Today, we shape a snowflake. The University of
Houston's College of Engineering presents this
series about the machines that make our
civilization run, and the people whose ingenuity
created them.
A delirious profusion of
children's books on science appeared in the early
nineteenth century. We'd invented fast rotary
printing presses, and new kinds of cheap paper to
feed them. Now education raced ahead of
schools. Good schools were few and far between on
the American frontier, but you could buy a cheap
book.
And what books there were -- richly illustrated
with prints and engravings of nature's beauty. It's
not surprising that natural science books then, and
ever since, have gravitated toward one of nature's
beauties in particular -- the snowflake.
You and I know that snowflakes derive their beauty
from the crystal structure of ice. But we were
still debating the existence of molecules in the
nineteenth century. We wouldn't analyze crystal
structures with X-ray
diffraction until the twentieth century.
In 1872, John Tyndall showed rare insight in a book
on The Forms of Water. In it, he veered in
his own description of snowflakes to explain how
molecules must bond to one another. We didn't yet
know the structure of ice, but he knew structure
was there. And that structure determined the
exquisite beauty of snow.
By 1919, one typical book for a younger audience
says flatly that the crystal structure of snow is
"a peculiar arrangement of the molecules of
matter." That book included four pages of fine
snowflake photos -- a dazzling variety of forms.
Now a new book: Librecht's and Rasmussen's, The
Snowflake: Winter's Secret. Here, a physicist
and a photographer take us to the heart of
snowflake formation -- clear analysis combines with
stunning photos. The frontispiece of the book is
not one, but ten, pages of photos.
A snowflake is built on a crystal structure in the
form of a hexagonal prism. It has six-sided
symmetry, but only in one plane. Snowflakes grow,
as molecules are attracted to points and cusps --
not to flat edges. Thus, a kind of fractal growing
and splitting spreads outward to give snowflakes
their remarkable forms.
The book shows how we can grow our own designer
snowflakes. It also provides a map, showing
how snowflake structures change with temperature
and humidity. My Minnesota childhood reemerges as I
trace that map. When I was a kid, I paid attention
to the way weather affected my snowball-making. The
snow at subzero temperatures was particularly
delicate and lovely; but it would never cohere into
a decent snowball.
Here in warm Houston, Texas, those varying forms of
snow are all pretty academic. I breathe in the cool
autumnal air of our January, and think about the
Rubaiyat, where Omar Khayyam describes the
fleeting snows of Persia:
The Worldly Hope men set their Hearts upon
Turns Ashes -- or it prospers; and anon
Like Snow upon the Desert's dusty Face
Lighting a little Hour or two -- is gone.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.
(Theme music)
K. Librecht and P. Rasmussen, The Snowflake:
Winter's Secret Beauty. Stillwater, MN: Voyager
Press, 2003. Much information from the book is
included in the web site: http://www.snowcrystals.net
J. Tyndall, The Forms of Water in Clouds &
Rivers, Ice & Glaciers. New York: D.
Appleton and Company, 1877. (Originally published
in 1872.)
W. A. Bentley, The Treasures of the Snow.
Science, Invention, and Plant Life (four
editors) New York: The University Society, 1921.
pp. 84-86. (My thanks to Margaret Culbertson, UH
Art and Architecture Library, for this fine old
book.)
