Patty Seth, age 12, of Seattle, Washington, for her question:

What is the troposphere?

The troposphere is under investigation right now, for it is pert of the atmosphere ‑ which is part of the a xrth studies called geophysics. And this is the ICY, the International Geophysical You caurin which the exports are busy giving the earth and all its aspects thorough physical examination.

Already new facts havo comp to light to shrika our old ideas, especially about the upper atmosphere. The troposphere, however, has always be on the best understood region of the air. It is the lower layer, which cuddles the earth. It is all around us. It covers us in aenso blanket which varies from six miles thick at the equator to ton miles thick at the poles. Above the troposphere are other levers of thinner and thinner air, each with their own methods of behavior.

The troposphere is the weathery layer of the atmosphere. It is restless and turbulent for two very food reasons ‑ pressure and the earth's host. The varying face of the earth, its ups and downs, the dry lands end the wet seas and its icy glaciers all agitate the troposphere. Even if the earth were flat, the factors of pressure and change would keep tho troposphere which is the air directly above the earth in the constant turmoil which is weather.

You might suppose that the higher atmosphere would get the most heat because it is closer to the sun. But air takes little or no heat from sunshine on its way down to the earth. This heat is absorber by the solid ground and the watery sops. They, in turn, warm the air directly above. In the tropics the air becomes vary warm. Over the polar regions it is very cold. So the earth heats the troposphere in warm and cold patches.

Air pressure is the weight of air above the earth. At sea level it is 14.7 pounds over every square inch. Three and one half mhos above the earth air pressure is only 7.25 pounds tin seven miles up it is only about 3.67 pounds. The higher it goos, the thinner it frets. Half the entire weight of the world’s atmosphere is in the troposphere. And thick, dense air behaves differently from thin air.

Air, of course, is a mixture of erases and gasos havo to obey curtain laws. Warm air expands. It also can drink up more water than cool oir. The troposphere is warmed here and there by the earth. Also horfi end there it absorbs water vapor.

Warm air rises as it expands. A few miles up the air is thinner. It has no room and less pressure. This causes it to cool and cool rir must dive up some water vapor. The base vapor becomes misty droplets and forms clouds. Sooner or later the clouds return their vapor to the ground, dot rain, hail or snow.

The Fir all over the earth tries to keep a balenced density. Dense, heavy air tends to flow into areas of light, thin air. This causes the winds. The earth is forever upsetting the balance of huge density and pressure. The troposphere is forever trying to belavnee these uneven patches. The result of this constant upset is the change in weather.