The forging of shafts requires heavier machinery even than this. The enormous mass of iron that is in this case to be forged, is bricked up in a furnace to be heated, and remains there many hours. The masonry is then broken away and the red hot beam is swung round under the hammer, as seen below. It is suspended from the crane by heavy chains, and is guided by the workmen by means of iron handles clamped to it at a distance from the heated part, as seen in the engraving in the adjoining column. The hammer is lifted by means of the cam below it, as seen in the engraving below. This cam is a projection from an axis revolving beneath the floor, and which, as it revolves, carries the cams successively against a projection upon the under side of the hammer, which is partly concealed in the engraving by the figure of the man. When the point of the cam has passed beyond the projection it allows the hammer to fall. [Illustration: HEATING A SHAFT.] [Illustration: FORGING A SHAFT.] While the process of forging such a shaft is going on, one man throws water upon the work, to effect some purpose connected with the scaling of the iron, while another, with an instrument called the callipers, measures the diameter of the shaft, to regulate the size, as the forging proceeds. [Illustration: THE LATHES.] The shafts, when forged, are to be turned in a lathe, and the engine used for this purpose is represented on the left in the engraving below. The shaft itself is seen in the lathe, while the tool which cuts it as it revolves, is fixed firmly in the "rest," which slides along the side. The point of the tool is seen in the engraving, with the spiral shaving which it cuts falling down from it. The shaft is made to revolve by the band seen coming down obliquely from above, at the hither end of the engine. The wheel by which the band turns the lathe has different grooves at different distances from the centre, in order that the workmen may regulate the velocity of the rotation--as different degrees of velocity are required for the different species of work. The _rest_, to which the cutting tool is attached, is brought slowly along the side of the shaft as the shaft revolves, by means of a long screw which is concealed in the frame of the lathe, and which is turned continually by the mechanism of the small wheels which are seen at the hither end of the engine. On the right hand of this view is represented another kind of lathe called a _face lathe_, which is employed for turning wheels, and flat plates, and interiors of cavities, and such other pieces of work as do not furnish two opposite points of support. In the fore-ground are a company of men drawing a massive piece of iron upon a truck, destined apparently to be turned in the left hand lathe. [Illustration: FINISHING.]