Complex picture of snowflakes long emerging

JERICHO, Vt. - With thousands of astonishing photographs taken with primitive equipment, a humble and home-schooled Vermont farmer named Wilson A. Bentley provided the world with visible evidence that there is truth behind the cliché: No two snowflakes are alike.

By capturing his crystal masterpieces - starting in 1885 - Bentley, without realizing it, also was cataloging a molecular enigma that continues to vex meteorologists and highway departments, plow contractors and the people who pay them.

Just as no two snowflakes are alike, nor are any two snowfalls. The flakes vary in shape, in liquid content, and in how they pile up, something we keep learning anew - much more often than we've cared to the last two winters. All that helps explain why those accumulation forecasts often come in ranges big enough to drive a plow truck through.

Some of Bentley's stunning work is on display here, inside a muted-red mill building, picturesque even by Vermont standards, along with his ingenious apparatus, consisting of a bellows camera, blackboard tray, and microscope. From his first successful picture until his death at 66 in 1931, he took 5,000 snowflake photographs.

"Bentley did it up right," said Kenneth Libbrecht, an astrophysicist and ice-crystal expert at the California Institute of Technology who has become a modern-day Bentley. "What Bentley did was really introduce the world to the world of snowflakes."

Bentley's photos, published in a book in 1931, affirmed for the world that flakes come in endless varieties.

Meteorologists say that computer models are getting better at estimating the liquid content of storms, but that that has limited value. The old rule of thumb was that an inch of precipitation yielded 10 inches of snow. But recent research has shown that snow-liquid ratios can vary widely. An inch of liquid might mean 20 inches of snow - or five. Accumulation also is a function of the types of flakes that fall, and that's far harder to nail.

The size, shape, and type are determined during a crystal's long descent to the ground through chaotic layers of air of different temperatures, humidities, and wind speeds.

In the last decade, said Jeff Waldstreicher, director of the National Weather Service's Scientific Services Office, scientists have reached a deeper understanding of the importance of the snow-crystal types.

Crystal categories can range from seven to 80, depending on the classification system, Libbrecht said. ("I liken it to classifying bread," he said.)

It is known, however, that the best accumulators are dendrites, those classic hexagons so often replicated in holiday decorations - and favorite subjects of Bentley's. They tend to form during storms when temperatures in the high atmosphere are around zero Fahrenheit.

The heavy accumulation that fell in a compressed period the night of Jan. 26 was due in part to a harvest of dendrites that blossomed at the height of the storm.

Unlike other types, such as columns, needles, and plain hexagonal plates, they stack efficiently because they have space - that is, "air" - between their branches, Waldstreicher said.

For meteorologists, chasing the dendrite has become something of a hot pursuit. "Forecasters are very attuned to the conditions supporting dendritic snow crystals," said Dave Novak, a scientist at the government's Hydrometeorological Prediction Center.

Libbrecht doesn't know or particularly care where his flake research will lead, if anywhere, and is willing to let serendipity take its course.

Likewise, Bentley had no idea that he was documenting a scientific riddle that 21st-century computers would try to resolve.

As is Libbrecht, Bentley was fascinated by the flakes themselves. His family was poor, but he persuaded his parents to buy him a microscope and a bellows camera. He caught his flakes on a black tray, and, working in an unheated room attached to the farmhouse, he placed them on a microscope slide. Standing at the back of the camera, he adjusted the magnification with a cord attached to the focusing screw. Thus he was able to take pictures of flakes magnified several hundred times.

What Bentley found was a "far greater elegance of form than the simple outlines exhibit," he wrote. He correctly surmised that the flake was imprinted with the buffeting of winds and thermal changes encountered on its earthward journey: "Was ever life history written in more dainty hieroglyphics!"

He gave presentations in his village, which were sparsely attended. "I guess they've always believed I was crazy, or a fool, or both," he said of his neighbors. But eventually his articles were published in national magazines, and his reputation spread.

On April 1, 1926, he appeared at the Franklin Institute to read from his paper on the "Marvels of Snowflakes and Water Forms."

Through it all, Bentley said, the flakes never disappointed him. "Every crystal," he wrote, "was a masterpiece of design."