The children stood by the railing of the deck for some time after they came up from below, gazing at the shores, and admiring the various pictures of rural beauty which the scene presented to the eye. At length, becoming a little tired, they went and sat down upon one of the settees, where they could have a more comfortable position, and still enjoy a good view. Not long afterward, the captain, who had been walking up and down the deck for some time, came and sat down by them.
"Well, children," said he, "are you glad to get to the end of the voyage?"
"Yes, sir," replied Jennie. "I am glad to get safe off of the great sea."
"And I suppose that you must be very glad, sir," added Rollo, "to get to the end of your responsibility."
"Ah, but I have not got to the end of my responsibility yet, by any means," said the captain.
As he said this, he rose from his seat, and looked out very attentively forward for a minute or two. At length he seemed satisfied, and sat down again.
"Well, you have got through all the danger, at any rate," said Rollo, "now that we are inside the land."
"On the contrary," said the captain, "we are just coming into the danger. There is very little danger for a good ship, whether it is a sailing ship or a steamer, out in the open sea. It is only when she comes among the rocks, and shoals, and currents, and other dangers which thicken along the margin of the land, that she has much to fear. Ships are almost always cast away, when they are cast away at all, near or upon the land."
"Is that the way?" replied Rollo. "I thought they were cast away at sea. I am sure it looks a great deal safer here than it does out in the middle of the ocean."
"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."