Man has always especially wanted to do something about rain. Too often there isn't enough rain. Of all the calamities which nature visits on the earth in the course of operating her weather machine-hurricanes, tornadoes, lightning, hail, floods-droughts are the worst.

Probably more millions have died of starvation for lack of rain that would nourish the crops than have died in all the storms of history put together.

In 436 B.C. thousands of Romans threw themselves into the Tiber rather than starve to death. The Bible tells how Joseph advised the Pharaohs on measures to relieve hunger in Egypt. In India, one year ten million people-one third the population of Bengal-died when the monsoon rains failed. Here in our own country we still remember the Dust Bowl years of the 1930's when the topsoil from millions of acres of Midwestern farmland blew away on the wind.

Nothing has changed. If anything, the specter of famine has increased. In 1974 nutritionists warned of "what may be the worst famine in the history of mankind" having begun with "between 30 million and 100 million people . . . now slowly starving to death . . . at least five million of then likely . . . to die this year."

The United States Weather Bureau, now the National Weather Service, once defined a drought as being when 21 days or more go by with only 30 percent of the rainfall normal for that time and place. In England an "absolute drought" is 15 or more rainless days in a row. Another measure of a drought is 85 percent or less of normal rainfall for the year.

By any of these measures there is always a drought going on somewhere. This means land is out of production, which could hardly be spared in any case. Only II percent of the earth's 3.5 billion acres is now considered suitable for crops

"Drought," says the Encyclopedia Britannica, "is the most serious physical hazard to agriculture in nearly every part of the world."

So it is that man has wanted to coax more rain from the passing clouds. In earliest times, when superstition ruled in matters of the unknown, he used magic in his efforts to turn the trick. In parts of Africa even today the rainmaker with his drums and other paraphernalia of his trade is a key member of his community.

The Indians practiced an assortment of rainmaking rituals. They smoked special pipes, burned tobacco by the stack. and shot arrows at the clouds-perhaps to spear the rain out of them. The Indians prayed, danced, and chanted. The Choctaws hung a fish around a tribesman's neck and stood him in the nearest stream until either it rained or somebody in authority came up with a good explanation of why it didn't.

If it chanced to rain in the wake of any of these proceed ings the rainmaker got the credit. Who could say it wasn't he who did it-or would want to argue about it? If it didn't rain, it was remembered that last time it did. He couldn't be expected to score every time.

Professor James P. Espy, a pioneer authority on the weather, had noticed that thunderstorms and rain often followed a prairie fire or a forest fire. He therefore proposed in 1841 that forty acres of timber be burned every seven days at twenty mile intervals along a six-hundred-mile front from north to south on the western frontier of the country to put an end to drought.

During the Civil War it was noticed that it often rained in the wake of big battles. Several scientists thought smoke from the guns had something to do with it. To investigate this idea, Congress in 1890 put up $9,000 for rainmaking experi ments with explosives.

One of the more colorful proposals to bring down the rain came from G. H. Bell of New York. He proposed building a series of towers 1,500 feet high-one set of towers to send saturated air up to cooler air and have the moisture condensed into rain, the other set to suck in rain clouds and store them for use as needed.

1916, Charlie promised to have the city reservoir filled and four feet of water going over the top of Morena Dam by January 27.

On schedule, smoke-or whatever it was-was seen coming from a tank on top of the twenty-foot tower the brothers had built near the reservoir, southwest of the city. Four days later, with the rain coming down as no one could remember it ever having rained before, the lake was up fourteen feet.

By the target date of January 27, instead of only four feet of water going over the dam, a Niagara roared over the top and matters were badly out of hand. Under the pressure of the racing flood, a dam downstream gave way, loosing disaster on the valley below. Twenty people drowned. Hundreds lost their homes. Damage was counted in the millions of dollars. The onrushing torrent ripped out scars on the hills and moun tains which were still there years afterward.

If the mysterious "smoke" the Hatfields sent into the air from their little tower had anything to do with the rain that often seemed to follow, they may have been onto something without knowing what it was.

Every raindrop has a nucleus, a tiny speck of dust at its center like the stone in a peach. The air is filled with these particles. Even on the brightest day, when the sky appears to be immaculate, it contains particles, so small that they must be magnified thousands of times to be seen.

The particles come from many sources-salt spray from the oceans, from the soil, and from vegetation. They come from factory smokestacks, automobile exhaust pipes, jet air planes. They form on their own by chemical reaction in the atmosphere. "Condensation nuclei," weathermen call them.

Sharing the air along with these specks of dust is the mois ture which the sun draws from the oceans and land surface; This is present in the form of vapor. When this condense on the nuclei, it forms droplets, themselves so tiny that it would take 2,500 of them, laid side by side, to reach on inch.

The droplets cluster around the dust specks like swarming bees, piling on top of one another. If conditions are right what they form may grow into raindrops. Where a little while before there was blue sky, there is now cloud. It may be "clouding up" to rain-or to snow if it's winter.

If the temperature of the cloud is below the freezing point of thirty-two degrees Fahrenheit, nothing may happen, no matter how many water droplets or how many dust particles are present. At any temperature below freezing the cloud is "supercooled."

At five degrees, and not a moment before, the dust par ticles may start to take effect, causing the water droplets to begin to freeze, forming ice crystals. The cloud, in summer most often a cumulus, a word meaning "heap" or "mound, is seen ballooning skyward looking like a vast, dark cauliflower or the mushrooming dome of an atomic explosion.

Inside the cloud, the ice crystals are growing rapidly large as they collect droplets. In ten to twenty minutes, they are on their way to earth as snowflakes, growing still fatter as they bump into more droplets on the way down. They reach the ground as snow if it's freezing, as rain if it's above freezing.

This process of building ice crystals into snowflakes im proves as the cloud builds and gets colder. It does best at about thirteen degrees below zero.

But if there is a shortage of dust particles in the rising air and the clouds aren't cold enough, nothing much happens. Don't expect either snow or rain, however promising the situa tion looks. Without the nucleating bits of dust, no ice crystals form, no matter how cold it gets.

One would think that after a while, as it keeps getting colder, the droplets would freeze on their own account. After all, water freezes at thirty-two degrees. Not so in this situation. The water stays liquid until it gets as cold as it is at the North Pole.

Finally, at around forty below zero, the little droplets give up at last and "flash over" into ice crystals-all of them, so that there are none left to make rain or snow. What we see then is cirrus, meaning "curl," those graceful, high-flying clouds with the shape of brush strokes and mare's tails.

It is clear that nature's processes for getting the water back down to earth once the sun has hauled it up into the atmo sphere are not very efficient when measured by man's produc tion standards. Even though generous amounts of vapor are condensed into droplets and then into drops, very little of the airborne water makes the trip to the ground.

Most of it turns back into vapor. Much of what does start down evaporates on the way. Studies of thunderstorms in the eastern United States show that only about twenty per cent of the condensed water in these storms ever reaches earth as rain. In the more arid regions of the country, such as the Great Plains, the clouds are usually so high up that most of their rain disappears on the way down.

Over our heads continually flow great rivers of water. Scientists estimate that these rivers carry six times as much water as those that flow on the ground. But these aerial rivers spill extremely little as they pass-less than one drop in ten.

There is, however, a way to make these sky rivers give up a little more water as they pass.

The nuclei that become the hearts of raindrops can be put into the rain-bearing clouds artificially. Several things may be used. By far the best is silver iodide. When vaporized, silver iodide yields about 600,000 billion particles per gram, each a potential raindrop. (There are 450 grams in a pound.) Only a few grams of silver iodide may affect many hundreds of cubic miles of cloud in a brief time.

Silver iodide provides a kind of tap for turning on the water in clouds where it's too warm for nature's own nuclei to be effective. Silver iodide begins to work when the tempera ture in the cloud is twenty-five degrees, whereas little happens with natural nuclei until the temperature is much lower.

Since most of the water is in the part of the cloud where silver iodide works-about three quarters of the cloud- silver iodide improves on nature's means for making rain.

The fateful secret of how to make the clouds give up water was discovered by accident.