THE SCIENCE OF A SNOW-FLAKE. 
53 
crystal which we have been considering. In the Popular 
Science Revieiv, vol. v. pp. 52, 53, the revelation of the struc- 
ture of ice, by Professor Tyndall, has been very satisfactorily 
told.* The beauty latent in a block of ice has been prettily 
described by its discoverer as stars, each one possessing six 
rays, each one resembling a flower of six petals ; then the petals 
become serrated and spread themselves out like fern-leaves.” 
Such is the science of the snow-flakes, which make winter 
drear, and which do not usually give evidence of those forms of 
beauty that belong to it ; simply, because those geometric figures 
have during the driving onward of the cloud which 
Lifts the snow on the moimtains below, 
been hurried into irregular flaky masses. 
Professor Leslie supposed that a flake of snow, taken as nine 
times more expanded than water, descends thrice as slow ; hence 
the tendency of snow to be driven onward, and to accumulate 
into those drifts which so entirely block up roads, and gather 
into great and dangerous masses under the shelter of any 
obstructing object, often burying both man and beast. Some- 
times, when a strong wind blows over the surface of snow, 
portions of it are raised by its power, and passing onward 
gathers other portions, which by attrition assume globular 
forms. In a severe snow-storm in 1814 Mr. Howard saw 
several thousands of these natural snow-balls formed, and 
in my own garden I observed their formation on Sunday, 
December 8. Mr. Sherriff records an instance of balls being- 
found by him, in 1830, in East Lothian, varying from a foot to 
eighteen inches in diameter, which left hollow tracks in the 
snow. These are striking examples of the peculiar adhesive 
character of snow, which results from its needle-like crystalline 
structure. Every boy knows how hard he can make his snow- 
ball by squeezing it ; and if the pressure is applied with sufficient 
force, a ball of ice will result. In this case, however, something- 
more than the mere adhesion of the snow particles takes place. 
Some of the snow is, by the development of a small increment 
of heat, liquified ; this immediately freezes, and thus jnites the 
mass. This process is known as regelation. When a consider- 
able thickness of snow falls upon the surface of the earth, the 
lower portion consolidates by the combined influences described ; 
and if this takes place upon a mountain, the consolidated portion 
is pressed downwards and onwards, forming 
The glacier’s cold and restless mass, 
which 
Moves onward day hy day. 
* Glaciers and Ice, hy W. F. Barrett. Bead also Heat Considered, as a 
Mode of Motion, hy John Tyndall, F.R.S., pp. 108-111. 
