“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 allowed scope to follow the bent of his own inclinations.”

“Very good, Willis; for argument’s sake, let us take your headstrong young man, or rather the steam, for granted, and let us admit that it is as elastic as ever you please—­but what then?”

“Then you must imagine a piston in a cylinder, forced upwards when the steam is heated, and falling downwards when the steam is cooled.  Next fancy this upward and downward motion regulated by a number of wheels and cranks that turn two wheels on each side of the ship, keeping up a constant jangling and clanking, the wheels or paddles splashing in the water, and then you may form a slight idea of the thing.”

“Oh!” cried Jack, “we invented a machine of that kind for our canoe, with a turnspit.  Do you recollect it, Fritz?”

“Yes, I recollect it well enough; and I also recollect that the canoe went much better without than with it.”

“You spoke just now,” continued Willis, “of rival nations, who pounce like birds of prey upon every new invention; and so it is with the steamship.  An American, named Fulton, made a trial in the Hudson with one in 1807—­that is about five years ago—­and I believe the Yankees, in consequence, are laying claim to the invention.”

“Now that you bring the thing to my recollection,” said Fritz, “the idea of applying steam in the arts is by no means new, although, I must candidly admit, I never heard of it being used in propelling ships before.  The Spaniards assert that a captain of one of their vessels, named Don Blas de Garay, discovered, as early as the sixteenth century, the art of making steam a motive power.”

“I don’t believe that,” said Jack.