MEANS OF COMMUNICATION. 27 
nected with the locomotive by chains and hooks seen hanging from the 
buffer in jig. 9. 
A cock in the supply-pipe x (pl. 4, fig. 3), within reach of the engineer, 
serves to regulate the supply of water to the engine; and there is also a 
cock upon the tender to shut off the water entirely. The supply-pipe ter- 
minates in a chamber x (jig. 2), from which the water is taken by a pump 
which forces it into the boiler. 
Pl. 5, fig. 1, is a longitudinal section of Stephenson’s locomotive with 
variable expansion ; jig. 2, front view of the same, the end plate of the 
engine being removed ; jig. 3 @ is a horizontal section of the cylinders ; fig. 
4, a vertical section of the same; jig. 5 is a view of the pump; jig. 6, sec- 
tion of the end of the exhaust-pipe; jig. 7a, section through one of the 
slide-valves ; jig. 7b, a plan of the same; jig. 36, view of the piston with 
metal packing, seen in section in jig. 3c; and finally, fg. 8 illustrates the 
position of the different parts of the valve-gearing during the operation of 
the machine. As we have already explained the construction of a locomo- 
tive, it will be sufficient to enumerate those parts which differ essentially 
from the one already described- a is the main frame of the machine. The 
springs c rest upon the rods p, as already explained, the whole weight of 
the locomotive being carried by the rods £7; 6* is the dome, which is fur- 
nished, instead of a cock, with a slide-valve n’, the rod t of which passes 
through a stuffing-box in the steam-dome, and thence to the position of the 
engineer, where it is managed by the levers 66’. Upon the pipe which 
carries the steam from the boiler is a safety-valve, beyond the reach of the 
engineer, kept down by a spiral spring, as seen in fig. 1. @is the lower 
end of the chimney, @’ is the man-hole, oH are the steam cylinders. The 
cylinders FF have their valves upon the inside, close to each other ; this 
is rendered necessary, as we shall presently see, by the expansion arrange- 
ment. The exhaust-valves of both cylinders open into a common chamber 
Tt (fig. 4), whence the steam passes by the two side pipes to the exhaust- 
pipe #, which by means of a double-angled lever may be more or less 
closed by the engineer as required. The steam may also be thrown into a 
chamber, v, whence it is blown out beneath the locomotive through a slide 
valve, @ (jigs. 4-Ta@ and 76), also manageable by the engineer without 
leaving his station. The pistons 77 (jig. 3a) are furnished with spring 
metal packing, as seen in jigs.386 and 3c. The piston-rods o are connected 
with the cranks upon the driving-wheel shafts. The steam-pipe x carries 
the steam from the steam-dome to the valve-chest and cylinders, as in the 
former case, the valves receiving their motion from the shaft of the driving 
wheels, which have already been set in motion by the pistons. The variable 
expansion was effected by Stephenson by what is technically called link 
motion. For each valve there are two eccentrics by the side of each other, 
and so placed upon the main driving-shaft that one of them will drive the 
valve-rod forwards and the other backwards. The forward ends of these 
connecting-rods are united by a link, which has a slat in the middle, in 
which plays a pin connected with the end of the valve-rod. By this simple 
and effective arrangement the forward or backward motion is effected, with- 
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