The hammers had two faces; the upper faces struck on this 6-inch square bar, the lower faces struck the backs of the heavy tool-holders. These tool-holders were held in position in the manner shown. At the extreme back end they rocked downward upon a heavy cross-bar. At the front they rose against the 6-inch cross-bar. They were made with a heavy hook at the back, which prevented them from coming forward further than the projection at the bottom of this cross-bar permitted. A curved spring held them up to the cross-bar when the weight of the hammer was removed. Between the 6-inch cross-bar and the tool-holders and the hammer faces I introduced a sheet of heavy leather belting, which deadened the force of the blow. A stone-cutter uses a wooden mallet to drive the tooth-chisels and droves, because the impact of iron on iron has a disintegrating effect upon the stone, which the stone-cutters call “stunning the stone.” It produces a vibration in the body of the stone to a depth of perhaps ¹⁄₈ inch, and, however well the surface of the stone may appear when it is finished, after a while the outside will flake off to the depth to which these vibrations have extended. This leather buffer served the purpose of the wooden mallet, completely avoiding this difficulty. Incidentally also it made the building habitable, by transforming the blow into a dull thud, which at the rate of 1800 blows per minute from the six hammers was itself quite important to be done. The large screws on each side of the machine at the front were provided at the top with long nuts resting on a cross-bar and combined with worm-wheels. A shaft carrying two worms engaging with these wheels extended across the top of the machine, so that the nuts were rotated identically, and the front of the suspended frame was raised or lowered as the thickness of the stone or depth of the cut required. The machine could cut stone from the thinnest ashlar up to a thickness of about 3 feet. The hammers ran on rollers as shown. At the back the frame and hammers were carried on similar rollers on the same shaft. The ends of this shaft also turned in square heads of screws, and by a mechanism similar to that already described the back of the frame could be elevated or depressed to the height required and be set at any desired angle. The six tool-holders were made in the following manner: I got from England a bar of steel long enough to make them all. This was planed into the form shown in the section, and the sockets for the shanks of the tools were finished to an equal depth and perfectly in line. It was then parted, and the ends of each finished in a slotting-machine.