such as silks, gauzes, crapes, or fine muslins, on being examined, do not show the least displacement in their texture.

The hydro-extractor, as it is called, is made of various sizes, being calculated to hold from 100 pounds to 300 pounds of wet goods. It is most commonly worked by steam power; but hand-machines are con stantly in use in hospitals, asylums, and work houses, domestic and other establishments in which steam or water power cannot be obtained. They are made to hold six pairs of sheets at once, or any quantity of smaller articles of similar bulk, and the time required for the operation is not, in any case, more than five minutes.

Patent Folding Machine for folding Paper, Linen, or Cloth, by means of a series of serrated steel Folders.-J. Black, Edinburgh, inventor.

The appearance of this machine is that of a large box or table, with some few wheels and rollers in front. Its construction is so simple that there is very little to describe beyond the fact that inside the box are a number of knives or folders, which act in a similar manner to the one on the top, taking the sheet of paper and doubling it together, according to the number of pages, till it comes out of the machine, from the four rollers in front of it, a perfectly folded and pressed portion of a book ready for the binder. It is capable of folding any number of sheets, of any size, (which can be laid on by one or two boys,) with the most perfect accuracy. Its advantages consist not only in economizing the expense of labor, but also in space, the machine taking up no more room than would be occupied by two individuals folding by the old method. The machine can be worked by steam power, or one man at the wheel could propel six machines. Besides newspapers, it can be applied to the folding of note and other paper at the mill at the rate of 2,000 or more quires per hour.

Micrometric Apparatus, Self acting Lathes, Planing, Slotting, Drilling, and Boring, &c., Machines.-J. Whitwreth & Co., Manchester.

The first mentioned apparatus has been successfully applied to purposes of the greatest practical utility by affording means for the estab Tishing uniform standard of magnitude for taps, axles, and other important component parts of machinery, among which it is as necessary to maintain uniformity as it is to have a uniform language or a uniform system of numeration. By this instrument magnitudes so minute as even to elude the microscope have been submitted to mechanical measurement, and magnitudes so minute as not to exceed the one-millionth part of an inch are actually estimated.

Two perfectly plane and smooth metallic surfaces are first formed, partly by friction against each other, and partly by abrasion with a peculiar tool So plain are the surfaces of metal thus formed, that when one is laid upon the other no one part comes in closer contact than another, and there is included between them a stratum of particles of air, which act like infinitely smooth rollers, and the surfaces move in contact with one another with a degree of freedom, owing to the lubricity of the air, which must be felt to be conceived. If, however, the surfaces be so severely pressed against each other as to exclude the air, the contact becomes so complete that it is with great difficulty they can be separated. These surfaces, thus accurately formed, are used as standards

to test other plain surfaces, and with these are tested the ends of a' standard measure of metal, which is placed in an accurately formed horizontal metallic bed, one end bearing against a metallic pin. Another metallic pin, urged by a screw, presses against the other end; and if this metallic bar, by a change of temperature, or any other cause, suffers a change in its length amounting to the millionth part of an inch, that change is rendered perceptible by the following arrangement:

The pin which bears against its extremity is moved by a screw which has ten threads to the inch. On the head of this screw is a wheel, consisting of 400 teeth, which works in a worm driven by another wheel, the rim of which is divided into 250 visible parts. Now, since each thread of the original corresponds to the one-tenth part of an inch, each tooth of the wheel upon its head will correspond to the four thousandth part of an inch, and each division of the wheel attached to the worm will correspond to the millionth part of an inch.

It is found, in the application of this apparatus, that a change in the position of the wheel attached to the worm, through one of the 250 divisions, is rendered sensible at the point of the screw which bears against the standard bar; but, since the motion of the former wheel through one division can produce a motion amounting only to the millionth part of an inch in the point of the screw, this magnitude is thus rendered sensible.

To prove the accuracy of this micrometric apparatus, a standard yardmeasure, made of a bar of steel, about three-quarters of an inch square, having both threads rendered perfectly true, was placed in it. One end of the bar was then placed in contact with the face of the machine, and at the other end, between it and the other face of the machine, was interposed a small flat piece of steel, termed, by the experimenter, "the contact piece," whose sides were also rendered perfectly true and parallel. Each division on the micrometer represented the one millionth part of an inch, and each time the micrometer was moved only one division forward, the experimenter raised the contact piece, allowing it to descend across the end of the bar by its own gravity only. This was repeated until the closer proximation of the surfaces prevented the contact piece from descending when the measure was completed, and the number on the micrometer represented the dead length of the standard bar to the one-millionth part of an inch. Eight repetitions of the experiment in a quarter of an hour produced identical results-there not being, in any single case, a variation of one-millionth part of an inch.

This method of operating was termed "the system of proof by the contact of perfectly true surfaces and gravity;" and in connexion with it was shown another interesting experiment: when the micrometer was up within one division of the number where contact would be presumed to occur, the application of the finger to the centre of the steel bar sufficed t expand and lengthen it instantaneously, so as to prevent the descent of the " contact piece."""

The other method of proof was by having a small, simple battery, composed of a piece of zinc soldered on to a piece of copper, and plunged into rain water, without the admixture of any acid. This was connected with the two ends of the measuring machine, and also with a delicate galvanometer. On pursuing the same process of advancing the micrometer one division at a time-no effect was produced until the

last millionth of an inch of distance was traversed, and absolute contact occurred with the end of the bar, when the deflection of the needle of the galvanometer instantly betrayed the movement. Repeated experiments showed this to be unerring in the result; and on placing the finger on the middle of the bar, under the same circumstances as before mentioned, the expansion was instantly detected by the deflection of the galvanometric bar.

By the application of this instrument, standard gauges for axles, taps, and other parts of machinery which it is desirable to maintain uniform, are constructed, and have been adopted in large manufactories.

One of the large lathe machines is capable of turning shafts thirtysix feet long. The peculiarity of this machine is the combination of two cutting-tools, at the opposite sides of the shaft to be turned, which bear against each other, and are governed by a common motion. Another pair of similar cutting tools is also placed on the bed of the same. lathe. When a long shaft is to be turned, these four tools are brought to its middle point, and commence from that point cutting in opposite directions towards the extremities of the shaft. The advantage of the tools bearing on opposite-sides is that all flexure of the bar which may proceed from the pressure of the tool is prevented by their mutual reaction.

There is also another lathe of great magnitude, constructed on the same principle, for turning and boring the wheels of railway engines and carriages. The wheels, fixed upon their axles, are suspended between the two-faced plates of the lathe, and two pairs of cutting-tools are applied to opposite sides of them, in the same manner as has already. been described.

Civil Engineering, Architecture, and Building Contrivances.

The subdivision included the machines and implements used in hydraulic works, scaffoldings, and centring; machines used in the construction of bridges and tunnels, and expedients for crossing rivers and ravines; docks, harbors, and canal works; light houses and beacons; gas work and contrivances, for the production and distribution of artificial light; of roofs covering large areas of water works, and methods for the supply of towns with water; of sewerage, cleansing, paving, and the contrivances connected with the sanitary condition of towns; and also for the heating and ventilation of buildings.

It comprises some of the most important and interesting monuments of art; among which were found pile machinery, coffer dams, machinery for the construction of light-houses, diving-bells, and diving apparatus, boring apparatus, bridges of every form and material, canal machinery, harbors of refuge, breakwaters, jettings, wharves and piers, dredging machines, and machines used in harbor works, railway stations, and theatres, fire proof buildings, &c.

Model of the wrought iron bar Chain Suspension Bridge at Kieff, (Russia,) now erecting across the Dnieper; the largest work of the kind hitherto executed. Designed by C. Agnoles, Trafalgar Square, London.

This bridge has four principal openings of 440 feet each, and two side openings of 225 feet. On the right bank of the river is a swivel

bridge, which gives a free opening of 50 feet for the passage of boats, &c., on the river. There is a disadvantage in the suspension principle when the chains cannot be moved from shore to shore, as in this case, an island of masonry having to be formed in the river as a mooring abutment, to allow of the free passage for boats at the other side. There are, therefore, three abutments, two for the chains and one for the swivel bridge, and five piers; all these required coffer-dams of unusual size, particularly for the abutments. The chains are composed of broad, flat links, twelve feet long, and weighing about four hundred weight each. The tie rods which hang from the chains on each side are two inches in diameter, and are immediately connected to the girders which support the platform. The manner in which the platform is constructed is the chief novelty which has been introduced in their structure, and consists in a judicious combination of iron and wood, the object being to obtain a light and stiff platform. Two kinds of girders are adopted here, namely: trussed girders and tension girders; the trussed girders are chiefly composed of wood, and are deeper than the tension girders, which latter are rendered rigid by tension bars. One set of chains supports the trussed girders, and the other set supports the tension girders; and these occur alternately. The additional depth of the trussed girders is for the double purpose of stiffening the platform and supporting the foot-paths which are outside of the chains. The trussed girders are connected underneath, at each end, by longitudinal ties which run the whole length, and the balustrades separate the carriage-way from the foot-paths; they act conjointly with the ties underneath in checking any tendencies to undulation, the girders being also braced diagonally to prevent side play.

The whole of the machinery and iron used in the construction of the Kieff bridge was made in England, and weighs about 3,300 tons. Nine steam engines are employed, varying from eight to fifty-horse power, in pumping, driving piles, grinding mortar, and hoisting timber, &c. The cost of the bridge, when finished, is estimated at £400,000.

Model of Railway Bridge over the Wye, at Chepstow.—By Brunel.

This bridge is a novelty in engineering. It is composed entirely of wrought iron. One span is 300 feet, and the other 100 feet. The principle of construction adopted in spanning the 300 feet seems to be that of an extravagant trellis; and another principle of the same character as the Britannia tubes-that is, the top is subject to compression, and the bot tom to extension. This bridge has two lines for the up and down trains.

The span of 300 feet which we allude to more particularly consists of two huge, uncouth-looking trussed girders; the bottom of each girder is composed of two simple wrought-iron beams, which resist extension, and between which one of the lines runs; these beams are formed of boiler plates riveted together. The two girders are supported at two points, 100 feet apart from each end, from a wrought-iron tube above, which stretches across the whole span; and this tube resists the compression. This tube has also been raised at a considerable elevation above the bottom girders, so that the weights-such as trains, &c.— passing along the line, may be properly resolved or distributed over the tube by means of the tie rods and stays. The 100-feet spans are crossed simply by wrought-iron beams.

Model of One Arch of the High Level Bridge at Newcastle-upon-Tyne.Exhibited by Rasks, Crawshaw, & Co., of Gateshead, contractors for the Iron Works.

This bridge was designed by R. Stephenson, and is certainly a masterpiece of engineering. The banks of the Tyne, both at Newcastle and Gateshead, are exceedingly steep, and are connected by a viaduct 1,375 feet in length, running at a height of 112 feet above high-water mark. There are six principal openings, each of 126 feet span. The principle on which the bridge is constructed is the bow and string; the arches which form the bow are of cast iron, and the rods which form the strings are of wrought iron, to resist tension. There are four arches to each span, two on each side, which bear properly on the piers, through the medium of bed plates, on which the arches rest; the strings of each arch consist of two wrought-iron rods, keyed to the arches at the abutments. Cast-iron columns, connected to the arches, support a platform above, on which three sets of rails are laid, and they also support another platform below for a carriage road, the footpaths running between the two arches on each side. This road, in fact, runs along the strings, but has no connexion with them. The arches take the weight of both platforms above and below, having the strings independent, to resist only the tension. One cannot examine this bridge without having the mind strongly impressed with the rapid progress made in the mechanical art, a structure of this kind, particularly the iron work, requiring the adjustment of an immense number of parts; and yet no joints, and hardly any fastenings are to be seen-in fact, it is difficult to make out how it has been put together. The piers may look light to the eye for the superincumbent mass, but actually it is another striking feature in the structure, and speaks in favor of the progress in another branch of engineering known as civil.

Model of the Central Arch of the Anse Burn Viaduct on the Newcastle and North Shields Railway.-B. Green, Newcastle.

The great peculiarity of this bridge consists in the light and economical method of construction. The arches are of timber, built up of layers or planks sufficiently thin to allow being bent to the required sweep. The arch having thus been built up to the required size, is bound together by iron straps, bolts, &c. It is then scientifically strutted to resist and distribute whatever may be required.

Model of an Improved Lantern and Revolving Apparatus for Light and Signal Vessels at Sea.-W. Wilkins & Co., Long-acre.

The principal improvements in this apparatus consist in constructing the machinery to work beneath the deck, instead of in the lantern, as formerly. A vertical rcd, working in metal bearings, is attached to the mast, with a large gun-metal pinion fixed to the top of the rod at the height to which it is necessary to hoist the lantern, wherein a train of cog wheels is placed, to connect with the pinion and communicate the motion obtained therefrom to the traversing apparatus that supports the lamps and reflections.