The round beam which is seen issuing from the centre of the head of the cylinder is called the piston rod. The piston itself is firmly secured to the lower end of this rod within the cylinder. Of course, when the piston is forced upward by the pressure of the steam admitted beneath it, the piston rod rises, too, with all the force of the expansion. This is, in the case of the largest marine engines, a force of about a hundred tons. That is to say, if in the place of the cross head--the beam marked H in the engraving which surmounts the piston--there were a mass of rock weighing a hundred tons, which would be, in the case of granite, a block four feet square and eighty feet high, the force of the steam beneath the piston in the cylinder would be competent to lift it. The piston rod, rising with this immense force carries up the cross head, and with the cross head the two _side rods_, one of which is seen in full, in the engraving, and is marked S. There is a side rod on each side of the cylinders. The lower ends of these rods are firmly connected with the back ends of what are called the _side levers_. One of these side levers is seen in full view in the engraving. It is the massive flat beam, marked L, near the fore-ground of the view. It turns upon an enormous pivot which passes through the centre of it, as seen in the drawing, in such a manner that when the cylinder end is drawn up by the lifting of the cross head, the other end is borne down to the same extent, and with the same prodigious force. There is another side beam, on the other side of the cylinder, which moves isochronously with the one in view. The forward end of this other beam may be seen, though the main body of it is concealed from view. These two forward ends of the levers are connected by a heavy bar, called the _cross tail_, which passes across from one to the other. From the centre of this cross tail, a bar called the connecting rod rises to the crank, where the force exerted by the steam in the cylinders is finally expended in turning the great paddle wheels by means of the main shaft, S, which is seen resting in the pillow block, P, above. These are the essential parts of the engine, and we now proceed to consider the mode of manufacturing these several parts, somewhat in detail. [Illustration: THE CUTTING ENGINE.]