As it is necessary that trains should at certain places be “shunted”
or shifted from one line of rails to another, particularly at
stations where a great many tracks run side by side, and cross each
other to branch off to different parts, there are arrangements called
“points,” shifted by a lever or “switch,” so that they shall direct
the course of the train, and cause it to leave the former track
and enter upon a new one; this arrangement may be seen at fig. 5,
where the points are in the position to direct the engine coming in
the direction of the arrow on to the curved line A, and the dotted
lines indicate the position into which they would be shifted, if
necessary for the train to go straight on to the line B; this action
is effected by moving a lever which shifts the two bars a few inches
either way. When an engine or carriage has to be turned on to a
track at right angles to the one on which it rests, or where there
is not room for “shunting,” an apparatus called a “turn-table” is
used, which is shown at figs. 6 and 7; it is a round platform of iron
turning on its centre, and supported by friction rollers at the edge,
having on its surface raised rails in two or more directions, so that
it may be turned round half or quarter distance, according to the
position required. The engines and carriages used to run on railways
are of various constructions, but to a certain extent agree in their
chief particulars; the wheels are fixed to their axles, so that each
pair and the axle which joins them may be considered as one piece.
The axle projects a little way beyond the wheel, and on this part
it supports the engine or carriage, which is wider than the distance
from one wheel to its fellow. They are therefore entirely underneath.
They are of iron, made by machinery and have a projecting edge on the
inside of the “tire” of each, which is called the “flange” (see fig.
8); this flange does not run on the rail but within it to prevent the
wheels from slipping off. These flanges, when the pair of wheels and
axle are united, exactly fit in between the rails, so as to touch the
inside of each and form a sort of guide. Each carriage has two pairs
(except in a few cases, where three pairs are used), the engines have
usually three, and sometimes four pairs. The carriages rest upon
powerful springs, and are moreover furnished with springs to diminish
the concussion of one carriage against another; these last are acted
on by a sort of piston-rod, one of which is placed at each corner
of the carriage, and are called “buffers” (figs. 9 and 10); they
all coincide with each other, and form a set of springs all along
the train, which greatly reduces the shock which would otherwise be
felt when it is stopped. Another set of springs is connected with
the binding screws which unite each carriage, and these prevent the
sudden jerk which would result from the starting off of a train quite
inelastic in its length.
The engines used are of that class called high-pressure or
non-condensing, and there are two cylinders and pistons, which have
a stroke of about eighteen inches. The boiler is so contrived that a
large quantity of steam shall be rapidly produced; for this purpose
tubes of brass are made to pass side by side from the fireplace
through the boiler, and through these tubes the flame and hot air
must go before reaching the funnel, giving out in its course a great
amount of heat to the water and converting it rapidly into steam.
The steam from each cylinder passes at each stroke of the piston
into the funnel, assisting to form a draught which draws the flame
from the fire through the tubes and increases the fierceness of the
combustion. The necessity for two cylinders and pistons is owing to
the impossibility of having a fly-wheel, and as the driving wheels
of the engine have to be turned at an equal rate, the axle has two
cranks so placed that the greatest power of one piston is exerted
where the other exerts the least (see “Steam-engine”).