“First, tell me of all the substances that you can think of which are composed of animal fibres.”
“Fur,” said Rollo, “and wool.”
“And hair,” said his mother.
“Yes,” said his father, “and woollen cloth, and blankets, and carpets, and flannel, are made of such animal fibres. Now, can you tell me of any substances which are composed of vegetable fibres?”
“Hay,” said Rollo; and then he paused. He could not think of any others.
“Cotton,” said his father, “and flax. They are vegetable fibres; and cotton cloth, and linen, and paper, are fabrics made of vegetable fibres. Now, there are two reasons which make me think that the animal fibres are better non-conductors than the vegetable. One is, that they are expressly intended for non-conductors, and therefore would probably be so formed as most perfectly to answer their design.
“For you see,” continued Mr. Holiday, “that the wool, and the fur, and the hair, of animals is generally intended as a covering to protect them from the cold. That is, it is intended to keep the heat of the body from passing off, and being wasted in the air. Therefore they must be non-conductors of heat, in order to answer this design. Now, we find that everything in nature is admirably adapted to answer its design, and therefore we should expect that these substances, which are expressly intended to confine heat, would be the best non-conductors of heat in nature. That is one reason.”
“I think it is a very good reason,” said Rollo’s mother.
“So do I,” said Rollo.
“The other reason is this,” continued Mr. Holiday. “All the substances made of the vegetable fibres feel colder to the touch in cold weather than those made of animal fibres. For example, suppose you were to go, in a very cold night, into a room where there was no fire, and put one hand into a bed between the sheets, and the other between the blankets,—which would feel the coldest?”