical vessel o N, fig. 153, or within the dome; above the firebox, as in fig. 155, the entrance to the pipe is placed thus far above the water to prevent priming as much as possible. The supply of steam to the cylinder is regulated by what is termed a regulator." Various contrivances for this purpose are adopted. Fig. 150 explains a form much introduced. Two circular discs work in contact, one of which is fixed, and

66

fig. 150.

the other is made to revolve by a lever connected with it, and actuated on by another lever or handle outside the casing. Apertures are made in both discs to correspond with each other in shape and position; when the apertures in both plates coincide, a free passage is given to the steam; but when the movable disc is turned round, so as to present the solid parts of its face opposite the apertures in the fixed disc, the entrance for the steam is lessened in proportion as the apertures in the fixed disc are closed. The discs are fixed on the entrance to the pipe which passes the steam to the cylinders.

The reciprocating motion of the piston-rod is changed into the circular one of the driving-wheel by means of a connecting-rod, as in fig. 151: a is the piston-rod; b the connectingrod, the brasses of which embrace the cranked axle of the drivingwheels nn, as explained in p. 87, fig. 169, Mechanics and Mechanism ; the cranks are placed at right angles to each other, so that the motion is continuous. The slidevalves of the cylinder for admitting the steam to both sides of the piston are worked by eccentrics, as explained in p. 82, Mechanics and Mechanism, the position of which is shown in fig. 151.

fig. 151.

n

2

n

In order to give the necessary facility for working the engine so as to make it move backwards or forwards as desired, various ingenious arrangements have been introduced: it will suffice for our purpose to describe one of these, and that the most generally adopted. It is known as the "link-motion," and owes its invention to Mr. Stephenson. The movements are effected by four eccentrics, two to give the backward, two the forward motion of the engine; two eccentrics to each cylinder. Let bc, fig. 152, be the two eccentric-rods, b the backing eccentric, and c the forward eccentric : these are connected to the curved link a a, the radius of which is equal to that of a circle described by each eccentric-rod revolving round the centre of its eccentric. The backward and forward eccentric-rods are attached to the extremities of the links. The valve-rod which works the slide-valve of the cylinder is provided with a piece of metal which slides between the grooves made