versely at f, to fit the piston-rod, the transverse section of which at that part is rectangular. The slot fis 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, ¿, 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.

"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. As 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 inventors, 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 g g, with the shaft or axle e passing through it out of the common centre; this is therefore an ordinary eccentric. When steam is brought

fig. 130.

f

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

end are turned conical seatings, in which are fitted rings of metal k k, cut open on one side, leaving a lap-joint to prevent escape of steam. These rings are capable of being adjusted by bolts passing through the side plates 11, and are thus easily adjusted. The cranks gg are keyed on the shaft at right angles to each other, equidistant from a line drawn through centre of shaft and centre of piston; these cranks convey the power to the lower cranks, ii, by rods or drag-links h h. The vibrating rods ff are carried on the pedestal jj. The ends of the cylinder a do not require to be bored, as the whole wear takes place on the plates d and e. The plate e is dovetailed in and fitted fast; d, being loose in its parallel recess, which allows it to follow up the piston as it wears; the plate d is kept up to the face of the piston by springs behind it, or by admitting steam into the recess at the back of it. This plate serves another useful purpose; this is the prevention of priming in the cylinder: as the water increases in the cylinder, it forces back the plate, and rushes from one side of the piston until it escapes. Steam is admitted to act on the piston by means of a valve n through the steam-ports m m, open to the top and bottom of the piston alternately; the valve is worked by an eccentric o keyed on the crank-shaft p. This valve is on the equilibrum principle, and exhausts through the back, and works between two parallel planed surfaces; the wear that takes place being accommodated by a ring of metal o, similar to that employed for packing the piston. This form of engine is being employed in numerous instances, and with marked economical effect.

As the concluding portion of the present division of our treatise, we propose briefly describing the principles of action of two varieties of engine which have been successfully introduced into practice; these are the "Cambrian" and the "Disc Engine."

In the Cambrian engine the piston has a semi-rotatory motion given to it by the following arrangement: Let a a, fig. 133, be the external casing or cylinder; cb the arms of a piston vibrating on the axle d; the steam space is divided into compartments by the triangular abutments ef; the pipe g admits steam to the compartment m, and h into s; the steam is exhausted through o. By passages cut in the pistonshaft, diagonally, as in x; steam is admitted from the space s into t, and from the space m into n. The steam, on being admitted to one of the spaces, as m, passes into the opposite space n, and thus presses on both ends of the piston b and c, but on opposite sides; the strain on the working parts is by this arrangement much reduced. By this pressure on the alternate sides of the piston a reciprocating motion is produced in the piston-shaft d, which is communicated to the crank-shaft in the usual manner. A large number of engines on this principle have been successfully introduced.

fig. 133.

The movement of the "disc engine" is very peculiar; the most lucid exposition of its principle we have met with is that given by a "practical engineer," himself a well-known and able inventor, in the pages of the Expositor. We here append it: "The vessel in which the piston moves, the fixed recipient for the action of the steam, is the section of a hollow

sphere, such as would remain after two equal opposite segments were cut off. In this is fitted the piston, called from its form and peculiar movement a disc. The centre of the disc coincides with that of the sphere; and as its diameter is equal to that of the inside of the sphere, it can have no direct movement like the common engine piston; but it may perform an oscillatory motion, such as a top or a teetotum describes when their spinning force is nearly

exhausted; that is to say, each point in the periphery successively dips; and the lowest point seems to proceed round the periphery, though there need not necessarily be (nor is there in this engine) any absolute rotation. Like a wave each point in the disc in its turn rises and falls; and like the wave also, there is no onward motion. To understand the action more perfectly, we refer to the following diagram (fig. 134): a a is the spherical case we have described, b is the disc, and c a ball concentric with the axis d; ef are two conical covers, g is a crank, into which the end of the axis d is inserted. If the crank be now turned round, it will be seen that every part of the disc b will successively be brought into contact with the cones at two opposite radial lines; but the rotation of the axis of the crank need not necessarily cause the disc to perform any other than the oscillatory one we have described, and, as we have said, it cannot do so. There is a slot in the disc thus (fig. 135), and there is a partition in the engine extending from the outside to the ball and fitting the two cones. When we turn the

two cranks, therefore, the oscillatory motion will be performed by the disc and axis, the side of the slot rubbing up and down on the surface of the partition." It is difficult to describe the way in which the disc receives the effort of the steam; but it may be sufficient to state, that the struggle or force of the steam to enter and escape, passing through an entrance made in one of the conical covers on one side of the partition to the exit-pipe placed on the other side of the partition, forces the disc partially round, and acting on the ball c, makes the lever d rise and fall in the direction of the arrows, and thus communicates motion to the crank g.

The first patent for the disc-engine was taken out by a Mr. Dakeyne in 1830. His engine was not, however, put in practice. Henry Davies was the next inventor who turned his attention to this engine. He took out three patents, each combining successive improvements in its action, his last patent being taken out in 1844, in which his improvements had reference to working the engine expansively. He introduced a variety