“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.