Page images
PDF

packed with hemp round the collar, makes a tight joint; the piston, D, is affixed to the spindle within the cylinder, and fits it tight all round by means of leathers, applied as described in the beerengine; at E, fig. 4, a partition, called a saddle, is fixed in the cylinder, and fits against the back of the spindle tight by a leather. We have now a cylinder divided by the saddle, E, and piston, into two parts, whose capacity can be increased and diminished by moving the piston, with proper passages and valves to bring and convey away the water: this will form a pump. These passages are cast in one piece with the cylinder: one, d, for bringing the water, is square, and extends about ; round the cylinder; it connects

at bottom with a pipe, e, at its two upper ends opens into two large chambers, fg, extending near the whole length of the cylinder, and closed by covers, h h, screwed on : i k, are square openings (shown by dotted squares in fig. 3.) in the cylinder, communicating with the chambers: fg, 1 m, are two valves, closing their ends of the curved passage, d, and preventing any water returning down the passage, d: no, are two passages from the top of the cylinder, to convey away the water; they come out in the top of the cylinder, which, together with the top of the chambers, f, g, form a large, flat surface, and are covered by two valves, p 7, to retain the water which has passed through them. A chamber, K, is screwed over these valves: and has the air vessel k, fig. 1 and 2, screwed into its top ; from each side of this chamber a pipe, w w, proceeds, to which a hose is screwed, as shown in fig. 1. Levers, ac ar, are fixed to the spindle at each end, as shown in fig. 1, and carry the handles, H H, by which men work the engine. When the piston moves, as shown by the arrow in fig. 4, it produces a vacuum in chamber, f, and that part of the cylinder contiguous to it; the water in the pipe, e, then opens the valve, m, and fills the cylinder. The same motion forces the water contained in the other part of the cvlinder through the valve, q, into chamber, K, and thence to the hose through the pipe, w; the piston being turned the other way reverses the operation, with respect to the valves, though it continues the same in itself. The pipe, e, is screwed by a flanch to an upright pipe, P, fig. 5, connected with another square iron pipe, fastened along the bottom of the chest of the engine: a curved brass tube,

G, comes from this pipe, through the end of the chest, and is cut into a screw, to fit on the suction hose, when it can be used; at other times a close cap is screw. ed on, and another brass cap at H, within the chest, is screwed upwards on its socket, to open several small holes made in it, and allow the water to enter into the pipe ; in this case the engine chest must be kept full of water by buckets. The valves are made of brass, and turn upon hinges. . The principal advantage of the engine is the facility with which it is cleaned from any sand, gravel, or other obstructions, which a fire-engine will always gather when at work.

The chambers, f, g, being so large, al. low sufficient room to lodge a greater quantity of dirt than is likely to be accumulated in the use of the engine at any one fire; and if any of it accidently falls into the cylinder, it is gently lifted out again into the chambers by the piston, without being any obstruction to its motion: to clear the engine from the dirt, two circular plates, r r, five inches diameter, are unscrewed from the lids, h h, of the chambers fg, and when cleaned are screwed on again : these screw covers fit perfectly tight without leather, and can be taken out, the engine cleared, and enclosed again in a very short time, even when the engine is in use, if found necessary.

The two upper valves, p g, and chamber, K, can also be cleared with equal ease, by screwing out the air vessel, k k, fig. 1, which opens an aperture of five inches, and fits air-tight, without leather, when closed. The valves may be repair. ed through the same openings. The use of the air-vessel k k, fig. 1 and 2, is to equalize the jet, from the engine during the short intermittance of motion at the return of the piston stroke: this it does by the elasticity of the compressed air within it, which forces the water out continually, though not supplied quite regu. larly from the engine.

The engine from which our drawing was taken was made for the Sun Fire Insurance Company, in London, and from some experiments made by their agent, Mr. Samuel Hubert, appears to answer every purpose.

ENGINE, for raising water. The frame of the machine is of cast iron, nearly in the form of the letter A.; there are two of these frames, BB, (fig. 1, Plate PumpEngine,) screwed together by means of five wrought iron pillars, a a a a ; D is another smallerframe, to support the axis

of the fly wheel, connected with the other frame by three short pillars; E, is the fly wheel, turned by winches on the end of its axis; it has a pinion (13) of 13 leaves upon its axis, turning a wheel (48) of 48 teeth, on whose axis are two cranks b, b, opposite to each other, to work the pumps : ee, are the two crank rods, made each in two branches, and jointed at the lower end into two other rods, f f, which slide through holes made in the fixed bars, gog, fig. 2; the crank rods receive these bars between their two branches, and by this means, though the rods, f f, are confined by their guides to move truly vertical, the crank rods, e e, can partake of the irregular motion of the crank. The pump rods of the pumps are screwed to the rods, f f, by two nuts, and go down into the pumps, G H, sup#: from the iron frame by eight iron races, h h. The pumps consist of two barrels, G H, with valves at the bottom, allowing water to enter them freely, but preventing its return ; the buckets fixed to the pump rods fit the barrels truly, and have valves in them shutting downwards; I, is a chest bringing water to the valves in the bottom of the barrels; K, is another, communicating with the top of the barrels by two crooked passages, to carry away the water from them; the barrels are close at top, and the pump rods pass through close stuffing boxes, through which no water will leak by them. The action of the pump is the same as the common sucking pump : when the bucket is drawn up, the valve in it closes, and it forms a vacuum in the lower part of the barrel; this causes the water to ascend into it through the chest, I, to restore the equilibrium ; at the same time it raises all the water which was above it through the chest, K: on the descent of the bucket the valve at the bottom of the barrel shuts, and prevents the escape of the water; the valve in the bucket opens, and the water passes through it, ready to be raised at the next stroke. The barrels in question are 3% inches diameter, and 8 inches stroke. As the two cranks, b, b, are opposite each other, when one bucket is rising, the other is going down; by this means the power required to turn the machine by the handles is equalized, and also the quantity of water raised by the engine. - Engines for raising water, by the pressure and descent of a column inclosed in a pipe, have been lately erected in dif. ferent parts of the country. The principle now adverted to was adopted in

some machinery executed in France about 1731, and was likewise adopted in Cornwall more than forty years ago; but the pressure engine, of which we are about to give a particular decription, is the invention of Mr. R Trevithick, who probably was not aware that anything at all similar had been attempted before. This engine, a section of which, on a scale of 3d of an inch to a foot, is shewn in Plate

Pressure-Engines; one was erected about eight years ago at the Druid copper mine, in the parish of Illogan, near Truro. A B, represents a pipe six inches in diameter, through which water descends from the head to the place of its delivery, to run off by an adit at S, through a fall of 34 fathoms in the whole; that is to say; in a close pipe down the slope of a hill 200 fathoms long, with 26 fathoms fall; then oño, six fathoms, till it arrives at B, and thence through the engine from B to S two fathoms; at the turn B, the water enters into a chamber, C, the lower part of which terminates in two brass cylinders, four inches in diameter; in which two plugs or pistons of lead, D and E, are capable of moving up and down by their piston rods, which pass through a close packing above, and are attached to the extremities of a chain leading over and properly attached to the wheel Q, so that it cannot slip. The leaden pieces, D and E, are cast in their places, and have no packing whatever. They move very easily; and if at any time they should become loose, they may be spread out by a few blows with a proper instrument, without taking them out of their place. On the side of the two brass cylinders, in which D and E move, there are square holes communicating towards G, with a horizontal trunk, or square pipe, four inches wide, and three inches deep. All the other pipes, G, G, and R, are six inches in diameter, except the principal cylinder wherein the piston, H, moves; and this cylinder is ten inches in diameter, and admits a nine foot stroke. The piston rod works through a stuf. fing-box above, and is attached to M N, which is the pit rod, or a perpendicular piece divided into two, so as to allow its alternate motion up and down, and leave a space between, without touching the fixed apparatus, or great cylinder. The pit rod is prolonged down in the mine, where it is employed to work the pump ; or, if thc engine was applied to mill-work, or any other use, this rod would be the communication of the first mover. K L, is a tumbler, or tumbling bob, capable of being moved on the gudgeons, V, from its present position to another, in which the weight L, shall hang over with the same inclination on the opposite side of the perpendicular, and consequently the end, K, will then be as much depressed as it is now elevated. The pipe, R S, has its lower end immersed in a cistern, by which means it delivers its water without the posibility of the external air introducing itself; so that it constitutes a Torricellian column, or water barometer, and renders the whole column from A to S effectual, as we shall see in our view of the operation. The operation. Let us suppose the lower bar, K V, of the tumbler to be horizontal, and the rod, PO, so situated, as that the plugs, or leaden pistons, D and E, shall lie opposite to each other, and stop the water ways, G and F. In this state of the engine, though each of these pistons is pressed by a force equivalent to more than a thousand pounds, they will remain motionless, because these actions being contrary to each other, they are constantly in equilibrio. The great piston, H, being at the bottom of its cylinder, the tumbler is to be thrown by hand into the position here delineated. Its action upon O P, and consequently upon the wheel, Q, draws up the plug E, and depresses D, so that the water way, F, becomes open from A B, and that of G to the pipe R : the water consequently descends from A to C, thence to F, until it acts above the piston F. This pressure forces down the piston, and if there be any water below the piston, it causes it to pass through G G G into R.: during the fall of the piston, which carries the pit rod, M N, along with it, a sliding block of wood, I, (dotted) fixed to this rod, is brought into contact with the tail. K, of the tumbler, and lowers it to the horizontal position, beyond which it oversets by the acquired motion of the weight L. The mere rising of the piston, if there was no additional motion in the tumbler, would only bring the two plugs, D and E, to the position of rest, namely, to close G and F, and then the engine would stop ; but the fall of the tumbler carries the plug, D, upwards, quite clear of the hole, F, and the other plug, E, downwards, quite clear of the hole, G: these motions require no consumption of power, because the plugs are in equilibrio, as was just observed. In this new situation

the column, A B, no longer communicates with F, but acts through G upon the lower part of the piston H, and raises it; while the contents of the great cylinder above that piston are driven out through F, and pass through the opening at D into R. It may be observed, that the column which acts against the piston is assisted by the pressure of the atmosphere, rendered active by the column of water hanging in R, to which that assisting pressure is equivalent, as has already been noticed When the piston has ascended through a certain length, another slide or block upon the pit-rod (not seen) applies against the tail, K, of the tumbler, which it raises and again oversets, producing once more the position of the plugs D E, here delineated, and the consequent descent of the great piston H, as before described. The descent produced the former effect on the tumbler and plugs, and in this manner it is evident that the alternations will go on without limit, or until the manager shall think fit to place the tumbler and plugs, D E, in the positions of rest, namely, so as to stop the passages, F and G. The length of the stroke may be varied by altering the positions of the pieces, I, and the other lower down, which will shorten the stroke, the nearer they are together; as in that case they will sooner alternate upon the tail, K. As the sudden stoppage of the descent of the column, A B, at the instant when the two plugs were both in the waterway, might jar and shake the apparatus, those plugs are made half an inch shorter than the depth of the side holes, so that in that case the water can escape directly through both the small cylinders to R. This gives a moment of time for the generation of the contrary motion in the piston, and the water in G G G, and greatly deadens the concussion which might else be produced. See STEAM ENGINE. Some former attempts to make pressure engines upon the principle of the steam-engine have failed; because water, not being elastic, could not be made to carry the piston onwards a little, so as completely to shut one set of valves and open another; in the present judicious construction, the tumbler performs the office of the expansive force of steam at the end of the stroke. ENGINE for driving piles, used at building Westminster bridge, is constructed as follows: A, (Plate V. Miscel. fig. 3.) is the great shaft, on which are the great wheel and drum : B, the great wheel with cogs, that turns a trundle head with a fly, to prevent the horse’s falling when the ram is discharged; C, the drum on which the great rope is wound ; D the follower (with a roller at one corner) in which are contained the tongs, to take hold of the ram, and are fastened to the other end of the great rope, which passes over the pulley, near the upper end of the guides, between which the ram falls; E, the inclined planes, which serve to open the tongs, and discharge the ram; F, the spiral barrel that is fixed to the drum, on which is wound a rope with a counterpoise, to hinder the follower from accelerating, when it falls down to take up the ram ; G, the great bolt which locks the drum to the great wheel ; H, the small lever, which has a weight fixed at one end, passes through the great shaft below the great wheel, and always tends to push the great bolt upwards, and lock the drum to the great wheel; I, the forcing bar, which passes through the hollow axis of the great shaft, bears upon the small lever, and has near the upper end a catch, by which the crooked lever keeps it down; K, the great lever, which presses down the forcing bar, and dis

charges the great bolt at the time the .

long end is lifted up by the follower; L., the crooked lever, one end of which has a roller, that is pressed upon by the great rope, the other end bears upon the catch of the forcing bar during the time the follower is descending; M, the spring that presses against the crooked lever, and discharges it from the catch of the forcing bar as soon as the great rope slackens, and gives liberty to the small lever to push up the bolt. By the horse’s going round, the great rope is wound about the drum, and the ram is drawn up, till the tongs come between the inclined planes, where they are opened, and the ram is discharged. Immediately after the ram is discharged, the roller, which is at one end of the follower, takes hold of the rope that is fastened to the long end of the great lever, and lifts it up ; the other end presses down the forcing bar, unlocks the drum, and the follower comes down by its own weight. As soon as the follower touches the

[blocks in formation]

up the great bolt, and to lock the drum to the great wheel, and the ram is drawn up again as before. ENGINEER, in the military art, an able, expert man, who, by a perfect knowledge in mathematics, delineates upon paper, or marks upon the ground, all sort of forts, and other works proper for offence and defence. He should understand the art of fortification, so as to be able, not only to discover the defects of a place, but to find a remedy proper for them, as also how to make an attack upon, as well as to defend, the place. Engineers are extremely necessary for these purposes: wherefore it is requisite that, besides being ingenious, they should be brave in proportion. When at a siege the engineers have narrowly surveyed the place, they are to make their report to the general, by acquainting him which part they judge the weakest, and where approaches may be made with most success. Their business is also to delineate the lines of circumvallation and contravallation, taking all the advantages of the ground; to mark out the trenches, places of arms, batteries, and lodgments, taking care that none of their works be flanked or discovered from the place. After making a faithful report to the general of what is doing, the engineers are to demand a sufficient number of workmen and utensils, and whatever else is necessary. ENGRAFTING or Gn AfriNg, in gar. dening. See the article GaAfriNg.

ENGRAILED, or INGRAILen, in heraldry, a term derived from the French, hail; and signifying a thing the hail has fallen upon and broke off the edges, leaving them ragged, or with half rounds, or semicircles, struck out of their edges.

ENGRAVING. This term is at present confined to the art of excavating copper and wood, in lines, in sojudicious a manner, as to produce imitations of paintings and drawings when painted on paper. It is certain that engraving for the production of prints was unknown long after the practice of painting in oil had arrived to great perfection, but good prints are common from plates engraved in the fifteenth century, many of which are landscapes, most laboriously, and even excellently, performed by the graver, although it is well known that the instrument just mentioned cannot freely express those serrated and serpentine lines, necessary for foliage and short

D

[ocr errors]

grass intermixed with plants, since so admirably delineated in etchings. A goldSmith of Florence, named Maso Finiguerra, is said to have discovered the art; but this assertion must undoubtedly merely apply to his obtaining impressions from lines engraved originally without the least idea of such a result; were we to examine the subject closely, it might be proved, that outlines have been cut in metals, representing figures, &c. from the most remote periods of antiquity, but being subject to decay, they have not reached our time, as the more durable granites have done, embellished with hieroglyphics cut in them in a manner which might be printed on paper. Arguing from these premises, it may be inferred, that the ancients understood the art of engraving in metal, though without conceiving that the copies of their productions might be multiplied by means of ink on soft white cloth, or similar materials. Albert Durer, born in 1470, and who died at Nuremberg, 1528, is said to have been the first person on record claiming the name of an engraver in the long list of celebrated artists ; but certainly very excellent engraved brass figures, the lines filled with substances to show them more clearly, are now extant on tombs in some hundreds of churches in England, the dates of many of which are prior to the time of his birth. This fact will serve to prove that the printing of engraved plates was discovered between 1470 and 1528; indeed the perfection that engraving had reached in the latter century plainly demonstrates, that the use of the graver was by no means a modern discovery. The encouragement of the fine arts has ever been a distinguishing trait of the inhabitants of the continent of Europe; it is not wonderful, therefore, that engraving closely followed the footsteps of the parent arts, and flourished there in greater perfection than in England, where they have been in a state of miserable depression till within the last century, when literature was supposed to receive some aid from the graver; the booksellers, taking the hint, have encouraged the predilection of the public, which has operated as a stimulus to the artist, and the consequence is, that the graphic embellishments of British topographical and poetical works are equal, if not superior, to any in Europe. Historical engravings for the port folio and furniture seemed at one period to advance rapidly towards perfection, to which the late Alderman Boydell greatly

contributed; but the death of Strange, Hall, and Woollet, have been almost fatal to the hopes of the amateur, which rests, in a great measure, upon Heath, Sharp, Bromley, and a few others, as in this particular instance we do not include those eminent foreigners, who have or do at present reside in England. Whatever deficiencies we may discover in the prosecution of the arts in this country is, fortunately, not to be attributed to want of genius, or relaxation from study, in the artist; the chill of apathy in the rich, who view a wretched coloured aquatint with the same or more pleasure than the most laboured production of the graver, is the baleful cause of the languishing state of historical engraving. When persons capable of affording patronage are taught discrimination, future Woollets will fascinate the best judges of engraving. We shall now proceed to explain the methods of executing different descriptions of engraving. The graver, an instrument of steel, is the primary object for engraving on copper; it is square for cutting of broad lines, and lozenge for the finest, and must be tempered to that exact state, which will prevent the point from breaking or wearing by its action on the metal ; to obtain this state, is is customary to heat it when too hard on the end of a red hot poker, till it assumes a straw colour, and then cool it in oil ; if held too long, it will become blue, soft, and useless, till the process of tempering the steel is renewed. As it is possible a graver may be of the proper degree of solidity, except in some inconsiderable part, it would be well to rub it on the oil stone till that is ascertained. The graver is inserted in a handle of hard wood, resembling a pear with a longitudinal slice cut off, which is to enable the artist to use it as flat on the plate as his fingers and thumb will permit. In order to prepare this instrument for cutting a clear smooth line, great care must be taken, in sharpening it, that the original general form should be preserved, by laying the sides flat upon the oil-stone, and rubbing them so as not to round them in the least, after which the graver is to be held sloping towards the person, and rubbed thus till the point is extremely sharp ; besides these precautions, it will be necessary that the point should not be exactly in a right line with the lower part of the graver, but a little higher, that it may not |. too deep into the copper. In rub:

ing the sides of the graver, the usual

« PreviousContinue »