708 Marvels of the Universe 
again; and this upward and downward 
journeying process may have to be 
repeated several times before they are 
sufficiently heavy to enable them to 
break away from the grasp of the con- 
trolling power in which they are held. 
This is only a small part of Professor 
Wilson A. Bentley’s theory. It is well 
worth closer examination, inasmuch as 
he has devoted many years to the 
study of the phenomena of snow, 
by M. Quénisset. : . a 
Soe see ice and hail. The results he has 
Transverse sections of Hailstones, showing their ordinary internal arrived at are original, ingenious and 
structure, 
reliable. 
The central particles, or nuclei, consist of either tiny pyramid-shaped or star-shaped granular 
snow within the upper portions of very lofty clouds, which are violently expanding vertically. The 
ascending air-currents may develop into whirlwinds sufficiently rapid to enable them to carry 
upward with them all the raindrops and granular snow that come within their grasp. These are 
released or expelled from the grip of the powerful upward air-currents only at or near the summit 
of a spreading cloud. The smaller ones are blown out horizontally, and fall to the earth as ordinary- 
sized hailstones. The larger ones, caused by the melting and re-freezing, fall first and nearest to 
the central vortex, and as they fall earthward and become partly melted, they encounter strong 
horizontal indraught air-currents, and are drawn by them again into the ascending vortex and are 
again carried far upward and converted into ice and re-coated with granular snow, and eventually 
expelled again, as in the first instance, from the summit and spreading portions of the shower- 
clouds. This theory assumes that the summer hailstones begin as granular snow, and are partly 
melted by partial descent into warm air, and are congealed through ascent within the higher clouds. 
Powerful air-currents must blow upward through hail-producing clouds to sustain and buoy up the 
larger hailstones for the length of time necessary for them to “ grow’’ to so considerable a size. 
The rapidly rotating air-currents would account for the spiral markings displayed on many of the 
larger hailstones, and there is no known limit as to the number of times the hailstones may descend 
to lower strata of air and be forced upward again to colder regions. 
The hailstones shown below, which were picked up by M. Quénisset (to whom we are indebted 
for the illustration) on the lawn of the Observatoire Flammarion at Juvisy, seem to substan- 
tiate this theory, for they were made up of layers of ice alternately opaque and_ transparent, 
and were without a central core—a 
fact which points to their growth under 
different atmospheric conditions, such 
conditions being caused by variation 
in the air-currents. 
All this line of reasoning applies 
chiefly to the formation of summer 
hail. Unlike winter hail, summer hail 
occurs over very small areas and is 
purely a local phenomenon. In general, 
winter hail is the product of wide- 
spread general storms. The melted 
[By M. Queénisset. 
snow, that descends as liquid rain- 
Hailstones which fell at Juvisy in 1909, showing their composition i 
of different layers of ice. They are natural size. drops from the lower side of a warm 
