THE BOYS ARE DRIVEN OUT OF THE ROOT FORTRESS.

Sam was only partially conscious during the battle around his habitation. The fever, which now rose and fell at intervals, was usually highest during the forenoon, abating somewhat later in the day. When it was highest he was always in either an unconscious stupor, or a wild delirium. When the fever abated, however, his consciousness returned, and he was capable of talking and of understanding all that was said. In these lucid intervals, he insisted upon knowing all that had happened, so that he might tell the boys what was best to do. On this day Tom had a story of more than ordinary interest to tell him, about the battle and the chance of rescue which had so narrowly passed them. Sam was interested in it all as a matter of course, but he was still more deeply interested, it seemed, in the condition of the sand near the place where he was lying. He had dug a little hole with his hand, and feeling of the sand found it decidedly wet. Turning to Tom, he said:

"The river is rising rapidly, isn't it?"

"Yes; but how did you find it out?"

"By the sand. I've been watching it a good deal since the fall rains set in, as I'm afraid the river will drive us out of here. You see, the water works easily through the sand, and you can always tell what the level of the river is, if its banks are sandy, by digging down to where the sand is wet."

"Yes," said Tom, "but the river isn't within a hundred feet of us yet."

"You are mistaken. It is within six inches of us," said Sam.

"How's that?"

"Well, this bank is almost exactly level, and when the river gets above its edge it spreads at once all over it. Now the sand is wet within six inches of the top, and the river is within six inches of the edge of the bank. When it rises six or eight inches more, it'll be in here, and I'm afraid it will rise that much before morning. At any rate we must be ready for it."

"What can we do?" asked Tom in alarm. "There's no place to hide on the upper bank."

"We mustn't quit this bank, and we mustn't quit the drift-pile either," replied Sam. "You must find a good place, high up in the drift where, by pulling out sticks, you and Joe can make a place for us to stay in."

"But, Sam, what if the water gets to us there?"

"It won't get to us there."

"How do you know?"

"Because the biggest freshets always come in the spring, and the top of this drift-pile was put where it is by the biggest freshets, so the river won't go near the top in November. You see, as the drift floated on top of the water to its present place, the top of the pile must be the highest point, or very nearly the highest, that the water ever reaches. If you can find a good place therefore in the upper part of the drift-pile, we shall be safe there. But you'd better see about it at once, as the water may be in here before morning, and at any rate we mustn't allow ourselves to be taken by surprise. You'd better go to the river and set a stake first so you can tell how fast the water rises and know when to move into the new place."

Tom set his stake at the water's edge and then selected the most available place he could find for the new abode. He and Joe went diligently to work, rearranging the loose sticks of drift-wood and even carrying many of them clear out of the pile, so as to enlarge the hole they had found and make it as habitable as possible.

"The trouble is," said Tom when they had nearly completed their task, "that we can't make a smooth floor, and it's going to be rather uncomfortable lying on loose logs and big round sticks that run every which way."

"That's my business," said Judie looking in at the entrance. "I'm the housekeeper, you know, and I've thought of all that."

And sure enough the little woman had brought a great pile of small, leafy, tree branches and bush tops, with which she speedily filled up the low places between the timbers, and covered the timbers themselves to a depth of three or four inches, making a soft as well as a level floor. She had foreseen the difficulty, and borrowing Sam's knife, had worked with all her might to provide in advance against it. But the bushes and leaves were not all that she had brought. She had collected also a large quantity of gray moss with which to make a carpet for the springy floor.

"Now please don't tell brother Sam," she said when the boys praised her thoughtfulness and ingenuity. "I want to surprise him when he comes."

Tom and Joe promised, and Tom said they would have to call her their "little housekeeper" hereafter.

The river was still rising, but more slowly, it appeared, than it had done before. By Tom's calculations it was coming up at the rate of an inch in three hours, wherefore Sam thought they might safely remain where they were until morning at least, while if the water should come to a stand during the night, they would have no occasion to move at all, as a fall would rapidly follow, if the weather should remain clear.

Joe had worked faithfully at the task of preparing the new place of refuge, but he was not at all satisfied with the arrangement.

"I tell you, Mas' Tom," he said, "wood'll float, 'thout 'tis live oak, an' dis here drif'-pile 'll jest raise up an' float away, you'll see if it don't."

"Why hasn't it floated away long ago, then, Joe?" asked Tom.

"May be it has. How you know dis drif' didn't all on it come here las' time de river was up?"

"Well, there's too much of it for that, and besides, Sam says this place is safe, and you know he is always right about things when he speaks positively about them."

"Mas' Tom, don' you know Mas' Sam done been a-talkin' nonsense for two weeks now?"

"Yes; but that's only when he's out of his head."

"How you know when he's outen his head an' when he ain't?"

"We know he's out of his head when he talks nonsense."

"Well, maybe dis here 's nonsense. I jest knows it is, and dat's how I know Mas' Sam was outen his head when he said it."

Tom saw that Joe was not to be convinced, and so he contented himself with saying,

"Well, we'll see."

"Yes, dat's jest it. We will see, and feel too, when we all gets drownded in de water."

The water came to a stand about midnight, and was falling slowly the next morning. But when morning came it was raining hard, and the rain was evidently not a local but a general one, wherefore, Tom feared that the fall would shortly be changed into a rise, and that the bank would soon be covered. He watched his stake carefully, visiting it every half hour. At nine o'clock the river had fallen three inches, and was about eight inches below the bank. From nine to ten it fell only about half an inch. Between ten and eleven the fall was not more than a quarter of an inch. Between eleven and twelve no fall at all was perceptible. From twelve to one there was a slight rise. Between one and two it rose nearly an inch. The next hour brought with it a rise of two inches. By five o'clock the level of the water was barely two inches below the edge of the bank, and as it was rising at the rate of two or three inches an hour, Sam thought it time to remove from their old to their new quarters. The change was of advantage to the sick boy, who was now getting somewhat better at any rate, and when he found himself in the new place the interest he showed in examining all the details of its arrangements, was the best possible evidence of improvement.

"Come here, little woman," he said to Judie, "and give an account of yourself. You borrowed my knife yesterday, and somebody has been using it in cutting bush tops to make a smooth floor with, and the idea was a very good one. Can you tell me who it was?"

"Maybe it was Tom," she replied mischievously.

"No, it was not Tom," Sam answered. "He's too much of a great awkward boy to think of anything so comfortable. You must guess again."

"Joe, then," she said.

"No, it wasn't Joe, either," said Sam. "Joe can sleep on the edge of a fence rail as well as anywhere else, and he never would have thought of making our floor soft and smooth. Guess again."

"Maybe it was brother Sam," said Judie.

"Oh, certainly. It must have been I," replied Sam. "I must have done it. I'm so strong and active now-a-days. Yes, on reflection, I presume I did it, and the man in the moon helped me. Now I think it was a very thoughtful and helpful thing for anybody to do, so you ought to kiss me for doing it, and when the weather gets clear you must throw a kiss to the man in the moon, too, for his share." And with that he kissed the little housekeeper, and she felt herself abundantly repaid for her work and for the thoughtfulness she had shown. She was never so happy as when Sam praised her, "because he's such a splendid big brother," she would explain.

Tom, seeing that Sam was getting better at last, began to hope for his complete recovery, and the hope made him buoyant of spirit again. Judie, too, who watched and weighed every symptom in Sam's case, discovered to her delight that he was decidedly better, and the discovery made her as happy as a healthy girl well can be. Poor Joe seemed to be the only miserable one in the party. He said almost nothing, answering questions with a simple "yes" or "no," and sitting moodily in his corner, when he stayed inside the "drift cavern"—which was Sam's name for the new abode—at all. He spent most of his time, however, on top of the pile, where he watched the water and the clouds. The rain had ceased, but the river, which was now creeping over the broad bank, continued to rise.

"What is the matter with Joe?" asked Sam after the boy had gone out for the twentieth time.

"I think he's afraid we're all going to be drowned," said Tom.

"Drowned? How?"

"Well, he says wood will float, and so he thinks when the water comes up under the drift-pile, it will all float away."

"What nonsense!" exclaimed Sam. "Why didn't you tell him better, Tom?"

"I did; but he sticks to it, and—"

"Well, couldn't you explain it so that he would understand it and not have to trust to your judgment for it?"

"No, I couldn't. The fact is, I don't quite understand it myself. There isn't a stick in this whole pile that won't float, and I don't quite understand why the pile won't. But I don't doubt you're right about it, Sam. You always are right whether I understand how things are or not."

"Let me explain it to you, then. Do you know why some things float and others don't?"

"Yes, of course. Because the things that float are lighter than the things that sink."

"Not exactly. That log there is too heavy for you to lift, while you can carry a bullet between your thumb and finger. The log is many hundred times heavier than a bullet, but the log will float while the bullet will sink always."

"That's so," said Tom, "and I don't know what does make some things float and other things sink."

"Did you ever set a teacup in the water and see it float?"

"Yes, many a time."

"But if you fill it with water it will sink, won't it?"

"Yes, of course."

"Well, now I can explain the thing to you, I think. If a thing is heavier,—the whole thing I mean, than the amount of water it displaces,—that is, if it is heavier than exactly its own bulk of water, it will sink; but if it is lighter than its own bulk of water it will float."

"Oh, yes, I see."

"Now a bullet weighs a good deal more than its own bulk of water, and so it sinks. A log weighs less than its own bulk of water, and so it floats. An empty teacup weighs less than a solid body of water equal to it in size, and it therefore floats. If you fill it with water, however, you increase its weight without adding anything to the amount of water it displaces,—or rather, as you let water into all the hollow space, you lessen by that much the amount of water it must displace in sinking without taking away anything from its weight, and so it sinks; or, if you break the teacup you lessen the amount of water it must displace without lessening its weight, and so it sinks in that case, too. Do you understand that?"

"Yes, I think I do," said Tom; "but I don't exactly see how it applies to the drift-pile."

"I'll explain that presently. I want to make it plain first that the ability of a thing to float depends not on its weight, but on its weight as compared with that of a like bulk of water. This comparative or relative weight is called specific gravity, and in measuring the specific gravity of substances water is taken as the standard usually, though sometimes gold is used for that purpose. Now to come to the drift-pile. When the water rises say two or three feet, it will be above the level of the lower logs, and these would float away, if they were free, because their specific gravity is less than that of water. But there is twenty feet of other timber on top of them, and its weight must be added to theirs. The water displaced is exactly equal to their bulk, while the weight is many hundred times greater than theirs. Do you understand?"

"Yes, I think I do. You mean that the water must come high enough to pretty nearly cover the whole drift-pile before any of it can float."

"Yes. The pile must be considered as a whole, and it won't float until there is water enough to float the whole. The bottom logs can't float while those above them are clear out of water, if their weight rests on the bottom logs, as it does in the drift-pile. You see when you put anything into the water, it sinks until it has displaced a bulk of water equal to its own weight, and then stops sinking. In other words, that part of the floating thing which goes under the water is exactly the size of a body of water equal in weight to the whole thing. If a log floats with just half of itself above water, you know that the log weighs exactly the same as half its own bulk of water, or, in other words, that its specific gravity is just half that of water. Water two inches deep won't float a great saw-log, because a great saw-log weighs more than the amount of water it takes to cover its lower part two or three inches deep; and water two or three feet deep won't float a drift-pile twenty feet high, because such a drift-pile weighs a good deal more than a body of water two or three feet deep, of its own length and width. But even if the water were to rise to the top of the hammock, the pile wouldn't float away. It would float, of course, and some of the wood near its edges would be carried away, but the main pile would remain here, because it is all tangled together and can't go away except in one great mass. It is so firmly lodged against the trees as to prevent that, and as a freshet big enough to cover, or nearly cover it, would bring down a great quantity of new drift and deposit it here, the pile would grow bigger rather than smaller. But the river won't get very high at this season, or at any rate it won't rise to anywhere near the top of the hammock, as I have already explained to you, because it is evidently only the biggest freshets that ever come near the top, and the biggest freshets never come in the fall, but always in the spring. It isn't rising fast enough either. It isn't rising nearly so fast now as it was before it got over the bank."

"Why, how do you know that, Sam? You haven't been to look."

"No, but I know it, nevertheless, simply because I know that water, left to itself, will find its level."

"I don't see what that's got to do with it," said Tom.

"Perhaps not, but it has something to do with it for all that," replied Sam; "and I can make you see how, too."

He paused, to think the matter over and determine how to present it to Tom's comprehension.

"You see," he then resumed, "that the river inside its banks is about four hundred yards wide. When it rises above the banks, however, it spreads out over the level ground, and becomes, in some places, many miles wide, averaging a mile at least in width. Now there is only a certain amount of water coming into the river every hour. The rain has stopped, but the soil is full of water, and so there is about as much running into the river now as there was while the rain lasted. But the surface of the stream is now many times greater than it was, and as water finds its level, all that comes into the river spreads out over its whole surface, and of course doesn't raise its level nearly so much as the same quantity did while the stream was still within its banks. Do you understand now?"

"What a great big brother you are, Sam, anyhow!" was all the reply Tom made.