_APPLICATION 66._ Explain why clouds are formed high in the atmosphere; why we have dew at night instead of in the daytime; why clothes dry more quickly in a breeze than in still air; why clothes dry more quickly on a sunny day than on a foggy one. [Illustration: FIG. 159. The glass does not leak; the moisture on it comes from the air.] INFERENCE EXERCISE Explain the following: 411. A gas-filled electric lamp gets hotter than a vacuum lamp. 412. You can remove a stamp from an envelope by soaking it in water. 413. We see our breath on cold days and not on warm days. 414. The electric arc is exceedingly hot. 415. Rock candy is made by hanging a string in a strong syrup left open to the air. 416. Dishes in which candy has been made should be put to soak. 417. Moisture gathers on eyeglasses when the wearer comes from a cold room into a warm one. 418. Sprinkling the street on a hot day makes the air cool. 419. You cannot see things in a dark room. 420. Where air is rising there is likely to be rain. SECTION 45. _Softening due to oil or water._ Why does fog deaden a tennis racket? How does cold cream keep your face from becoming chapped? Let us now imagine that animal and plant substances have suddenly lost their ability to be softened by oil or water. All living things soon feel very uncomfortable. Your face and hands sting and crack; the skin all over your body becomes harsh and dry; your mouth feels parched. The shoes you are wearing feel as if they had been dried over a radiator after being very wet, only they are still harder and more uncomfortable. A man driving a horse feels the lines stiffening in his hands; and the harness soon becomes so dry and brittle that it cracks and perhaps breaks if the horse stops suddenly. The leaves on the trees begin to rattle and break into pieces as the wind blows against them. Although they keep their greenness, they act like the driest leaves of autumn. I doubt whether you or any one can stay alive long enough to notice such effects. For the muscles of your body, including those that make you breathe and make your heart beat, probably become so harsh and stiff that they entirely fail to work, and you drop dead among thousands of other stiff, harsh-skinned animals and people. So it is well that in the real world oil and water soften practically all plant and animal tissues. Of course, in living plants and animals the oil and water come largely from within themselves. Your skin is kept moist and slightly oily all the time by little glands within it, some of which, called _sweat glands_, secrete perspiration and others of which secrete oil. But sometimes the oil is washed off the surface of your hands, as when you wash an article in gasoline or strong soap. Then you feel that your skin is dry and harsh.