the foundry smith, &c., and a place is also provided for the clay mill. In the centre of the square is a triangle for breaking iron: the back end of the square is left vacant, to facilitate future additions.

Between the wet dock and the side of these squares of building, is a quay, alongside which vessels lie to get in their engines; the end of the fitting shop is turned to this quay. Instead of cranes in the fitting shop, winches travelling on beams, such as are now generally employed by masons, are employed, and these beams extend through the end of the house and across the quay to the dock, so that a piece of machinery may be lifted in the fitting-shop and deposited within the vessel in the dock, without the necessity of any intermediate process. To support the beams carrying the travelling winches outside the house, pillars stand on the edge of the quay, and the portion of the beams which hang over the quay, are securely trussed by means of iron rods. The roof is continued along over the beams, both to give increased strength and to protect the workmen from the wet, when putting engines on board.

On the opposite side of the dock is the boiler shed, and in continuation of it is the building yard. The boiler shed is a very large structure; it contains smiths' shops for preparing the smith work necessary for boilers and iron ships, and is provided with rivetting and punching machines, and other necessary implements. The boiler shed is lighted from the roof, and the boilers are lifted by means of a travelling carriage running on beams near the roof, arranged as in the fitting shop, and similarly projecting over the dock, so as to put boilers on board. The whole of the roofs are made of iron, which are as cheap as timber roofs, and greatly preferable in every way. A railway runs round the dock, and doors open to the wharf from the foundry, carriage shop, and locomotive shop; so that any heavy article, whether engine, boiler, locomotive, railway carriage, or casting, may be set either on board ship, or on a railway, without incurring the trouble and expense of intermediate removal.

In the tools employed in the construction of locomotives, great improvement may be introduced; and in settling the particular plan of locomotive to be adopted, reference must be had to facility of manufacture. The present method of constructing iron ships is rude and primitive. If a form of vessel be fixed upon for which a mathematical expression may be found, a machine may be contrived that will bend the ribs to the right curve and bevel, and also bend the plates to the right shape. The plate with thickened edges, introduced by Mr. Fairbairn, appears to afford the greatest facilities in the manufacture of iron ships; and if machinery be introduced that will form the parts accurately, it will be possible to make large pieces of a ship by means of the rivetting machine; and the only hand labour that will then be requisite, will be that necessary for fastening these pieces together when put into their places. A rivetting machine, however, will probably be invented, that will rivet the parts in their places; and if the frames be accurately punched, and accurately set, the application of such a machine does not appear to be difficult. Two strong rollers might be made to travel up on the frame to which the plate to be rivetted had just been applied, and these rollers, if suitably formed and suitably directed, would suffice to accomplish the rivetting operation. To guide the rollers, a carriage with four wheels, of which the rivetting wheel was one, would have to be applied upon the inside of the frame; upon this carriage a small cylinder would be set, connected with a vacuum pipe by means of a flexible tube, and so soon as the cylinder was put in operation the carriage would mount up on the frame, the wheels of the carriage being armed with projecting spurs to enter the rivet holes, and thus enable it to advance. Such an instrument would not be applicable, either at the extreme bow or the extreme stern, on account of the curves there to be met with; and the bow and stern would either have to be plated by hand, or to be formed separately by the ordinary rivetting machine, and to be then put in their places. For strong vessels with thick plates machine rivetting is especially desirable, as, with the force imparted by hand rivetting, it is difficult to make the rivets fill the holes.

The loose system pursued in some factories, of allowing the inferior foremen or workmen to fix the shape and dimensions of cocks, bolts, and other subordinate parts, is one likely to lead to much confusion, and is not to be commended. Every thing should be drawn in the drawingoffice, even the spanners, oil-cups, and gauge-cocks; and for any misfit, the person who has made the drawing should be responsible, provided his dimensions have been followed. It should be the part of the foreman not to design portions of the work, but to see the work properly executed; and no foreman should be permitted to alter or add to a drawing on any account whatever. Should he perceive any mistake or omission, he should come to the drawing-office to have the requisite alteration made, but should not be suffered to make it himself. It is only by a rigorous adherence to this plan that mistakes and confusion are to be avoided, or that an accurate record can be kept of the work which has been done. The practice with the London engineers is to make their working drawings to a scale of 1 inches to the foot,-representing portions, however, of such parts as the top ends of the side rods, bottom of connecting rod, &c., of which the form cannot readily be found from the measurements of a rule, of the full size. The drawings are fixed upon boards, and varnished so as to preserve them from the effects of grease; and a ledge of wood is nailed round the edges to keep them down, and prevent the drawing from being rubbed when the boards are piled one upon another. Erection drawings should be given to the foreman of the erecting shop, with all the centres marked in their

proper places; and the size should be given to which the cylinder is to be cast, as well as the size to which it is to be bored. Every erector should have a box for holding his hammers, chisels, and files; and every finisher a drawer for holding his tools. Steel straight edges are preferable to wooden ones for most purposes, and the different workshops should be supplied with them. All tools going out of the factory should be weighed, and weighed again when they are brought back. It will generally be found the best economy for factories to make their own gas, and all the workshops should be well lighted, so as to save candles. Flexible tubes, fitted at the ends with heavy candlesticks, will be necessary to supply gas for the erectors.

To make the manufacture of engines profitable, it is necessary to be able to get good orders, and to be able to manufacture cheaply. Orders are most easily got by makers who have a name: yet a name is not in all cases of itself a sufficient attraction, and other allurements must be presented. The ability to give money accommodation will, in many cases, establish a preference, but the chief reliance should be placed upon the activity of the managing head, who, with competent engineering knowledge, should be a thorough man of business, and whose function it should be to agitate unceasingly among the persons likely to require engines made. In fixing the plan of engine, the highest scientific attainments. should be put in requisition; but the plan once fixed, the production of engines ceases to be a profession, and is as much a trade as building or weaving, and, to be profitable, must be pursued on the same system. A fastidious taste, or a wavering disposition, are only barriers to commercial success; and those will make most money who, instead of distracting themselves among superlative refinements, will look chiefly to getting the work done. Improvements have their price as well as their recompence, and, to be profitable, they must be introduced at rare intervals, and then only after they have been satisfactorily tested, so that their success is certain. In their designs and their model experiments, engineers may be as revolutionary as they please; but a manufactory should be a conservative institution, and can never be made profitable amid perpetual changes. The form selected should be preserved intact until the accumulation of new improvements is such as to justify and compel the introduction of another combination, which should in its turn be retained until a new crop of improvements has been raised equal in value to the former. Manufacture is thus reconciled with progress; and the alternative is averted of tedious and expensive production, or a gradual lapse into antiquity.

The most important element of prosperity, however, in the conduct of factories that we can discern, is that of making the workmen employed participators in the profits realised, whereby their energies are effectually enlisted, and their ingenuity stimulated to the device of cheaper methods of manufacture. If this innovation be generally carried into effect, strikes will become impossible; and the ingenuity of the workmen, at present a barren field, will spring up into new forms of life and productiveness. The collective inventive genius of the operative classes is a mine of unspeakable wealth, and will at once be rendered available by making it the interest of the workman to plan cheaper methods of manufacture. The managers of factories are generally made participators in the profits realised, and the most beneficial results have sprung from the arrangement; but the principle has not been generally extended to the workmen, though recent experiments show that, in their case, it might be applied with equal advantage. M. Leclaire, a house painter in Paris, has for some years made his workmen participators in the profits of his establishment; and, in a pamphlet recently published, he speaks of the system in the highest terms of praise. Lord Wallscourt has long pursued a similar plan in the cultivation of his estates in Ireland, and its operation has been such as to stimulate the supine Irish peasant into active industry, and to shed pros-, perity and gladness over a district that was formerly the abode of famine and despair. In reply to our inquiries, Lord Wallscourt says, "I have tried the plan for seventeen years, and have found it to answer much beyond my hopes; inasmuch as it completely identifies the workmen with the success of the farm, besides giving me full liberty to travel on the continent, for a year at a time, and upon my return, I have always found that the farm had prospered more than when I was present." Lord Wallscourt's practice is to reckon every workman as the invester of as much capital as will yield, at five per cent. per annum, the sum paid to him in wages. In a factory conducted on this principle, the capital requisite for the erection of the necessary works, and for carrying the business on, would be regarded in the light of a debenture, upon which a sufficient rate of interest to cover the risks would have to be paid, before any profits could be divisible among the workmen; but a certain rate of wages would be secured to the workmen as a minimum, whether there were profits or not. The profits might be divided every year; and, to avoid a partnership transaction, might be distributed as gifts instead of profits, whereby, too, any workman discharged for misconduct would have no further claim upon the establishment. This is the plan pursued both by Lord Wallscourt and M. Leclaire, and we have their testimony to show that it is in every respect satisfactory.

It is clear that the principle of a fair division of profits satisfies every aspiration of industry. Machinery, instead of being the competitor of the working man for subsistence, will, so soon as this great principle gains an effectual introduction, be his assiduous slave. If machinery ploughs, or spins, or toils in the mine, it is for him that it will perform these beneficent

abours; and whatever benefit the introduction of machinery brings, he will participate in it in a fair proportion. Every intellectual capacity will be brought into increased exercise; invention will be stimulated, and -improved modes of construction will be devised. We own we think that even six hours of work in the day would be enough; for with good machinery, efficient direction, and such activity as must arise when men are made participators in the profits arising from their labours, as much work may be done in six hours as in ten or twelve hours according to the present system.

Such, then, are the chief considerations which suggest themselves to us in connection with the management of factories. The factory should be commodiously situated, and should aim at the production of large quantities of the same kind of work, so that the requisite tools and appliances may be introduced to make the production a manufacture, and the men will only have tasks to perform with which they have long been familiar. So soon as the plan is settled, all considerations of scientific excellence should be dismissed, and the work should be conducted as if the only object to be considered were the production, at the cheapest rate, of certain hundreds of tons of finished castings and polished smith work. Of course quality must not be sacrificed in the aspiration after cheapness; but the quality being fixed, the question is how to produce the articles required at the cheapest rate. We believe that the adoption of the principle of dividing the profits with the workmen, will add to the employer's gains, and diminish his anxieties; while to the workman it will bring such ameliorations as will at once place him in his true position in society. With the termination of the existing system, the strife now subsisting between masters and men must cease, and they will be knit together for the future by an identity of interests, which will gradually grow up into a mutual confidence and regard.

MANAGEMENT OF ENGINES.

We have already, at page 203., given directions for the management of the pumping engine, and as the management of the rotative mill engine is identical with that of the marine engine, we shall restrict our remarks under this head to the subject of marine and locomotive engines. Marine engines require more intelligence for their management than any other description of engine, partly in consequence of their great size and complication, and partly on account of the serious consequences an accident may entail, if the vessel be at the time in a critical situation from stormy weather or adverse winds. On foreign stations, too, the engineer is thrown very much upon his own resources should an accident occur, and the least weighty consequence of his ignorance or neglect will be to damage seriously a very expensive machine. To the management of marine engines, therefore, our present remarks will be chiefly directed, as if this part of the general subject be mastered, the other branches of it will cease to present any difficulty which the most moderate reflection may not surmount.

The first and weightiest duty of the steam-boat engineer is, to see that the boilers are properly cared for. The length of the watch is generally about four hours, and the engineer on watch should be in perpetual attendance on the boiler, to see that the feed is properly maintained. If the boiler be blown off by means of blow-off cocks, the operation should be performed twice in the watch, or once every two hours. The feed should be so set that the water will rise in the course of two hours from a little below the middle to near the top of the glass gauge tube, and in opening the blow-off cocks the water should be allowed to subside from near the top of the glass gauge tube to a little below the centre. This, it is true, is a very indefinite quantity, for the area of the water level varies in different boilers, and the glass tubes are of different lengths; but the engineer will soon discover the exact quantity of blowing off requisite for the particular boilers he works the rule being to blow off so frequently or so much as to prevent any accumulation of scale within the boiler. We wish here to repeat again that in every case in which there is an accumulation of scale in the boiler, the fault lies with the engineer, who is either ignorant of his duty or inattentive to it. The scale should never be thicker than a sheet of paper in the worst parts, with the black iron showing in other places; and the operation of blowing off must be carried so far that this thickness will never be increased. In some boilers the scale in the water spaces is suffered to accumulate until the spaces are completely choked up in some places, and the iron of the flues then gets red hot, and is bellied inwards by the pressure. When this takes place, the only plan to pursue, if the salted parts be not easily accessible from the interior of the boiler, is to cut large manhole doors in the flues, and to quarry out the salt with appropriate instruments. As much may be quarried out every voyage as can readily be accomplished, and the manhole doors may in the meanwhile be closed by means of cross bars and bolts in the usual fashion. As soon as the boilers are clear, these holes may be covered with plates rivetted on, but if the boilers be considerably worn, the manhole doors will last as long as the boilers, and need not be removed.

In boilers furnished with brine pumps, reliance must not be placed upon the pumps always acting well, and once every watch some water must be drawn off from the boiler to be tested by a salt gauge, to see whether it is too salt or not. There is no salt gauge which is received as a standard, but the engineer may easily make one as follows-Take a glass phial or eau de Cologne bottle, pour into it so much shot that it will nearly sink in

sea water, and then cork it tightly. Take any convenient weight of boiling water, say 33 lbs., add thereto 1 lb. of salt, and then put the phial into it turned upside down, so that the shot will rest against the cork; make a mark at the point at which the water stands on the phial; this represents the saltness of sea water. Add then another pound of salt to the water, marking the point on the phial at which the water stands, and repeat the operation until 12 lbs. of salt have been added, at which point the water will have received as much salt as it can dissolve; transfer the marks upon the bottle to a paper scale, which paste on the inside of the bottle in exactly the same position as the original marks. You will then have a salt gauge which will tell the saltness of brine from the point of sea water up to the point of saturation. Reckoning sea water at 1, the water within the boiler should not exceed the saltness represented by 4, at which point the water contains ds of salt. This, though a tolerably correct instrument, is obviously a rude one, and it is preferable to have salt gauges properly made by the glass-blower, but graduated by a boiling solution on the principle we have described. A salt gauge is merely a hydrometer, and may be made by any person conversant with the manufacture of those instruments.

The safety of the boilers being assured, the next point the engineer on watch has to look to, is to see that the pressure of the steam is properly maintained. Here almost every thing depends on the fireman. One fireman will keep the steam up with a moderate consumption of coal, while another, with an increased consumption, will not prevent the pressure from declining, and yet it is hard to say wherein lies the difference of manipulation. It is a common fault, however, with lazy or ignorant firemen, to pile up the coal at the mouth of the furnaces, while the bars at the after end are nearly bare, and if there be any holes in the fire, the cold air will rush up through them and greatly diminish the efficacy of the fuel. Opening the furnace door frequently has also a pernicious effect, and should be avoided as much as possible. It is desirable that the bars should have a considerable inclination, to facilitate the descent of the fuel upon them, and thus keep the after end of the bars effectually covered. Bars are to be preferred that are made of malleable iron, as they are more durable than cast iron bars, and may be made thinner, whereby they more effectually distribute the air among the burning fuel. Bars three quarters of an inch thick on the upper edge, tapering to one quarter of an inch thick on the lower edge, seem to answer very well when the bars are of malleable iron. The greater width between the bars at the under than at the upper edge, facilitates the admission of the air, and the descent of the ashes and cinders. Bars are usually set ths of an inch asunder, but this width must be diminished if the coal be very small, and can be diminished with impunity when the bars are thin.

If the boiler when tolerably well fired is still short of steam, a few windsails should be set up and their ends directed into the engine room, so as to send into it a larger supply of air; or by setting the foresail the draft may sometimes be increased. In some cases the hatches through the deck into the engine room are too small to admit the necessary supply of air to the furnaces, and they must then be enlarged, or new ones opened. Partially closing the damper will sometimes increase the generation of steam, and in such cases it is expedient to place a sheet iron hanging bridge at the end of the flues, where they enter the chimney. In the case of tubular boilers, however, this cannot be done; but a sliding perforated plate, or Venetian damper, may be so applied to the ends of the tubes, as to retain the hot air for a longer period within them, thereby increasing the efficacy of the fuel. Whatever be the steam producing powers of the boilers, a vacuum should never be suffered to be formed within them, as it is impossible to blow off if there be a vacuum in the boilers, and the gauge cocks, moreover, will in such case cease to afford any indication of the height of the water level. If the pressure of the steam cannot be maintained, that grade of the expansion cam must be used, which will cut off the steam at such a point as will keep the pressure at the right pitch; or if there be no expansion gear, the throttle valve must be so far closed as to keep the steam gauge nearly up to the point answering to the load on the safety valve. Partially closing the throttle valve of an engine, will have nearly the same effect as the use of an expansion valve, if there be any lap on the steam slide; for the steam, though it presses on the piston with the full force at the beginning of the stroke, when the motion of the piston is slow, cannot maintain the pressure on account of the smallness of the opening, when the motion is quickened; the pressure within the cylinder therefore declines, and if, before the motion becomes slow again, as it will do towards the end of the stroke, the steam be shut off by the lap on the slide, an effect will be obtained almost identical with that which would have followed the application of an expansion valve. The action is further illustrated by the indicator diagram, fig.343. page 248, to which it is sufficient to refer. Partially closing the throttle valve checks priming, and opening the throttle valve or the safety valve suddenly has a great tendency to produce it, as has already been mentioned at page 83. When the boiler primes, the speed of the engine is sure to be diminished, in consequence of the large quantity of water the air pump has then to deliver, and it will be expedient in such cases partly to shut off the injection water. When priming begins, engineers generally close the throttle valves, diminish the supply of injection water, and open the furnace doors. If the priming be very strong, so as to cause the water to leave the boilers very quickly, it is necessary to have a few buckets of water at hand. to throw in upon the fire the instant the water subsides below the glass tube. It will not do then to set about the drawing of fires, for all the damage may be

may come out and occasion serious breakages without giving any such warning. The same remark applies to any of the main cutters which are not made with a taper, such as the cross-head or cross-tail cutters of some engines, which may come out without giving intimation of the danger. The main cutters about an engine should all be provided with screws, such as is represented in the connecting rod strap in our plate of details, to prevent the cutters from going either back or forward. Generally speaking, cutters have a tendency to work further in, whereby, if the tendency be not counteracted, they will cause the bearings to heat.

done before the fires can be drawn, but the engineer must open the furnace doors and throw in a few buckets of water, standing to the one side to escape the backward rush of the steam, which would otherwise scald him. The fires will not be put out by this regimen, but will be so far damped as to prevent them from doing any injury to the boiler, even though it be a tubular one with brass tubes. The same urgent haste is not necessary, if boilers have begun to salt from the stoppage of the blow-off pipes, and there it will do to draw the fires preparatory to pumping out their contents by the deck pump, if they cannot be blown off through the deck pump sea cock into the sea. But in the case of the water being suddenly carried out of the boiler by priming, or of the water having been suffered to subside too far by the neglect of the feed, the best plan is to quench the fires in the way we have described. If from the neglect of the feed, the flues or furnaces have become red hot, on no account must cold water be thrown in by the pump, else the sudden pressure within the boiler thus created will be sure to make the heated places bulge down, and may perhaps burst the boiler. A plate which has bulged down may be set up again by lighting a fire against it, so as to make the plate red hot, and then forcing it up with a screw jack.

One of the greatest dangers that can occur to a boiler, is that of a safety valve jamming or refusing to act. Every boiler ought to have a safety valve of its own, and if this valve should jam, the steam has still a means of escape through the stop valves into the other boilers, the safety valves of which are not likely to be similarly affected; nevertheless cases have occurred in which the safety valves have all been rendered inoperative, and it behoves the engineer to prepare himself for such an emergency. In one of these cases the cone, which is frequently placed in the ball of the waste steam pipe, became loose, and jammed itself into the mouth of the pipe, whereby, though the safety valves were all open, the escape of any of the steam was prevented. The pressure of steam in the boiler increased until it broke some of the boiler stays, and the engineer being unprepared how to act in such a dilemma, the boiler would no doubt have burst, had not the waste steam pipe given way, when the ball was shot to a great height into the air. In this case the pressure would have been immediately relieved by opening the blow through valves of both engines, and at the same time opening the furnace doors to check the production of steam. The existence of a dangerous pressure within the boiler is always shown by the steam gauge, the mercury of which is blown out when the pressure of the steam becomes dangerously high. If both safety and stop valves were to become fixed at the same time, so that the steam could neither gain access to the engine nor escape by the safety valve, the best plan would be to open the blow-off cocks and all the gauge cocks, throw open the furnace doors, and quench and draw all the fires. Such an accident, however, can hardly happen, and we have never known it to occur in practice.

Two or more fires are usually cleaned every watch, depending on the number of the furnaces and the quality of the coal. The fires to be cleaned are suffered to be burned down until there is very little else than clinker left upon the grate, and the whole of this clinker is then raked off, and the fire is lighted afresh. The operation of cleaning the fires is usually performed just before the termination of the watch, and the whole of the ashes are then hoisted up and thrown overboard, the firemen on watch filling the ash-buckets, and the firemen about to come on watch hoisting them up and emptying them into a shoot in the paddle wheel, or over the ship's side. There ought to be a cock on each side of the stoke-hole, about 2 in. diameter, for the admission of water from the sea for quenching the fires and other uses.

Such are the chief points which solicit the engineer's attention in the working of the boilers. In the management of the engines, the first point to be looked to is that the cutters are neither too slack nor too tight, and that none of the brasses are heating. In the generality of engines, the bearing most apt to heat is the crank pin, but much depends on the proportions of the parts, which differ in different engines. It is usual to lubri cate the crank pin, when it heats, with sulphur and tallow, which is supplied through a funnel cup instead of the ordinary oil cup, and the same discipline is observed in the case of other bearings. This plan answers well enough when the heating is not considerable, but it will sometimes be necessary to cool the bearing by cold water applied by means of the hose communicating with the deck pump. If the cast iron parts, however, such as the plummer blocks of the main shaft or their covers, become hot, it may crack them to throw cold water upon them suddenly, and in such cases it will be better to begin with hot water from the boiler, shutting off the boiler cock gradually from the pump, and opening the sea cock gradually until cold water is projected upon the bearing. In the malleable iron parts of the engine, cold water may be applied to hot bearings without this precaution, and the best remedy there for a troublesome bearing is the application of the water hose. Bearings, however, rarely heat unless they are too tightly screwed up or the supply of oil to them has been neglected, and they must be slackened and lubricated as well as cooled with water. The heating of a bearing very frequently injures the surface of the metal, and cuts away the brass very much it should therefore be checked at the. outset, and in replenishing the oil cups, which the engineer should periodically do, he ought to feel the bearings to make sure that they are not hot. He should see at the same time that none of the cutters are working loose. A looseness of any of the main bearings will generally manifest its existence by a jerk in the engine, but some of the cutters of the parallel motion

The state of the vacuum will be shown by the vacuum gauge attached to the condenser, and if it be imperfect, the cause must be ascertained and the fault corrected. If the hot well be much more than blood warm, more injection water must be admitted, and if the vacuum is still imperfect, there must be some air leak, which the engineer must endeavour to discover. Very often the fault will be found to lie in the valve or cylinder cover, which must then be screwed more firmly down, or in the faucett joint of the eduction pipe, the gland of which will require to be tightened, or the leaking part puttied up. The cylinder and valve stuffing-boxes may at the same time be supplied afresh with tallow, and the door of the condenser examined, if the engine be provided with one. The joints of the parts communicating with the condenser are usually tried with a candle, the vacuum sucking in the flame if the joint be faulty; sometimes the cover of the foot valves leaks air into the condenser, but in side lever engines, this is a very difficult part to examine when the vessel is under weigh.

The power actually exerted by an engine is determined by the indicator, the operation of which we have already explained at page 170., but we may here give a few directions for the use of the young engineer, showing how he may take indicator diagrams himself, and how he may interpret the figures thus obtained. In the case of a steam vessel there is more trouble in applying an indicator than in the case of a land engine, as the proper amount of travel for the string cannot be so easily procured. The most convenient arrangement appears to be to add a small wheel and axle, or wheel and pinion, to the indicator, so that a string attached to the piston-rod and wound on the wheel will give the right motion to the cylinder on which the paper is fixed. The indicator may then be applied to all sorts of engines, whether fixed or oscillating, without involving the trouble of a new method of attachment for each, but the string being tied to the top of the piston-rod, the motion will be reduced at once to that suitable for the paper cylinder, by means of the wheel and axle. It will do, however, when the proposed wheel and axle is not in readiness, to attach the string to any part of the parallel motion, or any part of the side lever which partakes of the motion of the piston. The parallel bar and parallel motion shaft are often selected. If the motion be taken from the side lever, the string must be attached in the central line of the beam, for if attached on the top of the beam near the main centre, the motion may not be the same as that of the piston, and a distorted figure will be obtained. Perplexity is sometimes cast over indicator diagrams in consequence of the improper attachment of the string, and in all cases of apparent anomaly, the first point to be inquired into is the point about the engine, to which the string has been attached. It is a good exercise for engineers to attach the indicator string to parts about the engine which they know to be wrong, in order to familiarise themselves with distorted diagrams, whereby they will be able to detect the imperfection and the causes by which it has been produced.

Fig. 339. is a cylinder diagram of the City of Aberdeen steamer. The atmospheric line running through the centre of it shows the point at which the pencil of the indicator stands when there is neither pressure nor vacuum below the indicator piston, and it is traced by suffering the pencil to make a line upon the paper wound round the drum before the cock of the indicator is opened. From the point A, near the left-hand top corner of the figure, the pencil starts on its course, and on the cock being opened, it immediately flies up and forms the upper line of the figure, which repre

sents the pressure of the steam, and for every tenth of an inch-or other distance which in the graduation of the instrument is taken to represent a pound pressure-that the pencil rises, the pressure within the cylinder is that number of pounds above the atmosphere. By the time the paper reaches the extremity of its horizontal travel, the slide valve has shut off the steam and opened the passage to the condenser, when the pencil descends to a position beneath the atmospheric line corresponding to the degree of exhaustion existing within the cylinder. The bottom line of the diagram therefore represents the quality of the vacuum, and by the time the paper has travelled back to the same point from which it set out, the slide valve has closed the eduction passage and again let the steam into the cylinder, when the pencil again springs up to the position due to the pressure of the steam. It is clear from the consideration of this action, that if the steam experienced no obstruction in entering or leaving the cylinder, the figure would be a perfect parallelogram; the pencil would be instantaneously forced up to its highest point, where it would remain until the travel of the paper had terminated, when it would be instantaneously forced down to its lowest point, where it would remain until forced up again by the pressure of the steam. In practice, however, this state of things cannot exist; the steam requires time to enter the cylinder and time to escape from it, and the diagram is more or less rounded at the corners in proportion to the obstruction thus presented. The more square an indicator diagram is at the corners, the more fully is the engine working up to its power with the given pressure of steam. If the corner marked "expansion corner" be cut away very much, the engine is working to a proportionate extent expansively. If the "eduction corner be much rounded or slanted away, then the eduction passages are too small. If the "lead corner" be much slanted off, then the amount of lead given to the engine is great, or in other words, the steam side of the slide is opened before the end of the stroke. If the "starting corner," or the steam corner, as it might be called, is slanted off, then the steam does not gain admission to the engine sufficiently early. Every change in the engine which occasions a rounding or slanting away of the corners of the diagram, diminishes the power of every stroke; for the space enclosed by the pencil line represents the power of a stroke of the engine, and the area of that space is diminished by every rounding away of the corners. It does not follow, however, that the peculiarities of structure which give a diagram cut away at the corners are necessarily pernicious in all cases. Expansion produces the effect referred to; yet it is known to be beneficial, from the diminished power of the engine being more than compensated by the saving in steam. It is found advantageous to the working of the engine to give some lead to the valve, so that the cutting away of the lead corner of the diagram to a moderate extent is not to be looked upon as a defect; but the eduction corner should be as square as possible, and any rounding of the steam or starting corner is a defect arising from want of lead, or rather from lead on the wrong side, the steam valve not opening until some part of the stroke has been performed. To compute the power of an engine from the indicator diagram, divide the diagram in the direction of its length into any convenient number of equal parts by lines drawn at right angles with the atmospheric line; set down the lengths of the spaces formed by these lines in measurements of a scale accompanying the indicator, and on which a tenth of an inch usually represents a pound of pressure; add up the total lengths of all the spaces, and divide by the number of spaces; which will give the mean length, or what is the same thing, the mean pressure upon the piston in pounds per square inch. Multiply the number of square inches of area in the piston by the number of pounds on the square inch, and by the speed of the piston in feet per minute, and divide by 33,000, which gives the actual number of horses' power: or we may square the diameter of the cylinder, multiply by the effective pressure per square inch, and by the

motion of the piston in feet per minute, and divide the product by 42,017, which gives the same result.

A horse-power is represented by a load of 33,000 lbs., raised one foot high in the minute, which is equal to 528 cubic feet of water raised through the same distance. Mr. Watt, when he first applied his engines to perform work that had previously been performed by horses, felt that some such unit as a horse-power would be convenient in enabling him to estimate the size of engine required. He therefore made experiments to ascertain the weight that might be lifted per minute by the strongest London horses, and found it on the average to be 33,000 lbs. raised through one foot in the minute. It is only the strongest horses, however, that can lift so much; and Mr. Smeaton had previously found that 22,000 lbs. raised one foot high in the minute is as good a performance as can be had from horses of average strength working eight hours a day. Mr. Watt, however, appears to have been desirous that his engines should exceed rather than fall short of their nominal power, and therefore fixed upon a larger performance. In modern engines, the mechanical efficacy of the dimension of engine answering to a horse-power has been greatly increased, so that every horse-power of an engine rated at 100 horses, that is, every nominal horsepower, may lift 66,000 pounds one foot high in the minute, instead of 33,000. A nominal horse-power, therefore, is now merely a commercial unit by which engines are bought or described; but the dimension of engine answerable to this nominal power, is that represented by the actual power in Watt's original engines. A table of these dimensions is given at p. 214., and the result is expressed with tolerable nearness by our rule, p. 107., and d 2v by the rule is another rule which gives tolerably 6000 5640 accurate results, and which, expressed in words, is,-Subtract 1 from the diameter of the cylinder in inches, and square the remainder, which multiply by the velocity of the piston in feet per minute, and divide by 5640 the result is the horse-power. The speeds of piston, with different lengths of stroke, are given at p. 214. This rule gives 0 for the power of an engine with a cylinder 1 inch in diameter, the whole of the power of such an engine being considered to be absorbed by friction, which is relatively greater in small engines.

(d-1)'v - H. P.

Fig. 340. represents an indicator diagram taken from H.M.S. Spiteful, made with a different indicator, in which the graduation is more nearly one-eighth than one-tenth of an inch to the pound of pressure. The scale is shown at each end of the diagram. In this case, the pencil, starting from the atmospheric line, immediately rises up to 5 lbs. pressure; but from the beginning of the stroke the pressure slowly declines, showing that the steam is wire-drawn, and at about three-fourths of the stroke the pressure declines more rapidly, showing that at that point the steam is cut off, leaving the rest of the stroke to be performed by expansion. Before the stroke is completed, the pressure in the cylinder has fallen to between 2 and 3 lbs. below the pressure of the atmosphere. The slanting away at the eduction corner shows that the eduction passages are of insufficient area, and the lead corner shows that there is more lead given to the valve than is usual. The following are some of the dimensions of this engine:- Diameter of cylinder, 63 in.; length of stroke, 6 ft.; stroke of valve, 15 in.; cover on steam side, 3 in.; cover on exhausting side, 1 in.; size of ports, 253 by 63 in.; load on safety valve, 6 lbs. per square inch. By computing, according to the rules given at p. 90., the amount of expansion due to the amount of lap and stroke of valve here given, it will be found that the steam will be cut off when from one-third to one-fourth of the stroke remains to be completed, which the diagram shows to be the case.

Fig. 341. is an indicator diagram taken from the air pump of the same vessel, the Spiteful, the diameter of which is 3 ft. 1 in., and the stroke 3 ft. 3 in. The diameter of the waste water pipe is 12 in. When the air pump bucket was at the bottom of its stroke, the indicator pencil was at a, showing a vacuum in 1hs the pump of about 12 lbs. on the As the bucket

45 square inch.

rose, the air and vapour in the pump was compressed till the pencil reached the point b, showing a pressure of about 6 lbs. above the atmosphere. At this -0 point the delivery valve seems to have opened, and allowed the pent up vapours to escape, when the pencil fell to the point c, but here the water in the pump 5 seems to have come against the cover, forcing up the pencil to its highest point, d, which shows a pressure of about 8 lbs. above the atmosphere. From this point the pressure appears to diminish to e, 10 during the ascent of the bucket, and from e to ƒ during the downward stroke. The diagram, however, from d downwards to ƒ, is anomalous, for how can the pres

5

sure be supposed to descend from d to e when the bucket is still ascending, and wherefore does the line slant away from e to f, when it ought to fall perpendicularly, in consequence of the immediate formation of a vacuum in the pump, caused by the descent of the bucket? It appears to us that the cover of the air pump must have leaked air at the time this diagram was taken, and we think further that the string leading to the indicator must have come against some part of the engine towards the end of the o top stroke, thereby shortening the string, and quickening at that point the travel of the paper, whereby the slanting off, proper to the recoil of the spring from d to e, and to the imperfect vacuum from e to f, would be exaggerated. Fig. 342. is another indi- 5cator diagram, taken from an air pump, which in this case is that of the City of Aberdeen; and here, it will be seen, there is no distortion such as that which occurs in the Spiteful's diagram. The following are some of 10the dimensions of the parts of the City of Aberdeen's engines which have reference to 12 the diagrams we have given. Diameter of cylinder, 62 in.; length of stroke, 5 ft. 6 in.; lap on steam side of valve, 1 in.; pressure of steam, 7 lbs.; lead, in.; dia

4

a

meter of air pump, 37 in.; length of stroke of air pump, 3 ft.; diameter of waste water pipe, 12 in.; height of mouth of discharge pipe above Fig. 342.

h

-10

12

In marine engines the air pump is always made of a larger size than that commonly used for land engines; for when the speed of the engine is momentarily diminished by the waves rising around the paddle-wheels, the injection water is all the while running into the condenser in undiminished quantity, and unless the air pump be very large, it will be unable at such times to deliver the water.

Fig. 343. is an indicator diagram taken from the cylinder of a land engine 54 in. diameter, and 5 ft. 6 in. stroke, erected by Mr. Fairbairn. The steam

Fig. 343.

Atmospheric Line.

INDICATOR DIAGRAM TAKEN FROM THE AIR PUMP OF THE STEAM VESSEL CITY OF ABERDEEN.

delivery valve, 7 ft. 8 in. The pressure on the air pump bucket due to this head of water is about 4 lbs. on the sq. in. The scale of the diagram is th of an inch to the pound pressure, and the pressure shown by the diagram is about 5 lbs. on the inch; so that about 14 lbs. on the inch is required to open the delivery valve, and overcome the friction of the passages. The vacuum in the pump is about 12 lbs. on the inch. The pencil in indicator diagrams very generally makes a few oscillations up and down before it indicates the true pressure. This is caused by the momentum of the indicator piston; and it is therefore expedient to make it as light as possible.

We may here, by way of example, compute the power required to work the air pump of the Spiteful, taking the diagram to represent the power actually expended. We may first divide the diagram by the dotted lines, 1,2, and 3, into four equal parts, which parts we may again subdivide, making eight ordinates altogether. The pressure per square inch on the bucket will therefore be,- during the first eighth of the stroke, 0; during the second eighth, ; third 1; fourth, 2; fifth, 6; sixth, 13; seventh, 15; eighth, 18; the mean of which is 7. From this has to be deducted the pressure which assists the bucket in its descent, whether from the leakage of air or otherwise, and which is, during the first eighth, 8; during the second eighth, 1; and during the remainder of the stroke, 0. This gives a mean of 1.25 lbs., which, deducted from 7, leaves 5.75 lbs. on the square inch. The weight of water lifted by each stroke, taking the delivery valve to open at the point c, will be 395 lbs., which, divided by 1104, the square inches of area of the bucket, gives 357 lbs. of pressure per square inch, produced by the water lifted each stroke, making 6.107 lbs. effective pressure per square inch opposing the ascent of the bucket. This is equivalent to 3.053 lbs. resisting the motion both ways, or since the air pump is about th of the capacity of the cylinder, it is equivalent to a fifth of 3-053 lbs. or 611 lbs. per square inch acting on the piston. Hence the number of horses' power expended in working the air pump of this engine is found by multiplying the area of the piston in square inches by 611 lbs., then multiplying by the speed of the piston in feet, and dividing by 33,000.

INDICATOR DIAGRAM OF A LAND ENGINE THROTTLED BY THE ACTION OF THE GOVERNOR,

in the boiler is of a pressure of 3 lbs. on the square inch, which pressure is not reached in the cylinder, and there therefore appears to be condensation in the steam pipes. The pressure is tolerably well maintained at the commencement of the stroke, on account of the slowness of the motion at that time; it rapidly declines as the speed of the piston quickens, but rises somewhat towards the end of the stroke, in consequence of the diminution of the piston's speed. If the valve had been furnished with sufficent lap to cut off the steam at half stroke, the diagram would have followed the direction of the dotted line, and the effect would have been superior. The engine is obviously working much below its power.

The attendants upon engines should prepare themselves for any casualty that may arise, by considering possible cases of derangement, and deciding in what way they would act should certain accidents occur. The course to be pursued must have reference to particular engines, and no general rules can therefore be given; but every marine engineer should be prepared with the measures to be pursued in the emergencies in which he may be called upon to act, and where every thing may depend upon his energy and decision. If the ship springs a leak, the water may generally be kept under by injecting from the bilge, and every steam-vessel should be provided with cocks for this purpose. These cocks should not communicate with any rose within the condenser, as the water drawn from the bilge is not clean water, and a rose within the condenser would probably soon become choked up. Should there be no injection from the bilge, a great deal of water may be lifted out by partly opening the snifting valves, but should they be of such a construction as not to admit of being opened by a handle, or should they be in an inacessible position, the cover of the foot valve, or the man-hole door of the condenser, may be slackened. If the snifting valve cannot be opened readily, the injection may be shut off, so that the engine will heat and vitiate the vacuum, and the valve will then open of its own accord during the descent of the air pump bucket. When raised, it must be prevented from closing again by something being wedged in below it: the steam will then be condensed in the air pump, and the water drawn