[LLOYD] THE STRUCTURE OF HAILSTONES 49 
secondary set of arms disposed in a plane normal to a plane in which 
an original set of arms had been formed and melted away or broken 
off. In other instances an almost botryoidal form had been assumed 
(figures 3, 7), but no suggestions of growth by aggregation, (and such 
is known to occur) could in any case be seen. One instance (figure 
10) was difficult to understand, but most likely was a remainder 
after melting. 
The following explanation of the origin of the monoplanal radiate 
structure ‘as above described is offered. 
The hailstone is built up on an original spheroidal or top-shaped 
nucleus. 
As a result of rotation in one plane the chief mass is built on the 
equatorial zones. The rate of rotation is sufficient to allow the arms 
to be built up stalactite-fashion, but is not rapid enough to throw 
off the water. The water tends to collect also in the under face of the 
lens and, by freezing, forms mammillae. Alteration of the plane of 
rotation may occur more easily when the rate of rotation is slow, 
and a second set, or additional sets, of radiating arms may result. 
This explanation assumes the conditions such as alternate freezing 
and thawing, sustained flight, and the like, which need not be discussed 
here. 
The evidence seems conclusive that the arms are not derived 
from large projecting crystals, as Loomis (/.c.) has stated; nor is the 
botryoidal appearance due to the coalescence of originally separate 
hail. 
A severé.hail storm occurred also on the evening (at 7.30) of 
January 28, 1916. The hailstones were (a) single and top-shaped, 
due to the lower surface growing more rapidly than the upper.! The 
upper end is always loose and spongy in texture and roughly concave. 
Or (b) compound, due to the coalescence of separate top-shaped 
hail. It is worthy of note that in most instances the component 
members were frozen together side by side, to form a saucer-like 
mass, the axes “of the component hail converging above (figure 13). 
The writer would offer the following suggestion for the further 
study and recording of the form of hailstones, in view of their evanes- 
cent character and the suddenness and brevity of the opportunities. 
It should be quite easy to make moulds of hailstones by means of 
plasticine by pressing two blocks of suitable size against a hailstone 


1 Russell, R. Hail. London, 1893. 
