Air, the great carrier of water, in its wonderful strength and restlessness, bears vast layers of cloud to and fro, wafts away superfluous damp, drenches the dry and thirsty earth, fills ponds and lakes, feeds--nay, actually makes--the rivers, never flags in its ceaseless energy. If clouds hang low or fogs arise, we are glad of the moving air which sweeps them elsewhere. If the soil is caked and plants droop, we are glad of the moving air which brings rain. Thus our wants are supplied, and the wide water circulation of earth is carried on. Without circulation, without motion, stir, change, there can not be life. Stagnation must mean death. Our earth, without her ocean of moving air, would be a world of death. Without air, earth would be in great measure a soundless world. Silence would reign here, as probably it does reign on the moon. Sound, as it commonly reaches our ears, depends for its very existence upon air. Let the concussion of two bodies be ever so mighty, if there were no air to bear away the vibrations of that concussion, there could be no crash of sound. True, sound-waves can be conveyed through a liquid or through a solid as well as through air; and we might be conscious of the ground’s vibrations, but our ears would hear no noise. So an airless world would be a silent world. Without air, supposing we could ourselves exist, we should hear no trickling brooks, no rush of waterfalls, no breaking ocean waves, no sighing of the wind, no whisper of leaves, no singing of birds, no voices of men, no music, no thunder, no one of the thousand concomitant sound-waves which together make up the babble and murmur of country and town. Those only who are perfectly deaf can know what such silence means. Without air our world would not be in darkness; for light does not, like sound, depend mainly upon air for its transmission. Light travels through regions where air is not; and if light is communicated by waves, they are not waves of air. But though the absence of air would not deprive the earth of light, it would make a very great difference in the kind and degree of light received. Without air the blue sky would be black as ink; stars would glitter coldly in the daytime beside a glaring sun; deep shadows would alternate with blinding dazzle, and all the soft tints of sunrise and sunset would be wanting. Earth would be like the almost airless moon--all fierce whiteness and utter blackness--with no gray shades, no rosy gleams, no golden evening clouds; nay, without air there could be no clouds. On the moon is no twilight; for no air-particles float about, reflecting the sunlight from one to another, and forming a soft veil of brightness, to reach further than the direct sunlight alone can reach.