“Yes, sir,” said Rollo. “I believe I do.”
“I will ask you some questions then, and see if you can answer them. When we toast bread, is the heat applied by radiation or conduction?”
“By——radiation, sir,” said Rollo.
“Yes; when we bake bread in an oven, is it by radiation or conduction?”
“By conduction,” said Rollo.
“Yes,” said his father, “because you perceive that the fire has all been taken out from the oven, and the bread is baked by the heat of the air which surrounds it. I don’t know but that there may be also some radiation from the sides of the oven, which are very hot; but no doubt a great deal of the heat is conveyed to the bread by conduction.
“When things are boiled, is the heat applied by radiation or conduction?” said his father.
“By conduction from the water,” said Rollo.
“Yes; and when they are roasted?”
“By radiation,” replied Rollo.