"These were little plates of ice, very flat, very polished, very transparent, about the thickness of a sheet of rather thick paper...but so perfectly formed in hexagons, and of which the six sides were so straight, and the six angles so equal, that it is impossible for men to make anything so exact."

"I only had difficulty to imagine what could have formed and made so exactly symmetrical these six teeth around each grain in the midst of free air and during the agitation of a very strong wind, until I finally considered that this wind had easily been able to carry some of these grains to the bottom or to the top of some cloud, and hold them there, because they were rather small; and that there they were obliged to arrange themselves in such a way that each was surrounded by six others in the same plane, following the ordinary order of nature."  -- Descartes, 1635 [2]

   In 1665 Robert Hooke published a large volume entitled Micrographia, containing sketches of practically everything Hooke could view with the latest invention of the day, the microscope. Included in this volume are many snow crystal drawings, which for the first time revealed the complexity and intricate symmetry of snow crystal structure. (Note that an excellent, yet inexpensive, digital version of Micrographia can be purchased from Octavo.)

   Wilson Bentley (1865-1931) was an American farmer and snow crystal photomicrographer, who during his lifetime captured some 5000 snow crystal images.   More than 2000 were published in 1931 in his famous book, Snow Crystals, which remains in print to this day.  Some images from Bentley's collection can be seen at the W.A.Bentley web site.

   Ukichiro Nakaya was the first person to perform a true systematic study of snow crystals, which resulted in a giant leap in our understanding of how snow crystals form. Trained as a nuclear physicist, Nakaya was appointed to a professorship in Hokkaido, the North Island of Japan, in 1932, where there were no facilities for nuclear research.  Undaunted, Nakaya turned his attention to snow crystals, which were locally very abundant.  He then made a superb series of very detailed observations of all types of frozen precipitation, clearly identifying and cataloging all the major snow crystal types.  Unlike Bentley, Nakaya photographed the great variety of snow crystal types, not just those that were the most beautiful and symmetric.
   Nakaya's real triumph, however, came from growing artificial snow crystals in the laboratory under controlled conditions.  From the study of these artificial snow crystals Nakaya was able to describe the crystal morphology under different environmental conditions, which provides an extremely important clue for understanding the physics of snow crystal formation.
   The bulk of Nakaya's work was published in 1954 in a beautiful book entitled Snow Crystals: Natural and Artificial.  Though long out of print, Nakaya's book offers a superb look at a scientific investigation which begins with almost nothing, and proceeds through systematic observation toward an accurate description of a fascinating natural phenomenon.