“I don’t know,” said his father, “that it is very strange, if we consider how it operates. It keeps the heat from passing either way. Hay has no warmth in itself. If you put hay about your feet when you are riding, it will keep them warm, because the warmth is in your feet already, and the hay keeps it from going away. On the other hand, if you put hay around a lump of ice, it will keep it cool, because the ice cannot melt unless some heat gets into it from the sun and air, and the hay impedes the progress of the heat in going in, as well as in coming out. It is just so with furs or blankets. They don’t make things warm. They only keep them from getting cold.”
“But, father,” said Rollo, “if my feet were very cold, and I were to wrap them up in blankets, wouldn’t it make them grow warm?”
“Yes,” said his father, “they would grow warm, but not because of any warmth in the blankets. The warmth would be produced in your body by the blood, and the blankets would keep it from escaping. That is all. Blankets and furs would be the best things to put up ice in, to keep it cool. They keep the heat from going off from our bodies, and so, in the same way, they would keep heat from going in from the sun and air to the ice.”
“Why don’t they keep ice so, then?” said Rollo.
“Because it would be very expensive. Shavings, and tan, and such things, will do nearly as well, and they are a great deal cheaper. Branches of trees would do very well, if the leaves were on. Once I heard of a boy who made an ice-nest, that kept the ice all summer.”
“How did he do it, sir?” said Jonas.
“Why, he found a little hollow on the north side of a hill, and he covered the bottom of it with hemlock branches a foot thick. Then he piled up square blocks of ice upon the branches till he made a pyramid of ice as high as his head, and as large on the bottom as a large table. Then he heaped up straw and shavings all around it till the ice was covered very thick. He also contrived to put some sheets of bark over it, to keep the rain off; and thus he kept his ice nearly all summer.”
“I should like to try it,” said Jonas.
“It would be better for you to make a little building,” said Mr. Holiday; “that would be much more convenient to get into. You would only have to make the walls double, and fill the space between with tan, or shavings, or straw, or any other substance like that, to keep the heat out.”
“Let us do it, Jonas,” said Rollo. “I should like a little ice-house very much.”