opened unless something had prevented it. His opinion was that the accident arose from excessive internal pressure, forcing down the top of the fire-box, and from the explosion of the gas as stated in the report. The corresponding piece of copper which Mr. Fairbairn had taken away with him on the morning of the explosion was then produced for the inspection of the jury. Mr. F. pointed out the part which corresponded with the blackened edge of the other part of the fire-box, and it appeared perfectly sound, without any signs of a fracture.

The following is the letter referred to in our introductory remarks. "I have pleasure in affording you such information as it is in my power to give respecting the construction of the fire-box of the Manchester and Leeds Company's engine Irk which exploded the other day. The inside shell of the fire-box is made of copper three-eighths of an inch thick (the tube plate was of course thicker.) The dimensions of the horizontal section of the inside shell are 3 feet 5 inches × 3 feet 3 inches. The sides of the inside shell are well stayed to the sides of the outside (iron) shell by bolts placed, say 54 inches apart. The roof of the inside shell is flat, and is stayed in the usual manner with strong bridging bars, seven in number, each being 5 in. deep by 14 in. thick, and extending from back to front over the roof of the inside shell. The whole was most strongly stayed, and was of ample strength, I should say, to sustain a pressure of 150 pounds on the square inch, or more than twice the working pressure. There was no defect or flaw visible. The sketch below, may, perhaps, serve to explain to you the mode of construction, which is similar to that adopted on the Liverpool and Manchester Railway.

A, inner casing of fire-box; B, bridging bars; C, outer shell of casing; D, fire door; F, fire bars.

The fracture took place along the angle intersected by the line O P. The edges of the plates along that angle were as if cut clean by a pair of shears. The entire roof came down like a door turning on its hinges, as on the centre R. The sides of the inner shell were torn by the fracture into saw teeth. It was certainly a defect in construction not to make the bars B. long enough for their ends to rest upon the extreme angle at O P and R, and accordingly this angle has proved to be the weakest part; but this fact is not sufficient to account for the explosion, which, if I may hazard an opinion, is only to be explained on the assumption of an excessive pressure of steam in the boiler. Constructed as I understand the safety valves were, and as those of too many locomotive engines are, nothing is easier than to render them absolutely useless. You have only to screw the nut until the index pointer reaches the bottom of the scale, where it is stopped by coming in contact with the end of the slip in which it travels, and you make the safety valve a fixture, which no pace, short of one sufficient to break or bend the lever, can move.

The remedy which puts the control of the safety valve beyond the reach of any workman, is to put a small collar or ferrule over the screw at a, fig. 2, so as to prevent the index pointer P from ever reaching the bottom of the scale, screw the nut as you may. When the steam begins to blow off strong, the workmen have a strong temptation to put on extra pressure to prevent noise and waste of fuel. S represents Salter's balance.

Herapath's Jour.

Description of the Great Britain Steam Ship.

Though many descriptions have been given of the Great Britain, we are induced to insert the following, as being the most clear and succinct that we have seen, and which we copy from an interesting pamphlet just published by Capt. Claxton, entitled "A Description of the Great Britain Steam Ship," &c.

The length of the keel 289 feet. Total length, 322 feet. Beam, 51 feet. Depth, 32 feet 6 inches. Feet of water when loaded, 16 feet. Displacement, 2,984 tons. Tonnage by Old Measurement, 3,443 tons. Plates of keel nearly one inch thick. Plates of Bottom varying to of an inch at extremes, and to ths generally. Topsides an inch, and at the extreme aft 7-16ths. The ribs are framed of an angle iron, 6 inches by 34 inches; inch thick and 7-16ths. Distance of ribs from centre to centre, amidships, 14 inches, increasing to 21 inches at the ends.

Ten iron sleepers run through the engine rooms, gradually diminishing in number, to the fore end of ship and under the boilers, the platform of which they support-in midships they are 3 feet 3 inches in depth, supported by angle irons in the form of inverted arches, and a short distance from each other. She has five water-tight partitions. Stows 1200 tons of coal. 1000 tons of measurement. The engines weigh 340 tons. The boilers 200 ditto, and hold 200 tons of water. The main shaft is 23 inches in diameter in the centre, and 24 inches

in the bearings; in the rough before turned, it weighed 16 tons. It has been lightened by a hole of 10 inches diameter, and bored through. A stream of cold water passes through the cranks and this hole when the engines are at work. The screw shaft is in one long and two short, or coupling, parts. The part next the engine, solid, 28 feet by 16 inches diameter. The hollow intermediate shaft 65 feet, by 2 feet 8 inches diameter; the screw part is 25 feet 6 inches, and also 16 inches diameter; the total length is 130 feet, and it weighs altogether

36 tons.

The screw is of six arms, 15 feet 6 inches in diameter, 25 feet pitch, and weighs 4 tons. The main drum is 18 feet diameter, and drives 4 chains, weighing 7 tons. The screw shaft drum is 6 feet in diameter, and the weight with the pull when working is equal to 85 tons on the bearings of the main shaft. The cylinders are four in number, 88 inches each. Stroke 6 feet. Power 1000 horses. The condensers are of wrought iron, 12 feet by eight, and 5 deep. Under the whole. space of the engines, up to the top, the angle irons are doubled. The upper, main and saloon decks are of wood, the two cargo decks are of iron. The officers and seamen are all accommodated on two decks under the forecastle.

From the ship's bottom to the upper deck, runs on either side, for the whole length of the engine and boiler space, a strong iron partition forming below the coal bunkers; and above, the servants' accommodations on one side, engineers' cabins and stokers' accommodations on the other, besides 26 water-closets. She has six masts, fitted with iron rigging, adopted in consequence of its offering two-thirds less resistance than hemp,-a great point going head to wind.

The plain sails of a 52-gun frigate, that is, without bunting, royals, stay-sails and steering sails, number something short of 5000 yards of canvas, and the plain sails of the Great Britain amount to 4,943 yards. She carries four large life-boats of iron, and two boats of wood in the davits, and one large life-boat on deck; they are built according to a patent taken out by Mr. Guppy, and are capable of carrying four hundred people. Nautical Mag.

Description of Ellis's Turn-Table. By B. RoтCH, ESQ. V. P.

This ingenious invention obviates one of the greatest objections to the turn-table, which is, its being supported on numerous small friction-rollers under its outer edge, as well as on a central pillar. The object of these rollers is to facilitate the turning of the table when the heavy weight of an engine or carriage is upon it; but this weight is so excessive, that coming, when passing over the table unequally, first on one edge, as it enters upon it, and then on the other, as it passes from it, the table gets pressed down, first on one side, and then on the other, with such rapidity and violence of strain as to cause a great noise of successive jarring blows, and a constant derangement and damaging of the rollers.

Ellis's turn-table prevents all this, by doing away with these rollers,

and allowing the outer edge of the table to rest firmly, and without rollers, on a solid support, or circular bed, made to receive it. It is also supported on a central pillar, on which the centre of the table bears firmly and steadily at the same time. When the table is left in this condition, which may be called its position of rest, the bearings are so firm that the engines and carriages roll steadily over it without noise or jar, just as if it were a part of the railway itself; but the central pillar is so arranged as to be easily acted upon by a compound lever, on the principle of the lever of a weighing machine, and the table may, in fact, be made into a weighing machine by adapting a steelyard and weights to this compound lever; and, when it is required to turn a carriage or engine on the table, it is rolled on to it while remaining firmly and steadily in its rest position, and, when the weight is placed on its centre, and has an equal bearing over the table, the table is lifted from its circular bearing all round the outer edge by the compound lever, and thrown entirely on the centre pillar, the bottom of which resting on a pivot, the whole may be turned round with the greatest ease the distance required, and the table then let firmly down again on its solid circumferential and central bearing, or to what is called its rest position.

This plan is very simple, very effective, and saves an immense amount of wear and tear in the item of turn-tables. It has already been extensively adopted.

Trans. Soc. Arts.

Ancient Tunnel.

According to the French papers, a new and remarkable assertion of the powers of ancient practical science has been brought to light, in the city of Marseilles, to dispute the triumphs of the present. That town is, it seems, suddenly about to be endowed with a ready-made tunnel, of larger dimensions and greater extent than Mr. Brunel's extraordinary performance below the Thames. There has long been known to exist a subterranean passage, which tradition reported to lead from the parish of St. Victor to an issue beneath a tower in the fort St. Nicholas,-passing, therefore, at the mouth of the port, under the deep sea, where float the line-of-battle ships! For many years, the termini have been encumbered with rubbish; and no one had ventured to verify the tradition by attempting the perilous passage. This daring, and even rash, enterprise has been, however, successfully achieved by M. Joyland, Engineer of Roads and Bridges, and M. Matayras, architect. Repairing, with some friends, to the ancient abbey of St. Victor, they penetrated, by a long flight of steps, to the bottom of the tunnel; and, clearing the way before them, finally emerged by the Port St. Nicholas The work, which they suppose to be Roman, is, they report, in nearly perfect preservation. A few parts only are in want of repairs, whose cost they estimate at not more than from 16,000/. to 20,000/.; and proper approaches are all that will then be wanting. The tunnel is a single arch, has a width of more than sixty feet, and is one fourth longer than that of London!

London Athenæum.

Explosion on board the "Gipsy Queen."

It is our painful duty to record a frightful and fatal accident which occurred on Tuesday, Nov. 12, involving the death of Mr. Jacob Samuda (well known on account of his connexion with the Atmospheric Railway,) and nine other persons on board the steamboat the Gipsy Queen, lying at the mooring buoy, off Brunswick Wharf, Blackwall; in consequence of one of the joints of the steam-pipe leading

from the boilers to the cylinders giving way as explained in the evidence hereafter given. The Gipsy Queen is a new iron boat of about 500 tous burthen, recently built by Messrs. Jacob and Joseph Samuda, with a pair of engines of the collective power of 150-horses (nominally) on the bell-crank principle as patented by Mr. Jacob Samuda. For the sake of reference we again give the engraving.

It appears from the evidence that the explosion was in no way connected with the construction of either the engines or the boilers, but simply in the method of making the joints, or rather in the fixing of the steam-pipe leading from the boilers to the cylinders. On the day of the accident the vessel ran down the river to try the engines, which it is stated worked admirably and perfectly satisfactory to all parties present, that during the trip the steam was not more than 10 lb.