ressure of the atmosphere."

Forester was going on to explain to Marco how it was that the steam was
condensed in the cylinder, when the conversation was suddenly
interrupted by the sound of the engine bell, which was the signal for
the engine to stop. The thumping sound of the machinery and of the
paddle wheels accordingly ceased, and the boat began to move more
slowly. Presently, the bell sounded once more, and the piston rod slowly
rose out of the cylinder, and then slowly descended again.

"They are going very slowly," said Marco.

"Yes," replied Forester, "the water is low, and I suppose that the
channel is narrow."

Just at this moment, they perceived a strange sensation, as if the
steamboat had been suddenly pushed backwards. Marco was startled. He did
not know what it meant.

"There we are," said Forester.

"What?" said Marco. "What is it?"

"Aground," said Forester.

"Aground?" repeated Marco.

"Yes," said Forester; "that's the sensation produced when a ship goes
aground upon sand or soft mud."

So saying, Forester left the engine, and went up to the upper deck,
followed by Marco. There were several persons there, looking out upon
the water.

"Yes," said Forester, "we are aground. You see by the trees upon the
bank that we are not moving."

Marco saw that they were at rest. He asked Forester what they were going
to do.

Just at this moment the little bell sounded, and the engine, which had
been stopped when the boat went aground, was put in motion again.

"They are going to back the engine, I suppose," said Forester, "to try
to draw her off."

But the boat would not move. The engine did not seem to have power to
release her from her confinement.

"What shall we do now?" asked Marco.

"Why, whenever a ship is aground," said Forester, "the first question
is, what is the state of the tide?"

"Because," continued Forester, after a moment's pause, "if the tide is
_rising_, it soon lifts the vessel off, and enables her to go back, or,
perhaps, forward, if the water is not very shallow. But, if the tide is
_falling_, it leaves her to rest more and more upon the sand, and she
cannot get off until the water has gone entirely down, and then rises
again. She cannot get off, in fact, until the water has risen higher
than it was when she first grounded."

"And how is it now?" asked Marco.

"I presume the tide is going down," said Forester; "and if so, we must
wait here until it rises again." So s