1572

THEORY AND PRACTICE OF ENGINEERING.

Book II.

440 _

ij^ir

Fig. 2937. loch and Stephenson’s chair.

Fig. 2938. loch’s chair.

i.

Fig. 2939.

project above, or fall below, thecorresponding one of that withwhich it is in contact, and so toform the union of the rail andchairs, that they should alwaysremain perpendicular: this con-trivance relieved the carriagesfrom the sudden jerks to whichthey were previously subject,and diminished the resistanceoffered to the wheels in theirtransits over the rail.

Brunton and Shield's Railway.

— The rail is fastened to thechair, which has only one cheek,by a screw-bolt, which draws aconcave nutt tightly against aconvex protuberance on the rail,holding it firmly against the up-right cheek of the chair: thethread of the screw, however,being exposed to the action of

the weather, is, in the course of time, apt to break,when turned’for the purpose of tightening the joints.

Loch obtained a patent for another chair, in whichthe pin was dispensed with : the rails were united atthe ends by means of a half lap passing each other,when they were set on edge 3 inches : upon the outerside of each rail was a circular projecting knob, andon one of the inner sides a similar knob, whichentered a cavity cast to receive it, and prevented the ^rails from being drawn out in the direction of theirlength : the rails maintained their proper position,and were prevented fromrising by their ownweight. Other meanshave been adopted tomaintain the rails on theirchairs without a pin;some have round knobscast on their ends, which ~enter cavities answeringto them, and are keptin their places, thus ob-taining a level surfacethroughout, which is thechief result to be arrived at.

One of the first malleable rails formed by rolling-bars was made in the year 1820, whicheffected a great change in all that were afterwards manufactured. The process consists ofpassing bars of iron heated red-hot between two rollers so grooved that they give the re-quired form; the under side of the rail issometimes made elliptic^, by fixing it on afalse centre. This kind is usually rolledout into 15 feet lengths, and laid on 3 feetbearings, with their ends formed with halflaps.

The Liverpool and Manchester line hadrails of this description, weighing 35 poundsper lineal yard with square ends, and a squareprojection on one side, which, by driving aniron key into a hole on the other, force it intoa recess cast in the side of the chair to receiveit. The key was in form of a wedge, and driven longitudinally.

The chairs were secured to stone blocks, 2 feet square and 12 inches thick, by iron pinsdriven into wooden plugs, previously inserted in the stone. In Loch’s patent the key isdriven on each side above the projection at the bottom of the rail, so that it is kept fromrising, which became necessary when the rails were made in 15 feet lengths, the alterations

h O

Fig. 2940.

Fig. 2941.

Fig. 2942

Fig. 2943.