which is a much safer proverb to be guided by.

Marco's first impulse was, to go at once and tell the captain of the steamboat that he had lost his bucket. But he did not know exactly where he could find him. He looked at his office window, and found that it was shut. He asked one of the waiters, whom he met coming up stairs from the cabin, if he knew where the captain was. But the waiter did not know.

Presently, he saw a gentleman walking back and forth upon that part of the deck which is in front of the door of the ladies' cabin. He thought that he was the captain. Marco walked up to him, and accosted him by saying:

"Are you the captain of this boat, sir?"

"Am I the captain?" asked the man. "Why? What do you want to know for?"

"Because, if you are," said Marco, "I have lost your bucket."

"Lost my bucket!" repeated the gentleman. "How did you lose it?"

"I lost it overboard," said Marco.

Here the gentleman laughed, and said, "No, I'm not captain; but you seem to be an honest sort of boy. I don't know where the captain is."

All this, though it has taken some time to describe it, took place in a very few minutes; and the boat had now advanced only so far as to be opposite the steam mill which Marco had seen just before he had left Forester. Marco happened to see the mill as the boat moved by it, and he went immediately to the side of the boat to get a better view of it.

There was a chimney for the smoke, and a pipe for the waste steam, at the mill. From the steam-pipe there issued a dense column of vapor, which came up, however, not in a regular current, like the smoke from the chimney, but it was puffed up in regular strokes, making a sort of pulsation. While Marco was looking at it, Forester came along, and stood looking at it too. There were a great many logs lying about the sh.o.r.e, and enormous piles of boards, which had been sawed, and which were ready for the vessels that were to come and take them away.

"What makes the steam come up in puffs?" asked Marco.

"Because, it is what they call a high pressure engine," said Forester.

"It works against the pressure of the atmosphere. All such engines throw out the steam in puffs."

"Why do they?" asked Marco.

"Do you know what the cylinder of a steam engine is?" said Forester.

"Not exactly; I don't remember it very well," replied Marco.

"Come with me, then," said Forester, "and I will show it to you."

So saying, he took Marco to the engine of the boat, and showed him, in the midst of the machinery, a large iron vessel, shaped like a hogshead, only it had straight sides. Marco could not see much more than the top of it.

"That is the cylinder," said Forester. "It is the _heart_ of the steam engine, as I may say--the seat of its power. All the other machinery is only to aid the cylinder, and to convey the power to the point where it is wanted to do the work. Thus, the place where the steam exerts its power, and on which the whole movement of the machinery depends, is the cylinder."

Marco observed that a long iron rod, large and solid, and very bright, kept ascending and descending through the top of the cylinder, as if pushed up and drawn down again by some force within. Forester told him that that was the piston rod.

"The piston rod," said Forester, "is fastened, at its lower end, to the _piston_, which is a flat plate of iron, made to fit the inside of the cylinder exactly."

"First," said Forester, "the steam comes in below the piston, and drives it up; and then it is stopped from coming in below, and is forced in above, and so drives it down."

"And how does the other steam get out?" asked Marco.

"There are two ways of getting rid of the steam that is below the piston when the piston is coming down," said Forester. "One way is, to open a pa.s.sage to let it out _into the air_. On this plan, when the piston has been driven up, the steam is cut off from coming in below the piston, and is admitted above. At the same instant, the pa.s.sage is opened to let the lower steam out. Of course, the steam that comes in _above_, drives the piston down, and forces the steam that is _below_, out into the air.

They generally have a pipe to convey it away, and as the piston goes up and down, the steam comes out in puffs, as you saw it in that mill."

"Yes," said Marco, "I understand that; and now what is the other way?"

"That kind of engine is called a _high pressure_ engine," said Forester, "because the piston, in coming down, has to drive out the steam from below, against the pressure of the atmosphere; for the atmosphere above pa.s.ses into the pipe, and resists the movement of the steam in coming out. It requires a greater force of steam to work the piston on this plan than it does upon the other."

"What is the plan of the other?" asked Marco.

"On the other plan," said Forester, "the steam under the piston is condensed, that is, turned suddenly into water; and this leaves a vacancy or void below the piston, so that the piston can be forced down much more easily than if it had to drive the steam out before it, against the pressure 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 saying, he began to look about for somebody of whom he could inquire. He soon heard a gentleman say to another that the tide was falling, and that they should have to stay here three hours.

"That's rather provoking," said Marco.

"Oh, no," said Forester. "Perhaps we can go ash.o.r.e."