Length of stroke, 12 feet; length of beam, 24 feet; depth of beam in the middle, 10 feet. The form of the beam is that of an elongated parallelogram, the outer frame or skeleton is made in one piece of wrought iron, inside of which is fitted another frame of cast iron, carrying the axis.
4. River Steamers for Shallow Waters.—A steamboat running on the Ohio, from Pittsburgh to Cincinnati, had a pair of direct acting engines with 32-inch cylinders and 8 feet stroke. There was no main crank shaft connecting the two paddle wheels, but each engine worked its own wheel independently of the other. This arrangement enables the boat to be steered with greater facility round the sharp turns encountered in the tortuous course of the river. The framework and outer bearings of the paddle wheels are supported by suspension rods, which are, as it were, slung over beams, and framework strongly constructed, and fixed in the centre of the vessel. The main deck is 280 feet long, and 58 feet wide. The paddles are 38 feet in diameter, having twenty-four floats, 12 feet wide by 28 inches in depth. For shallow rivers, flat-bottomed steamers, propelled by a paddle-wheel at the stern, are commonly used. Two were being built of iron in New York, drawing only 2½ feet of water,
