“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.”
“No,” said his father, “it is not very bright: but the surface is polished, you see, somewhat, and this prevents its radiating much. Still it radiates more of the heat than it would if it was of silver, and polished as bright as possible. But a common iron tea-kettle, black upon the outside, would radiate heat much faster than this one.
“There is another thing for you to understand and remember,” continued his father; “and that is, that those substances which radiate heat best, also receive heat by radiation the best.”
“I don’t know exactly what you mean by receiving heat by radiation, sir,” said Rollo.
“Suppose,” said his father, “that we were to cut out a square piece of sheet iron, such as the stove pipe is made of, as large as the palm of my hand, and also a piece of silver, like that which a tea-pot is sometimes made of, and have it polished as perfectly as possible. Suppose, then, that we were to carry both of these out, and lay them down in the sun. Or suppose we hold them up before the fire, so that they would receive the radiation from the fire. Now the iron plate would receive the rays of heat more rapidly than the other, and become hot the soonest.”
“Would it, sir?” said Rollo.
“Yes,” replied his father; “or, if you were to lay them down in the sun out of doors, the effect would be the same.”
“I wish we had such pieces to try it,” said Rollo.
“Did not you ever observe how cold bright brass andirons are, long after the fire has been built in the fireplace?”