88 bullftik: museum of comparative zoology. 



Thomas Russell (1895, p. 98-100) gives a few statistics regarding- 

 the falls of hail as follows: — Hail falls during thunderstorms in 

 summer and during the hottest part of the day. It rarely forms 

 layers six inches thick. On Aug. 13, 1851, hail fell in New Hampshire 

 to the depth of 4 inches. On July 24, 1818, it fell on the Orkney 

 Islands to the depth of 16 inches, on August 17, 1830, in Mexico City, 

 to the depth of 16 inches. In the Yellowstone valley in ^Montana a 

 fall of 14 inches has been recorded . . . .Hail is more common at 15,000 

 feet than at sea-level, it forms at elevations from 5,000 to 16,000 feet; 

 the greatest size of hailstones is found below 5,000 feet. It falls most 

 frequently on the lee side of rising ground . . . .There are on the average 

 fifteen hail storms a year in France, five in Germany, and three in 

 Russia. 



In the Antarctic region hail uow falls but rarely. Commodore 

 Wilkes alone reports two instances. Fog there gives rise to some 

 crusts of ice. (Fricker, 1900, p. 244). 



Alfred R. Wallace (1892, p. 299) states that he had good authority 

 for hail having once fallen on the upper Amazon at a place only three 

 degrees south of the equator and about 200 feet above the level of the 

 sea. Humboldt (1852, 2, p. 217) instances a ease of hail faUing at 

 Paruruma in the Orinoco valley on a plain near sea-level. He states 

 that hail in the tropics generally falls only at an elevation of 300 

 toises (about 600 meters). 



The Shaler Memorial Expedition encountered in July, 1908, at an 

 altitude of 900 meters on the campos of Sao Paulo between Bury 

 and Faxina (p. 13), a hailstorm which covered the ground as thickly 

 with hail as do many similar storms in New York and New England. 



I cite these instances of hailstorms with their attendant circum- 

 stances because hail presents us now with a means of precipitating ice 

 at low altitudes in regions near the equator where snow never falls. 

 Hailfalls appear to increase toward the hot regions of the globe and 

 to diminish in frequency of occurrence towards the polar tracts. Thus 

 the probability of glaciers originating from hailfalls in .subtropical 

 regions would seem to be as great as from snowfalls, provided the 

 hailstorms came frequently enough to overcome the effect of melting 

 due to the higher temperature of those parts of the earth's surface. 

 Hailstorms like thunderstorms are secondary movements of at- 

 mospheric vapor normally engendered in the wake of cyclones of far 

 greater size and with a much longer path, and we do not at present 

 know what geographic conditions, if any, would cause in Permian 

 times a succession of hailstorms sweeping with the regularity of 



