Gloria McClinton, age 13, of Natchitoches, La., for her question:

Are the same clouds always in the sky?,

A cloud is always busy going somewhere and changing itself as it goes. For it is no more than a puff of mist, so much like the plume of steam which boils forth from the spout of a kettle. So the cloud that passes overhead is gone for good, wafted on the breezes. Tomorrow it may be a different kind of cloud. It may have fallen as rain or evaporated into the air.

All clouds, of course, are formed from vapor in the air. They are light enough to float aloft, but they are not lighter than air, then they start to sink, slowly, slowly as soon as they are born. For a while they may be held aloft by rising currents of warm air, but sooner or later, down they tumble as rain, sleet or hail.

All this is part of the great water cycle which keeps the earth replenished with moisture. The vapor in the air is water gas. Laundry dries outdoors because the warm air drinks up the moisture and turns it into this invisible vapor. The air is thirsty because it is warmed by the ground it tce.3hes, and the ground is warmed by the 'reaming sun. The warmer the air, the more thirsty it becomes, the more vapor it can hold. But if warm, vapor‑ladened air becomes cooler, it must give up some of its vapor. This vapor becomes mist, the filmy stuff from which clouds are made.

Sometimes a cloud forms right on the ground. We call it a fog. As the sun rises it may warm the ground anal the ground may warm the air above it. The warmer air may evaporate the fog into vapor and the fog disappears.

Most clouds form above the ground. This is because warm air expands and rises.  As it expands it cools itself and, if it has any surplus vapor, it must turn it into fine droplets of water, or cloud mist. As a rule, the white cumulus clouds of a summer's day are formed in this way. Certain clouds form maybe six miles above our heads where the air is very chilly. They are made of fine fragments of ice and look like whispy white feathers. We call them cirrus clouds. They are the high flying clouds most likely to catch the blazing colors of dawn and sunset.

Any cloud, no more than a puff of misty is very sensitive to changing conditions and in the air above our heads conditions are very changeable indeed. Patches of warm air are forever clashing with patches of cool air. Breezes blow up and down and in all directions. The cloud is at the mercy of all these changing elements. Tomorrow we may see a cloud that looks a lot like one which passed overhead today. But it will be a different cloud, on its way somewhere else and changing as it goes.