When storm clouds come boiling over Lake Zurich toward Ernst Spoehel's cornfields, the Swiss farmer knows just how to prevent a vicious hailstorm from devastating his crops.
His sense of imminent danger honed by 20 years of experience, Spoehel rushes to his barn, loads a small plastic rocket with a packet of silver iodide, and fires it into the clouds a mile above him.
"You can see the front coming, and when you have the feeling that danger is near, you start to shoot," he explains.
Spoehel and hundreds of other farmers are convinced that they immunize the clouds against hailstorms by peppering the skies with their rockets.
Scientists and insurance companies are more skeptical.
Both sides agree that hailstones form when masses of cool and warm air collide, causing small droplets of moisture in the air to condense around particles of dust and freeze. Strong winds can suck the particles to elevations up to five miles, allowing them to grow as they rise until they are so heavy they fall as hailstones.
In theory, at least, the exploding silver iodide packets cause the moisture to crystallize into countless tiny bits of ice that melt into harmless raindrops as they fall.
Farmers around the world live in fear of hailstones that can pound their crops into the earth.
"A heavy storm can produce stones as big as an egg," noted Hans Scharpf, spokesman for the Swiss Hail Insurers Assn.
Hailstorms are especially prevalent around mountain ranges such as the Alps, which block moving air masses and force them to dump precipitation on whatever lies below.
To meet the threat, Swiss farmers have been firing silver iodide into clouds since the 18th Century, said Spoehel, a board member of the Swiss Assn. to Combat Hail.
About 190 communities in the German and French-speaking parts of Switzerland are members of the association, and many help finance the hail-busting rockets, which cost about $50 each.
Spoehel said his rockets have protected him from hail except for one time, when a storm front moved into the area so quickly that the rockets had no time to take effect.
A barometer hangs on the kitchen wall, but he gleans most of his weather information from his cable television, which broadcasts satellite pictures of Europe and regular updates on humidity, wind speed and air pressure.
The farmers get their rockets from Hans Hamberger AG, a fireworks manufacturer that is Switzerland's sole supplier of the devices.
Manufacturing chief Kurt Abegglin said Hamberger sells between 2,000 and 3,000 each year, almost all to Swiss customers, although some go to Sweden and Africa.
However, Scharpf of the Hail Insurers Assn. thinks the rockets provide more psychological than actual relief. He said most proponents take out large hail-insurance policies as well.
"These people are farmers, and sometimes they have to watch a storm destroy their crops in the space of 10 minutes," he said. "That is a whole year's work just wiped out. They have to try everything they can. Whether it works or not is another question, but they have to do something."
Swiss hail insurers, who pay about $28 million annually for crop damage, helped finance a seven-year study by the Federal Institute of Technology that used large Soviet rockets to seed clouds, Scharpf said.
"According to that experience, it had no effect whatsoever," he reported. "There was just as much damage done by storms where rockets were fired as there was when no rockets were fired."