It is hard to think of a natural phenomenon that has more intrinsic delight and fascination than a snowflake. Sure, the things pile up and please skiers and dismay drivers, but taken one by one, each snowflake is not only pretty, it has enough complexity and mystery about it to delight any careful observer. In _The Snowflake: Winter's Secret Beauty_ (Voyageur Press), two careful observers have documented what intrigues them about snowflakes. Kenneth Libbrecht is head of the physics department of Caltech, and he not only rushes out with a magnifying glass when it snows, he grows snowflakes artificially in his lab. Patricia Rasmussen is a photographer who started taking pictures of snowflakes with her own equipment and then used Libbrecht's special apparatus. This is a book a little larger than a hundred pages, but the pictures are elegant, and the text tells the current explanations, as far as we now know them (there are still mysteries), of why snowflakes look the way they do.
The famous snowflake pictures of William Bentley inspired Rasmussen to start taking pictures of snow. Bentley's pictures are carefully reproduced white-on-black images, but Rasmussen has experimented with colored light to give multicolored pastels that shine on and through the hundreds of crystals depicted here. There are plenty of the six-armed variety, but also triangular snowflakes, and twelve, eighteen, or twenty-four armed ones, as well as tiny ice crystals shaped like needles, prisms, barrels, or bullets. can form at the right conditions. Different humidity and temperature produces the shapes. For the familiar snowflake, each arm experiences the same microclimate, so each changes in the same way. One arm of a flake thus does not "know" what the other arms are doing so it can turn itself out identically; they are all simply products of identical environmental history. As can be suspected, snowflakes that develop in the same regions have the same general design. But of course, everyone knows that no snowflakes are identical. Libbrecht considers whether this question is really true, and finds it cannot be answered without close considerations of "What is a snowflake?" and "What is identical?"
Snowflake science is here presented clearly and with good humor by someone who obviously loves his work. Libbrecht demonstrates that since a snowflake is a billion billion water molecules grabbed from the atmosphere, some of them are from your own exhalations. He does the calculations to show that about a thousand of the water molecules in every snowflake you see in this book (and of course, any other snowflake) come from you. "Thank you for your contribution," he says, "and keep up the good work." Jaunty and illuminating scientific descriptions, plus the most beautiful pictures of snowflakes ever made, make this a volume that can be valued for eye-catching brilliance or mind-engaging elucidation.