The steam-boats on the Atlantic rivers are differently constructed from those of the west, as the same necessity for light draught of water does not exist, while they are more especially intended for passengers; their cabins are, frequently, under deck, while those on the western rivers, constructed for carrying heavy cargoes as well as passengers, have their cabins, generally, in two tiers above the deck, hence the preference given to high pressure engines from their being lighter and occupying less space. The condensing or low pressure engine is much more prevalent in the Eastern boats, and is more economical in fuel than the high pressure: their boilers are usually circular; there is great variety in the form and construction of the furnaces and flues, and the boilers designed for burning wood are, of necessity, of greater external dimensions than those designed for burning coal, although the proportions of steam space may be smaller in the former than in the latter. These boilers are frequently worked at 18 to 20 pounds on the square inch, but 12 pounds is considered the medium. The expansive action of the superheated steam in these engines, the greater space allowed for the engines to work in, and the generally admirable form of the boats, will, of course, tend to reduce the quantity of fuel required. The stroke of the piston, in some of the fastest American boats, is as much as 10 or 11 feet, and the connecting rods 13 to 19 feet long: the engine is worked at a much quicker rate than in England, the piston passing through the space of 500 feet in a minute, at which speed the whole machinery is found to work more smoothly than at a slower rate. It has been remarked by competent judges that, though the English engine is more perfect and more highly finished than the American, the advantage of superior workmanship is more than compensated in the American by greater length of stroke and the connection. American engineers consider the English engine, as applied to marine purposes, too confined, and until steam of a higher pressure is used, the boat must be of inferior speed to those of the United States. A Boulton and Watt engine[157] of 30-inch cylinder and 4-foot stroke, making twenty-five revolutions in a minute with 3½ pounds of steam, is estimated as a 30-horse engine; but the force of this engine, it is argued by Americans, will be increased one-third if steam of 7 pounds be used; “lengthen the cylinder,” they remark, to 8 feet and drive the piston through that space in the same time, that is, 400 feet instead of 200, use the same quantity of steam by shutting it off at half the stroke, and the American engine as compared with the English will be nearly an 80-horse instead of a 30-horse power. [Sidenote: Great speed of American lake and river steamers.]