There are _two_ engines and _four_ boilers; thus the machinery is all double, so that if any fatal accident or damage should accrue to any part, only one half of the moving force on which the ship relies would be suspended. The heads of two of the boilers are to be seen on the left of the view. They are called the _starboard_ and _larboard_ boilers--those words meaning _right_ and _left_. That is, the one on the right to a person standing before them in the engine room, and facing them, is the starboard, and the other the larboard boiler. It is the larboard boiler which is nearest the spectator in the engraving. The boilers, the heads of which only are seen in the engraving, are enormous in magnitude and capacity, extending as they do far forward into the hold of the ship. In marine engines of the largest class they are sometimes thirty-six feet long and over twelve feet in diameter. There is many a farmer's dwelling house among the mountains, which is deemed by its inmates spacious and comfortable, that has less capacity. In fact, placed upon end, one of these boilers would form a tower with a very good sized room on each floor, and four stories high. The manner in which the boilers are made will be presently explained. The steam generated in the boilers is conveyed to the engine, where it is to do its work, by what is called the steam pipe. The steam pipe of the larboard engine, that is, of the one nearest the spectator, is not represented in the engraving, as it would have intercepted too much the view of the other parts. That belonging to the starboard engine, however, may be seen passing across from the boiler to the engine, on the back side of the room. The destination of the steam is the _cylinder_. [Illustration: GENERAL VIEW OF A MARINE ENGINE.] The cylinder, marked C, is seen on the extreme right, in the view. It may be known, too, by its form, which corresponds with its name. The cylinder is the heart and soul of the engine, being the seat and centre of its power. The steam is generated in the boilers, but while it remains there it remains quiescent and inert. The action in which its mighty power is expended, and by means of which all subsequent effects are produced, is the lifting and bringing down of the enormous piston which plays within the cylinder. This piston is a massive metallic disc or plate, fitting the interior of the cylinder by its edges, and rising or falling by the expansive force of the steam, as it is admitted alternatively above and below it.