The first snow of the season fell on the day I visited Wilson Bentley's photography collection. It was just a dusting, the flakes so tiny and sparse I could barely distinguish them against the white marble of the buildings on the Mall and the soft gray of the sky. I tried to catch some on my jacket sleeve, holding my arm close to my face to examine the delicate crystal structures, but had little success. The flakes were fleeting, turning to vapor not long after they landed.
But Bentley's photographs, which are stored in a locked, climate-controlled room at the Smithsonian Institution Archives, are as breathtaking as the day he took them more than a century ago. Each glass plate contains a single, perfect snowflake that was caught outdoors in subzero weather, magnified under a microscope, photographed and traced by hand to reveal every detail of its filigreed form.
“They’re just fascinating,” said Pam Henson, director of the Smithsonian's institutional history division. “We all see snow all the time. But we don’t really see snowflakes.”
Bentley saw snowflakes, in all their complexity and diversity. He is considered a pioneer in the field of photomicrography (taking images of objects under a microscope) and helped spark scientific interest in understanding the crystal structure of snow. His photographs gave way to research on the atomic structure of water, the intricacies of weather and the conditions that affect how crystals grow. He is credited with discovering that, at least in nature, no two snowflakes are exactly alike.
Born in 1865 in the village of Jericho, Vt., Bentley was raised to be a dairy farmer like his father. Except for a year or so at the local schoolhouse, he was educated almost entirely by his mother, a former schoolteacher. It was she who gave him his first microscope when he was 15.
The teenager used his new instrument to examine every small thing he could find — pebbles, raindrops, bits of feather, flower petals. But snow beguiled him most of all.
“Under the microscope, I found that snowflakes were miracles of beauty; and it seemed a shame that this beauty should not be seen and appreciated by others,” Bentley would later tell an interviewer. “Every crystal was a masterpiece of design and no one design was ever repeated. When a snowflake melted, that design was forever lost. . . . I became possessed with a great desire to show people something of this wonderful loveliness, an ambition to become, in some measure, its preserver.”
At the time, cameras capable of photographing microscopic objects were just being developed, and none were available to a boy in rural Vermont. If Bentley wanted a tool for taking photos through a microscope, he would need to invent it.
It took two years of trial and error to develop a method that worked, which Bentley explained in a 1922 article in the magazine Popular Mechanics.
First, he removed the eyepiece from his microscope and connected it to a long bellows camera, then placed a black card over the lens of the instrument in lieu of a camera shutter. The apparatus was set up in an unheated room, to delay the moment when flakes sublimate (change from solid to vapor).
Using a blackboard with wire handles, Bentley would catch several snowflakes, which he examined with a handheld magnifying glass. The best flakes were lifted with a feather onto a glass slide, and placed beneath the microscope's objective. He lifted the card acting as his shutter and began counting off the desired length of exposure — anywhere between 8 and 100 seconds. To give his images their distinctive black background, Wilson then scraped some of the light-sensitive pigments off the negative, hewing to the outline of the crystal.
“The day that I developed the first negative made by this method, and found it good, I felt almost like falling to my knees beside that apparatus,” he told the American Magazine in 1925. “It was the greatest moment of my life.”
Over the following decades, Bentley amassed a collection of some 5,000 snowflake photographs and published several dozen journal articles on snow, ice and weather, earning a reputation as a formidable citizen scientist. Admirers began to call him “the Snowflake Man.” The classification system he developed for flakes, which included flowerlike plates, star-shaped stellar dendrites, capped columns, needles and more, is still used today (although it has since been expanded to more than 120 categories).
By 1904, Bentley decided his growing collection ought to be stored somewhere safer than his wooden farmhouse. So he wrote to the Smithsonian asking if the institution wanted 500 of his “best examples.”
According to Henson, the curator of the geology department at the Natural History Museum (then called the U.S. National Museum) was unimpressed by Bentley's offering.
“In the 1880s, you see the professionalization of science,” she said. Scientists weren't just people who loved, observed and attempted to understand the world — they were people with advanced degrees and research positions at prestigious institutions. Bentley had never gone to college, and despite his devotion to photomicrography, he still earned his living as a dairy farmer.
“To someone like the curator, George Merrill,” Henson said, “Bentley would have seemed to be an amateur who didn't know much.”
Luckily, Samuel Pierpont Langley, the secretary of the Smithsonian, had an interest in atmospheric science. He told Bentley that he would pay to have the images copied and stored at the archives. “I am deeply grateful for your kindly help,” Bentley said in reply.
Though Merrill underestimated the scientific value of the photographs, Bentley sensed that they revealed something important. In 1902, he described in the Monthly Weather Review his hunch that the crystal structures of snowflakes reflect the conditions under which they formed: “These interior details reveal more or less completely the preexisting forms that the crystals assumed during their youth in cloudland,” he wrote. “Was ever life history written in more dainty or fairy-like hieroglyphics? How charming the task of trying to decipher them.”
He was onto something. In the 1930s, Japanese physicist Ukichiro Nakaya began growing the first synthetic snow crystals in his lab. Nakaya's experiments confirmed what Bentley had speculated: The shape of a snowflake is controlled by the temperature and humidity of the air in which it crystallized.
What's more, snowflakes' symmetric shapes hint at the behavior of the water molecules they're made of. They come in hexagonal plates and six-pointed stars because water molecules form tetrahedrons, which always stack up into six-sided structures. This phenomenon still fascinates physicists.
“How molecules behave collectively . . . that's something that we're still trying to get a handle on,” said Kenneth Libbrecht, whom some call “the modern-day Bentley.”
Libbrecht, who is chairman of the physics department at Cal Tech, began studying snowflakes in an effort to understand how molecules organize themselves into complex crystal structures — a major mystery in material science. Working with ice was a strategic decision, he said, “because there are very few things you can just throw down the drain these days, but water is one of them.”
But, like Bentley, Libbrecht soon became captivated by the sheer loveliness of the flakes he analyzed. In a growing chamber that he built, he has created and photographed countless “designer snowflakes.”
University of Alaska at Fairbanks geophysicist Matthew Sturm, a friend of Libbrecht's and a fellow snow researcher, noted that snowflakes have a long legacy of helping scientists understand the world at the tiniest level. That legacy extends from Libbrecht's lab to Nakaya to Bentley all the way back to the German astronomer Johannes Kepler.
In 1610, while caught in a snowstorm in Prague, Kepler became the first person to muse that snowflakes' hexagonal form must be a result of the stacking of frozen “globules” that were “the smallest natural unit of a liquid like water.”
Today, we would call those “globules” molecules.
“Snowflakes really led the way into people beginning to feel that there must be these elemental things, molecules and atoms, but the only time they really manifest themselves is when we see a really beautiful crystal in solid,” Sturm said. “Snowflakes opened that molecular world at a macroscopic level.”
While we talked, Sturm — who had called me from a cabin in New Mexico — noted that flakes were starting to fall outside his window. Delighted, I told him it was snowing here in Washington, too.
“You know,” he said, “if we made these snowflakes out of cut crystal they'd be worth a fortune. But they just fall out of the sky. Nature gives us millions and millions of them.”
It sounded like something Bentley would say. The “Snowflake Man” never tried to make money from his photographs, though he spent thousands of dollars producing them. It was only at the urging of his friend William J. Humphreys, chief physicist for the United States Weather Bureau, that he eventually compiled 2,500 of his best images in a book.
“Snow Crystals” published in November 1931, but Bentley didn't get to enjoy much of the acclaim. A month later, he died of pneumonia.
He had gotten sick walking in a snowstorm.
Tales From the Vault: Science museums are home to vast research collections, most of which the public never gets to see — until now. Once a month, Speaking of Science will go behind the scenes at our favorite museums to introduce readers to the fascinating objects and people we find there. Read past installments here.