engines, which have since acquired such extraordinary powers of velocity. The system was first brought to the test on this railway, which was opened on the 17th of September, 1825. The Stockton and Darlington Railway was the first public railway, perhaps, in the world, where this powerful mode of transit was carried successfully into effect. But, about this period (1824), the Hetton Colliery Railway was likewise worked by steam power.

ENGINE, AS LONG USED UPON THE KILLINGWORTH RAILROAD.

The following is a description of an engine which was long in use at Killingworth Colliery Railroad, and which continued to be used, without material alteration, till the year 1829, which affords the means of judging of the actual state of advancement which the locomotive system had attained at that period. Fig. 52. represents a side, and fig. 53. an end, elevation.

The boiler of the engine was made of malleable iron, cylindrical, with hemispherical ends; having a cylindrical tube passing through it within 2 inches of the bottom. In one end of this tube the fire grate was placed, and at the other end

the chimney. The boiler rested upon a square frame, supported by springs (a a), two on each

side. The chairs on which the axles rested were made to slide up and down within the guides (bb), and the action of the springs was communicated to them by a pin passing through a hole in the frame of the engine, one end of the pin resting on the back of the spring, and the other end on the upper side of the chair or bearing. The wheels were thus made to yield to the inequality

of the road. The cylinders were placed vertically, and partly within the boiler at a a. The piston

rods were attached to the cross beams B B, C C. The rectilinear motion of the piston rod was preserved by the slides (s s s s) fixed to the projecting arms (c c), and kept perpendicular by the braces (dd). The connecting rods (B C, C D) were

attached to the cross beams by ball and socket joints, and at the other end by similar joints to a pin fixed upon one of the spokes of the engine wheel (D D). The pins projected outwards, and upon one of these pins, on each side, a crank (Dƒ) was fixed, within which the connecting rod of the pistons worked, as shown in the end view. A rod (fg D) fixed at one end to the crank and at the other to the pin in the wheel of the other cylinder connected the whole together, and kept the pistons always in the same position with respect to each other; and the rod, being keyed fast at each end, prevented any slipping of the wheels without the whole partook of the motion. The wheels of the engine were 4 feet in diameter, the spokes made of cast iron, and the axles of wrought iron, 31 inches in diameter. The steam was communicated from the boiler to the cylinder through a passage, the area of which was regulated by a sliding lever, or handle, which regulated the velocity of the engine. The steam, after being admitted to the top and bottom of the cylinder by a sliding valve, escaped by the pipe (r r) into the chimney. The slide valve was opened and shut by an eccentric, connected to the lever f g h, communicating motion to the arm i k, through it to the lever kl, to the rod 7 m, to the cross head m n, and so to the rod no, of the sliding valve.

The boiler was supplied with water by a force pump P, which was fixed to the side of the boiler, and worked by a rod t. p is the man-hole door to get access to the boiler; v is the safety valve, with the weight w to regulate the pressure.

The performance of this engine in 1829, weighing with the tender (the carriage which accompanies a locomotive engine with the supply of water and fuel), about 10 tons, was equal to convey 10 tons at the rate of six miles an hour, the evaporating power being equal to 15 gall. of water per hour.

Notwithstanding the work which the locomotive engines at this period could perform, fixed engines were generally preferred, and many powerful engines were in use for working inelines, as has previously been pointed out at the colliery railroads in England and Scotland. It is necessary to keep this in view, as it may tend to explain the report which was given in upon the Liverpool and Manchester Railway; for, although the importance of locomotive engines was gradually becoming to be more estimated, still the knowledge respecting them was very limited and confined within a narrow range; and they were generally considered at that time as less efficient as a prime mover than fixed steam engines.