"He sendeth out his word, and melteth them: he causeth his wind to blow, and the waters to flow."—Psalm cxlvii.
168. How is the greater warmth of animals provided for in the winter?
It is observed that, as winter approaches, there comes a short woolly or downy growth, which, adding to the non-conducting property of their coats, confines their animal warmth.
In small birds during winter, let the external colour of the feathers be what it may, there will be found a kind of black down next their bodies. Black is the warmest colour, and the purpose here is to keep in the heat, arising from the respiration of the animal.
169. How is warmth provided for in animals that have no such coats?
They are furnished with a layer of fat, which lies underneath the skin. Fat consists chiefly of carbon, and is a non-conductor.
170. Why are summer breezes said to be cool?
Because, as they pass over the heated surface of the body, they bear away a part of its heat.