Water in the world
The earth, Including Its oceans and atmosphere, ls a giant distillation system whose operation brings about the distribution of fresh water throughout the world, from the frozen wastes of polar regions to the burning equatorial deserts. Stated in the simplest terms, distillation, condensation and liquid flow are the elemental processes which, on a grand scale, distribute and circulate throughout the world the water which ls essential for all life. Water in liquid form absorbs heat energy, chiefly from the sun, and the absorbed energy changes the water from liquid to gaseous form. Transported in the atmosphere, the vapour later meets cooler conditions and condenses as precipitation, some of which replenishes the water in land areas. Because water is continually being transformed from liquid to vapour and back to liquid again, the whole sequence of events ends where It began. That ls, the condensed moisture in the form of precipitation runs Into or off the surface of the earth, and a part of It collects in rivers which flow to the ocean. The events together form what is called the hydrological cycle.