A few days after Rollo’s father gave him the instructions on the subject of combustion which are contained in the last chapter, Rollo saw Jonas going across the yard about the middle of the afternoon, with a lantern in his hand. Of course Rollo called out to him with the usual question in such cases,—

“Where are you going, Jonas?”

“I’m going out into the pasture to set some heaps on fire.”

“Well,” said Rollo, “and I’ll go too.”

Rollo ran into the parlor to ask his mother if he might go too. He happened to meet his father just coming in at the front door. He accordingly asked him instead.

“Yes,” said his father, “but I’m rather afraid to have the heaps set on fire this afternoon. I am afraid that the fire will run.”

“Run?” repeated Rollo.

“Yes,” replied his father. “Tell Jonas he must be very careful not to let the fire get away from him.”

Rollo ran off in pursuit of Jonas. When he got to the back yard again, he saw Jonas going down the lane almost out of sight.

“Jonas!” said Rollo, calling out as loud as he could, “Jo—nas!”

So saying, he ran off after him. He clambered over the great gate which led into the lane, because he thought that he could climb over it quicker than open it. As soon as he reached the ground on the other side, he ran on, calling out,—

“Jonas! Jonas!”

But Jonas did not seem to hear him. At any rate he did not stop. On the contrary, Rollo was himself stopped, by hearing a voice behind him, as if near the house, calling,—

“Rollo! Rollo!”

Rollo turned to see who it was. It was his cousin James, who was running towards him with all speed. Rollo waited for him to come up. James tried to open the gate, but could not.

“Climb over,” said Rollo.

So James climbed over, and soon reached the place where Rollo was standing, and the two boys walked on together. James said that he had come to play with Rollo that afternoon. Rollo said that he was very glad, and he told James that he and Jonas were going to make some fires in the pasture.

The heaps which Jonas was going to set on fire, were heaps of decayed wood, consisting of old stumps, logs, and roots, and other rubbish which he had gathered up from the ground and piled up in the pasture some weeks before. By being left in heaps, so that the sun and air had free access to them, they had become thoroughly dry, and were all ready to burn with a touch. There were not a great many of the heaps, for it was only a small part of the pasture which had such logs and stumps left in it. The place was on the side of a deep dell, with a brook flowing through the middle of it at the bottom. Rollo and James crossed the brook upon a log, and then ascended the steep side of the hill, among the heaps which Jonas was burning.

Jonas had set two heaps on fire and was just putting a burning brand into the third heap. Rollo and James wanted Jonas to let them set the heaps on fire. He told them that they might; and the boys accordingly went to work, taking brands from the heaps which were already burning, and carrying them to the others. The heaps were not only very dry, but quite hot, on account of the influence of the rays of the sun beating upon them; and, besides this, there was a fresh breeze blowing, which made the fires burn up very fiercely. The fires which had been first made soon became so hot, that the boys could not get near them to take any brands from them.

Thus they went along from heap to heap, setting them on fire, only Jonas succeeded in setting them on fire much faster than James and Rollo. Jonas looked around at them at one time, and he found them endeavoring to kindle a fire at a large heap which had been built up around a tall stump. The stump was twice as high as Rollo’s head. Rollo and James were kneeling down upon the ground, and blowing the end of the brand, by which they were trying to kindle the fire. But they did not succeed. Instead of that, the wind blew the smoke into their faces.

“Make the fire on the windward side,” said Jonas.

“Which is the windward side?” said James.

“The side that the wind blows against,” replied Jonas.

“Yes,” said Rollo, speaking to James, “we have got our fire on the wrong side. Let us move it round to the other side, and the wind will blow it for us.”

So they took up their brands, and put them upon the other side of the heap. The wind fanned them a little, but did not make them blaze.

“Just put some dry pieces on,” said Jonas, “and leave them. As soon as they get heated a little, they’ll blaze.”

The boys followed Jonas’s direction, and, after putting a few dry pieces upon the smoking brands, they left this heap, and went to another; though they had first to go back to one which was on fire, and get some more brands.

“How do you set them on fire so fast, Jonas?” said Rollo.

“Why, I don’t stop to watch them,” said Jonas, “to see them burn. I put a brand down upon the windy side of the heap, and then cover it with dry pieces, and leave it, and let it burn up in its own time. It will burn as soon as it has time to get heated.”

“Yes, James,” said Rollo; “my father explained it to me. When wood gets heated above a certain point of heat, it takes fire. Sulphur takes fire before it gets heated so hot.”

“O Jonas,” said Rollo, “why didn’t you pile up this heap?”

Rollo had come to a place where there was a long log lying upon the ground, broken to pieces and decayed, and near it several fragments of roots and stumps scattered around.

“O, come away, come away from there, Rollo,” said Jonas; “there is a wasp’s nest there.”

Rollo and James ran off back towards Jonas.

“A wasp’s nest?” said James.

“Yes,” said Jonas. “I began to pile up that wood, and heard a buzzing under the log; and I looked down, and saw some wasps buzzing about a hole. We must burn up the wasp’s nest.”

“Well,” said Rollo, “come and do it now.”

Jonas was coming to burn up the wasp’s nest; but, as he was passing along towards it, his attention was suddenly arrested at seeing that the flames from one of the fires were beginning to spread rapidly upon the ground. There was quite a large circle in the grass, which had been burned over and blackened, and, at the outer edges of it, the flames were still spreading rapidly,—driven by the wind.

“Look! look!” said Jonas; “our fire is running.”

“Yes,” said James; “it is burning up all the grass.”

Jonas ran to the edge of the circle, and began trampling upon the flames, to put them out. The flames were very light, for the grass was thin, and so the fire was easily extinguished at any one spot; but, while Jonas was putting it out in one place, it was spreading in another, and he could not put it out so perfectly but that it would flame up and begin to spread again when he went to another place. James and Rollo stood by somewhat frightened, and not knowing what to do.

“We must get some water,” said Rollo, “from the brook. I’ll go and get a pail.”

“No, a watering-pot,” said James, “a watering-pot will be best. Let’s go and get a watering-pot.”

“No,” said Jonas; “we must whip it out with bushes. I’ll cut some bushes. Come down here with me.”

So Jonas ran down to the bank of the brook, where there were a number of low fir-trees growing. Now, the leaves of the fir-tree are very small and slender, but they stand very thick upon the branches, so that they make a very thick and heavy foliage. Jonas cut off a branch of the fir-tree, and gave it to Rollo. Then he cut off another for James, and another larger for himself; and, armed with these, the boys hastened back to the fire.

They began to whip and brush the little line of flame, and they found that they could put it out very easily. Every blow which Jonas struck, extinguished a line of the fire as long as his branch. Rollo and James threshed the ground with great vigor, too, and they put out a great deal of the fire. In fact, they soon extinguished all the flames which were creeping up the side of the hill from this first fire, except at one end, where it had got into some thistles, which Jonas had mowed down some time before, and which were now lying upon the ground dry and warm, and so thick that they made quite a hot fire. Rollo was whipping upon these thistles, when Jonas said,—

“Stop, Rollo; it is of no use to whip such a hot fire as that; it is only wasting your strength.”

“Then we can’t stop it,” said Rollo.

“Yes,” said Jonas; “wait until it has gone over the thistles, and burned them up, and then it will come to the thin grass beyond, and there we can whip it out.”

So the boys stopped to rest while the thistles were burning, surveying, in the meantime, the large space which had been burned over, and which looked scorched and blackened.

“Now, all that grass is spoiled,” said Rollo.

“O, no,” said Jonas; “it hasn’t hurt the grass. It has only burned the dry tops and the weeds. The roots of the grass are all safe, and the ashes left by the fire will make them grow all the better next summer.”

“Then, Jonas, let’s burn the ground all over.”

“No,” said Jonas; “if so large a surface gets on fire, we can’t stop it, till it runs into the fence, and sets that on fire,—or else gets over into the other field.”

So saying, Jonas pointed to a large level field or pasture over the fence, where the grass and weeds were much higher than where they were. The grass and weeds in this other field extended back some distance to a piece of woods; and Jonas said that, if the fire got into the woods, he could not tell how far it would go, or what mischief it would do. “So you see we must be sure and not let the fire get away from us,” said he.

Just then, Jonas saw that the fire was beginning to spread from another of the heaps; and he went to it to watch it. He said he was going to let it run a little way before he put it out, for he knew that if a piece of the ground around the heap was once burned over, the fire would not spread again from the heap.

So he waited, and, when the circle from that heap had become as large as he wished, he and the boys whipped it out; and then they went back to the first fire, which was now getting beyond the thistles, so that they whipped that out too. Rollo and James felt much relieved, now that they perceived that, by the aid of their fir-branches, they had the fires so entirely under their control.

About this time, Rollo saw his father coming through the trees, on the other side of the brook. His father had been a little afraid that Jonas would get into difficulty with his fires, and had come out to see. He found, however, that Jonas knew how to manage the business. He took a branch, and began to help the three boys whip the fires, as fast as they spread beyond the limits which they concluded to allow them.

“I didn’t know that the grass would burn so before,” said Rollo.

“It will not,” said his father, “unless it is both hot and windy. This is an illustration of what I explained to you the other day. When grass is heated above a certain point it takes fire. Now, when one blade of grass is burning, it does not usually produce heat enough to raise the next one to such a degree of heat that it will take fire; but this afternoon it will; for now the heat of one little tuft burning is enough to heat the next one sufficiently to cause it to take fire, because it is already partly heated by the sun.”

“And the wind helps,” said Rollo.

“Yes,” replied his father, “the wind helps in two ways. It blows up the grass that is burning, and makes a greater fire of it, and then it blows the hot air and flame against the grass next to it. Thus it makes the heat greater, and at the same time drives it against the fresh grass. I presume this fire would not spread at all if there was no wind. You see, in fact, that it does not spread much in any direction, except where the wind blows it.”

“And if there was a wind, and yet the grass was not hot, would it spread then?”

“No,” said his father, “I presume not. For instance, in the evening, when the ground and grass are cool, I don’t think the fire would run on the ground. That is, I don’t think the heat of one row of blades would heat the next row enough to make them take fire, unless they were partly heated by the sun beforehand.”

“I should like to try it some windy evening,” said Rollo.

“There would be the dew in the evening also, which would tend to prevent the fire’s running.”

By this time, all the heaps had been set on fire, and the circle of fire which spread out from each one had been whipped out; so that there was now not much danger that the fire would spread, and Mr. Holiday went away. Jonas, however, said that he must stay and watch the heaps, and Rollo and James concluded to stay with him. But, after a short time, they became tired of poking the embers; and so Rollo proposed to James to go with him, and help him make some charcoal.

“I have learned how they make charcoal,” said Rollo.

“Well,” said James, “I’ll go; but what good will charcoal do us?”

“Why, we can make gunpowder out of it,” said Rollo.

“Well,” said James, “I should like to make some gunpowder very much.”

So the boys went away towards the house, to get the wood to make their charcoal.

What objection did Mr. Holiday make at first, to having the heaps set on fire? How was Rollo arrested when he was in pursuit of Jonas? What were the heaps composed of which Jonas was going to set on fire? In what condition were they in respect to inflammability? Was there anything besides their dryness which made them particularly inflammable at this time? Describe Rollo’s attempt to set a heap on fire. What course did Jonas pursue? Describe the appearances exhibited when the fire began to run. How did Rollo’s father explain to the boys the causes which made the fire run in the grass that afternoon more than at any other time? Describe the mode which Jonas adopted to stop the progress of the fire in the grass. Did he always stop it as soon as it first began to run? Why not?