THE GROWTH OF THE STEAM-ENGINE. 



273 



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 con- 



Fig. 38. Gurnet's Steam-Carriage, 1833. 



ducted 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 3i 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- 



VOL. XII. 18 



