Linda Pruvenok, age 12, of Gary, Ind,,

What holds the rain up in the clouds?

A drenching downpour for 24 hours drops about two and a half inches of rain  The weight of this water dropped, say, on the state of Indiana, is almost three billion tons  For the weight of one inch of rainfall is 2,300 tons per square mile  The weight of one inch of water over an area is 113 tons  A sharp shower lasting an hour would dump 50,000 tons of water on the 100 acres of beautiful park land in Gary, Indiana ‑ to say nothing of the streets and buildings  It is natural to wonder what holds these tons of water up in the clouds and what makes them finally come tumbling down 

The fact is, all that water is not in the air above our heads before it starts to rain, The air may be saturated, which means that it holds as much moisture or water vapor as it possibly can  But this could not amount to more than one inch of rainfall  And, as we all know, it sometimes rains for days at a time, The extra moisture which forms into raindrops and keeps tumbling down is drawn into the storm area from afar, A constant supply of moist, rising air must keep flowing in to keep the rain falling 

The rain forms from the tiny, misty droplets from which clouds are made, It takes about 2500 of these midget droplets of water to measure one inch  That' era smaller than grains of dust, smaller than the tiny motes that you sometimes see dancing in a beam of sunshine  And, like these tiny fragments, cloud droplets era also small enough to float in the air • for a time, But finally the dust settles, and so do the cloud droplets 

 In perfectly calm air, it would take a cloud droplet 16 hours to sink down through one mile of air, But, of courses the air is rarely calm  There is almost always a wind or at any rate a gentle breeze blowing  And even the softest breeze is enough to keep the cloud droplet floating aloft and wafting along  This is how a cloud with its load of misty moisture stays in the air 

When the misty droplets form big raindrops, however, they feel the pull of the earth’s gravity and they are pulled down to the ground  However, it takes about a million droplets of mist to form one raindrop large enough to fall, The mystery is how these droplets merge with one another to form raindrops, For in the aloud they float around with as much space between them as the stars seem to have in the sky 

The scientists suspect that there are several ways in which the fine droplets can gel‑into sizable drops, The process is called coalescence, Some of the droplets are giants compared with others and it may be that smaller droplets tend to collide with them, much as meteors collide with the earth  In this way, the big droplets would get bigger and bigger 

In some cases, at least, the aloud droplets must have a nucleus around which to gel  This may be a fragment of ice, dust, soot or salt tossed up into the air by the pounding sea, The nucleus collects moisture as it falls this way and that through the misty cloud, Lightning forms oxides with nitrogen as it ripe through the air and these oxides may also form nuclei around which the droplets gel into raindrops large enough to come pelting down.