Ever since men abandoned their nomadic life and started growing their own food, they have been trying to influence the weather. That simply meant pleasing the weather gods by offering prayers, dances and sacrifices, a practice that went on for thousands of years and still continue to this day. It was not until the close of the 19th century that more drastic measures were taken towards weather modification. One of the first devices tested was the “Hail Cannon”.
The Hail Cannon is a funnel-shaped device that supposedly disrupt formation of hailstones by creating shock waves. An explosive mixture of acetylene and oxygen is ignited in the lower chamber of the machine. As the resulting blast passes through the neck and into the cone, it develops into a shock wave, which then travels at the speed of sound through the cloud formations above. It’s believed that the shockwave disrupts the growth phase of hailstones.
A modern hail cannon at a field in Germany. Photo credit
The device is repeatedly fired every 4 seconds over the period when the storm is approaching and until it has passed through the area. What would otherwise have fallen as hailstones then falls as slush or rain. It is said to be critical that the machine is running during the approach of the storm in order to affect the developing hailstone. Depending on the size, a single hail cannon can protect a large swath of agricultural land.
Hail cannons were first used in the mid-19th century by Italians. They fired small, specially made cannons filled with gunpowder at clouds that threatened to hail on their orchards and vineyards. Today, Mike Eggers Ltd, a New Zealand based manufacturer is the principal supplier of hail cannons in the United States. These machines sell for as much as $50,000 a unit and provide coverage over a radius of one-third of a mile.
The effectiveness of hail cannons is inconclusive. Farmers who use them, swear they work, while others point out that thunder also creates shockwaves which are much more powerful, yet they doesn't disturb the growth of hailstones. Meteorologists also disagree the science behind the hail cannon, or the lack of.
Meteorologist Steve Johnson explained to Fox News, that the only way to suppress hail is by ice nucleation. “If you inject a tremendous number of embryos into the birth area of the thunderstorm, then it competes for the same water -- and you'll have more beneficial rain falling than a few large hailstorms,” he explained.
Hail cannons at the 3rd International Congress on Hail Shooting held in Lyons in 1901. Photo credit.
Incidentally, the first hail cannon tested in 1896 was built on this very principle of ice nucleation. The idea was first floated in 1880 by an Italian professor of mineralogy who stated that the formation of hailstorm could be prevented by injecting smoke particles by means of cannons fired at thunderstorms.
The first testing was performed in Austria by M. Albert Stinger, the Burgomaster of Windisch-Feistritz, and a famous wine grower. Stinger built a vertical pointing muzzle-loading mortar, resembling an upright megaphone about 2 meters tall. When fired, the mortar produced large smoke rings that rose to 300 meters.
Stinger built several of these cannons and tested them over a two year period during which he observed no hail. Word of Stinger’s success spread across Europe, and public enthusiasm grew, especially in Italy where vine growers suffered great loss due to hailstorms. By 1899 there was 2,000 hail cannons operating in Italy alone. At the end of 1900, the number grew to 10,000.
One of the larger models of hail cannon. Photo credit
The cannons proved to be successful, for the most time. Whenever they failed to suppress hail, it was generally blamed on improper firing. Unfortunately, when many cannon protected crops were lost during major outbreaks of damaging hailstorms that occurred during 1902-1904, many farmers began to have doubts. By 1905, cannons were largely abandoned.
Hail suppression efforts essentially ended in Europe until they were reawakened in the late 1940s and 1950s in the United States, by means of aircraft based cloud seeding. Somehow, hail cannons came back into the game, and they have found use beyond agriculture. Nissan, the U.S. based car manufacturer, employs hail cannons at their Mississippi factory to protect their brand new vehicles parked in the factory's shipping yard. Nissan insisted that the hail cannons work and they have seen evidence of hail in the area, but not over the plant.
Scientists believe that hail cannons don’t work at all, but disproving them is hard because weather itself is unpredictable.
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