gines and a steam road-roller were tried. The following were the principal dimensions: Weight of engine complete, five tons four hundred-weight (11,648 pounds); diameter of steam-cylinder, 7¾ inches; stroke of piston, ten inches; revolutions of crank to one of driving-wheel, seventeen; diameter of driving-wheels, sixty inches; length of boiler over all, eight feet; diameter of boiler-shell, thirty inches; load on driving-wheels, four tons ten hundred-weight (10,080 pounds). The boiler was of the ordinary locomotive type, and the engine was mounted upon it, as is usual with portable engines. The engine valve-gear consisted of a three-ported valve and Stephenson-link, with reversing lever, as generally used on locomotives. The connection between the
Fig. 39.—Modern Road-Locomotive.
gearing and the driving-wheels was effected by the device called by builders of cotton-machinery a Jack-in-the-box gear, or differential gear. By this combination, the effort exerted by the engine is made equal at both wheels at all times, even when the engine is turning a corner. The following is a summary of the conclusions deduced from the trial, and published in the Journal of the Franklin Institute: A traction-engine may be so constructed as to be easily and rapidly maneuvered on the common road; and an engine weighing over five tons may be turned continuously without difficulty on a circle of eighteen feet radius, or even on a road but little wider than the length of the engine. A locomotive of five tons four hundred-weight has been constructed, capable of drawing on a good road 23,000 pounds up a grade of 533 feet to the mile, at the rate of four miles an hour; and one might be constructed to draw more than 63,000 pounds up a grade of 225 feet to the mile, at the rate of two miles an hour. It was further shown that the coefficient of traction with heavily-laden wagons on a good macadamized road is not far from 4100; the traction-power of this engine is equal to that of twenty horses; the weight, exclusive of the weight of the engine, that could be drawn on a level road, was 163,452 pounds; and the amount of fuel required is estimated at 500 pounds a day. The advantages claimed for the traction-engine over horse-power are: No necessity for a limitation of working-hours; a difference in first cost in favor of steam; and in heavy work on a common road the expense by steam is less than twenty-five per
