182 THE MODERN STEAM-ENGINE.
This carriage was loaded with heavy masses of iron, and
attached to trains of coal-wagons on the railway. By re-
peated experiment, varying the weight of the traction-car-
riage and the load hauled, Hedley ascertained the propor-
tion of the weight required for adhesion to that of the loads
drawn. It was thus conclusively proven that the weight of
his proposed locomotive-engine would be sufficient to give
the pulling-power necessary for the propulsion of the coal-
trains which it was to haul.
When the wheels slipped in consequence of the presence of grease, frost, or moisture on the rail, Hedley proposed to sprinkle ashes on the track, as sand is now distributed from the sand-box of the modern engine. This was in October, 1812.
Hedley now went to work building an engine with smooth wheels, and patented his design March 13, 1813, a month after he had put his engine at work. The locomo- tive had a cast-iron boiler, and a single steam-cylinder 6 inches in diameter, with a small fly-wheel. This engine had too small a boiler, and he soon after built a larger en- gine, with a return-flue boiler made of wrought-iron. This hauled 8 loaded coal-wagons 5 miles an hour at first, and a little later 10, doing the work of 10 horses. The steam- pressure was carried at about 50 pounds, and the exhaust, led into the chimney, where the pipe was turned upward, thus secured a blast of considerable intensity in its small chimney. Hedley also contracted the opening of the ex- haust-pipe to intensify the blast, and was subjected to some annoyance by proprietors of lands along his railway, who were irritated by the burning of their grass and hedges, which were set on fire by the sparks thrown out of the chimney of the locomotive. The cost of Iledley's experi- ment was defrayed by Mr. Blackett.
Subsequently, Hedley mounted his engine on eight wheels, the four-wheeled engines having been frequently stopped by breaking the light rails then in use. Hedley's
