one only being bolted to the cylinder flanges; the inner one is a plain disc, nicely fitted to the internal diameter of the cylinder, and faced for the circumferential portion of the piston to work against. This plate is capable of the most accurate adjustment by means of screws, which are of a peculiar arrangement; two screws, a hollow and a solid one, being employed. A hollow bolt screwed on the outside is first fitted into threads in the external cover, so as to project slightly through into the interior, and press against the exterior surface of the inner set-up plate. Through the centre of this hollow bolt a solid one is passed, and screwed into the disc by a thread cut for a short distance near the end of the bolt. By this contrivance the hollow bolt presses firmly against the back of the set-up disc, whilst the inner solid bolt, when turned, pulls the disc tight against the former, and enables the engine-attendant to set it accurately, so as to work with the least possible friction in the piston. The latter being used out, and only a narrow ring of metal being left near the circumference for frictional wear, the irregularity of wear found in the action of two plain discs of great area is not found here, as the difference in the distances passed through by the outer and inner portions of the bearing ring of the piston is quite inappreciable. Under a pressure of steam of 22 lbs. the engine made 70 revolutions per minute, consuming 2 cwt. of slack coal in 24 hours, having a power of 12 horses. We have been thus particular in describing this engine, as it may be taken as an excellent type of this peculiar class; one abounding in high ingenious mechanical contrivances, and one, moreover, which has passed the ordeal of practical working with a high degree of satisfaction.

The "elliptic rotatory engine" is one of the most successful examples of the modern attempts to apply steam-power directly to a revolving cranklever, so as to economise steam, lessen the weight, simplify the constructive details, and convey the power directly to its work. Such an engine is, indeed, practically equivalent to the causing the steam to lay hold of and actuate the crank or revolving shaft, just as the hand turns round a winch, without the intervention of joints, levers, and connecting-rods. It is the invention of Mr. William Hyatt, the engineer to Champion's extensive Vinegar Works, of Old Street Road, St. Luke's, London, and is being carried out by him, in conjunction with Mr. Wright, the managing proprietor of the works. The essential peculiarity of the engine is to be found in the fact, that the steam-cylinder is bored elliptically, in order that the revolving piston within it, when set upon a shaft disposed eccentrically in relation to the minor axis of the ellipse, may fit accurately to the elliptic surface throughout the entire revolution. This is a peculiar and unlooked-for characteristic of the elliptical figure. The true action is only to be secured when the amount of ellipticity is exceedingly slight, the centre of motion of the revolving piston-shaft being in a line intersecting the minor axis, at about one-third the length of such axis. That such an engine does work in the most satisfactory manner, is now practically exemplified at the Old Street Vinegar Works, where the engine, from which our drawings, in figs. 127, 128, and 129, were made, is in daily operation. (1853.)

Fig. 127 is an external longitudinal elevation of the engine in working order. Fig. 128 is a corresponding end-elevation at right angles to fig. 127,

the front end cover of the cylinder being removed to show the piston within. Fig. 129 is a plan of the engine.

The short steam-cylinder, a, open at each end, and fitted with two end

covers, is placed with its axis horizontal upon the base-plate b, being bolted down thereon by four projecting eyes c; the horizontal piston-rod, or

fg. 128.

main-engine shaft, d, is passed eccentrically through the cylinder, and in the vertical line of the minor or conjugate axis of the ellipse. The castiron rotatory piston e is suitably fitted with packing-pieces, and slotted trans

fig. 129.

versely at f, to fit the piston-rod, the transverse section of which at that part is rectangular. The slot ƒ is for the purpose of allowing of the selfadjustment of the piston during its revolution in working, by sliding laterally over the squared shaft or rod d; or, instead of this more direct sliding action, a frame may be introduced to carry anti-friction-rollers, working upon the shaft-surface, and adjustable by the aid of screws and wedges. The packing of the piston-which packing is, at the same time, a portion of the working steam-pressure surface-consists of two metallic strips or ribs, g, of the length of the cylinder, the outer projecting surface of such ribs being rounded, whilst their inner flat sides are fitted into shallow groves h, formed diametrically opposite to each other along the piston, and in its axial line. The actual working packings are strips of metal, i, fitted on their inner sides to the external rounded surfaces of the pieces, g, whilst their outer surfaces bear against the interior of the cylinder. These outer-rubbing surfaces of the packings, i, are considerably rounded in transverse section, the radius of curvature being slightly less than that of the quickest curve of the cylinder's bore, so that the packing may work round the sharpest elliptic curves with facility; and helical springs are set in behind the packing-pieces, to admit of a free adjustment during working. The flat-end packing, for keeping the piston steam-tight at its two ends, is composed in each case of the brass-ring j, let into the end of the piston, and having two projections, k, upon it, passing through slots in the end of the strips g, thus forming a simple and effective end-packing. A small brass-plate, k, is let into the end of the strips, i, to complete the end-packing. The piston-rod is supported in a stuffing-box, 7, on the outside of each cylinder end-cover; and the engine in the present case being a single one, the shaft has a fly-wheel, m, keyed upon it, the heavy rim of the wheel being cast hollow at certain parts to balance the overhang of the piston. That end of the shaft which passes away to the machinery to be driven is supported in a pedestal, n, bolted down on the base-plate; this bearing, in conjunction with the pair of stuffing-boxes, being the only bearings requisite. When one end only of the shaft is used for driving, no working valves are required in this engine, the steam being admitted in a constant stream by either of the two opposite ports o, the only variation of the current being when the slot ƒ is horizontal, this being the dead centre of the engine; and both ports are then closed. Or, by another slight modification, the steam and exhaust ports may be made to extend a long way round the cylinder, in order that the engine may have no dead point, the steam being admitted to the back of the revolving piston-blade before it is entirely shut off from the front side. For reversing, an ordinary three-way cock answers every purpose, one cock being set on each side of the cylinder, and put in connection by means of two doublebranched pipes; so that either side may be made the steam ingress side. The steam acts equally well in both directions of revolution, the effective pressure being that upon the overhang or eccentricity of the piston, which is constantly varying in effective area throughout the revolution; the piston being, indeed, a direct-acting crank-lever for turning the shaft. For lubrication, an oil-reservoir, p, is set on the top of the cylinder, a stop-cock, q, being fitted beneath it to command the flow through the pipes r, which have each two branches for lubricating the bored portion of the cylinder and the flat-end cover-surfaces. The length of the axial line of the cylinder

of the engine is 24 inches, whilst its diameter or bore is to be defined by an ellipse with a major axis of 20 inches, and a minor axis of 18 inches. This engine is called a 30-horse, whilst with a pressure of 32lbs. of steam the indicator has shown a power of 50 horses. Our readers may judge of its compactness by comparing this power with the area actually occupied, as shown in our drawing.

As

"We think we may safely point to Mr. Hyatt's engine, as being the simplest and most compact of the really effective existing examples of the direct-pressure rotatory class. It is evidently applicable for all the purposes to which the ordinary engine can be applied, as well as to many which are beyond the reach of the old form. With an actuating power applied to its shaft, it at once becomes a forcing or exhausting pump; and, slightly modified, it becomes suitable for the purposes of locomotion. a railway engine, it is proposed to use two cylinders-one on each driving axle-the axles being thus made the engine piston-rods; whilst the dead points are of course avoided by the usual expedient of setting the lines of greatest effect at right angles to each other, the axles being coupled in the common way. But the most obvious application of the engine is for screw propulsion. The screw-shaft becomes the piston-rod; and as there is no reciprocation about it, any reasonable speed is attainable, whilst the power is conveyed direct to the screw. Indeed, the practical valve of this motor is, in our opinion, as great, as its peculiar mechanical action is elegant."

A steam-engine, to which much attention has been directed of late, is that known as Simpson and Shipton's Reciprocating Steam-Engine. To an arrangement of parts of simplicity in detail, it adds the novelty of a movement remarkable for its originality. Although in many respects resembling at first sight an engine of the rotatory plan, it is nevertheless a reciprocating engine, only differing, in the words of the inventors, from the ordinary engine in the means adopted for obtaining the revolving motion direct out of the rectilinear, the principle through which power is obtained being the same as in the ordinary reciprocating engine; a piston acted upon by steam being propelled in a rectilinear direction in a cylinder or steam-chamber, which, in the present case, is square or rectangular instead of circular, the germ of the engine being "an eccentric revolving in its own diameter;" and which is, in fact, the piston and crank combined in one body; this having in itself two distinct motions, rectilinear and revolving. The following is derived from the inven

e

f

tors, descriptive of the principle and arrangement of the engine. In fig. 130 suppose a to be a crank filled up completely between the sides of the steam-chamber ef; when steam is admitted above the crank a, as shown by the arrows, it moves into the position shown by b; in that position, however, it will be observed that the crank will be too short to fill up the chamber, and the steam would consequently rush past it to the lower part of the chamber; it therefore becomes necessary to change the form of the crank, making it such that, at every position, the space between ef may be filled up; this form resolves itself into the circle 9 9, with the shaft or axle c passing through it out of the common centre; this is therefore an ordinary eccentric. When steam is brought

fig. 130.

to act on its surface, it is propelled into the dotted position ii; and from its being eccentric, a revolving motion is obtained during its pro

fig. 131.

pulsion. In fig. 131 is a transverse section, and in fig. 132 a longitudinal section, showing the arrangements by which this principle is carried

out. a is the steam-chamber or cylinder; b the piston, keyed on eccentric to the shaft c, and carried on the rods ff, vibrating from the crankshaft pedestals. This piston is turned true on the periphery; and in each