Winterlust. Bernd Brunner

sound in their hollows. And while it’s snowing, the world becomes even more hushed, because snowfall thickens the air and forms a barrier that diminishes the distance sound waves travel. Once snow compacts it reflects sound much better.

      Direct physical engagement with snow, the tactile experience of icy cold, with its incomparable combination of crunchiness and softness, is an elementary matter. But people respond to it differently. It makes some people happy. In Languedoc in southern France, a region not exactly known for heavy snowfall, people call the flakes “white flies” or “white butterflies.” Others see falling snow as a winding sheet draping itself over every living thing in nature. In his poem “Winter,” from 1820, John Clare described the season as spreading “his hoary shroud” over the path the weary traveler must follow. James Joyce, in his 1914 short story “The Dead,” perfectly captured the pall snow can cast over the landscape: “Yes, the newspapers were right: snow was general all over Ireland. It was falling on every part of the dark central plain, on the treeless hills, falling softly upon the Bog of Allen and, farther westward, softly falling into the dark mutinous Shannon waves.”

      In contrast to a bucketful of water, a bucketful of freshly fallen snow is up to 95 percent air. Consequently, jumping off a three-hundred-foot (100-meter) cliff into a slope covered in freshly fallen snow doesn’t necessarily end fatally, as it would if you were to jump into water from that height. As soon as the proportion of the snowpack’s air sinks by half, down to 45 percent, it’s called firn snow. If it compresses further, it becomes ice. When it’s very cold, the compressed snow becomes brittle and breaks under pressure, to the accompaniment of surprisingly loud crunching noises—acoustic waves created when a large number of crystals in the snow cover fracture. When it’s warmer, the ice crystals initially warp under pressure, not breaking as easily, and the resulting sound is more of a creak than a crunch.

      In the mountains, snow cover can vary substantially within the space of a few yards, and even the shape of the surface plays a role. The stability of snow cover is unpredictable: in one place, you might sink in deep and have difficulty digging yourself out; in another, the snow might support you safely. If you observe certain areas year after year, you become familiar with the particular spots and corners where snowdrifts accumulate.

      Snowfall figures are standard elements of winter weather reports, creating the impression that measuring snowfall is easy. It’s not. For a long time, people made do with a table of a known size placed in a location sheltered from the wind. After a snowfall, the snow that accumulated on top was packed into a zinc jug and weighed. Since snow doesn’t simply fall from the sky, but is also blown around by the wind, it never falls evenly. It’s only possible to gather reliable information if many measurements are taken from different locations in the same area. Over the decades, a number of methods have been devised to obtain more meaningful data. Only a few have caught on, however, one of them being ultrasound sensors that calculate snowfall by measuring echoes in the snow.

      In winter, the air is cleaner, because the water droplets that form ice crystals bind with dust particles—or pollen, mushroom spores, or bacteria—before they freeze. You could say that every snowflake carries within it the secret of its genesis. Some people claim snowflakes trap the aroma of certain plants: depending on the direction of the wind, a trace of pine resin, damp bark, or wood smoke might emerge from the snow. Or the air might smell unusually fresh—a touch of electricity, perhaps, caused by the higher degree of ionization of the air when it snows. Is there a hint of ozone? In sunlight, nitrogen ions in snow react to form nitrogen oxide, which is the precursor to atmospheric ozone; sulfur compounds have also been detected.

      For other people, the smell of snow is associated with a certain color: blue, for example—a case of synesthesia, when a sensation stimulates another sensory reaction in a different part of the body. People who experience snow as “crunchy” or “sticky” when they eat it sometimes sense a metallic taste in their mouths. Snow on the tongue can also simply accentuate bacteria or lingering remnants of food. In the presence of certain snow algae, snow can take on a reddish hue, causing people to speak of “blood snow” or “watermelon snow.” In times past—in the mountainous regions of France, for example—red snow was thought to be a bad omen or a sign that a heavy snowfall was imminent.

      It requires a certain amount of experience to recognize animal tracks in the snow—and maybe a touch of imagination to spin them into a story. You might trace the chaotically meandering tracks of foxes along the hawthorn hedge, marking scent as they go. If the edges of the paw marks are indistinct, they must be a few days old. A trail straight as an arrow leads across a field. A rabbit chased by a fox, zigzagging as it tries to escape—to no avail. Here tufts of tawny fur surround a patch of snow stained red. A crow is already at the scene. Over there, a golden eagle pressed a snow grouse into the soft whiteness of a heather-covered slope before it flew away with its catch. Aside from such details, the glittering landscape seems mostly peaceful.

      “How full of creative genius is the air in which these are generated! I should hardly admire more if real stars fell and lodged on my coat.” Henry David Thoreau, firmly rooted in his beloved landscape in Massachusetts, was known for walking outside every day no matter what the weather. When he followed the tracks of foxes that gamboled through the fields, he was, as he recorded on January 30, 1841, treading “with such a tiptoe of expectation, as if I were on the trail of the Spirit itself which resides in these woods.”

      In his 1843 essay “A Winter Walk,” Thoreau conjured up images of a field mouse sleeping in a cozy tunnel under the turf, an owl sitting in a hollow tree, and rabbits, squirrels, and foxes settled into their respective shelters. “In winter,” he wrote, “nature is a cabinet of curiosities, full of dried specimens, in their natural order and position.” From dawn until dusk, he observed nature near his house. “The recent tracks of the fox or otter, in the yard, remind us that each hour of the night is crowded with events, and the primeval nature is still working and making tracks in the snow.”

      When he made his observations, Thoreau focused on his immediate sensations: “We hear the sound of wood-chopping at the farmers’ doors, far over the frozen earth, the baying of the house-dog, and the distant clarion of the cock, though the thin and frosty air conveys only the finer particles of sound to our ears, with short and sweet vibrations, as the waves subside soonest on the purest and lightest liquids, in which gross substances sink to the bottom. They come clear and bell-like, and from a greater distance on the horizon, as if there were fewer impediments than in summer to make them faint and ragged.”

      Thoreau cherished the idea that there was a dormant, subterranean fire in nature that never went out and could not be damped down, not even by the extreme cold—and it would be precisely this fire that would melt the great snow in the end. He established a connection between his special form of romanticism and the science of his time. Headstrong, groundbreaking, he has yet to be surpassed as a topographer of nature’s sights, sounds, smells, and other subtler signals.

      The crystals in snow are intrinsically pellucid. To us, they appear white because they absorb and then emit all colors of sunlight to approximately the same degree—a mechanism that also applies to the guard hairs of polar bears. Freshly fallen snow seems whitest in sunlight because the reflective surface is especially large, strewn as it is with myriad small crystals. And when the sun is shining brightly, it is advisable to wear sunglasses to prevent snow blindness. Indigenous Arctic peoples devised a way to shield the surface of the cornea from intense shortwave ultraviolet radiation: a narrow oval of bone or wood strapped onto the head and skillfully furnished with an eye slit and ornamentation to protect the wearer from potentially irreparable visual impairment. The earliest known examples, found in the western coastal region of Alaska, are two thousand years old—the world’s first sunglasses, if you will.

      Although freshly fallen snow appears white, a hole deep in the snow shimmers a beautiful blue, because the snow crystals below are compressed and absorb the red and yellow portions of sunlight more strongly than they do the blue. In 1953, anthropologist Gilbert Durand described snow as a substance that “cannot simply be classified as and reduced to frozen ice.” Snow, he wrote, defies complete categorization because every experience with it is slightly different. He thought of November as snow’s spring and January as its summer, and he was of the opinion that night never