IV. Then, in the distribution of different animals, there is not less to engage our attention. The rein-deer is the support and comfort of the Laplanders. It lives constantly on the scantiest, and apparently least nourishing diet, and when brought into warmer climates it soon languishes and dies. The camel only flourishes where there are large sandy deserts, with precarious supplies both of water and solid food; and to fit him for his peculiar line of usefulness, he has a receptacle to contain a stock of water, which he can at pleasure turn into his stomach, and can go eight or nine days without a fresh supply; he eats any kind of vegetables, however dry they may be; and a pound a day is sufficient to support him for weeks together; though he is very much larger than any of the animals which inhabit your country. It is usual for camels to go the whole distance from Cairo to Suez, in Egypt, without tasting a morsel, and this remarkable faculty has been supposed to arise from the hump upon their backs. When the animal is well fed, this hump, which is of a fatty substance, fills out and becomes solid; but when his food is scanty, it wastes away, and its substance appears to go to the nourishment of the more vital parts of his frame. His large feet rest upon the sand without sinking in, and at the rate of about two miles an hour, he will travel thirty miles a day over a parched desert, bearing a burden of seven or eight hundred weight. He is called by the Arabs the Ship of the Desert. [Illustration] V. You may see that there is, in every variety of circumstance, something that enjoys itself, and has a place to fill up and a part to act amongst the creatures which God has made. But this is not all: the existence of the cold of the Poles, and of the heat of the Tropics, is necessary to the well-being of the whole. The free air that surrounds the globe, which we breathe, and through which we see, and hear, and smell, and move, is the same in composition in every part of the world. It contains just the same proportions of the two gases, oxygen and nitrogen, in the coldest and the hottest climates, in the deepest valleys and on the tallest mountains. Now, this air, considered on a large scale, is always blowing from the Poles towards the Equator. The more direct rays of the sun heat that portion of the earth's surface which lies in the Torrid Zone, and therefore the air above it is perpetually ascending to the upper regions of the atmosphere, to make room for that which presses upon it from the Poles, because it is cooler and heavier. It is this process, united with the motion of the earth on its axis, which causes the Trade Winds and Monsoons.