Mar. 04, 2015

Picture of the Week: A Single Snowflake

by Nathalia Holt

Click to enlarge images
Stars, bullet rosettes, dendrites, plates, needles, columns, and clusters—there’s scarcely a shape that a snowflake hasn’t formed. When they pack together into tall snowdrifts, it’s hard to imagine that each crystal is distinct, never to be seen again. But it’s true: No two snowflakes are alike, as the adage goes. The man who coined the phrase was Wilson Bentley, a Vermont farmer who found such splendor in the snow that he wanted to capture it for everyone. In his desire to document each flake, he pioneered a technique called photomicrography, which uses a camera to capture images viewed through a microscope.
Bentley’s obsession with snowflakes began in 1880, when he was 15, according to at least one account. His mother was a teacher and had a microscope, which he used to study snowflakes under its objective. The pleasure was fleeting—he could barely sketch their intricate designs before the crystals melted away. 
A few years later, Bentley decided to try photomicrography, a field still in its infancy. Bending the microscope’s body back from the base at a right angle enabled him to attach a camera bellows. He removed the eyepiece from the microscope and relied on the objective lens, swapping out different magnifications to see the snow crystal close up.
To isolate a single crystal, Bentley caught snowflakes as they fell from the sky on a black tray (which he kept clean with a turkey feather), then used a wooden splint to delicately transfer the crystal onto a glass slide. Once it was under the lens, he focused the image and quickly took a picture. This was a time before film, so he developed the images on plates, preserving the ethereal beauty in each crystal for generations. (For more on Bentley’s process, read his detailed account in Popular Mechanics Magazine.)
Bentley captured the first photomicrograph of these icy masterpieces in 1885. He published the picture of the snow crystals featured above, along with hundreds of others taken during the winter of 1901-1902, in an edition of Monthly Weather Review.
Photomicrography has changed a bit since Bentley’s day. “We don’t use glass photographic plates anymore, for one,” says Kenneth Libbrecht, a physics professor at Caltech. He uses photomicrography to investigate, among other phenomena, the complex patterns that snow crystals form. Libbrecht has designed and built his own photomicroscope, incorporating such modern touches as a digital camera and improved optical lenses. (Take a snowflake safari with Libbrecht in the video below.)
Physicists aren't alone in finding photomicrography useful. Indeed, biomedical researchers studying the body’s ability to repair itself are also refining the technique, using it to study how injury affects the brain and the spinal cord, for instance.
In December 1931, Bentley fell ill after trudging six miles though a snowstorm, desperate to capture its crystals, according to a friend’s reminiscence. He succumbed to pneumonia just before Christmas day, a victim of the winter air he loved. Fittingly, as some reports recount, during his funeral in Vermont, snow fell lightly on his grave. 


About Nathalia Holt

Nathalia Holt is a microbiologist and author of Cured: The People Who Defeated HIV and the forthcoming Rise of the Rocket Girls: The Women Who Propelled Us from Missiles to the Moon to Mars. Follow her @nathaliaholt

The views expressed are those of the author and are not necessarily those of Science Friday.
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