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the top of the boiler to the tender effects a considerable gain of lateral leverage. The boiler is surmounted by a dome over the firebox, and from it the supply of steam to the cylinder is taken, and the exhaust-pipe passes through the water-tank on its way to the chimney, thereby heating the feed-water. The crank shaft is coupled to the axis of the windlass by means of universal joints, as in driving a threshing machine by horse gear. The two winding drums are supported by standards rising from the framing of a four-wheeled carriage. They have a to-and-fro motion on a common axis independently of each other, for coiling and uncoiling the rope on to or off from the barrels, the distance at every revolution being equal to the diameter of the rope. By this mode of reeling and unreeling the rope on to and off from horizontal drums the line of draught is maintained in its true position, and the wear and tear upon the rope otherwise experienced when the drums are stationary and when the reeling apparatus works to and fro on the common plan, greatly reduced. The ropes are guided off from and on to the drums by two guide-pullies, the larger one being for changing the direction of the rope as the movable anchors are shifted along the headland. The lever for reversing the motion of the drums is shown in the left hand of the engine-driver, and the other levers are conveniently situated at hand, so that he has entire control both of his engine and anchor. The windlass can be placed on the other side of the engine, and be driven from the opposite end of the crank-shaft if so required.

Double-drum ploughing engines are made on the same principle for the other systems of steamculture. One drum is carried on the door seen in front of the boiler, and the other on the tender behind, and driven by intermediate gearing from the crank-shaft. They are all locomotive, and capable of hauling implements, &c. to and from the field.

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LANGTUN. OF

Fig.

The engraving fig. 6, represents Howard's selfmoving anchor. Its advantage over other anchors is its simplicity of construction and selfmoving action, by which an anchorman at each anchor is saved. It consists, as will be seen from the illustration, of a low carriage on four disc cutting coulters, like those used on some old ploughs. Each coulter has a barrel to prevent it sinking too far into the ground, and on to which a road wheel is bolted when travelling to or from the field. The four road wheels are not shown in the cut. When at work they are placed in the box on the further side, to counterbalance the pull of the rope, and thus keep the offside coulters into the ground. There are two pullies, round which the rope passes, an improvement on the common construction of one anchor pulley. The drum seen on the further side is for winding up an anchored rope ahead, in the common way. The peculiar novelty is in the double clutch gear on the axis of the small driving spur pinion seen inside the clutch lever, which extends across the face of a driven spur wheel. The clutch is held into gear by a spiral spring on the axis, and a lever clutch forces back the clutch and spring out of gear. Thus, when the strain is upon the two anchor pullies, the spiral spring on the axis permits the driving half of the clutch to revolve without rotating the driven half; but when the implement begins to leave the anchor, and the pullies to move the other way, the ratchet cams or teeth of the clutch come into action, setting the multiple spur gear and winding drum in motion. The righthand pulley centres over the axis of the small driving pinion already noticed, to which it gives motion by bevel gear; and

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the calculation of the spur gear is to wind up rope sufficient to work the anchor forward the breadth of the implement during the time it traverses the length of the land. It is thus the slack rope that moves the anchor, and the additional strain upon it barely keeps the rope between the anchor of the nearest rope porter off the ground. There are two ways of regulating the forward motion of the anchor to the length of the field, the one by different sets of spur gear, and the other by throwing the clutch gear out of action for a bout. This latter is done by the ploughman leaving his implement and by means of the lever already referred to, as seen in the engraving, forcing back the half clutch so as to prevent the action of the spring; and this he can do during the time the pull of the rope is being reversed at the engine.

Fig. 7 is the turning cultivator of the Messrs. J. and F. Howard. It is steered by two broad angular-rim front wheels, and is capable of working to any required depth in crossing as well as in breaking up stubble land. Its novelty is the peculiar mechanism for lifting out of and taking on fresh ground in turning at land's-end. A sledge-brake foot, with a turn-table heel, is pendent from the axle of each main wheel. When the

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7.-Howard's Turning Cultivator.

trailing rope becomes the hauling rope the wheel backs on to this turn-table heel, thereby raising that side of the implement out of the ground. The heel is also a fulcrum on which the opposite side of the implement is raised by the leverage of the rope-guide; so that in pulling the wheel on to the turn-table the tines of the cultivator rise instantaneously, and, as the pull continues, the implement wheels round on its heel, taking on its full breadth of fresh ground. As soon as it is fairly turned in, the wheel rolls forward off the turn-table, when down drops the cultivator into work without missing an inch of land, the headland being left of uniform breadth. All other turning cultivators miss a triangular bit at the side, and more or less the breadth of the implement at the end; so that the headland is uneven in breadth, ragged, and difficult to cultivate. The operation is self-acting, the ploughman having only to attend to his steerage at land's-end. The tines are so arranged as to cut out the wheel tracks.

The steam plough must necessarily be a one-way-plough, turning the furrow slices all in one direction. To remedy this three plans have been adopted: (1) two sets of ploughs, one set with right-hand breasts, and the other set with left-hand breasts; (2.) modifications of the old Kentish turnwrest plough, on the principle represented by Ransome's turnwrest; and (3.) two sets turning on a common longitudinal axis on the principle represented by Howard's turnover one-way-plough [PLOUGHS, E. C. S.]; but at present the first plan only is in use. Two

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sets, a right and left, naturally suggested itself as the best form of implement; but the practical difficulty experienced in the field was to raise the sets, turn in, and take on fresh ground at land's-end. Two plans have been successfully reduced to practice: (1.) springs, and (2.) the balance principle. Thus, McRae used springs, one to each plough, the ploughs in the set being raised individually as they reached the headland. The Messrs. Howard also used springs, but raised each set in a common frame, the ploughs in each set rising out of and falling into work together. The Fiskens used the balance principle in 1855. Their implement had the two sets, each in its own frame, the two frames being connected by bell-crank levers, so that they balanced each frame on its own fulcrum. David Greig conceived the idea of placing the two sets in a bent frame, and making them "see-saw," or balance on the axle of two wheels; and he and Mr. Fowler reduced it to practice in 1856. They were however obliged to purchase Fisken's patent plough before they could use their own. Fisken's steam plough thus fell to the ground. It was taken up by the Messrs. J. and F. Howard, who connected the two frames by chains over pulleys, instead of bell-crank levers and connecting-rods; but they were not al

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this, for the expense of rope continues to be heavily felt. The wear and tear on the common wire rope used by Osborn and subsequently by Smith and Fowler, was so great as virtually to render its use a failure. It is otherwise with steel wire rope, although the outlay, wear and tear, are still great. The improvement of steel wire rope is therefore no secondary question in profitable steam-culture.

The investment of capital in steam-culture is so great as to prevent many farmers from adopting steam in preference to horses, hence companies are formed who contract at so much per acre. A 12-horse steam-engine and windlass, fig. 5, two anchors, fig. 6, a cultivator, fig. 7, with the necessary rope and rope porters, &c., cost about 1000l.; a 12-horse ploughingengine, carrying two drums and one anchor, fig. 6, with the other auxiliaries, about 900l.; and two 12-horse engines, each with one drum, &c., 1400l.

The profits on steam-culture, as compared with horse-culture, have been variously estimated at from 12 to 20 bushels more corn per acre in favour of the former; and the results of the investigation of the Royal Agricultural Society of England of several hundred farms cultivated by steam, fully confirm the

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lowed to use it until the Fisken's patent expired. Howard's chainbalance plough has three wheels, two on the land and one in the furrow; but they are now (August, 1873) bringing out a twowheel "see-saw" balance plough, fig. 8, which, from the trials made, promises to be a superior implement. In its general outline it closely resembles the balance ploughs of Fowler and Co., but is simpler and stronger in construction, as will be seen from the engraving, and much more effective in the steerage. The two central wheels are made of wrought iron, and the beams of flanged steel. The steerage is similar to that of one of their double-furrow ploughs. The form of the plough bodies is similar to that of their horse ploughs; the cut shows ploughing breasts; these may, however, be removed and digging breasts put on. They are made without sole and side plates, each set having a friction-wheel which runs in the last furrow; the wheel of the raised set being most conspicuous in the illustration, a four-furrow plough. Beams are made to carry any number of ploughs required.

Harrows, seed and manure drills, clod-crushers and rollers for steam, closely resemble in principle those used for horse power. Harrows, clod-crushers, and rollers work each under a to-andfro steerage carriage, similar in principle to those shown in fig. 1 and fig. 2, viz., Howard's to-and-fro cultivator. The steerage frames of harrows will do for rollers and clod-crushers. The seed and manure drills turn at land's-end, somewhat similar to a turning cultivator. Broadcast sowing machines, and also manure distributors, when constructed separately, work on the to-and-fro principle. But, with the exception of harrows, machines of this class are not yet much in use.

The substitution of steel for iron in the manufacture of the hauling rope is one of the greatest improvements recently effected in steam-culture. Too little attention has been paid to

ARTS AND SCI. DIV.-SUP.

truth of the general opinion. It is a well-known fact, however, that land under steam tillage continues to improve, whilst expenses decrease.

STEAM ENGINE [STEAM AND STEAM ENGINE, E. C., vol. vii. col. 780; CONDENSER, E. C. S., col. 609; AIR PUMP, ib. col. 72; BOILER, ib. col. 315; FUEL, ib. col. 1082; INDICATOR, ib. col. 1358; GOVERNOR OF STEAM ENGINES, ib. col. 1166]. The convertibility of heat and work forms now the first principle of a scientific theoretical system, in which the whole of the operations of the production, properties, action, and use of steam are looked at from a new point of view. Not only are the ordinary processes of evaporation, expansion, condensation, &c., more clearly understood, but the dynamical theory of heat has thrown light on the less obvious phenomena of the action of steam in the steam engine, and the results of theory have in this department greatly influenced, and will in the future still more influence practical engineering. The scope of the present article will only permit the very briefest reference to some of these results.

The modern theory of the steam engine is of recent growth: Sadi Carnot having been the first to consider the problem how work is produced in the steam engine. He noticed that whenever work was produced by the action of heat, there was a flow of heat from a hotter to a colder body. Starting from the false basis of reasoning that heat was an indestructible material body, he was led to conclude that work was done by the caloric falling from a higher to a lower temperature. Hence he was led to conclude that the ratio of the work done by a perfect engine, to the heat taken from the source of heat, was a function of the initial and final temperatures only. We now know that during the performance of any mechanical work by a heat engine, part of the heat is destroyed as heat, and transformed into work, one

6 K

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can be converted into work in the most perfect engine, and in any actual engine the proportion of heat converted into work will be less than this, and the heat transferred to the colder body and wasted, so far as the purpose of the engine is concerned, will be greater. To Dr. Joule is due the most accurate determination of the mechanical equivalent of heat, and to Rankine, Clausius, and Sir W. Thomson the re-examination and correction of Carnot's reasonings. It will be seen that the quantity of heat available for conversion into mechanical work is proportional to the range of temperature at which the engine works; it will be greater as the initial temperature of the steam is greater, and as the temperature at which the steam is rejected is lower, and this is in accordance with ordinary practical experience.

Saturated Steam. [BOILER, E. C. S. col. 315.] It may be convenient here to state very briefly the properties of steam as produced in ordinary steam boilers. The steam produced by the evaporation of water under constant pressure is termed saturated steam. For any given pressure there is precise temperature at which the water evaporates and produces steam; the steam so produced has a definite weight per cubic foot or density; and a definite amount of heat is employed in its production.

Density of Steam. Sir W. Fairbairn and Mr. Tate have experimented on the density of steam, and have found for the volume of one pound of steam, under the pressure p lbs. per sq. inch, the following expression, which agrees very nearly with the results of their experiments :

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ture of 1 lb. of water from t°, to t°, and evaporating it at the
latter temperature, the whole heat expended, called the total
heat of 1 lb. of steam, is
H-966-07 (t,-212) +t2-ty
111403 t2-ty

Conversely each pound of steam at a temperature t, condensed and reduced in temperature to t, will give up that amount of heat.

Supersaturated and Superheated Steam. Thus far we have considered steam in its ordinary and popular sense as the vapour produced from water at constant temperature and pressure. It is now to be observed, however, that steam, removed from contact with water, may be heated, and its pressure will then increase according to a quite different law from that which governs steam in contact with water. Steam so heated is called superheated steam, and the heat may be supplied not only by the direct contact of a heated body but also in certain cases by the friction or expansion of the steam itself. The density of superheated steam is less than that of saturated steam of the same temperature. Steam when produced from water is liable, when the ebullition is violent, to take up particles of unevaporated water, and the weight of a cubic foot of such steam is of course greater than that of a cubic foot of ordinary steam. Such steam is called supersaturated steam.

Mechanical effect due to the evaporation of water. Suppose & cubic feet of water placed at the bottom of a cylindrical vessel, and covered by a closely-fitting piston, loaded to p lbs. per square foot. Let then the water be converted into steam by heat, and let v be the volume of the steam. Then the work done by the steam on the piston, during the evaporation of the water and its transformation by heat from the volume s to the volume, will be p (v-s) foot lbs. If s is the volume of 1 lb. of water, this is the external work of the evaporation of 1 lb. of water; and since s is small, it is equal to p r foot lbs. very nearly.

Employment of expansion. In many engines the steam is admitted to act against a piston, and when it has done p v units of work on it, it is allowed to escape into the atmosphere. Suppose it is now asked whether this is the best way of using the steam, and whether we have thus got all the work the steam is capable of doing, it must be answered that the steam can still do work, by the expenditure of the heat it contains, if we provide suitable means for availing ourselves of it.

There are two ways of proceeding. If we double the size of the cylinder, and, after allowing v cub. ft. of steam to enter, we close connection with the boiler and allow the steam to expand

which for calculation may be put in the following form, which with diminishing pressure, as the piston completes the stroke,

is still more exact:

log. v=2.516-0·939 log. p.

It is probable that the results of this formula are more exact than those obtained from the empirical expression of Fairbairn and Tate, for steam in the state in which it is commonly used, but the difference within the range of the experiments is not

very great.

p =

X 147

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Ρ

the steam will do work by its expansion. Engines in which the steam is admitted for part of the stroke, and then allowed to do work by expansion, are termed simple expansive engines. The second way of proceeding is this: after the steam has done into the atmosphere or the condenser, we may allow it to pass v units of work in one cylinder, instead of allowing it to pass into a second and larger cylinder. During its expansion into the larger cylinder it will do work just as if the expansion were Pressure and temperature of Steam. The exact relation between the pressure and temperature of steam can be best completed in a single cylinder. Engines of this kind are termed expressed by a rather complex formula. But for practical pur-ducting material, the only advantage of the second plan over the compound engines. Supposing the cylinder were of non-conposes and for pressures of 6 to 60 lbs. the following simple first would be that the two cylinders could be so arranged that formula is quite accurate enough, where p is the pressure in lbs. the work of the steam could, by proper arrangements, be made per square inch and t the temperature Fahr. more uniform during any given period of time, than with the first arrangement, and compound engines have this advantage over simple expansive engines, that the couple of rotation, tending to turn round the crank shaft, is more uniform when two are of conducting material, there is a special indirect process by which the benefit of expansive working is diminished. Ordinary steam during its expansion lowers its temperature and partially condenses, the condensed steam deposited on the sides of the cylinder evaporates into the air or condenser during the period of exhaust, and cools the cylinder sides, and these have to be reheated at the beginning of the next stroke by condensation of fresh steam. This process is termed the liquefaction of steam. [See LIQUEFACTION, E. C. S., col. 1474.] The waste of heat from this cause is generally less in compound than in simple engines, and during the last few years compound engines have been very largely used, especially for marine purposes, and remarkable conomy of fuel has been attained.

For pressures of 60 to 120 lbs. add 1 lb. to the results of cylinders are used. With actual engines, in which the cylinders

this formula. The inverse formula is

t = 147/p-40

and above 60 lbs. pressure

t = 147 p 41

Latent Heat of Steam. The heat which disappears during the evaporation of water, and which is used up in performing the mechanical work involved in the change of state is called the latent heat of evaporation. The latent heat of one pound of steam, produced at the constant temperature t° Fahr. is given by

the formula

L=966-07 (t-212)

The steam jacket is a casing of hot steam which surrounds the whose L is in British thermal units. In raising the tempera- cylinder, and to some extent, if not completely, it prevents the

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liquefaction of steam during the expansion. Introduced originally by Watt, and long used in Cornish engines only, it had been neglected or misunderstood by engine builders, till a very recent period. It is now universally used, in the best engines, in which steam is worked expansively, whether simple or compound.

Superheating the steam is another means which has been tried of diminishing the liquefaction. The superheated steam parts with some of its heat during expansion without condensing. When superheating apparatus was first applied to marine engines working at about 20 lbs. pressure above the atmospheric pressure, a considerable economy of fuel resulted, due chiefly to this prevention of condensation in the cylinder. It was found practicable to superheat the steam to about 350 Fahr., but above that temperature the steam destroyed the lubricants of the cylinder and injured the engine. With superheating carried to that extent in the cases above mentioned, as much as one-fifth to one-fourth of the fuel was in some cases saved. But more recent engines for marine purposes are usually constructed to work at pressures of 60 to 80 lbs. per square inch, and steam of those pressures is already at so high a temperature that no margin is left for superheating, without incurring the risk of burning the lubricants. Superheating, which a few years ago promised to lead to great economy, is now very generally abandoned, and the same results are obtained in modern high pressure engines by the use of the steamjacket and by the use of compound engines.

Condensing and non-condensing engines. If after doing work on the piston the steam is allowed to pass into the atmosphere, the atmospheric pressure acts against the piston as a backpressure during the return stroke, work has then to be done against the atmospheric pressure, which is useless work, and which diminishes the useful work of the engine. We obviate this by the employment of an air-pump and condenser. [See CONDENSER, E. C. S., col. 609]. Of late, in marine engines, surface condensers have been very widely adopted for reasons given in the article just cited.

Transmission of movement in engines. All the early steam engines were beam engines. The work of the piston was communicated first to a great oscillating beam, and thence to the shaft to be driven. Of late, beam engines have been altogether superseded by direct acting engines, excepting in the case of large pumping engines, which are still very often beam engines. In the direct acting engine, the piston communicates its motion directly through a simple connecting rod to the crank-shaft of the engine. The advantages of the direct acting engine are its greater simplicity and cheapness, and that it can be run at a greater speed than the beam engine. This last advantage is due, partly, to the absence of the heavy beam, the inertia of which had to be overcome at every change in the direction of its motion, and partly to the fact that the direct acting engine can be so placed on its framing that the strains are directly resisted by the framing, while in the beam engine they were transmitted to the walls of the building.

The most ordinary type of engine is now the horizontal direct acting engine. It was long thought objectionable to place the cylinder horizontally, because the weight of the piston acting always on one side would, it was thought, wear it oval. But it is found that if the temperature of the steam is not so high as to prevent proper lubrication, the ovalisation of the cylinder is not a serious evil. In large engines the piston rod is prolonged through both ends of the cylinder and carried on adjustable slides at both ends.

Mode of ascertaining the power of engines. [See INDICATOR, E. C. S., col. 1358.]

Combined vapour engines. We have seen above that the efficiency of a heat engine is greater in proportion as the temperature at which the steam is rejected is lower. Now in ordinary engines it is not possible to work the condenser at a lower temperature than 100° to 120°. Hence it occurred to M. du Trembley to employ the heat rejected in the condenser of the steam engine to evaporate some liquid of low boiling point. The vapour so produced was used to work a second engine, and then condensed, at a much lower temperature than that of the steam engine condenser. Thus the range of temperature of the combined engine was greater than that of ordinary steam engines.

M. du Trembley used ether, which was evaporated by the condensation of the steam. Three engines were constructed, and, so far as economy of fuel is concerned, they were quite successful. Unfortunately it was found impossible to prevent leakage of the

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ether at the joints of the apparatus. The ether leaking out formed in the air an inflammable mixture, and frequent explosions occurred. M. Lafond substituted chloroform for ether, and a vessel was fitted with engines constructed to work thus, but with no greater success.

The injector. In feeding boilers with water, a small plunger pump has been most generally used. But some years ago a remarkable invention was introduced from France, under the name of Giffard's injector, as a substitute for the pump. The injector is simply a jet pump, in which a steam jet, instead of a water jet, supplies the momentum which drives the water into the boiler. [JET PUMP, E. C. S. col. 1398.]

Locomotive engines. Special attention has been directed lately to the construction of locomotives suitable for the traction of trains on railways having excessive gradients. One of the first railways on which a long and steep incline required to be surmounted, was the line from Turin to Genoa. The gradient there is 1 in 33 on the average for a considerable distance, and the maximum gradient is 1 in 29. That line was worked with two engines, coupled footboard to footboard, a plan which was fairly successful, but the working expenses were large.

On the Soemmering inclines, between Vienna and Trieste, with a maximum gradient of 1 in 40, engines designed by M. Engerth were used, and are known as Engerth engines. These engines originally were constructed with the firebox overhanging the trailing axle, and partially carried by the first axle of the tender. In this way an enormously large boiler could be carried. Various attempts were made to drive this axle of the tender from the cylinders of the locomotive, and thus to utilise the tender weight for adhesion. But the complication thus involved proved a serious evil, and the plans must be considered to have failed. At Soemmering, M. Engerth used toothed wheels to connect the tender-axle with the locomotive-axles. On the Steierdorf inclines he used linkwork with no greater success. Mr. Sturrock, of the Great Northern Railway, finding the need of engines of great tractive power for heavy goods trains, has sought to utilise the tender in another way. He places steam cylinders under the tender, and supplies the steam from the boiler of the locomotive. In this way, for short distances, where the speed needed to be accelerated, sufficient steam could be obtained to work both the locomotive and the tender; on other parts of the line the locomotive worked without the tender. This plan has not been extensively adopted. The most remarkable modification of the locomotive for steep gradients is, however, that proposed by Mr. Fell, and used on the temporary line over Mont Cenis. On that line a mid-rail was laid between the ordinary rails, and this mid-rail wa3 gripped by four horizontal wheels pressed against it by springs. These springs virtually increased the adhesion of the locomotive. The horizontal wheels were worked by a peculiar linkwork arrangement, connecting them with the vertical wheels. Mr. Fell has also proposed to use independent steam cylinders to work the horizontal wheels. The complication of these engines was found to involve a considerable wear, but on the whole they performed their work successfully. Whether they will ever be much used will depend, chiefly, on the need of such excessive gradients as required to be surmounted at Mont Cenis. The last modification of the locomotive needing mention is that known as the Fairlie engine. In the Fairlie engine, we have the double engines of the Turin line combined into a single machine. There are two boilers placed end to end, and carried on a single framing, the fire-boxes being at the centre of the engine. Beneath the boilers are four steam cylinders, two in front and two behind, the front engines working two pairs or three pairs of coupled wheels under the front boiler, and the back cylinders working a similar set under the other boiler. Without another peculiarity of construction, such an engine would not be workable on a line having curves, the wheel base would be too long and rigid, and the engine could not adapt itself to the curves. Hence Mr. Fairlie places each pair of cylinders, with its set of wheels on a separate bogie truck, on which the boiler rests on a central pivot. These bogies swivel round independently under the boiler when the engine runs round curves. The mechanical arrangements are extremely ingenious, and these engines have worked with perfect success on several difficult railways.

STEAM ENGINES, AGRICULTURAL. In every department of agriculture steam is superseding horse power. [TRACTION ENGINES; STEAM CULTURE; STEAM ROAD ROLLERS; E. C. S.]

It is common to distinguish agricultural steam engines in classes; viz. (1) fixed engines; (2) portable engines; (3) semi

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portable engines; (4) vertical engines. Engines are also designated according to the nature of the boilers used-as a Cornish boiler, a tubular boiler. An illustrated example of each of these classes will suffice. Thus fig. 1 represents a fixed engine of the Messrs. Clayton and Shuttleworth, of Lincoln. Steam has hitherto been chiefly supplied by Cornish and Lancashire boilers, but water-tube boilers are now beginning to be used, of which there are numerous examples, as Howard's, Root's, Holloway's, Paxman and Davey's, &c. The engraving requires little explanation. The cylinder is steam jacketed, and the crank-shaft and bearing are bedded on a common casting supported by mason work. The cast-iron foundation-plate is planed on the upper and under sides, so as to facilitate fixing and removal by tenant farmers not occupying their own premises. The principle of the engine is direct action, thereby simplifying the working parts and reducing their wear and tear. The governor is of the most improved sort; the exhaust goes into the water-tank, heating the feed water, so that every provision is made for the economy of fuel and steam.

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Fig. 1.-Fixed Steam Engine.

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