274 



THE POPULAR SCIENCE MONTHLY. 



gines and a steam road-roller were tried. The following were the 

 principal dimensions : Weight of engine complete, five tons four hun- 

 dred-weight (11,648 pounds); diameter of steam-cylinder, 7f 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 con- 

 sisted 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 

 manoeuvred 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 t |~q ; the traction- 

 power of this engine is equal to that of twenty horses ; the weight, ex- 

 clusive 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 esti- 

 mated 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 



