Jacob Abbott

“ So that, you see, when we are going to speak philosophically of that peculiar process by which bodies are actually consumed by fire, it becomes necessary to have some term to denote that process alone, and not all the other kinds of burning. Now, the word the philosophers use for this purpose is combustion. The burning of a stick of wood upon the fire is combustion, but the burning of your finger against a hot iron is not combustion, and the burning of bricks in a brick kiln is not combustion. ”

“ Why, when we say that a little girl was out in the sun, and burned her face and neck, we do not mean that her face and neck were consumed, or that they felt a painful sensation,—but that the skin was reddened by the sun’s heat. So, when we say that the grass was all burned up in the drought, we mean that it was dried and withered. Thus burned and burning are used to denote a great variety of effects produced by heat, which effects are very different from each other in their nature. ”

“ But then I don’t know what we should have done for hay all the next winter for our oxen and cows. Father was much more afraid for the barn than for the house.”
“O Dorothy!” said Rollo. “Why, there was all the furniture in the house, and that would have been burned up.”
“No,” replied Dorothy, “there was not much furniture; and what there was we could have got out while the house was burning. The hay was the great thing—the winter’s stock of hay.”
And thus ended Dorothy’s account of the fire in the woods. ”

“ Rollo sat, as before, upon the front seat; but, by turning a little in his seat, he could hear what his father said very well.
“Let us see,” said his father; “where did we leave off?”
“About the chips,” said Rollo’s mother.
“And the hay,” said Rollo.
“Yes,” said his father. “We’ll take the case of the hay. Should you think, from what I told you, that hay would be a good or bad radiator?”
“Good,” said Rollo.
“Why?” asked his father.
“Because,” replied Rollo, “it is not bright and polished.”
“Right,” said his father. “And should you think that it would be a good or a bad receiver of radiation?” ”

“ What is charcoal good for?”
“It makes a very hot fire. They use it when they want a great heat. Blacksmiths use it in their forges.”
“I wish I had a little forge,” said Rollo.
“They use it to make gunpowder, too,” said Jonas.
“How?” said Rollo.
“Why, they take some charcoal, and some sulphur, and some saltpetre, and pound it up together, and it makes gunpowder.”
“That’s what I’ll do with my charcoal,” said Rollo, jumping up from his seat. “I’ll make some gunpowder. I’ll ask my mother to give me some sulphur and saltpetre, and I’ll make some gunpowder.” ”

“ There is always such a stream of air rising up from every fire, great or small, even from a lamp.”
“Why, father, is a lamp a fire?” said Rollo.
“Certainly,” said his father, “it is a small fire made by burning oil on the top of a wick, and the hot air rises in a constant stream above it. So in a room, if there was no chimney over the fire, all the air that had passed through the fire, and become heated, would ascend to the top of the room. ”

“ Jonas then took up the paper carefully by the two sides, bending the two sides upward at the same time, to keep the filings in the middle of the paper. In this way he raised the paper above the lamp, which was upon the table before him, and then holding it in an inclined position, he let the sand slide down into the flame of the lamp. To Rollo’s surprise and delight, it produced a column of sparkles rising up from the flame, which were of the greatest brilliancy and beauty.
“Yes,” said Rollo, “they burn, they burn most beautifully. ”

“ Now, you must remember that the sun shines only upon the upper surface of the hay, and, if it is ever so good a receiver of radiation, it is only the upper surface that can be warmed by the direct rays. In order to melt the snow, the hay has not only got to receive the heat from the sun by radiation on the upper surface, but it has also got to convey it down through this space of three inches by conduction. Now a substance may be a very good radiator, and a very good receiver of radiation, while it is a very bad conductor. ”

“ Holiday, “which takes fire very easily, but it burns with a very pale and light flame. Oil must be heated much hotter before it will burn; but, when it does burn, it gives a large and bright flame; so that oil is good for lamps, it gives so much light when it burns.
“Spirits of turpentine,” continued Mr. Holiday, “inflames easily, and burns brightly too. So does phosphorus.”
“What is phosphorus?” said Rollo.
“Why, it is a substance that burns very easily. It looks like wax, but it burns very easily, and with a very bright flame indeed. It takes fire before it is as hot as boiling water.” ”

“ Holiday, “that the wool, and the fur, and the hair, of animals is generally intended as a covering to protect them from the cold. That is, it is intended to keep the heat of the body from passing off, and being wasted in the air. Therefore they must be non-conductors of heat, in order to answer this design. Now, we find that everything in nature is admirably adapted to answer its design, and therefore we should expect that these substances, which are expressly intended to confine heat, would be the best non-conductors of heat in nature. ”

“ So is wood. A heap of shavings is a very slow conductor, because it consists of wood and air together.”
“How is that?” said Rollo.
“Why, the little interstices between the shavings are all filled with air; and the heat, in passing through, has to go through the thickness of a shaving first, and then through a small space of air; then through another shaving, and then a little more air; and so it works its way along very slowly, and with great difficulty. Therefore, if any thing is covered with shavings, heat neither gets into it nor out of it very easily. It is the same with hay.” ”

“ 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. ”

“ Then Rollo wanted to know what conduction and radiation meant. His father explained them to him while they were waiting for the tea to be brought in.
“There are two ways by which heat moves,” said his father. “One way is by shooting swiftly through the air like light. Hold your hand up before the fire.” ”

“ So, you see, a single blade of hay, laid upon the snow under the rays of the sun, would make the snow melt the faster; but a layer of it three inches thick would keep it from melting. A layer of two feet thick would perhaps keep it from melting all summer.”
“Why, father,” said Rollo, “I should think it would make it warmer.”
“No,” said his father; “it would keep the warmth from getting to it, because it is a slow conductor. If any thing already warm is covered up in hay, it keeps it from getting cool; if any thing already cool is covered up, it keeps it from getting warm.” ”

“ There was a brush fence running along at the edge of the woods, and a log fence leading from the brush fence to our barnyard. The brush fence was all on fire, and it was blazing up very high, and beyond it, in the woods, the ground was covered in every direction with heaps of logs, and branches, and old trees, all on fire, and burning furiously. The air was full of smoke and sparks, and the wind was driving them directly towards our house and barn.
“Just then I heard behind me a great crackling, which burst out very loud and suddenly. ”

“ 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.” ”

“ For some reason or other, I don’t understand exactly what, a large piece of iron cannot be heated very hot in a small fire, even if the fire entirely covers it. I don’t think that any fragment of iron much larger than one of Jonas’s filings could be heated in a lamp so as to take fire. But it could be heated hot enough in a forge. The end of the iron which a blacksmith heats is often in a state of combustion when he takes it out of the fire. ”

“ A bright tea-pot, made of metal, is a bad radiator, and that makes a good tea-pot.”
Rollo laughed.
“Its being so bright prevents its radiating the heat of the water within it very fast away, and so the water keeps hot longer. But a stove pipe, which is of dark color, and not polished, is a good radiator. They make them so on purpose. A stove pipe made of some bright metal would look a great deal better, but it would not warm the room so well.”
“But, father,” said Rollo, “this copper tea-kettle isn’t white, nor very bright.” ”

“ Holiday held the book between Rollo’s hand and the fire, and Rollo said that he could not feel the heat.
“Now,” said his father, “I will take the book away suddenly, and we will observe what will be the effect. If the heat moves slowly through the air, it will be some time before you begin to feel the warmth; but if it shoots through to your hand quick, you will feel it immediately.” ”

“ At any rate, the powder looked like nothing but a heap of gray dust.
“The proof of the pudding is the taste,” said he; “so we’ll try it.”
He accordingly took up about half a tea-spoonful of the gunpowder, and put it upon the shovel, and he asked Jonas to hold it in the fireplace, so that, if it did burn, the smoke might go up chimney. Rollo wanted to touch it, and his father gave him leave. So he took up a small coal of fire with the tongs, and touched the top of the little heap. To their great pleasure and surprise, it blazed up suddenly and violently.
“Yes,” said Rollo, “it’s gunpowder! ”

“ 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. ”

“ But if it was a knitting-needle, or an iron rod longer still, it would take some time for the heat to pass from one end to the other. Heat moves quickly by radiation, and slowly by conduction.
“Now, if you should go to the stove,” continued Mr. Holiday, “and put your hand upon it, you would burn it by conduction; that is, the heat would be conducted through the iron to your hand. But if you should hold your hand before the fire so near that the heat would come from the coals through the air to it, burning you, then you burn your hand by radiation. ”

“ That is the reason why a thin shaving takes fire so much more easily than the outside of a large piece of wood. The outside of a large piece is kept cool by the parts of the wood behind it, which touch it, while the shaving is heated through very soon.”
“I didn’t know that before,” said Rollo.
“In the cities,” continued his father, “the lamp-lighters, that trim and light the street lamps, always cut the wick off, when they trim the lamps, in a slanting direction, so as to leave a point of the wick projecting up on one side. ”

“ QUESTIONS. What did Jonas say when Rollo told him about burning the iron filings? How did he make the filings? Did the experiment of burning them succeed? Why will not a large piece of iron burn in the flame of a lamp? What did Mr. Holiday say to Rollo’s proposal to hold the end of a knitting-needle in the lamp? Why will not the terms that are employed in common conversation answer for philosophical use? ”

“ This air becomes heated, and swells, and so grows light, and rises out of the way, and more cold air comes in to the stove pipe, and gets heated in the same way by conduction. So the air is continually coming up against the stove and pipe at all parts, and it gets heated by conduction, and then rises and floats away over the room, and thus helps warm the room. But in a common fireplace all the heat which is conducted off goes back among the bricks of the chimney, and does not help warm the room. ”

“ The heat that comes from the sun is radiated.”
“Yes, father,” said Rollo, “I understand what radiation is; now tell me about conduction.”
“Very well,” said his father; “suppose you had an iron crowbar here, and should put one end into the fire, among the burning coals, and let it remain there while you took hold of the other end with your hand. Now, the heat would gradually extend along the bar, from the hot end in the fire towards your hand, through the substance of the iron.” ”