, "there is, or at least was, in one of the
Scottish rivers, a ship without either oars or sails."

"Yes, very likely; but it did not move."

"It did though, and, what is more, against both wind and tide."

"I wish we had your wonderful ship here just now, it is just the thing
to suit us under present circumstances," said Jack.

"So it would, Master Jack, for it sails against currents, up rivers,
and the crew care no more about the wind than I do about the color of
the clouds when I am lighting my pipe."

"You don't happen to mean that the _Flying Dutchman_ has appeared on
the Scotch coast, do you, Willis?"

"Not a bit of it, I mean just exactly what I say. It is a real ship,
with a real stern and a real figure-head, but manned by blacksmiths
instead of mariners."

"Well, but how does it move? Does somebody go behind and push it, or
is it dragged in front by sea-horses and water-kelpies?"

"No, it moves by steam."

"But how?"

"Aye, there lies the mystery. The affair has often been discussed by
us sailors on board ship; some have suggested one way and some
another."

"Neither of which throws much light on the subject," observed Jack;
"at least, in so far as we are concerned."

"All I can tell you," said Willis, "is, that the steam is obtained by
boiling water in a large cauldron, and that the power so obtained is
very powerful."

"That it certainly is, if it could be controlled, for steam occupies
seventeen or eighteen hundred times the space of the water in its
liquid state; but then, if the vessel that contains the boiling water
has no outlet, the steam will burst it."

"It appears that it can be prevented doing that, though," replied
Willis, "even though additional heat be applied to the vapor itself."

"By heating the steam, the vapor may acquire a volume forty thousand
times greater than that of the water; all that is well known; but as
soon as it comes in contact with the air, nothing is left of it but a
cloud, which collapses again into a few drops of water."

"That may be all very true, Master Fritz, if the steam were allowed to
escape into the air; but it is only permitted to do that after it has
done duty on board ship. It appears that steam is very elastic, and
may be compressed like India-rubber, but has a tendency to resist the
pressure and set itself free. Imagine, for example, a headstrong young
man, for a long time kept in restraint by parental control, suddenly
let loose, and allowe