"I suppose so, to your eyes," replied the captain. "But you will see, by reflecting on the subject, that it is, in fact, just the contrary. If a very violent storm comes up when the ship is out in the open sea, it can ordinarily do no harm, only to drive the ship off her course, or perhaps carry away some of her spars or sails. If there is no land in the way, she is in very little danger. But it is very different if a gale of wind comes up suddenly in such a place as this."

"And how is it here?" asked Rollo.

"Why, in the case of a good steamer like this," said the captain, "it makes no great difference here; for we go straight forward on our course, as long as we can see, let it blow as it will. But a sailing vessel would very probably not be able to stand against it, but would be driven off toward any rocks, or sand banks, or shores that might happen to be in the way."

"And so she would certainly be wrecked," said Rollo.

"No, not certainly," replied the captain. "As soon as they found that the water was shoaling, they would anchor."

"How do they know when the water is shoaling?" asked Rollo.

"By the lead," replied the captain. "Did you never sound with the lead and line?"

"No, sir," replied Rollo.

"Well, they have a lead, and a long line," rejoined the captain, "and they let the lead down to the bottom by means of the line, and so learn how deep the water is. The lead is round and long. It is about as large round, and about as long, as Jennie's arm, from her elbow to her wrist, and there is a small cavity in the lower end of it."

"What is that for?" asked Rollo.

"That is to bring up some of the sand, or mud, or gravel, or whatever it may be, that forms the bottom," replied the captain. "They put something into the hole, before they let the lead down, to make the sand or gravel stick. When they see the nature of the bottom in this way, it often helps them to determine where they are, in case it is a dark night, or a foggy day, and they have got lost. It is very easy to measure the depth of the sea in this way, where it is not over a few hundred fathoms."

"How much is a fathom?" asked Rollo.

"Six feet," replied the captain; "that is as far as a man can reach by stretching out both hands along a wall. If the water is only a few hundred fathoms deep," continued the captain, "we can sound; but if it is much deeper than that, it is very difficult to get the lead down."

"Why, I should think," said Rollo, "that the lead would go down to the bottom of itself, no matter how deep the water was."

"It would," said the captain, "were it not for the line. But the line has some buoyancy; and, besides, it makes a great deal of friction in being drawn through the water; so that, when the line begins to get very long, it becomes very difficult for the lead to get it down. As they let out the line from the ship, it goes more and more slowly, until at last it does not seem to move at all."

"Then the lead must be on the bottom," said Rollo.

"No, that is not certain," said the captain. "It may be only that the quantity of line that is out is sufficient to float the lead. Besides that, the currents in the water, which may set in different directions at different depths, carry the line off to one side and the other, so that it lies very crooked in the water, and the weight of the lead is not sufficient to straighten it."

"Then they ought to have a heavier lead, I should think," said Rollo.

"Yes," said the captain; "and for deep-sea soundings they do use very heavy sinkers. Sometimes they use cannon balls as heavy as a man can lift. Then they take great pains, too, to have a very light and small line. Still, with all these precautions, it is very difficult, after some miles of the line are run out, to tell when the shot reaches the bottom. In some of the deepest places in the sea, the line, when they attempt to sound, is all day running out. I knew one case where they threw the shot overboard in the morning, and the line continued to run out, though slower and slower, of course, all the time, until night. It changed its rate of running so gradually, that at last they could not tell whether it was running or not. It seemed to float idly in the water, sinking slowly all the time; and yet they could not tell whether it was drawn in by the drifting of the portion of the line already down, or by the weight of the shot. So they could not tell certainly whether they had reached bottom or not.

"There is another thing that is curious about it," added the captain; "and that is, that, when a line is let out to such a length, they can never get it back again."

"Why not?" asked Rollo.

"It is not strong enough," said the captain, "to bear the strain of drawing such an immense length out of the water. There is a very considerable degree of friction produced in drawing a line of any kind through the water; and when the line is some miles in length, and has, besides, a heavy ball at the end of it, the resistance becomes enormous. Whenever they attempt to draw up a sounding line of such a length, it always parts at a distance of a few hundred fathoms from the surface, so that only a small part of the line is ever recovered."

"I should not suppose it would be so hard to draw up the line," said Rollo. "I should have thought that it would come up very easily."

"No," said the captain. "If you draw even a whiplash through the water, you will find that it draws much harder than it does on the grass; and if a boy's kite were to fall upon a pond at a great distance from the shore, I don't think he could draw it in by the string. The string would break, on account of the friction of the string and of the kite in the water. Sometimes, in naval battles, when a ship is pretending to try to escape, in order to entice another ship to follow her, away from the rest of the fleet, they tow a rope behind, and this rope, dragging in the water, retards the ship, and prevents her from going very fast, notwithstanding that all the sails are set, and she seems to be sailing as fast as she can."

"That's a curious way of doing it," said Rollo; "isn't it, Jennie?"

Jennie thought that it was a very curious way indeed.

"There is no difficulty," said the captain, resuming his explanations, "in finding the depth of the sea in harbors and bays, or at any place near the shore; for in all such places it is usually much less than a hundred fathoms. So when in a dark night, or in a fog, the ship is driven by the wind in a direction where they know there is land, they sound often; and when they find that the water is shoal enough, they let go the anchor."

"And so the anchor holds them," said Jennie, "I suppose, and keeps them from going against the land."

"Yes," said the captain, "generally, but not always. Sometimes the bottom is of smooth rock, or of some other hard formation, which the flukes of the anchor cannot penetrate, and then the ship drifts on toward the land, dragging the anchor with her."

"And what do they do in that case?" asked Rollo.

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