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Looks
Like Snow
For
many of us stuck in the midst of a frozen winter, snow has
become a four-letter word bordering on profanity. The white
stuff falls from the skies, accumulating on roofs, sidewalks,
car windshields and the cold earth. We shovel, sweep, brush,
scrape, blow and plow it. We often curse it, but occasionally
we revel in its beauty as it falls, spreading an insulating
quiet across the land.
Snow is made up of flakes with a remarkable diversity in crystalline
shapes. While the claim that no two snowflakes are the same
may be true, their vast numbers make it highly unlikely that
anyone would look to scientifically test this hypothesis.
In a typical 10-inch snowfall one can expect upwards of a
million snowflakes in a 2-square-foot area. While the breadth
of snowflake variation may be astounding, they also have some
equally amazing commonalities in structure. Perhaps by looking
a little deeper into the snowflake we can persevere a little
better through the remaining snows to fall.
Snowflakes have perplexed humans for some time. Over 2,000
years ago the Chinese scholar T’ang Chin used his knowledge
of alchemy to proclaim, “Since six is the true number of water,
when water congeals into flowers they must be six pointed.”
The six-pointed flowers he refers to are snowflakes. T’ang
Chin’s writings provide one of the earliest known references
to the hexagonal shape fundamental to the formation of snowflakes.
References to the six-pointed structure of snowflakes would
not appear in European texts until the 13th-century writings
of the Scandinavian Albertus Magnus. Some four centuries later
Western snowflake scholarship received a critical boost when
the German astronomer Johannes Kepler wrote an essay in 1610
entitled “On the six-cornered snowflake.” In this discourse
by the scientist best known for showing how planets revolve
around the sun, Kepler reasoned that snowflake shape resulted
from the way globules of water packed together. Later in the
17th century, the refinement of the microscope allowed English
inventor, physicist and mathematician Robert Hooke to make
detailed snowflake sketches. These drawings would confirm
the importance to snowflakes of the number six, put forth
by T’ang Chin on the other side of the planet nearly 2,000
years earlier.
It was not until the later half of the 18th century that European
science began to establish the connection between air temperature
and snowflake form. In 1762, a French snowflake freak by the
name of M. Guettard hypothesized that temperature was the
determining factor in flake shape. Guettard’s hypothesis would
remain untested until the 1930s, when a Japanese researcher
with the help of some rabbits finally put it to a test.
Ukichiro Nakaya, a researcher at Hokkaido University came
up with an interesting approach to determining the effects
of temperature on flake form. After setting up a room in which
he could control the temperature down to 22 degrees below
0 Farenheit, Nakaya used the tips of rabbit hairs to grow
artificial snowflakes. As he lowered the temperature, Nakaya
found that the crystals of ice that formed on his rabbit hairs
changed.
In the temperature range of 32 to 26.5 F Nakaya’s snowflakes
were flat and platelike with hexagonal shapes. As the temperature
dropped to between 26.5 and 23 F, the hexagonal crystals took
on a more needlelike shape. Dropping below 23 F down to minus
13 degrees, his flakes took on the shape of stars with six
points that displayed elaborate feathery branchings. From
minus 13 degrees down to minus 22 F, Nakaya’s snowflakes took
on the form of prism-shaped crystals. While he had shown temperature’s
role in snowflake shape, Nakaya also noted humidity as another
important factor. Later research would add wind and barometric
pressure to the list of influences.
Snowflakes got their big American debut as an art form in
1931 when Vermont farmer Wilson Bentley published his book
Snow Crystals. The book included about one third of
the 6,000 photos of flakes he’d taken since the 1880s, often
using nothing more than a box camera and simple microscope—coupled
with a wealth of patience. Bentley’s photos brought to the
public’s eye the variation, hexagonal structure and awesome
beauty of the snowflake. So how do these beauties take shape?
Snowflakes form on particles in the atmosphere. A distinct
hexagonal symmetry emerges in the process of flake formation
as water molecules interlock with four other water molecules
through their hydrogen bonds. As additional water molecules
are attracted to the forming flake they attach to the corners
of the hexagon and may lead to elaborate six-pointed star
formations, though mystery still surrounds some of these dynamics.
According to Kenneth Libbrecht, chair of Cal Tech’s physics
department and author of The Snowflake, Winter’s
Secret Beauty, a typical snowflake is made up of a billion
billion water molecules. Of these, about a thousand have come
from each of us through exhalation and evaporation.
As they form and fall to earth, snowflakes attract from the
atmosphere substances like potassium, sulphate, calcium and
nitrates that make snow an important fertilizer, enriching
soil as it melts. It also cleanses the air as it falls. Snow,
like rain, also picks up pollutants like sulphur dioxide,
resulting in acid snow, threatening the life of rivers and
lakes.
If you’d like to get a better look at snowflakes before the
winter’s gone, get a piece of dark material and attach it
to a piece of cardboard. Take this and a magnifying glass
outside and let them acclimate to the cold. Once everything
is chilled down you can catch snowflakes on your material
and check the little wonders out directly.
So as those flakes fall, check them out and remember just
how amazing these frozen bits of water can be.
—Tom
Nattell
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