“They make them of some substance formed of animal fibre,” said his father, “because that makes the best non-conductor. The article, when ready, can be put upon any handle which is likely to get hot, and, being a non-conductor, it stops the heat from coming from the handle to your hand. You can take up any hot thing by means of it,—unless it is hot enough to burn the animal fibre of which the non-conductor is composed.”
“I wish that I could see one,” said Rollo.
“Well,” said his father, “you can, when you get home. Dorothy has got one, I dare say.”
“Dorothy!” repeated Rollo.
“Yes,” said his father. “She calls it a holder.”
“O, a holder,” said Rollo. “I did not know you meant a holder.”
“Why, a holder is a non-conductor made of animal fibre, and intended only to stop the passage of the heat from the iron handle to your hand.”
“I thought it was only to keep our hands from touching the handle.”
“No,” said his father, “for an iron holder would do that; but an iron holder would soon get hot, and be of no use. That is, an iron holder would allow the heat to pass across very soon to your hand. It must be a non-conducting holder.
“And now,” continued Mr. Holiday, “you understand fully the philosophy of the copper tea-kettle. The iron heater was the reservoir of heat. As it was a good conductor, it conveyed the heat rapidly into the bottom of the tea-kettle, and so into the water. The water, being a good conductor, conveyed the heat to the sides of the tea-kettle, but they were made bright and polished, so that they should not radiate it fast into the air. Still, however, they radiated the heat considerably; but the waste was supplied by fresh heat from the heater. At first, the heat came faster from the heater than it was radiated from the sides of the kettle, and so the water was made to boil. But gradually the heater became less hot, and so did not conduct heat so fast into the bottom of the tea-kettle,—until, at length, there was a time when the supply was just equal to the waste; that is, the heat was conducted in just as fast as it was dissipated by radiation, and the temperature was kept at the same point.”