Fig. 3. Horizontal sections of the boiler, and a general plan of the engines. Figs. 4 and 5. Outline and section of a cylinder, steam-valves, and a foundation-plate. Fig. 6. Piston valves, to work in the valve-cases. Figs, 7 and 8. Side and edge views of the propelling vanes or screw. And 9 and 10. Development of the screw. The same letters and figures of reference are used to identify the same parts whenever they occur throughout the drawings. The Boiler. A A A A represents the outline of the boiler in figs. 1, 2, and 3, which is about 11 yards square in the plan. B B B B is a vertical section through the fires, near the middle of the width, showing the direction of the heated air and flame. a a, the furnaces; bb, the middle flues; and c c, the upper flues. On the boiler plan, in fig. 3, the portion marked d d shows a horizontal section through the line e e, (see fig. 2 ;) the portion marked ff, a section through at gg; and the part marked h h, a section through the line at i i. Within the boiler, and opposite the holes for the escape of steam to the engines at O, there is an inclined plate fixed, to prevent "priming," the top edge of which the steam has to pass. The entire boiler is divided by two vertical partitions, jj and kk, thereby forming three distinct sections, either of which may be put out of use if necessary. To each section there is a sluice, or slidevalve, fixed in the casting at D, with its face towards the boiler, the edges of which are planed to form wedges with the points upwards, so that by its being drawn up by the rod, it is at the same time forced hard between the seat frame and inclined brass bars, therefore shutting off the steam from that section of the boiler. CC C, figs. 1, 2, and 3, are an outline, section, and plan of the chimney. Through the head of the boiler, above the upper flues, there are two wroughtiron tubes of about 15 inches diameter, forming two holes through the boilers "'thwart ships." In each of these holes there is a second wrought-iron pipe, of. about 12 inches diameter, the object of which is to form a tie to keep the ship's sides from spreading, and also to act as a strut against external resistance. The vertical parts of the flues and water spaces are kept in their position by stay-bolts, some of 14 inch diameter, and others of 1 inch diameter, from 15 to 20 inches apart, and supported by props, with shoes and caps riveted to the flues. The boiler is to be furnished with six water gauges, safety-valves, blow offs, water-valves, and all the usual appurte nances. The Engines. DDDD are the steam cylinders, which are four in number. E, fig. 4, piston; and F, piston-rod. G G are sections of the steam-valve cases and side-pipes, in which m (fig. 5) is the steam branch from the boiler, containing the throttle-valve; n is the expansion slide-valve, working against a fixed plain flat face, but perforated with holes, as seen at p in fig. 4. qqqq are brass linings; rrr is the eduction passage from cylinder to condenser. H is an escape-valve in the cylinder cover; as also at I, for the bottom. J J is the foundation-plate; K, condensers; M, airpumps; N, hot well; PP, boiler and bilge pumps; ss, steam pipes to the engines; t, beam for parallel motion; uu, guide standards for piston-rod; v, connecting rods to the crank; w, air-pump connecting-rod; PPPP, wood framing for support of upper works; Q, main shaft; R R, cranks; S, main drivingwheel; T, lower pulley; U, shaft leading to screw. The dimensions of the principal parts are as follow: ft. in. Two foundation-plates for cylinders, length.... 27 0 Width (parallel)... Height of outside ribs, at the middle Weight of each, from 16 to 17 tons Length of main wrought-iron shaft Diameter at centre for driving-wheel Diameter for eccentric bearings and cranks.... And is intended to be bored through its length In diameter Weight in the rough, as from the forge, upwards of 16 tons. Diagonal framing for support of shaft, of very hard and strong foreign wood, of from 10 to 14 inches on the side, proposed to be cased with 4-inch wroughtiron plates. Cranks, thickness at large hole.... 1 Width at the head.. Diameter of large driving-wheel, said to be intended 66 3 6 26 0 11 000 15 0 The ribs are framed of angle iron, 6 inches by 34, by inch thick at the bottom of the vessel, and ths thick at the top. The mean distance of the ribs from centre to centre is 14 inches, and all these ribs will be doubled; the distance is then increased to 18 inches, and then gradually to 21 inches at the extremities. The boiler platform is of plate-iron, supported upon ten iron kelsons, of which the centre ones are 3 feet 3 inches deep. These kelsons are formed like the floorings, of iron plates placed on edge. The hull is divided into five distinct compartments, by means of substantial water-tight iron bulkheads. The decks, which are of wood, consist of the cargo deck, two cabin decks, and the upper deck." The "farther dimensions and particulars," last given, are extracted from the able and valuable treatise on Iron Ship Building, by Mr. Grantham, of Liverpool, and were supplied to him by Mr. Guppy, and therefore may be presumed to be correct, though I am unable to reconcile some parts with my own observation. From the keel being mentioned as above, it would probably be inferred by most readers, that it has an external projecting keel, similar to a timber-built ship, but such is not the case. The only external projection along the midships is the edges of the central plate, which lies horizontally, and to each edge of which the first rows of plates, forming the hull, are riveted. The ends of the central keel-plates are formed into long scarf joints and well riveted, and the first two or three longitudinal rows of plates have their laps, or external projecting edges pointing upwards, or clencher-build inverted, and above this the edges are downwards, in the ordinary manner, both of which methods appear to be based on scientific reasons. "The mean distance of the ribs," I think will be found to be from 18 to 20 inches from centre to centre, instead of "14," that is, about the midships, with gradually increasing spaces towards stem and stern. At the engine room, for the purpose of giving greater strength than appears was originally intended, there are nine new additional intermediate double ribs introduced, and sixteen additional reverse ribs riveted to the original framing, but in no other part did I see the "ribs doubled." The cost of a 46 gun frigate, fully equipped with stores for foreign service, is 39,2687. during war,* (from which deduct 20 per cent. for peace rates,) and may be built ready for launching by 61 men in 12 months at the peace rate. There are to be six masts, on which will, it is said, be spread 1700 square yards of canvass when all set, which is only about ths of that of a 46 gun frigate, while the length of the upper deck of the Great Britain is about 24th times, and deck surface 24 times as much as the above named frigate, though probably the area of the midship transverse section at the load line is very little more in the Great Britain than in that of the frigate. The displacement of the frigate fitted and fully equipped for foreign service, is not quite half that given by Mr. Grantham of the Great Britain, which is rather more than a loaded 74. The centre of impact of the wind on all the sails of the frigate, where it is concentrated into one point, is about 8 feet before the centre of flotation, and about 62 feet above the load water-line. It is probable that this situation of the concentrated force of wind on the horizontal line, would be found to be nearly in the proportionate situation of a great many paddle-wheels in steamers, and to be the position of most advantageous effect whether impelled by the wind on sails, or by the According to Mr. Edge's most able calculations of ships of war. resistance of the water against the paddle-wheels, though it cannot be used as an argument against the stern situation of the screw propeller, provided the vessel's head can be kept as steady and with as little detraction from the "ship's way" arising from the use of the helm, as if the impelling force were "forward of midships," but of which there appears no record of satisfactory experiments. I have been informed by a gentleman who witnessed experiments made with the Archimedes, that he has seen the helm "lashed a-midships" in calm weather, and water still, when she has made a perfectly straight line, and which proved, it is alleged, how easily the steering could be effected; but to my mind, it proved nothing of the kind, though it did prove, that the centre of the screw was in the centre line of the plane of greatest resistance and immersion. any other result been obtained in such a proportionately long and fine vessel, it must have proceeded from some extraneous or disturbing cause. Had The mould lines of the Great Britain, and of her general construction, as well as the minutia and details of minor parts, appeared to be in beautiful proportions and harmony; and without pretending to much judgment in such matters, I may venture to say, that considering the materials used in construction, having to provide capacity and strength for powerful engines, and a form the most suitable for stern propulsion, as also to attain great speed, and other consequent circumstances, that the symmetry and gracefulness cannot be surpassed, and reflect the greatest credit on the nautical draughtsman (I believe Mr. Paterson, of Bristol,) for having given the lines of construction for as elegant a piece of marine architecture as can be found in any part of the globe. At the same time I know not that this eulogium applies to the flatness of the sides from the engines for a considerable distance upwards, but think it probable that such a departure from a more graceful curve may have been decided on from an idea that the flatness (which appears a defect) may be the more efficacious in preventing rolling in a heavy sea, provided the centre of gravity of the whole mass, when equipped for a voyage, should be found to be in a favourable position. The entrance from |