In a dark room shine a light beam, say from a flashlight, through a clear glass of water. Look at the beam from the side so you can see the scattered light. (It helps if there is a black background.) At the same time look at the direct, transmitted light, for example, by reflecting it from a piece of white paper. Now add a little milk, one or two drops at a time, and stir the water. The scattered light will become bluish as the transmitted light become yellowish and then reddish. As you add even more milk, the scattered light becomes white because of repeated scattering, and you have made a white `cloud'.

You can see the blue of the air directly if you have enough air with a dark background, and something black with which to compare the color of the air. An otherwise dark room viewed from the outside through an open window makes a good dark background. To block all extraneous light, view the window through a long mailing tube. Since you will want to be as far as possible from the window (30 or 40 m), over the far end of the tube with some aluminum foil in which you have made a small (several millimeters) hole. To avoid light entering the hole at tan angle, wrap a piece of black paper around the far end of the tube so it extends 15 or 20 cm beyond the foil. Look toward the window when the sun is to one side or overhead. Then the only light entering the tube will be the sunlight that is scattered by the air between you and the window. This should look distinctly bluish compared to he dark surrounding of the aperture in the foil. What happens to the blue as you change your distance from the window?