These cylinders though very massive and ponderous are not the heaviest castings made. They are much exceeded in weight by what is called a bed plate, which is an enormous frame of iron cast in one mass, or else in two or three separate masses and then strongly bolted together, to form a foundation on which the engine is to rest in the hold of the ship. The bed plate can not be seen in the view of the engine room already given, as it lies below the floor, being underneath all the machinery. A bed plate weighs sometimes thirty-five tons--which is the weight of about five hundred men. Such a mass as this has to be transported on ways, like those used in the launching of a ship. It is drawn along upon these ways by blocks and pullies, and when brought alongside the ship is hoisted on board by means of an enormous derrick, and let down slowly to the bottom of the hold--the place where it is finally to repose, unless perchance it should at last be liberated by some disaster, from this dungeon, and sent to seek its ultimate destination in the bottom of the sea. The engraving below represents the forges, where all those parts of the machinery are formed and fitted which consist of wrought iron. The room in which these forges are situated is called the smith's shop, in the plan. In the back-ground, a little to the right, is one of the trip hammers, in the act of striking. The trip-hammer is a massive hammer carried by machinery. The machinery which drives it may at any time be thrown in or out of gear, so that the blows of the hammer are always under the control of the workman. The iron bar to be forged is far too heavy to be held by hand. It is accordingly supported as seen in the engraving, by a crane; and only guided to its place upon the anvil by the workmen who have hold of it. The chain to which this bar is suspended comes down from a little truck which rests upon the top of the crane, and which may be made to traverse to and fro, thus carrying whatever is suspended from it further outward, or drawing it in, as may be required. All the cranes, both in the smith's shop and in the foundry, are fitted with the same contrivance. These trucks are moved by means of a wheel at the foot of the crane. [Illustration: THE FORGES.] On the extreme right of the picture, and somewhat in the distance, may be seen another trip-hammer with a bar upon the anvil beneath it, this bar being suspended likewise from a crane. When the iron becomes too cold to yield any longer to the percussion, the hammer is stopped, the crane is swung round, and the iron is replaced in the forge to be heated anew; and at length, when heated, it is brought back again under the hammer as before.