scientifically fitted, might be overrun by an adversary, and come up on the other side. He claimed the introduction into the navy of the air-tight compartments, by constructing a vessel upon the plan of a ship within a ship — the outer, sectional compartments each independent per se for coals or stores; the inner to contain compartments and accommodation, if necessity demanded, for the crew. The oval form would secure the means of withstanding, externally, any compression; it would facilitate the delivery of coals from the bunkers, and if any one of those bunkers was perforated or stove, you possessed the engine-power, to be exerted from within, of expelling the water, by forcing in air, making every such valve self-acting from the interior.

STEERING SCREW FOR STEAMERS.

Some experiments have recently been made by the British Admiralty on a new arrangement of that screw propeller which has for its object steering, as well as the propulsion of a vessel. The peculiarity of the screw is that a universal joint is placed within the hollow boss of the screw, which is thereby connected with the main shaft, the centre of gravity of the screw and the centre line of the rudder intersecting the centre line of the main shaft, so that the entire weight of the screw is borne by the shaft; and by means of a tail or spindle to the screw, projecting from the boss working in the rudder, or an iron carrier in lieu of rudder, whatever may be the movement of the tiller or wheel, it communicates an equal movement to the screw, which becomes not only the propelling but also the guiding power of the ship. One of these screws, fitted to a naval steamer of sixty-horse power, has been tried upon the Thames, and the result is reported in the London Post, as unequivocally satisfactory,-"clearly demonstrating that it is no longer needful to apply double screws, hydraulic steering apparatus, or add any other extra complications to the machinery of a steamer, when by a wave of her own screw, her motion can be directed and controlled at will."

RAILWAY TUNNELS IN GREAT BRITAIN.

At a recent meeting of the Institution of Civil Engineers, Mr. J. S. Fraser stated that the aggregate length of the tunnels, now daily traversed by railway trains in the united kingdom, amounts to eighty miles; and, supposing their cost to have been on an average fifteen pounds per lineal yard, their construction must have caused the expenditure of six and a half millions sterling.

STEEP RAILWAY INCLINE.

The Bhore Ghaut Incline of the Great Peninsular Railway of India has occupied more than seven years in construction, and during the great-* er part of that time there have been 45,000 workmen daily employed upon it. The incline is a series of tunnels through mountains of rock, and viaducts stretching across valleys, alternating with each other; each part a triumph of modern science and skill.

The incline reaches at one long lift the height of 1,832 feet, the highest elevation yet attained by any railway incline. It is 15 miles long, and its average gradient consequently 1 in 46.39. The highest gradient is one in 37, and the sharpest curve 15 chains radius. The

tunnels are twenty-five in number, the greatest length of any of them being 341 yards. There are eight viaducts, one consisting of eight arches of 50 feet and being 129 feet high, and another, of a like number of arches, with a maximum height of 143 feet. The quantity of cutting amounts to 2,067,738 cubic yards, and of embankments to 2,452,308 cubic yards. There are twenty-two bridges of various spans, and seventy-four culverts. The total cost of the works has been £1,100,000, or £68,750 a mile.

STEAM BOILER EXPLOSIONS.

With reference to these destructive accidents, Dr. Joule, at a recent meeting of the Philosophical Society, of Manchester, England, stated his belief that, in nearly every instance, rupture took place simply because the iron, by wear or otherwise, had become unable to withstand the ordinary working pressure. Various hypotheses, set up to account for explosions, were worse than useless because they diverted attention from the real source of danger. He believed that one of these hypotheses — that which attributed explosions to the introduction of water into a boiler, the plates of which were heated in consequence of deficiency of water - was quite inadequate to account for the facts; although weak boilers might be exploded at the moment of starting the engine, in consequence of the swelling of the water through renewed ebullition throwing hot water over the heated plates. The absolute necessity of employing the hydraulic test periodically had been pointed out so frequently that he considered that the neglect of it was highly criminal.

UTILIZATION OF THE TIDES.

Let us suppose (says a writer in the Chemical News) that by the action of the tides, the difference of level of the surface of the ocean at a certain spot is twenty-one feet between high and low water. Omitting for the present all consideration of the power of the subjacent liquid, what is the mechanical value of a space of one hundred yards square of this water? One hundred yards square by twenty-one feet deep, equal 70,000 cubic yards of water, which is lifted to a height of twentyone feet, or to 1,470,000 cubic yards lifted to a height of one foot. Now, since one cubic yard of water weighs about 1683 pounds, 1,470,000 cubic yards weigh 2,474,010,000 pounds, which is lifted in six hours. This is equivalent to lifting a weight of 412,335,000 foot pounds in one hour; and since one-horse power is considered equivalent to raising 1,800,000 foot pounds per hour, we have, locked up in every one hundred yards square of sea surface, a power equal to a two hundred and thirty horse power steam-engine; acting, be it remembered, day and night to the end of time; requiring no supervision; and costing nothing after the first outlay but the wear and tear of machinery. By means of appropriate machinery connected with this tidal movement, any kind of work could be performed readily.

THE PNEUMATIC DESPATCH.

In the Annual of Sci. Dis. 1863, p. 43, the application of the principle of forcing packages through tubes by atmospheric pressure to the conveyance of mail-bags in London, to and from the District Post

Office and the Euston Street Railway station (a distance of 1800 feet) was described as about to be put in practical operation. A recent report of the Pneumatic Despatch Company now states, - "That since the 20th of February, 1863, the authorities have discontinued their street conveyances, and intrusted the company with the transmission of the mails, and that the service of the district had since been entirely performed by the company. Thirty trains per diem (Sundays excepted) have been despatched with perfect regularity, and upwards of 4,000 trains have run without impediment or delay. The time occupied in the transmission has not exceeded seventy seconds. The daily cost of working has averaged £1. 4s. 5d.; and five times the number of trains could have been conveyed without any appreciable increase of expense."

The successful result of these experiments has induced the company to proceed to the laying of an additional line of pipe for further post-office accommodation, which will be 23 miles in length and 54 inches in diameter, at an estimated total cost of £65,000. It is confidently predicted that, in the course of a few years, the entire transmission of the London mails throughout the city will be accomplished by atmospheric pressure.

IMITATION RUSSIA SHEET IRON.

At a recent meeting of the Franklin Institute, Prof. Fleury presented specimens of imitated Russia sheet iron, made under the patent of Mr. Wm. Riesz from ordinary rolled iron, the original cost of which was 5 cents per pound; the expense of the process was 2 cents, making the total cost of the iron in its present condition, 73 cents per pound. He stated that "the inventor, who was for a number of years director of a large iron manufacturing establishment in Germany, had made it his particular study to examine theoretically and practically the manufacture of the iron which was imported in large quantities from Russia. By repeated analyses of the iron, and also through noticing its beautiful, smooth, and incorrodible surface (by scraping off the surface from a large number of sheets), he came to the curious conclusion that the Russia iron was not, as he had thought, and as the general impression among iron manufacturers still seems to be, covered by a film of carburet of iron, but that the smooth surface consisted of an atomic accumulation of a peculiar substance, a NITRIDE of iron combined with about 20 per cent. of carbon: the nitro-carburetted iron of Fremy. The quantity of carbon and nitrogen diminished gradually towards the centre, where the iron was nearly pure and very flexible. After years of experiments, he has finally succeeded in producing from ordinary sheet iron the best imitation of Russia sheet iron which, in my opinion, can be made.”

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Though the process is very simple, it requires considerable skill; but once learned, by short practice under the guidance of the inventor, it can be carried on in the most regular manner. The iron is cleaned in a sulphuric acid bath, then washed with an alkali and water, and placed in a peculiar mixture described in the patent, which prevents oxidation; it is then rolled with the before-named coating, and, after being re-heated, placed under the hammer to receive the required temper and smoothness."

PROTECTION OF IRON FROM RUST.

At a recent meeting of the Society of Arts, London, the question of preserving iron from rusting formed a subject of conversation. It was stated that galvanized iron wire for telegraphs was not affected with rust in passing through the rural districts of England; but that the coating of zinc on the iron afforded no protection to wires in cities. The acid gas generated by the combustion of fuel attacked the coating and decomposed it. A new substitute for covering telegraphic wire was desirable.

White

With respect to paints for coating iron, such as the plates of iron vessels, machinery, &c., Mr. John Braithwaite stated that pure red lead was the best. His experience dated as far back as 1806, with the use of red lead, and for fifty years he had used it with success. lead was more injurious than beneficial as a paint for iron. In April last, he inspected a well, two hundred feet deep, a short distance out of London, where he had put up an engine forty-five years ago; the long iron rods which had been placed in it had been painted with red lead, and the metal had remained unchanged in all that period. The same preservative effects of red lead paint on iron, he had witnessed upon other iron-work which had been many years in use.

ALUMINUM BRONZE.

It has long been an object with scientific inquirers to reduce the weight of the philosophical instruments which they have to employ. Especially is this the case with magnetical and astronomical instruments used in the triangulation of a country for a survey, or the highly important operation of measuring an arc of the meridian. Aluminum bronze supplies the long-sought desideratum. This metal is produced from a mixture of ten per cent. of aluminum with pure copper; and a most remarkable metal it is. Col. Strange, in a recent communication to the Royal Astronomical Society, thus enumerates some of its properties: Good gun-metal will break with a strain of 35,000 lbs. to the square inch; aluminum bronze requires 73,000 lbs to the square inch to break it. It resists compression equally well; it is malleable when heated; can be easily cast, and behaves well under the file. "It does not clog the file; and in the lathe and planing-machine, the tool removes long elastic shavings, leaving a fine, bright, smooth surface." Moreover, "it can be worked with much less difficulty than steel; tarnishes less readily than any metal usually employed for astronomical instruments, and is less affected by changes of temperature than either gun-metal or brass." This latter quality is especially important in instruments used for surveying in the tropics, as expansion by heat would very much impair their accuracy. It is remarkably well fitted to receive graduation, as it takes a fine division, which is pure and equable, surpassing any other cast metal in this respect. Col. Strange remarks that in its elasticity it is said to surpass even steel, and it would therefore appear to be the most proper material for the suspension strings of clock pendulums.

C. Tissier, Director of the Aluminum Works at Rouen, shows that one per cent. of aluminum in copper makes the latter more fusible, giving it the property of filling the mould in casting, at the same time

preventing it from rising in the mould. The action of chemical agents upon it is also weakened, and the copper gains in hardness and tenacity without losing its malleability, thus producing an alloy which has the malleability of brass, with the hardness of bronze.

Aluminum bronze has been selected by Col. Strange as the most appropriate metal for the construction of the large theodolite for the use of the Trigonometrical Survey of India. The horizontal circle of this theodolite is three feet in diameter, and the effect of using this alloy will be to keep the weight of the instrument within reasonable limits, notwithstanding its possession of means and appliances not hitherto bestowed on such instruments. In the manufacture of the alloy, Col. Strange says that extremely pure copper must be used; electrotype copper is best, and Lake Superior copper stands next, giving an alloy of excellent quality. The ordinary coppers of commerce generally fail, owing, it is said, to the presence of iron, which appears to be specially prejudicial. Further, the alloy must be melted two or three times, as that obtained from the first melting is excessively brittle. "Each successive melting, up to a certain point, determined by the working, and particularly the forging properties of the metal, improves its tenacity and strength." The present price of English-made 10 per cent. aluminum bronze is 6 shillings 6 pence per lb. This is four or five times that of gun-metal.

MALLEABLE IRON NAILS.

There is a description of nails of cast malleable iron coming into use for fixing slates on to the roofs of factories and similar buildings. They oxidize much less in damp air than common iron nails, or even copper ones. To manufacture them, very hot metal is run into ordinary sand moulds. These malleable iron nails are very brittle before being placed in the annealing furnace. Their sojourn in the furnace renders them very ductile. They are then put into polishing barrels, in which they are cleaned, whereupon they are thrown into a zinc bath to obtain a coating.-London Mechanics' Magazine.

IMPROVEMENT IN STEEL WORKING.

Mr. Anderson, Assistant Superintendent of Woolwich Arsenal, announces the discovery of a simple process by which steel is rendered as tough as wrought-iron without losing its hardness. This change is effected in a few minutes by heating the metal and plunging it in oil, after which the steel can be bent, but scarcely broken. The value of this discovery will be at once appreciated by those who are aware of the difficulties hitherto experienced in obtaining a suitable material for the interior tubes of built-up guns.

FILES MADE BY MACHINERY.

The manufacture of files by machinery is said to have been successfully commenced in Birmingham, England. The blanks are forged by machinery, and they are then cut with the French machine of M. Ber

not.

The machine, which is very compact, resembles a small steamhammer in its general appearance. It is provided with a vertical slide, carrying a chisel on the lower end. The top of this slide is pressed by a flat spring, which is governed by a cam mounted upon a shaft, and