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What’s Really Happening When You "Smell" Snow

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Does snow have a scent? The logical side of your brain may say no: Snow is just frozen water, and therefore odorless. But if you’ve ever predicted a big snowstorm based on a familiar tickle in your nose, you know the answer isn’t so straightforward. So what exactly is happening when you “smell” a meteorological event? The answer has less to do with specific odor molecules as it does with the climate in which you smell them.

For an episode of the podcast Physics Central, olfactory scientist Pamela Dalton laid out the perfect storm of physical conditions you interpret as the smell of snow. When temperatures approach freezing right before it snows, it’s actually harder to detect scents in the air than it is during milder weather. Cold weather slows down molecules in the air, and with less molecular activity, certain smells become less pungent. That means “smelling snow” is, in part, just smelling fewer odors outdoors than what you’re used to.

But if there was nothing else to it, a snowstorm would smell no different than a cold, dry day. The factor that determines the difference is humidity. Right before a snowstorm, the air is more humid than usual. This is what causes the flakes to fall: When the atmosphere hits the maximum amount of moisture it can hold, it reacts by dumping some of the moisture—whether in the form of rain, sleet, or in this case, snow—back onto the ground. That humidity has the added effect of giving your olfactory system a quick boost. To many people, the sensation of being able to smell with a warm, moist nose in freezing weather is linked with the promise of snow.

As all of that’s happening to the world around you, there are mechanisms at work inside your body that also help to explain the unmistakable scent of snow. You sense the cold air you breath with your trigeminal nerve, the same nerve that interprets sensations caused by tingly hot peppers or cool mint toothpaste (it also interprets other facial sensations and is why you might sneeze in sunlight). This is separate from your olfactory system, but you still lump the information it gives you with conventional scents like coffee or pine.

These elements—cold weather, humidity, and a stimulated trigeminal nerve—combine to create something that isn’t an odor, but a sensory experience you’ve come to associate with snow. That’s why when asked to describe the scent, people often use words like “clean,” “fresh,” and “cold"— a.k.a. things that don’t have much of a scent at all.

[h/t Physics Central]

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What Pop Culture Gets Wrong About Dissociative Identity Disorder
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From the characters in Fight Club to Dr. Jekyll and Mr. Hyde, popular culture is filled with "split" personalities. These dramatic figures might be entertaining, but they're rarely (if ever) scientifically accurate, SciShow Psych's Hank Green explains in the channel's latest video. Most representations contribute to a collective misunderstanding of dissociative identity disorder, or DID, which was once known as multiple personality disorder.

Experts often disagree about DID's diagnostic criteria, what causes it, and in some cases, whether it exists at all. Many, however, agree that people with DID don't have multiple figures living inside their heads, all clamoring to take over their body at a moment's notice. Those with DID do have fragmented personalities, which can cause lapses of memory, psychological distress, and impaired daily function, among other side effects.

Learn more about DID (and what the media gets wrong about mental illness) by watching the video below.

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Scientists Reveal Long-Hidden Text in Alexander Hamilton Letter
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Age, deterioration, and water damage are just a few of the reasons historians can be short on information that was once readily available on paper. Sometimes, it’s simply a case of missing pages. Other times, researchers can see “lost” text right under their noses.

One example: a letter written by Alexander Hamilton to his future wife, Elizabeth Schuyler, on September 6, 1780. On the surface, it looked very much like a rant about a Revolutionary War skirmish in Camden, South Carolina. But Hamilton scholars were excited by the 14 lines of writing in the first paragraph that had been crossed out. If they could be read, they might reveal some new dimension to one of the better-known Founding Fathers.

Using the practice of multispectral imaging—sometimes called hyperspectral imaging—conservationists at the Library of Congress were recently able to shine a new light on what someone had attempted to scrub out. In multispectral imaging, different wavelengths of light are “bounced” off the paper to reveal (or hide) different ink pigments. By examining a document through these different wavelengths, investigators can tune in to faded or obscured handwriting and make it visible to the naked eye.

A hyperspectral image of Alexander Hamilton's handwriting
Hyperspectral imaging of Hamilton's handwriting, from being obscured (top) to isolated and revealed (bottom).
Library of Congress

The text revealed a more emotional and romantic side to Hamilton, who had used the lines to woo Elizabeth. Technicians uncovered most of what he had written, with words in brackets still obscured and inferred:

Do you know my sensations when I see the
sweet characters from your hand? Yes you do,
by comparing [them] with your [own]
for my Betsey [loves] me and is [acquainted]
with all the joys of fondness. [Would] you
[exchange] them my dear for any other worthy
blessings? Is there any thing you would put
in competition[,] with one glowing [kiss] of
[unreadable], anticipate the delights we [unreadable]
in the unrestrained intercourses of wedded love,
and bet your heart joins mine in [fervent]
[wishes] to heaven that [all obstacles] and [interruptions]
May [be] speedily [removed].

Hamilton and Elizabeth Schuyler married on December 14, 1780. So why did Hamilton try and hide such romantic words during or after their courtship? He probably didn’t. Historians believe that his son, John Church Hamilton, crossed them out before publishing the letter as a part of a book of his father’s correspondence. He may have considered the passage a little too sexy for mass consumption.

[h/t Library of Congress]

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