mechanical engineering have, however, produced several superior machines for punching, by which the work is executed with great rapidity and precision.

In the course of our description of the manufacture of the Conway and Britannia Bridges we shall have to refer to a most ingenious combination of mechanism invented for punching the plates of those bridges by Mr. Roberts, of Manchester; but, in the mean time, we may refer to a clever application of the principle of the hydrostatic press for the purposes of punching, riveting, and shearing metal plates, invented and patented by Mr. Charles May, of Ipswich. The patent is dated April 15, 1846, and entitled, for "improvements in machinery for punching, riveting, and shearing metal plates." The mechanism for the purpose of punching holes in metals consists of a strong frame of iron, shaped like a horse-shoe, one arm of which is fitted to contain a die, having a hole in it of the size of those intended to be punched in the plate. This die is secured in its position in the frame by means of a pinching screw, which also admits of its removal, and the substitution of other dies, according to the size of the intended holes. The extremity of the other arm is cast hollow, and fitted with a ram or solid piston, similar to that of an hydraulic press, and which, in this machine, carries the punch. The ram is truly turned on its cylindrical surface, and fitted to an annular casing bored on its inside to fit the ram, and turned on its outside, to fit the hollow space which is cast in the arm of the frame. Both the casing and the ram have an annular groove cut in their external surfaces, and fitted with cap-leathers, to prevent the escape of the water when the pressure is applied. Attached to the hinder end of the ram is a rod, which passes through a stuffing-box in the frame, and is attached at the other end to a spiral spring, by the action of which the ram and the punch upon it are withdrawn when the pressure ceases. The water is admitted from the pumps to act upon the ram through an aperture in the iron frame of the machine, the form of which admits its suspension from a traversing

crane, and thus being moved about at pleasure. In this case the plates to be punched will be applied to the machine vertically, while the action of the punch will be in a horizontal direction. The water is forced in behind the ram by means of two pumps, one of which should be considerably larger than the other, to bring the moving parts to the plates by a rapid action, succeeded by the small pump, which produces the pressure required to force the punch through the metal, and admits only of a slow movement.

The other parts of the invention comprise suitable means for riveting and shearing respectively by rams and pumps. The patentee defines his claim to be, first, the application of the pressure of a fluid, caused by means of pumps, for the punching of metals; secondly, the application of the pressure of a fluid, caused by means of a pump or pumps, for the riveting together plates of metal; and thirdly, the arrangement of a series of hydraulic rams, for the purposes of shearing metal plates. The slowness of movement of this machinery would, it must be feared, neutralise the economy of the power, and render it altogether inapplicable for extended adoption.

The third process involved in the joining of plates or bars of iron, viz. the riveting, is effected by heating the rivet, on which the head is already formed, passing it through the corresponding holes in the two parts to be united, and hammering the projecting end of the rivet into a head of increased diameter. While this is done by one workman, another strikes a liammer firmly against the original head of the rivet. As the rivet cools, its length becomes contracted, and thus tends to bring the two joined parts closely together. The greatest improvements yet effected in the process of and machinery for riveting is that patented by Mr. W. Fairbairn in 1833, by which invention steam is applied in a most effective manner, and the operation made susceptible at once of unexampled rapidity and effectiveness. Subsequent modifications of the apparatus invented by Mr. Fairbairn have been suggested by other persons, among which may be mentioned, one by Messrs

Schneider and Co., of Creusot, in France; also a later invention patented by Mr. James Garforth, of Dukinfield, Chester, fcr the direct application of the expansive force of steam to the dies for riveting. Mr. Garforth's patent is dated December 10, 1845, and granted for "certain improvements in machinery, or apparatus for connecting of boilers, and other purposes." The patentee "does not confine himself to the use of steam pressure, as the direct action of water, air, or any other elastic medium may be similarly employed without departing from the principle of his invention. He does not claim as his invention the exclusive use of the several parts of the machine he describes, except it be employed for the purposes of his invention, which consists in riveting metal plates by dies driven by the elastic force of steam, water, or other elastic medium."

The cutting or shearing of iron plates, in order to trim the edges or fit them for the space they are to occupy, is another important operation, for which several forms of apparatus have been produced. Formerly the lever-fly, already referred to as an instrument for punching holes, was adapted also to act as shears; the long arm of the lever being made to pass close to a fixed arm, and each of them fitted with a long cutter of steel. Machines of far greater power and efficiency are, however, now employed for this purpose. To prevent the curling or buckling which long plates are liable to suffer while being sheared, Mr. W. V. Wennington, of Staffordshire, patented a combination of machinery, on July 20, 1846, under the title of "improvements in, or improved methods of cutting plate and sheet iron." This invention consists in the combination of a rotary and continuous horizontal movement. The rotary movement comprises a circular cutter, set in motion by gearing; and the horizontal movement consists of another cutter attached to a traversing table, on which the iron plate is laid. The circular cutter is fixed on one end of a shaft which revolves in bearings fixed between vertical standards, the bearings being provided with regulating screws. The other end

of the shaft has a bevelled wheel, which may be alternately geared with each of two bevelled wheels sliding upon keys on the main shaft of an engine worked by steam or other power. By this means an alternate rotary motion is given to the circular cutter, while the table, moving on A rails, receives a traversing motion by means of a rack fixed to it, working into a cog-wheel keyed upon the shaft of the circular cutter, and immediately behind it. Each of the bevelled wheels sliding on the main shaft is thrown in and out of gear with the wheel on the cutter-shaft by a forked lever acting on a clutch, which lever is actuated by tappets fixed on the under side of the table, and thus an alternate backward and forward movement is given to the revolving cutter, and the traversing table and cutter.

SECTION III.

First Constructions of Wrought-Iron Plate Girders-Mr. Fairbairn's Patent Wrought-Iron Tubular Girders-Their application to Bridgebuilding-Bridge on the line of the Blackburn and Bolton RailwayBridges of the Liverpool Landing Stage-Great Bridge erected by Messrs. Fairbairn and Sons, on the line of the Manchester, Sheffield, and Lincolnshire Railway at Gainsborough.

THE first attempts to substitute wrought iron for cast iron, in the construction of girders, were made by joining plates vertically with rivets, and attaching a strip of angle iron on each side, both at top and bottom, so as to form artificial flanges to give the required strength at these parts. Girders thus formed, have been used as deck-beams in ships for fifteen years; indeed, Messrs. Fairbairn applied them in constructing floors in the year 1832. Some of these were constructed to be used in a building erected in 1847, at Portsmouth Dockyard, and were 41 feet 3 inches long, 2 feet deep in the centre, and reduced by a parabolic curve on the upper edge to a depth of 1 foot at the ends. The body of the girder was

composed of a double thickness of plates, each inch thick.

Fig. 1.

"

Fig. 2.

20 - 74

Centre

1.

An

These plates were each about 6 feet 9 inches long, and so arranged as that their joints alternated with each other. angle-iron was riveted on either side at the top, making the breadth of the girder over the top 9 inches; an angle iron was also riveted on either side at the bottom, but of larger dimensions, making the breadth over the bottom 16 inches; the rivets were g inch diameter. Fig. 1 shows the elevation of one of these girders, and Fig. 2 is a section through the centre to an enlarged scale. These girders were evidently formed in imitation of the proportions which have been found desirable in those of cast iron, the less tensile power of which requires additional material at the lower part of the section. Later inquiries, as will be mentioned hereafter, have shown the non-applic