HAIL (AS. hagol, Icel. hagl, ORG. hagal, Ger. Hugel, hail; probably connected with Gk. laix2vf, kachlex, pebble). Round, compact masses of ice that fall from the clouds to the earth, usually with rain. When these masses are as large as one-quarter of an inch in diameter or larger they are often spoken of as hailstones; when they are quite small and perhaps accompanied by rain they are known as sleet. Hailstones occur of all sizes from a quarter of an inch in diameter up to three inches in diameter; usually com paratively few hailstones fall at any one place, but cases are recorded in which the ground has been covered to a depth of several inches, and all vegetable life destroyed. The larger hail stones have a rather complex structure, being mostly composed of concentric layers of solid transparent ice and snowy-white or soft ice. In most cases the larger stones have a nucleus, which is either a foreign substance, such as a bit of gravel or a small pebble, or some larger object, such as those that are carried up from the earth by tornadic winds; or the centre is composed of a mass of snow, in whose interstices is held sonic gas, presumably air or oxygen, powerfully compressed within the central cavity. When this cavity is opened under water the inclosed gas is seen to expand, and, according to Jaentr, the gas seems to be held therein under a pressure of as much as fifty atmospheres.
The external surface of a hailstone is some times of beautiful regularity, as though it had grown by accretion of small particles during a slow and steady motion through the atmosphere, but this regularity is quite rare. More frequently the larger stones are irregular aggregations of masses of ice; of course, however-, such masses may have their shapes greatly altered when they strike the ground. The largest stones whose records are trustworthy have not exceeded two pounds in weight. Stones of two and three inches in diameter, weighing twelve and sixteen ounces, occur annually in Europe, India, and America. See the Monthly Weather Review for August, 1878.
A hail-storm is usually characterized by the formation of very high cumulus clouds, strong surface winds, considerable lightning and thun der, and heavy rain. It appears possible that hail may be formed either in the front of an advancing cool wave or in connection with a local thunder-storm or tornado. The former gives us the smaller hail and sleet; the latter gives us the larger and destructive hailstones. In the latter case it is quite common for the area of destructive hail to cover long, narrow strips of country as though it belonged on one side of the path of progression of some special cloud or vortex.
Protection against hail has been sought from time immemorial by different methods character ized by the gradual progress of our knowledge as to how hail is formed. In most ancient days the
church bells were rung and the saints invoked. The lightning-rod is called paragrele in France, but there is no evidence that it protects from hail. In recent years the belief and practice of the peasants of Styria. and Northern Italy has spread through Austria and Southern France to the effect that a special form of cannonading may, by bombarding the clouds, prevent hail, the theory being that if hail is formed by a process of crystallization in still air, then the cannonading by disturbing the stillness would prevent the hail. But all these ideas are delusions, and the bombardment has no appreciable effect upon the hail-storms. The most rational method of coun teracting the injury done by hail is by adopting a method of hail insurance by which the losses of a' few persons are distributed among many. The total amount of damage done by hail and light ning is summed up statistically in the annual reports of the Chief of the Weather Bureau and in the special reports in the Monthly Weather Review. In the United States in 1899 there were 563 persons killed and property valued at $4,000,000 ( 7) was destroyed.
The method of formation of hail is as yet but little understood. It seems to be demonstrated that when a rising mass of air cools to the dew point and below, it begins to form a cloud; as it continues to ascend, it cools to a temperature where hail is formed or rather hail and rain simultaneously. Higher than this it cools to a temperature where snow is formed. The ordinary hail may be formed in the second region, but the large hailstones of complex structure must have been carried up and down many times from the rain region to the snow region forward and backward until they become too large and heavy tc be held up any longer. In accordance with these ideas it is found that a very large propor tion of the destructive hail Occurs between ten A.m. and four P.M., and a very small proportion between 6 P.M. and 8 A.M. See Von Bezold, Thermodynamics of the Atmosphere (originally published at Berlin, 1888 and 1889; translated in full in Abbe, Mechanics of the Earth, Wash ington, 1891) ; Ferrel, Recent Advances in Me teorology (Washington, 1886).
In the Monthly Weather Review for Septem ber, 1900, is given a table showing the annual frequency of bail-storms for a unit area of one hundred miles square, as derived from the rec ords of each State in the Union. This table is as follows: In addition to the preceding, records made in the States of Connecticut, Rhode Island, Massa chusetts, Maryland, pelaware, and in the District of Columbia, may be summed up into one aver age—i.e. 3.0 per cent.