THE LOCOMOTIVE
UNCLE PAUL showed his nephews the following picture, and explained it to
them.
[Illustration: An old-time Locomotive]
“This picture represents a locomotive. The boiler where the steam is
generated, the boiling pot, in short, forms the greater part of it. It
is the large cylinder that goes from one end to the other, borne on six
wheels. It is built of solid iron plates, perfectly joined together with
large rivets. In front the boiler terminates in a smoke-stack; behind,
in a furnace, the door of which is represented as open. A man, called a
stoker, is constantly occupied in filling the furnace with pit-coal,
which he throws in by the shovelful; for he must keep up a very hot fire
to heat the volume of water contained in the boiler and obtain steam in
sufficient quantity. With an iron bar he pokes the fire, arranges it,
makes it burn fast. That is not all: skilful arrangements are made to
utilize the heat and warm the water quickly. From the end of the furnace
start numerous copper pipes which traverse the water from one end to the
other of the boiler, and terminate at the smoke-stack. You will see some
in B where the picture supposes a part of the casing taken away to show
the interior. The flame of the furnace runs through these pipes,
themselves surrounded by water. By this means the fire is made to
circulate through the very midst of the water, and so steam is obtained
very quickly.
[Illustration: A modern Locomotive]
“Now look at the front of the locomotive. In A is seen a short cylinder
closed tightly, but represented in the picture with a part of the
outside removed to show what is within. There are two of these
cylinders, one on the right, the other on the left of the locomotive.
Inside the cylinder is an iron stopper called a piston. The steam from
the boiler enters the cylinder alternately in front of and behind the
piston. When the steam comes in front, what is behind escapes freely
into the air by an orifice that opens of itself at the right moment.
This escaping steam ceases to press on the piston, since it finds its
prison open and that it can get out. We do not try to force doors when
other outlets are open. So does steam act: the instant it can escape
freely, it ceases to push. The entering steam, on the contrary, finds
itself imprisoned. It pushes the piston, therefore, with all its
strength and drives it to the other end of the cylinder. But then the
rôles immediately change. The steam that hitherto has been pushing,
escapes into the air and ceases to act, while on the other side a jet of
steam rushes in from the boiler and begins to push in the contrary
direction.”
“Let me repeat it,” said Jules, “to see if I have understood it
properly. Steam comes from the boiler, where it forms unceasingly. It
goes into the cylinder before and behind the piston by turns. When it
gets in front, that behind escapes into the air and no longer pushes;
when it gets behind, that in front escapes. The piston, pushed first one
way, then the other, alternately, must advance and retreat, go and come,
in the cylinder. And then?”
“The piston is in the form of a solid iron rod that enters the cylinder
through a hole pierced in the middle of one of the ends, and just large
enough to give free passage to the rod, without letting the steam
escape. This rod is bound to another iron piece called a crank, and
finally the crank is attached to the neighboring wheel. In the picture
all these things can easily be seen. The piston, advancing and
retreating in turn in the cylinder, pushes the crank forward and back,
and the crank thus makes the great wheel turn. On the other side of the
locomotive the same things are taking place by means of a second
cylinder. Then the two great wheels turn at the same time and the
locomotive moves forward.”
“It isn’t so hard as I thought,” Jules remarked. “Steam pushes the
piston, the piston pushes the crank, the crank pushes the wheel, and the
engine moves.”
“After acting on the piston, the steam enters the same chimney that the
smoke comes out of. So you can see this smoke-stack sometimes throwing
out white puffs, sometimes black. These latter are smoke coming from the
furnace through the tubes that go through the water; the others come
from the steam thrown out of the cylinders after each stroke of the
piston. These white puffs, in rushing violently from the cylinder to the
smoke-stack after acting on the piston, make the noise of the engine as
it moves.”
“I know: _pouf! pouf! pouf!_” exclaimed Emile.
“The locomotive carries with it a supply of coal to feed the fire, and a
supply of water to renew the contents of the boiler as fast as
evaporation may require. These supplies are carried in the tender; that
is to say, in the vehicle that comes immediately behind the locomotive.
On the tender are the stoker, who tends the furnace, and the engineer,
who controls the passage of the steam into the cylinders.”
“The man in the picture is the engineer?” Emile asked.
“He is the engineer. He holds his hand on the throttle, which allows the
steam from the boiler to enter the cylinders in greater or less
quantity, according to the speed he wishes to obtain. By one movement of
the throttle, the steam is cut off from the cylinders and the engine
stops; by another movement the steam is admitted and the locomotive
moves, slowly or rapidly at will.
“The power of a locomotive is no doubt considerable; however, if it is
able to draw with great speed a long train of cars, all heavily loaded,
this is due, above all, to the preparation of the road on which it runs.
Strong bars of iron, called rails, are fixed solidly on the road, all
along its length, in two parallel lines, on which all the wheels of the
train roll without ever running off. A light flange with which the
wheels are furnished keeps the train from slipping off the rails.
“The iron road not having the inconveniences of other roads, that is to
say the ruts, pebbles, and inequalities that impede the progress of
carriages and cause the waste of much energy, the whole traction of the
locomotive is utilized, and the results obtained are wonderful. A
passenger engine draws at a rate of twelve leagues an hour a train
weighing as much as 150,000 kilograms. A freight engine pulls at about
seven leagues an hour a total weight of 650,000 kilograms. More than
1300 horses would be necessary to replace the first locomotive, and more
than 2000 to replace the second, if they were employed to transport
similar loads with the same velocity and to the same distances by the
aid of cars running on rails. What an army of horses it would require
with wagons running on ordinary roads having all the inequalities that
cause such a great loss of energy!
“And now, my little friends, think of the thousands of locomotives
running daily in all parts of the world, annihilating distances, as it
were, and bringing the most distant nations together; think what a vast
number of machines of all kinds, moved by steam, are ceaselessly working
for man; think how the engine that makes a warship move, sometimes
represents in itself the united strength of 42,000 horses; think of all
these things, and see what inconceivable development of power man’s
genius has given to him with a few shovelfuls of coal burning under a
pot of water!”
“Who first thought of the use of steam?” asked Jules. “I should like to
remember his name.”
“The use of steam as a mechanical power was proposed nearly two hundred
years ago by one of the glories of France, the unfortunate Denis Papin,
who, after giving the first suggestion of the steam-engine, source of
incalculable riches, languished in a foreign land, poverty-stricken and
forlorn. To realize his fruitful idea, which was to increase man’s
motive power a hundredfold, he could hardly find a paltry half-crown.”
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