“There is very little empirical evidence in favor of the effectiveness of these devices.”
When an item’s Wikipedia entry says that, the device probably doesn’t work. More likely, it’s the equivalent of snake oil — a product with questionable (at best) efficacy but exceptional and aggressive marketing. In this case, though, it retails for a bit more than the $5.99 price tag on your typical cure-all elixir. Our mystery item hearkens back to the 18th century, costs roughly $50,000, and, by the way, is really, really loud. It’s called a “hail cannon” and it (doesn’t) keep away the hail.
Basically, here’s how it works — that is, “works” as in “functions.” A bunch of natural gas is exploded inside the mechanism which sends out a shock wave — evidenced by a load roaring sound — up to the clouds. The shock wave travels at the speed of sound (of course) and, in theory, disrupts the formation of hail in the clouds targeted above. While not all that useful for most of the population, preventing hailstorms (if possible) is of critical value to farmers, for whom snow, rain, and slush is a mere nuisance, while hail is a destroyer of crops. So when storm clouds approach, farmers turn on the hail cannon — which blasts out its noise every few seconds until the storm passes. Here’s one in action — playing basketball. (Really.)
As one can imagine, the horrific noise emitted by the machines has lead to a number of quarrels between hail cannon-armed farmers and their neighbors. And, again, they almost certainly are ineffective: thunder, which is much more powerful shock wave, doesn’t disrupt the formation of hail.
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