“Yes,” said his father, “but they are not precise in their signification. They are vague and ambiguous, and so philosophers, when they wish to speak accurately, employ other terms, which have an exact signification.”
Rollo looked perplexed. He did not understand at all what his father meant. In the meantime, his mother had brought a fresh bundle of lamp-lighters from the closet, and had lighted her lamp with one of them, and was just going away. As she was going out, however, she said to her husband,—
“Please to wait a minute, until I come back, for I should like to hear what you are going to say.”
“Well,” said he; “and you, Rollo, may come and sit down by me, and I will explain it to you when mother comes back.”
So Rollo came and took a seat on the sofa by the side of his father, saying,—
“Father, I wish you would have a bottle of spirits of turpentine for us to light our lamps by.”
“It is not of much advantage in a family,” said his father, “where the lamps are lighted in various parts of the house, and only a few in all to be lighted. But where there are a great many, it is quite a saving of time to have a little spirits of turpentine to tip the wicks with. In an illumination they always touch the wicks so, and by that means they can light up suddenly.”
“But, father, why will the wick light any quicker?”
“Why, different substances take fire at different temperatures. For instance, if you were to put a little heap of sulphur, and another little heap of sawdust, on a shovel together, and put them over a fire, so as to heat them both equally, the sulphur would take fire very soon, but the sawdust would not until the shovel was very nearly red hot. So if you were to put oil in a little kettle over the fire, and spirits of turpentine in another kettle, and have the fire the same under both, the spirits of turpentine would inflame long before the oil. There is a great difference in different substances, in regard to the temperature at which they inflame.”