There is a difference certainly between man and whale in the matter of breathing. A man has to take in fresh supplies of air constantly, and if he is beyond reach of air for more than a few minutes he dies. A whale comes to the surface for about ten minutes, spouting out enormous supplies of used-up air and taking in enormous supplies of fresh air, after which it can remain under water for half an hour or more: some say an hour. Then a fresh bout of noisy breathing becomes an absolute necessity. This, however, is merely a matter of internal arrangement. The whale has an immense reservoir of blood, which, being thoroughly purified by the air during ten minutes of vigorous breathing, serves slowly to supply the creature’s requirements while below. But the need for air, and the effect of that air upon the blood, are much the same in man and whale. Small creatures, as well as big ones, spending much time under water, and yet breathing air, have to come regularly to the surface. If our world had no ocean of air, there could be on earth no men, no quadrupeds, no whales or fishes, no birds or insects, no forms of life. Like the ocean of water, the ocean of air knows no repose or stagnation. What we call stillness on the most sultry of summer days does not mean absolute stillness. Though not enough wind may stir to lift a feather, yet the air is in ceaseless motion, to and fro, hither and thither. The whole atmosphere is a vast and complicated system of air-currents, and each lesser portion of air has its own lesser circulation. You can not lift your hand without causing a tiny breeze; you can not turn a wheel without making a minute whirlwind; and every separate air-movement draws other movements in its train. There is water enough on earth for all needed purposes; but we should find ourselves in direful straits if the whole water-carrying from lakes and rivers for men and animals had to be performed by human agencies. Far from this, a mighty apparatus is provided. The scanty aid that man can give only shows how little he is capable of. The entire atmosphere is a tremendous pumping engine, an enormous watering machine, always at work; always receiving supplies of liquid from the ocean, from seas, lakes, rivers; always showering this water down again upon the land, as needful drink for plants and animals, as needful cleansing for all things.