“How can I get some?” asked Rollo.
“You can get some at a blacksmith’s shop,” said his father. “The filings commonly accumulate behind the vice, and you can get plenty of them there. The next time you go by a blacksmith’s shop, you had better go in and ask him to give you some.”
“Well,” said Rollo, “so I will.”
“And now do you understand,” said his father, “why it is that you can light a lamp more easily when there is a little spirits of turpentine on the wick?”
“Yes, sir,” said Rollo. “The spirits of turpentine need not get so hot before it catches fire, and so you don’t have to hold the lamp-lighter so long, and burn your fingers.”
“Will oil always take fire when it gets to a certain degree of heat?” asked Rollo’s mother.
“Yes,” said his father, “I suppose so.”
“And yet,” said she, “the lamp seems to take fire much more easily at some times, than at others.”
“Yes,” said Mr. Holiday, “that is true. If the wick is cut square across, and rises up only a very little way above the tube, it is very difficult to light it, because the tube itself and the oil below keep the upper end of the wick cool. It is very hard to heat it, in that case, hot enough to set it on fire. But if the wick projects considerably out of the tube, then it is out of the way of the cooling influence of the metal, and you can heat the upper end more easily.”
“I never thought of that,” said Rollo.