Where does the most evaporation take place? From the surface of the rivers, the lakes, and the ocean. What becomes of the water when evaporated? It is formed into fogs and clouds. In what kind of air does evaporation go on most rapidly? In air that is warm and dry. Does evaporation take place in cool air? It does; because clothing will dry during the coldest weather of winter. Why does water evaporate more in warm air than in cold air? Because the warm air can hold more of the fine particles of water, and, therefore, can absorb more. Why does water evaporate more slowly in damp weather than in dry weather? Because the damp air contains so much moisture that but little more can pass off into it. What example have we of this? Wet clothes dry much more slowly when the air is damp than when it is dry. Why do clothes dry more rapidly in windy weather? Because the damp air in contact with them is blown away, and the dry air is constantly taking its place. Is heat necessary in evaporation? Heat is necessary to produce evaporation. Why do our hands feel cold when wet? Because the water on our hands evaporates, and thus heat is taken from them. Why is the air cooler after a rain? Because evaporation then takes place from every wet object, and this absorbs heat from the air. Why does watering streets and roads cool the air? Because the water evaporates and absorbs heat from the air, making it cooler. Why do we feel cold when our clothes are wet? Because the moisture in them evaporates and absorbs heat from our bodies. Why is wet land always cold? Because so much heat is absorbed from the land in the evaporation which is constantly taking place. What becomes of the dew that collects on plants and other objects at night? It is evaporated. How does the sun hasten the evaporation of the dew? By supplying the heat needed to change the dew into a vapor, the sun hastens its evaporation. Why do bread and biscuit become hard when kept a few days? Because the moisture in them passes off into the air, and thus they become dry and hard. How can they be kept moist and soft for a longer time? By keeping them in a covered vessel, so that evaporation will take place more slowly, they may be kept moist for a longer time. Radiation. When we stand near the fire, why do we feel warm? Because the fire gives off heat which makes us feel warm. How does the fire give off heat? It gives off heat in straight lines, and in every direction. What is this giving off of heat called? It is called _Radiation_ of heat. Does the sun radiate heat? The sun does radiate or give off both heat and light. How do heat and light from the sun come to us? They come together in the sunbeam. Does heat travel as rapidly as light? Yes; heat and light travel together at the rate of 200,000 miles in a second of time. Do all substances radiate heat equally well?