What men have learned within the last four centuries, has taught us that only a small portion of the surface of the earth is uninhabitable. Man, by the wonderful constitution of his nature, is enabled to bear the extremes of heat and cold better than any of the animals that are sent for his use, each of which is adapted for the particular climate in which it may be placed. Under the most extreme variations of the temperature of the atmosphere, the heat of our bodies, when we are in health, is never increased or diminished more than a very few degrees; so that a thermometer, with the bulb put into the mouth of an Esquimaux, in a climate much below freezing, will be only three or four degrees below what it will be in the mouth of an inhabitant of the East Indies, where the temperature often exceeds 100 degrees. The dog is almost the only animal that is prepared to accompany man in all climates. The form and habits of this faithful creature vary most surprisingly, according to the circumstances in which he is placed; but he is everywhere the loving friend and faithful associate of man, and ready to defend him and to share his toil, in the hot and parched deserts of the East, or the icy regions of the North. There are a few animals that undergo remarkable changes, to enable them to bear the vicissitudes of the climate in which they may be placed. The hares and the foxes of the Northern regions become covered with white hair in winter. Now, it is proved, that a body hotter than the surrounding atmosphere which has a white covering, cools much more slowly than one covered with a dark colour: hence, the heat generated inwardly is preserved and economized by the winter coats of these animals, to the great benefit of their health and comfort. III. Some kinds of birds that love warm climates, are taught to assemble together at a certain season near the end of summer, almost to a day, and start off on a pilgrimage to distant lands, where nature is still blooming. There are these birds which all live nearly the same sort of life,--the swift, the swallow, and the house marten, which all bear a strong resemblance to each other. They all come to us from the south in spring, and take their departure before the next winter. The swifts form themselves into companies, and take their leave of us before the middle of August; the swallows do the same about the middle of October, and the martens at the end of the same month. Thus these happy creatures manage to live all their life long in summer and sunshine. [Illustration]