to be measured being placed between the cylinders, the small circle was turned until the two cylinders touched the opposite sides of the body, which being removed, and the large circle turned until the ends of the two cylinders were brought to touch the turns and parts of a turn required for this, gave the breadth of the body which had been interposed to the ten-thousandth part of an inch, and since the onetenth of one of the divisions could be readily estimated, the size of the body could be thus estimated easily to the one-hundredth-thousandth part of an inch. Mr. Whitworth stated, that in the accuracy required in modern workshops, in fitting the parts of tools and machines, the two-foot rule heretofore in use is not, by any means, accurate enough; his object was to furnish ordinary mechanics with an instrument which, while it afforded very accurate indications, was yet not very liable to be deranged by the rough handling of the workshop; and he conceived this instrument secured those advantages. It surprised himself to find how very minute a portion of space could be by it, as it were, felt. By it the difference of the diameters of two hairs could be rendered quite palpable.-(Ib.)

Ibid.

Description of an Air-Duct to be used in Glass Furnaces, for the Prevention of Smoke. By Z. M. GREENHOW.

Smoke, it is assumed, must be prevented by the supply, under proper conditions, of additional quantities of oxygen gas. Though this intention has been successfully carried out in steam engine and other furnaces, no attempt has been successful to prevent the annoyance occasioned by glass furnaces. One of Mr. Greenhow's models represented the reverberatory furnace used in the manufacture of crown glass. In this kind of furnace the smoke and products of combustion escape through the openings in the sides, which give the workmen access to the pots of glass, and are unprovided with flues. To provide the necessary supply of fresh air, Mr. Greenhow proposes a perpendicular air duct (made of the same refractory clay of which the glass pots are constructed,) rising through the middle of the fire, and supported by the stone arch on which the bars rest. This airduct rises to the height of five feet within the furnace, is one foot in diameter, and distributes, through numerous apertures, any quantity of air that may be required for the completion of the combustion of the fuel; and from its situation in the centre of the furnace, it must soon acquire and communicate a high degree of temperature to the air it transmits. Mr. Greenhow showed a second model of a steam engine furnace with a horizontal air-duct placed anterior to the bridge which it crowns and overlaps. At this situation heated air is distributed through small apertures, so as to mingle with the burning gases, and insure their more complete combustion.—(Ib. )

Ibid.

On the Alteration that takes place in Iron by being exposed to long continued Vibration. By Mr. W. LUCAS.

At Cork, this subject was again brought forward, and certain spe

cimens of iron exhibited, in order to show the effects produced upon the iron by being exposed to a certain degree of concussion, or vibration, during the process of swaging, and again restored to its original state by being annealed, in accordance with the results detailed by Mr. Nasmyth, at Manchester, in 1842; in addition to these, also were exhibited specimens of portions of the same iron that had been exposed to the concussion of a large tilt hammer, working at the rate of about 350 strokes per minute, which occasioned the bars of iron to break short off at the point of bearing in the course of twenty-four hours; there was also shown a portion of one of the hammer shafts, the texture of which had evidently been altered, probably by the long continued and repeated concussions to which it had been exposed, for instead of breaking with the peculiar splintery fracture common to wood, it broke with a peculiar short fracture, and this, I am informed, is a common occurrence. In continuance of these experiments upon the effects of concussion, or vibration, Mr. Lucas laid before the Section the results of some further experiments.-(Ib.)

Ibid.

Iron Steamboats.

"The Wonder," an iron steamboat built by Messrs. Ditchburn and Mair, the successful builders of iron vessels, for running between. Southampton and Havre, made a trial trip down the river Thames on the 27th of September last; her length is 160 feet, breadth of beam 22 feet, depth of hold 12 feet 9 inches, draught when light 5 feet 6 inches, when loaded 6 feet 6 inches. She is fitted with three engines on the atmospheric principle, by Messrs. Seaward and Capel, of the Canal Iron Works, Black wall; each engine has an open topped cylinder 53 inches diameter, with a 3 feet 6 inches stroke, they work on the direct action principle; the lower end of the piston rods move on a joint attached to the top of the piston, and the other end is connected to the crank of the paddle-wheel shaft, the 3 cranks being placed at different angles, so that when one piston is at the top of the cylinder, another is at the bottom, and the third about the middle; the three cylinders exhaust their steam into one condenser, with one air-pump. The engines during the trial made 38 and 39 strokes per minute, the paddle-wheels are 19 feet diameter to the extremity of the float boards, and are on the self-feathering principle, being a modification of Morgan's paddle-wheel; the nominal power of the three engines, at a velocity of 220 feet per minute, is equal to 150 horses, but the real effective power is nearer double, as proved by the great velocity of the vessel. She ran the mile distance in 4 minutes 17 seconds against tide, being a velocity equal to 14 miles per hour, the tide running at the time about 24 miles per hour. The boiler is of the tubular principle, with five furnaces, and is only 7 feet 6 inches long; it is furnished with a brine apparatus for constantly drawing off a certain quantity of water, this water is pressed by the force of the steam through a pipe dipping down to near the bottom of the boiler, and coming out in the front near the top, where it is furnished with

a cock to regulate the emission of the water, this pipe passes along the front of the boiler, then along side of the engine room to a cistern in which the water runs, and is allowed to overflow to the outside of the vessel. The water for supplying the boiler is taken from the hot well, and forced by the feed pump through a pipe which passes backwards and forwards two or three times in the brine cistern just described, and thence into the boiler; by this process the boilers are supplied with water nearly at a boiling temperature. There are several other ingenious contrivances adopted by Messrs. Seaward and Capel for working the valves, &c. Civ. Eng. & Arc. Journ.

Her Majesty's Steamship Rattler with Smith's Screw Propeller. This fine steam frigate, after having made a great variety of experiments with the different propellers that have been projected by Mr. Smith, Mr. Woodcroft, Mr. Blaxland, Mr. Steinman, Mr. Sunderland, and other persons, in order to ascertain their comparative merits, lately made her final trial in the river. The screw that has been found to produce the highest rate of speed with the smallest consumption of power, is that of Mr. F. T. Smith, known as the inventor and adapter of the Archimedean screw. The Admiralty have in consequence determined to send the Rattler to sea, fitted with a propeller in accordance with the suggestions of that gentleman. The last trial was made partly with the view of ascertaining the precise rate of the ship in steaming in smooth water with Mr. F. T. Smith's propeller, and partly to determine its effect as compared with what had been done with other propellers that have been recommended to the notice of the Admiralty. On this occasion the average of twelve trials at the measured distance in Long-reach showed a speed of 9.9 knots, or 11 statute miles, an hour, which rate of speed, considered in comparison with the small amount of power, viz., 200 h. p., the amount of power of the engine of the Rattler, in relation with her tonnage, 888 tons, ranks her performance higher in the history of steam navigation than the performance of any vessel of her class, either in the service of her majesty, or in the commercial steam navy of the empire. It should be mentioned that the Rattler was built in every respect as a sister ship to her majesty's steam ship the Prometheus, with this difference, that the Prometheus has paddle-wheels. The Prometheus, on her trial at the measured distance, reached only to the rate of 8 knots an hour. The Rattler has already got her masts on board; she is rigged with a foremast like a frigate, or sloop, her middle and mizen masts are rigged as schooner masts, her gun carriages are also on board, and she is ordered to be equipped for sea as speedily as possible; and in consequence of the complete success which has attended the application of the screws to her, several others, we believe six, iron ships of a large class are forthwith to be constructed on the same principle. The trials were made under the superintendence of Mr. Lloyd, chief engineer of Woolwich dockyard, and Captain Smith, R. N., of the royal dockyard.

London Times.

On Crystals in the Cavities of Topaz, which are dissolved by heat, and re-crystalized on Cooling. By Sir DAVID BREWSTER. Sir David gave a brief notice of the discovery which he had made, about twenty years ago, of two new fluids in the crystalized cavities of topaz, and other minerals. One of these fluids is very volatile, and so expansible, that it expands twenty times as much as water with the same increase of temperature. When the vacuities in the cavity which it occupies are large, it passes into vapor, and in these different states he had succeeded in determining its refractive power, by measuring the angles at five feet. Total reflection takes place at the common surface of the fluid of the topaz. The other fluid is of a denser kind, and occupies the angles and narrow necks of cavities. The cavities, however, in which the soluble crystals were contained, are of a different kind. They (viz. the cavities,) were imperfectly crystalized, and thus they exist in specimens of topaz which contain the cavities with the two new fluids; they contain none of the volatile and expansible fluid, which is doubtless a condensed gas. The crystals which occupy them are flat, and finely crystalized rhomboids. When heat is applied, they become rounded at their angles and edges, and soon disappear. After the topaz has cooled, they again appear, at first like a speck, and then recrystalize gradually, sometimes in their original place, but often in other parts of the cavity, their place being determined by the mode in which the cooling is applied. ́ We understand that Prof. Liebig, who regards these fluids and crystals as peculiarly interesting, has made arrangements to investigate their nature, when taken out of their cavities by Sir David Brewster,—an operation of extreme difficulty, owing to the small size of the cavities. which contain them, and the rapid disappearance of the volatile fluid, which rises into a drop, and contracts into a flat disk, as if it were endued with vitality, finally vanishing and leaving a sediment behind it, which, when breathed upon, again becomes fluid.-Pro. Brit. Ass.

Heath's Cast-Steel.

Lond. Athenæum.

Before the introduction of Mr. Heath's process, which consists in adding carburet of manganese to the melting pot, all steel which was to be worked into a fine edge was made of iron procured from one mine only, that of Dannemora, in Sweden. It was consigned to a house at Hull, at a cost of 387. per ton, in quantities not exceeding 1100 tons per annum, and marked L in a hoop. The prite limited its use; but by means of this patent the inferior sorts of iron, as those at 157. per ton, may be made available. Steel is made by it which has all the beauty of cast-steel, and all the welding advantages of shear steel. In the manufacture of table knives its advantages have been manifest. Formerly these articles were made by tilting, or rolling, square bars of steel into the necessary shape, thus making blade, shoulder, and tang in one piece; so difficult was this process, that two wasters in a dozen knives were always thrown aside, and workmen's wages were double. Now, the steel blade, made by this process is welded with the iron tang.

Lond. Min. Journ.

Variation of the Boiling Point of Water in Vessels of different Materials.

M. Marcet (Ann. de Chim. et de Phys. v. 449,) has made a series of accurate experiments upon the variations of the boiling point of water, dependent upon the nature of the vessel in which it is made. to boil. The following are the results of his researches:-1st. The boiling point of water in glass vessels is from 100.3° to 102° cent., varying with certain circumstances, more especially with the different kinds of glass. In these cases the temperature of the vapor of water is constantly the same, and some hundredths of a degree lower than when water is boiled in metallic vessels. 2d. Whatever the nature of the vessel in which the ebullition takes place, the temperature of the vapor is always lower than that of the water from which it is generated. This difference in the case of glass vessels is about 1.06° cent.; in metallic vessels 0.15° to 0.20° cent. There is only one exception to this rule, which is, when the interior of the vessel, whether of glass, or metal, is covered with a thin coat of sulphur, or gum lac, or any other substance which exercises a repulsion of water; the boiling water and the vapor then have the same temperature. 3d. Contrary to the opinion generally admitted, it is not in metallic vessels that the boiling point is lowest under an increased pressure, but in glass vessels covered internally with a thin coat of the substances mentioned above. 4th. In glass vessels having the internal surface perfectly smooth, and free from foreign matter, water and alcohol can be heated several degrees above their boiling point before they enter into ebullition. Water can thus be heated to 105° cent. If the experiment does not succeed, it is because there is foreign matter adhering to the glass. The experiment may be performed successfully with a new vessel, by first heating sulphuric acid in it to 150° cent., then washing it out with pure water.

Lond. Journ. Arts & Sciences.

Apparatus to enable the Blind to Read and Write.

The Reverend W. Taylor gave an explanation of an apparatus, invented by Mr. Littledale, of York, by which the blind can write and read. The following is a description of the instrument, as given in the local papers:-"Into a case, probably a yard long, and three or four inches square, is fitted a slide, something like one section of a letter-rack used in printing offices for depositing the type when not in use. This slide is adapted to any alphabet, or to arbitrary characters. At one end of the case there is a hammer, under which the paper is placed, and as the letters are brought up successively, by the application of an ingenious contrivance at the opposite end of the case, the hammer is raised, and by its fall they are impressed, or rather embossed, upon the paper, so that blind persons may distinguish them by the touch. When the first letter of a word is printed, the hammer is raised, and that causes the letter to move away, and,