those with sliding valves and steam ports, and those with conical valves and seats, of which the latter kind are the best. The former kind have for the most part hitherto consisted of a circular valve and face, with radial apertures, the valve resembling the out-stretched wings of a butterfly, and being made to revolve on its central pivot, by connecting-links between its outer edges or by a central spindle. One of these regulators is shown in fig. 325., which makes its mode of operation sufficiently apparent. This Fig. 325.

sive of the mitre; and Stephenson's 15 in. engine contains a pair of 4 in. diameter. The latter dimension is preferable, as large safety-valves are much less liable to adhere to their seats than small ones. Safety-valves require to be tested occasionally; and the best method consists in attaching the valve joint-pin to one end of an ordinary pair of scales, when the overbalancing weight at the reverse end will indicate the real pressure upon the valve, which exceeds the nominal pressure by the weight and friction of the lever, with its joints and spring-balance, and the adhesion of the valve to its seat. To bring this adhesion to a minimum, it is a good plan to make the lip of the valve-seat somewhat flatter than a mitre, that is, at a less angle than 45° with the horizon: 30° answers very well.

The safety-valve is pressed down by means of a lever, as shown at page 198; and a screw at its extremity is attached to a spiral spring balance. To find the pressure per square inch, we have only to multiply the weight indicated on the scale, by the ratio of the two arms of the lever, and divide the product by the number of square inches in the area of the valve; but to save the trouble of calculation, the ratio of the arms of the lever is made so as to be expressed by the number which represents the area of the valve, so that the weight marked on the balance is the pressure per square inch upon the valve. Some allowance must be made for the weight of the valve itself, and part of that of the lever. It is expedient to put a stop upon the screw by which the lever is screwed down or the tension of the spring increased, so as to prevent the pressure from exceeding a safe amount. Lock-up valves, which were intended as a precaution against the recklessness or neglect of the engineer, have fallen into disfavour, as from such valves being inaccessible and seldom being required to act, they became fixed in their Fig. 326.

species of regulator is easily worked, but is not very accessible, and as the faces are merely projecting rims round the holes, the steam will leak through, and the engine may go on unless the regulator be critically closed. In some of Stephenson's engines with variable expansion gear, the regulator consists of a slide valve covering a port on the top of the valve chests. A rod passes from this valve through the smoke-box below the boiler, and by means of a lever parallel to the starting lever, is brought up to the engineer's reach. Cocks were at first used as regulators, but were given up, as they were found liable to stick fast. A gridiron slide valve has been used by Stephenson, which consists of a perforated square plate moving upon a face with an equal number of holes. This plan of a valve with a small movement gives a large area of opening. In Bury's engines a sort of conical plug is used, which is withdrawn by turning the handle in front of the fire-box; a spiral groove of very large pitch is made in the valve spindle, in which fits a pin fixed to the boiler, and by turning the spindle an end motion is given to it which either shuts or opens the steampassage according to the direction in which it is turned. The best regulator would probably be a valve of the equilibrium description, such as is used in the Cornish engines.

Safety Valves and Fusible Plugs. The safety-valves, as we have observed, are placed upon the dome, in Bury's and Stephenson's engines; but it has been found much better to place them on the cylindrical part of the boiler, as is the arrangement in the engines constructed by Mr. Dewrance for the Liverpool and Manchester Railway, because when an engine commences to prime, the water projected from the blast-pipe generally causes an unusual generation of steam, which escapes at the safetyvalve, and in its passage of course accumulates and lifts the surface-water and foam at whatever point of the boiler the safety-valves are situated; thus the farther they are placed from the steam-dome the better, as they will then diminish the evil of priming, which, if placed upon the steamdome, they would only aggravate. Indeed, if the safety-valves are properly situated, an engineman has the great advantage of being able to check or stop the priming of the boiler on the instant, by causing his safety-valves to blow off strongly. It is requisite to place the safetyvalves upon a tubular pillar, of such altitude as to prevent the escaping cloud of steam from obscuring the look-out of the engineman. Bury's 14 in. engine contains a pair of safety-valves of 24 in. diameter, exclu

SAFETY VALVE.

seats; but it is an easy thing to make a valve which can be raised, but cannot be forced down by the engineer, and such valves are in general use in steam vessels. In the engines of Cavé, Hick, and Jackson, one of the valves is permanently loaded a little above the usual pressure, and enclosed in a chest; it is usually made with bent, flat, steel springs, pressing against one another, and guided by standards screwed to the valve-seat. One of these valves is shown by fig. 326.

A plug of lead is usually fixed in the furnace crown, which melts if the boiler becomes short of water, and gives notice of the danger. In some engines a cock is attached to the top of the steam-dome, against which a small disc of fusible metal is retained by a ring of brass bolted to the cock, and which is intended as an antidote to explosions. When the cock is opened, the steam has access to the under side of the fusible plate, which when melted is forced through the small hole in the retaining plate; and the engineer being thus warned of the undue pressure, can shut the cock and take measures to reduce the pressure. This, however, is altogether a futile expedient, for the steam would be too much cooled in passing through this cock and small pipe to melt the metal and even if that defect were remedied, the objections still remain which we stated in page 83., as applying to all fusible plugs, and the danger is increased by leading the engineer to trust to a measure of safety that is inoperative in the hour of danger. Steam gauges have not been applied hitherto to locomotives, on account of the inconvenient height of the column of mercury requisite to balance the steam. But it would be an easy thing to make a steam gauge of moderate dimensions, by making the tube, whether straight or syphon, of glass closed at the top, so that the mercury in its ascent would have to compress the air above it; and the graduations would be equal, or nearly so, if the tube were made taper.

Cylinders and Valves.-The cylinders are made of cast iron, about threequarters of an inch thick, and should be of hard metal, so as to have but little tendency to wear oval from the weight and friction of the piston. The ends of the cylinder are made about one inch thick, and both ends are very generally made removable. At each end of the cylinder there is generally about half an inch of clearance. The valve is invariably of the three-ported description represented in page 199.: it is made of brass, and is

not pressed upon by the valve casing, as it is necessary in the absence of cylinder escape valves that the steam valve should be capable of leaving the face to enable the steam or air shut within the cylinder to escape when the train is carried on by its momentum, and also to afford an escape for the water carried over by the steam when priming takes place. The operation of priming, upon the cylinders and valves is very injurious, as the grit and sediment then carried over with the steam wears the pistons, cylinders, and valve faces very rapidly; so that if the water be sandy and the engine addicted to priming, the pistons and valves may be worn out and the cylinders require re-boring in the course of a few months.

The valve casing is sometimes cast on the cylinder: the face of the cylinder, on which the valve works is raised a little, so that any foreign matters deposited upon it may be pushed off to the less elevated parts by the valve. The area of the steam ports is in some cases one-ninth, and in others one-twelfth or one-thirteenth of the area of the cylinder; and the eduction one-sixth to one-eighth of the area of the cylinder,—proportions which allow at mean speeds of twenty-five to thirty miles per hour, a pressure little different from that of the steam in the steam pipes: for higher speeds the ports should be larger in proportion. The valve casing is covered with a door, which can be removed to inspect the valves or the cylinder face. Some valve casings have covers upon their front end as well as their top, which admits of the valve and valve bridle being more readily removed.

A cock is placed at each end of the cylinder to allow the water to be discharged which accumulates there from priming and condensation. The four cocks of the two cylinders are connected, so that by working a handle the whole are opened or shut at the same time. In Stephenson's engines with variable expansion, there is but one cock, which is on the bottom of the valve chest.

The valve lever is usually longer than the eccentric lever, to increase the travel of the valve. The pins of the eccentric lever wear quickly. Stephenson puts a ferule of brass on these pins, which being loose and acting as a roller, facilitates the throwing in and out of gear, and when worn can easily be replaced; so that there need be no material derangement of the motion of the valve from play in this situation. The starting lever travels between two iron segments, and can be fixed at the dead point or for the forward or backward motions. This is done by a small catch or bell crank jointed to the bottom of the handle at the end of the lever, and coming up by the side of the handle, but pressed out from it by a spring. The smaller arm of this bell crank is jointed to a bolt which shoots into notches made in one of the segments between which the lever moves. By pressing the bell crank against the handle of the lever, the bolt is withdrawn, and the lever may be shifted to any other point; when the spring being released, the bolt flies into the nearest notch.

We have already discussed the subject of locomotive pistons at pages 194. and 195., and can here only add that the pistons which consist of a single ring and tongue piece, or of two single rings set one above the other so as to break joint, are preferable to those which consist of many pieces. In Stephenson's pistons the screws are liable to work slack and the springs to break. The piston-rods are made of steel, the diameter being from oneseventh to one-eighth of the diameter of the cylinder. They are tapered into the piston, and secured there with a cutter. The top of the piston-rod is secured by a cutter into a socket with jaws, through the holes of which a cross-head passes, which is embraced between the jaws by the small end of the connecting rod, while the ends of the cross-head move in guides. Between the piston-rod clutch and the guide blocks, the feed-pump rod joins the cross-head in some engines. The guides are formed of steel plates attached to the framing, between which work the guide blocks, fixed on the ends of the cross-head, and which have flanges bearing against the inner edges of the guides. Steel or brass guides are better than iron ones. Stephenson and Hawthorn attach their guides at one end to a cross-stay,- —at the other to lugs upon the cylinder cover; and they are made stronger in the middle than at the ends. Stout guide-rods of steel encircled by stuffing-boxes on the ends of the cross-head would probably be found superior to any other arrangement. The stuffing-boxes might contain conical bushes cut spirally, in addition to the packing; and a ring cut spirally might be sprung upon the rod and fixed in advance of the stuffing-box with lateral play, to wipe the rod before entering the stuffing-box, and prevent it from being scratched by the adhesion of dust.

Fig. 327.

Feed Apparatus. — The feed-pumps are made of brass, but the plungers are sometimes made of iron, and are generally attached to the piston-rod crosshead, though in Stephenson's engines they are worked by rods attached to eyes on the eccentric hoops. There is a ball valve between the pump and the tender, and two usually in the pipe leading from the pump to the boiler, besides a cock close to the boiler, by which the pump may be shut off from the boiler in the case of accident to the valves. The ball valves are guided by four branches which rise vertically and join at top in a hemispherical form, as shown in fig. 327. The shocks of the ball against this have in some cases broken it after a week's work, from the top of the cage

BALL VALVE.

having been made flat and the branches not having had their junction at top properly filletted. These valve guards are attached in different ways to the pipes; when one occurs at the junction of two pieces of pipe it has a flange, which, along with the flanges of the pipes and that of the valve seat, are held together by a union joint. It is sometimes formed with a thread at the under end, and screwed into the pipe. The balls are cast hollow, to lessen the shock as well as to save metal: in some cases, where the feed-pump plunger has been attached to the cross-head, the piston-rod has been bent by the strain; and that must in all cases occur if the communication between the pump and boiler be closed when the engine is started, and there be no escape valve for the water. Spindle valves have in some cases been used instead of ball valves, but they are more subject to derangement. Slide valves might easily be applied, and would probably be found preferable to either of the other expedients. It would be a material improvement, we conceive, if the feed pumps were to be set in the tender, and worked by means of a small engine, such as that contrived by Messrs. Penn for feeding their tubular boilers. The present action of the feed pumps of locomotives is precarious, as if the valves leak in the slightest degree, the steam or boiling water from the boiler will prevent the pump from drawing. It appears expedient, therefore, that the pumps should be far from the boiler, and should be set among the feed water, so that they will only have to force. If the pump were arranged in the manner we have now recommended, the boiler could still be fed regularly, though the locomotive was standing still; but it would be prudent to have one pump still wrought in the usual way by the engine, in case of derangement of the other, or in case the pump in the tender might freeze. The pipes connecting the tender with the pumps should allow access to the valves and free motion to the engine and tender. This end is attained by the use of ball and socket joints; and, to allow some end play, one piece of the pipe slides within another, like a telescope, and is kept tight by means of a stuffing-box. Any pipe joint between the engine and the tender must be made in this fashion. The feed-pipe of many engines enters the boiler near the bottom, and about the middle of its length. In Stephenson's the water is let in at the smoke-box end of the boiler, a little below the water level. By this means the heat is more effectually extracted from the escaping smoke; but the arrangement is of questionable applicability to engines of which the steamdome and steam-pipe are at the smoke-box end, as in that case the entering cold water would condense the steam.

To ascertain the height of water in the boiler. gauge cocks and glass Fig. 328.

GLASS WATER-GAUGE.

tubes are provided, as in the case of marine boilers. One of these glass gauges is represented in fig. 328. The upward turn of pipe proceeding

PP 2

from the top of the tube in the interior of the boiler, is calculated to prevent the water from boiling down through the tube, as it sometimes will do if the boiler be too full. The downward turn of the tube at the lower end does not appear calculated to be of service. A small screw plug is placed on each socket opposite the cock to enable a wire to be introduced, to clear the cock, should it become choked. There are generally three gauge cocks attached to the boiler, - besides the glass tube,-the lowest of which should always run water, and the highest should always blow steam. If the water oscillates inconveniently in the glass tube, the evil may be checked by partially closing the cocks.

Wheels. The driving wheels are made large to increase the speed: the bearing wheels also are easier on the road when large. In goods engines the driving wheels are smaller than in passenger engines, and are generally coupled together, as in Bury's engine, represented in one of our plates. Wheels are made in various ways; they are very frequently made with cast-iron naves, and with the spokes and rim of wrought iron. The spokes are forged out of flat bars with T formed heads; these are arranged radially in the founder's mould, whilst the cast-iron centre is poured around them; the ends of the T heads are then welded together to constitute the periphery of the wheel or inner tire, and little wedge-form pieces are inserted where there is any deficiency of iron. In some cases the arms are hollow though of wrought iron, the tire of wrought iron, and the nave of cast iron; and the spokes are turned where they are fitted into the nave, and are secured in their sockets by means of cutters. Hawthorn makes his wheels with castiron naves, and wrought iron rims and arms, but instead of welding the arms together, he makes palms on their outer end, which are attached by rivets to the rim. These rivets, however, unless very carefully formed, are apt to work loose; and we think it would be an improvement if the palms were to be slightly indented into the rim, in cases in which the palms do not meet one another at the ends. When the rim is turned, it is ready for the tire, which is now often made of steel. The materials for wheel tires are first swaged separately, and then welded together under the heavy hammer at the steel-works, after which they are bent to the circle, welded, and turned to certain gauges. The tire is now heated to redness in a circular furnace; during the time it is getting hot, the iron wheel, previously turned to the right diameter, is bolted down upon a face-plate or surface; the tire expands with the heat, and when at a cherry-red, it is dropped over the wheel, for which it was previously too small, and it is also hastily bolted down to the surface plate; the whole load is quickly immersed by a swing crane into a tank of water about five feet deep, and hauled up and down until nearly cold; the tires are not afterwards tempered. It is not indispensable that the whole tire should be of steel, but a dovetail groove turned out of the tire at the place where it bears most on the rail, and fitted with a band of steel, which may be put in in pieces, is sometimes adopted, though at the risk of being thrown off in working. The steel, after being introduced, is well hammered, which expands it sideways, until it fills the dovetail groove, but it has sometimes come out. The tire is attached to the rim by rivets with countersunk heads, and the wheel is then fixed on its axle. The tire is turned somewhat conical, to facilitate the passage of the engine round curves-the diameter of the outer wheel being virtually increased by the centrifugal force, and that of the inner wheel correspondingly diminished, whereby the curve is passed without the resistance which would otherwise arise from the inequality of the spaces passed over by wheels of the same diameter fixed upon the same axle. The rails, moreover, are not set quite upright, but are slightly inclined inwards, in consequence of which the wheels must either be conical or slightly dished, to bear fairly upon them. One benefit of inclining the rails in this way and coning the tires is that the flange of the wheel is less liable to bear against the side of the rail, and with the same view the flanges of all the wheels are made with large fillets in the corners. Wheels have been tried loose upon the axle, but they have less stability, and are not now much used. Much controversial ingenuity has been expended upon the question of the relative merits of the four and six-wheeled engines; one party maintaining that fourwheeled engines are most unsafe, and the other that six-wheeled engines are unmechanical, and are more likely to occasion accidents. It appears to us that the four-wheeled engines have been charged with faults which do not really attach to them when properly constructed, for it by no means follows that if the axle of a four-wheel engine breaks, or even altogether comes away, that the engine must fall down or run off the line, inasmuch as if properly coupled to the tender, it has the tender to sustain it. It is obvious enough that such a connection may be made between the tender and the engine, that either the hind or the fore axle of the engine may be taken away, and yet the engine will not fall down, but will be kept up by the tender; and the arguments against the four-wheeled engines are nothing more than arguments against the want of such a connection. It is no doubt the fact that locomotive engines are now becoming too heavy to be capable of being borne on four wheels at high speeds without injury to the rails; but we fear the objection of damage to the rail applies to the sixwheeled engine with quite as great force, as the engineer has the power in that case of putting nearly all the weight upon two wheels, and if the rails be wet or greasy, there is a great temptation to increase the bite by screwing down the driving wheels upon the rail. A greater strain is thus not only thrown upon the rail than can exist in the case of any equally heavy fourwheeled engine, but the engine is made very unsafe, as a pitching motion will be given to it at high speeds, from being poised upon the central

driving-wheels, and the engine will also be more subject to oscillation. Stephenson makes his driving-wheels without flanges, to facilitate the passage of the engine round curves, and if six-wheeled engines be made at all, it appears to be expedient to construct them in that manner. But instead of making enormously heavy six-wheeled engines, it appears to us to be preferable to use four-wheeled engines of moderate weight, and to apply a sufficient number of them to a train to enable it to reach the required velocity. To this there is no doubt the objection, that the expense of the propelling power is greater by this arrangement, as a small engine requires a driver and stoker for itself as well as a large engine. But by making the tender double, with one engine before and another engine behind it, a single driver and a single stoker would suffice for two engines. The starting handles of both engines might be brought to the middle of the tender, so that the engines might be stopped or started simultaneously, and be made to operate in this respect like a single engine. This arrangement appears to us greatly preferable to that of making heavy six-wheeled engines, as the rail will be preserved from the injurious effect of excessive weight, and there will be less loss of power from contracting the blast-pipe when the fire and flue surface is increased by the addition of another engine. In all locomotives, there is a very material loss of power from the contraction of blast-pipe necessary to maintain the blast; at high speeds one half of the power of the engine is lost by the inadequate area of the steam passages of which the greatest loss is that arising from the contraction of the blast-pipe. Tenders are now made larger than heretofore, to obviate the necessity of so many coke and water stations; they should have glass windows all round them, to shield the engine driver from the weather, and enable him during the worst winds and rains to keep a steady look-out. Tenders can be put on any number of wheels, so that inconvenience is not likely to arise from their size and weight.

Cranked Axle. The cranked axle is made of wrought iron, with two cranks forged upon it, towards the middle of its length, at a distance from each other answerable to the distance between the cylinders; bosses are made on the axle for the wheels to be keyed upon, and there are bearings for the support of the framing. The axle is usually forged in two pieces, which are then welded together. Sometimes the pieces for the cranks are put on separately, but those so made are liable to give way. In engines with outside cylinders the axles are straight, the crank pins being inserted in the naves of the wheels. The bearings to which the connecting-rods are attached are made with very large fillets in the corners, so as to strengthen the axle in that part, and to obviate side play in the connectingrod. In engines which have been in use for some time, however, there is generally a good deal of end play in the bearings of the axles themselves, and this slackness contributes to make the oscillation of the engine more violent. The bearings of locomotive axles should, it appears to us, be made spheroidal, after the fashion we have already recommended for the paddle-shafts of marine engines, whereby end play becomes impossible; and the momentum of the piston should be balanced by the application of a weight to the wheel. If these precautions be observed, locomotives will not oscillate, whether made with outside or inside cylinders, if only resting on four wheels.

Connecting Rods. It is very desirable that the length of the connectingrod should remain invariable, in spite of the wear of the brasses, for there is a danger of the piston striking against the cover of the cylinder, if it be shortened, as the clearance is left as small as possible, in order to economise steam. In some engines the strap encircling the crank pin is fixed immovably to the connecting-rod by dovetailed keys, as shown in fig. 330., and a bolt passes through the keys, rod, and strap, to prevent the dovetail keys from working out. The brass is tightened by a gib and cutter, which is kept from working loose by three pinching screws and a cross pin or cutter through the point. The effect of this arrangement is to lengthen the rod, but at the cross-head end of the rod the elongation is neutralized, by making the strap loose, so that in tightening the brass the rod is shortened by an amount equal to its elongation at the crank-pin end. The tightening here is also effected by a gib and cutter, which is kept from working loose by two pinching screws pressing on the side of the cutter. Both journals of the connecting rod are furnished with oil-cups, having a small tube in the centre, with siphon wicks. The connecting rod, represented in figs. 329, 330., is a thick flat bar, with its edges rounded. Stephenson's connecting rod is made at the crank end, after the same fashion as the connecting rods of the Black Eagle and Retribution steamers, represented in the plates of those vessels; but instead of a malleable iron cap, a strap of round iron passes over both brasses, and is attached to the Tend of the connecting rod by means of nuts upon the ends of the bent iron, which is made thickest in the middle, to resist the strain. This plan has the defect of shortening the connecting rod when the brasses are screwed up, and the brasses require to be very strong and heavy. Hawthorn's connecting rod has a strap at each end, tightened by a gib and cutter; but, to obviate the tendency to shorten the rod, the piston-rod end is furnished with a cutter for tightening the brass outwards. The point of the cutter is screwed, and goes through a lug attached to the gib, and is tightened by a nut. It would be preferable to attach the lug to the cutter and the screw to the gib, as the projection of the screw, when the cutter is far in, would not then be so great. In the engines on the Rouen Railway the piston-rod end of the connecting rod has neither strap nor brass, but simply embraces the crosshead, while the crank end is hollowed out to admit brasses, which are

tightened by a gib and cutt r. The length of the connecting rod varies from four times the length of the crank to seven times. The long connecting rod has the advantage of diminishing the friction upon the slides. Fig. 329.

Fig. 330,

on both sides, so that the length of the eccentric rod may be adjusted; but it is better for the lugs of the hoops to abut against the necks of the screws,

Fig. 331.

Fig. 332.

CONNECTING-ROD ENDS AND STRAPS.

Eccentrics and Eccentric Rod. The eccentrics are made of cast-iron; and when set on the axle between the cranks, they are put on in two pieces held together by bolts, as shown in figs. 331, 332., but in straight axle engines they are cast in a piece and are secured on the shaft by means of a key. The eccentric, when in two pieces, is retained at its proper angle on the shaft by a pinching screw, which is provided with a jam nut to prevent it from working loose. A piece is left out of the eccentric in casting it, to allow of the screw being inserted, and the void is afterwards filled by inserting a dovetailed piece of metal. Stephenson and Hawthorn leave holes in their eccentrics on each side of the central arm, and they apply pinching screws in each of these holes. The screws sometimes slacken and allow the eccentric to shift, unless they are provided with jam-nuts. In the Rouen engines with straight axles, the four eccentrics are cast in one piece.

Eccentric straps are best made of wrought iron, as inconvenience arises from the frequent breakage of brass ones. When made of malleable iron, one-half of the strap is forged with the rod, the other half being secured to it by bolts, nuts, and jam-nuts. Pieces of brass are in some cases pinned within the malleable iron hoop, but it appears to be preferable to put brasses within the strap to encircle the eccentric, as in the case of any other bearing. When brass straps are used, the lugs have generally nuts

ECCENTRIC PULLEY.

and if any adjustment is necessary from the wear of the straps, washers can be interposed. In some engines the adjustment is effected by screwing the valve-rod, and the cross-head through which it passes has a nut on either side of it by which its position upon the valve-rod is determined. The forks of the eccentric rod are steel. The length of the eccentric rod is the distance between the centre of the crank axle and the centre of the valve shaft.

Valve motions.—In locomotives the eccentrics are now always fixed upon the axle, and two are used, one for the forward, the other for the backward motion: the loose pulleys have been given up on account of their liability to get out of order from the shocks to which they were subjected by sudden change of direction when worked at a quick speed. The arrangement whereby the motion of the eccentric is transmitted to the valve, is either direct or indirect. In cases of indirect attachment the motion is given through the intervention of levers, and there is some variety in the arrangements by which the reversing is accomplished. Alcard and Buddicome use a pair of eccentrics at the end of the axle, which is straight; the reversing shaft is placed below the level of the piston-rod, and to a lever keyed upon it are attached links of unequal length, connected at their upper extremities with the ends of the eccentric rods, one of which is above and one below the studs on the lever of the valve shaft, so that the upper eccentric rod, being in gear, gives the forward motion, and the lower gives the backward motion. In other engines, forks are situated above and below the stud of the eccentric levers; the forward eccentric rod is lifted up out of gear by a link depending from the lever on the reversing shaft, and by the same movement the backing eccentric is lifted into gear by a longer link connecting it to a lever, not upon the reversing shaft, but upon a shaft below it. Stephenson and Hawthorn have both used a similar arrangement, but admitting of the eccentric rods being both under the studs of the lever on the valve shaft, so that there is no danger, in the event of a disengaged rod falling down, or of any part of the gearing being bent or twisted by both rods being in gear at the same time. The motion of the eccentrics is now frequently transmitted directly to the valves. In Pauwel's arrangement of valve gearing, the valve works on the side of the cylinder, and the valve rod is prolonged in the form of a deep flat blade of a lozenge section, on each side of which a stud is fixed,—one being intended for the notch of the forward eccentric rod, and the other for that of the reversing eccentric. Above them is fixed the reversing shaft, from a lever on which depend two links of unequal length, which are jointed to the ends of the eccentric rods. By working this lever up or down, the eccentric-rods will be alternately engaged and disengaged, and will communicate their respective motions to the valve; or if the lever be kept in its mid position, both eccentrics will be out of gear, and the valve of course will remain stationary. Pauwel's engines are difficult to work, and are subject to shocks from going suddenly into gear: this arises from the whole weight of levers and rods being on the front of the reversing shaft, but the evil might be remedied by attaching a counterbalance to the shaft. Valves situated upon the sides of the cylinders, as in the engine of Stephenson, represented among our plates, are in many cases more easily connected with the eccentric, but they require springs to keep them up to the face, so that it appears preferable to make the faces of the two cylinders inclined to one another rather than upright, if valves on the sides of the cylinders are preferred. Stephenson's link motion is the most elegant, and one of the most eligible modes of connecting the valve with the eccentric yet introduced. The nature of this arrangement will be made plain by a

reference to fig. 333., where e is the valve-rod which is attached by a pin to an open curved link connected at the one end with the driving eccenFig. 333.

of the link motion might, it appears to us, be beneficially dispensed with by placing the shaft y in the plane of the valve-rod, and attaching a pin to

Fig. 335.

STEPHENSON'S LINK MOTION.

tric-rod d, and at the other with the backing eccentric rod ď, The link with the eccentric rods is capable of being moved up or down by the rod f and bell crank f", situated on the shaft g, while the valve-rod remains in the same horizontal plane. It is very clear that each end of the link must acquire the motion of the eccentric rod in connection with it, whatever course the central part of the link may pursue, and the valve-rod will partake most of the motion of the eccentric rod that is nearets to it. When the link is lowered down, the valve-rod will acquire the motion of the upper eccentric rod, which is that proper for going a-head; when raised up, the valve-rod will acquire the motion of the reversing eccentric, while in the central position the valve-rod will have no motion, or almost none. The link motion therefore obviates the necessity of throwing the eccentric rod out of gear; it also enables the engine to be worked to a certain extent expansively, though as a contrivance for working expansively, we cannot hold it as deserving of much commendation. The dead point of the link motion is where the line of the valve-rod bisects the angle formed by the eccentric rods. The maximum forward motion is when the rods are as figured, and the maximum backward motion when the rods d and d' are in the positions " and h'. The best forms of the link motions have side studs, to which the eccentric rods are connected, and these are placed so that at the greatest throw, whether backward or forward, the valve-rod and eccentric rod are in the same straight line, and the valve receives the full throw Fig. 334.

O

MELLING'S VALVE MOTION.

of the eccentric. A counter-weight is also attached to the shaft to balance the weight of the link and rods. The second eccentric and eccentric rod

HAWTHORN'S VALVE MOTION.

the centre of the link, which would work in the eye of the horizontal arm of the lever f. This lever would in such case require to be made much stronger than at present, as it would have to withstand the thrust of the eccentric, and the link would then virtually be a double-ended lever with a moveable centre. Where more convenient, the pin in the centre of the link might be moved in vertical or curved guides, instead of being attached to the lever f. The act of raising the link, and with it the eccentric rod, would in effect alter the position of the eccentric on the shaft, and if the eccentric rod were properly proportioned in length, would make the lead right on the reversing side.

The movement for working the valves is in some cases derived from the connecting-rod, as in the arrangement known as Melling's motion, represented in fig. 334., where the valve rod is attached by suitable connections to a pin in the connecting-rod.

A somewhat similar mode of working the valve has been employed by Hawthorn, of Newcastle, which admits of expansive action, and which is represented in fig. 335. The pin in the connecting-rod works in a link, to which arms are attached at right angles. The extremity of the lower of these arms is connected by a link and lever to a shaft, which is worked by the reversing handle, while the upper arm is attached to a lever upon the valve-shaft. Upon this shaft there is a double-ended lever, with either end of which a rod, in communication with the valve, gears, according as a forward or reverse motion is wanted. This valve-link is connected by a link with the starting-shaft. The central slot in the link permits the free end movement of the pin on the connecting-rod, while the lateral move