Page:Popular Science Monthly Volume 12.djvu/287

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herence, or of friction between the wheels and the soil, was 0.3. 5. A speed of seven miles an hour caused no special difficulty in managing either the locomotive or its load. At about this time M. Servel conducted

PSM V12 D287 Gurney steam carriage 1833.jpg
Fig. 38.—Gurnet's Steam-Carriage, 1833.

a series of experiments with a similar machine upon paved and upon macadamized roads, during what he described as the most trying of winter weather. He reports the following distribution of weight per cent.:

Weight of locomotive 41.4
"" wagons 18.2
"" paying load 40.4
Total 100

The average total weight of three loaded wagons, which was the usual load, was 22,575 kilogrammes, or about twenty-two tons. The experiment was made in 1867-'68 of applying these engines to the towage of boats on the French canals, with very encouraging results.

In 1871 several traction-engines were exhibited before the Royal Agricultural Society of England at Wolverhampton, and the judges made a series of careful tests, reported in its "Journal" for that year. The coal used on special trial amounted to 3.2 pounds per indicated horse-power per hour, and the evaporation of water was 7.62 pounds per pound of coal consumed, the average temperature of feed being 175° Fahr. The load drawn up the maximum grade of 264 feet to the mile on Tottenham Hill, which is 1,900 feet from top to bottom, was twenty-six tons, and including weight of engine thirty-eight tons, giving a coefficient of traction of 0.35. On a country-road sixteen miles long it drew fifteen tons at an average rate of 3½ miles an hour, using 2.85 pounds of coal and 1.94 gallon of water per ton of useful load per mile.

67. In October, 1871, the writer conducted a public trial of road-engines and steam road-rollers, on a well-macadamized road at South Orange, New Jersey. Two road-steamers (Fig. 39) or traction-en-