Hence, it is not heat alone that causes the clothes to dry; for in winter-time, though it is so cold that the clothes on the line freeze to stiffness, they dry nevertheless, if it be very windy. It is the wind which dries them by allowing fresh air to pass through them continually. For the same reason our housewives open doors and windows after a room has been scoured, so that by a thorough draft of air, the floor may dry quickly; a large fire in the stove or fireplace could not effect it so readily. From all this we may learn that the air absorbs particles of water. It will now be evident to every one, why water in a tumbler, standing uncovered at the open window for a few days, constantly decreases, until it finally disappears entirely and the tumbler is dry. Where has the water gone? The air drank it off, little by little, until at last the tumbler was emptied. "But," you will exclaim, "what does the air do with all the water it drinks? The air goes over the whole ocean; over lakes, rivers, brooks, and springs; over woods and fields, and everywhere it takes in particles of water. What becomes of them?" After being absorbed, the particles of water unite and form clouds; then they fall down in the form of fog, rain, snow, or hail. Many persons, even highly educated ones, have false ideas about these phenomena of the atmosphere. Some think a cloud is a kind of bag that contains the rain which is let fall by the cloud. This is entirely false. The clouds are nothing but fogs in the upper regions of the atmosphere; fog itself is nothing but a cloud immediately over ground. It is easy to obtain a correct idea of the formation of fog and rain; one need but observe for one's self. He who has ever blown upon his hands in winter-time in order to warm them, will have observed that his hands become moist from his breath. If a window-pane is breathed upon, it is covered by a thin coat of water. What is the cause of this? It arises from the fact that the air we exhale contains water-particles from our blood. We do not see them when it is warm, because they are airy themselves; everybody knows that they become visible so soon as the air turns cool; or that they appear like fog when one is in a cold room in winter; that they form drops when you breathe upon cold objects; that they freeze and become snow; nay, that in severe cold weather, after a long walk outdoors, they even cling to one's moustache like icicles. This may illustrate, that these particles of water are invisible in the warm air, but that when the air is colder they appear as fog; when still colder, as drops of rain; and in very cold weather they turn to snow, while in severe cold they freeze and form ice. CHAPTER VI. FOG, CLOUDS, RAIN, AND SNOW. The air imbibes particles of water from all parts of the earth; and thus charged with water it is the same and operates the same as our breath.