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 layers of warmer air—that is, it is whirled through alternate layers of snowy air and of misty air. The updraught that occurs during thunder-storms shows that such a movement takes place in cumulo-nimbus clouds; and when the hailstones become too heavy to be carried by the updraught they fall to the ground.

Hailstones usually vary in size from a quarter of an inch to half an inch in diameter. They are very rarely as much as an inch in diameter. In a few instances single stones more than two inches in diameter have been reported. In many instances several hailstones are frozen together, and hailstones “as large as a hen’s egg” are formed in this manner. Hail-storms are rarely more than a few minutes in duration.

They occur usually in the southeast quadrant of a cyclonic storm, having the same relation to the area of low barometer as does the tornado. The path of the hailstorm is rarely more than 3 or 4 miles wide—sometimes not more than half a mile—and it may traverse a distance of 25 or 30 miles, or more.

Sometimes the hail is scattered in windrows; and many cases in the United States have been reported where the wind-rows were several rods in width and more than 2 feet deep. Near St. Quentin, France, a windrow more than a mile long left a mass of ice which did not disappear for several days.

In western Europe hailstorms are very destructive to vineyards and growing crops. For many years the practise of “bombarding the air” was followed. Long-barreled mortars with bell-shaped bores were charged heavily with powder and aimed vertically. At times when storms were expected, thousands of charges were fired into the air with the expectation that the resulting convection of the air might prevent the formation of hail. There is no evidence to show that the practise prevents hailstorms.