Hokkaido, 1936

Nakaya

Letters sent from the sky

Six letters, each about a crystal someone saw fall. Read the weather in them, then grow the crystal to send back.

Coming soon to the App Store Read the story

For iPhone, iOS 17 or later. Free to begin.

The chamber, at −12 °C and 109 % of cloud Growing on this page, cell by cell, by the app's own model.

The room

A chamber that grows snow

  1. A night sky over a snowfield, the lights of a small laboratory on the horizon

    There is a room in Hokkaido where it is always winter, and a chamber that grows snow.

  2. The chamber's round glass window, frosted from inside

    It was built to answer one question: why is no snowflake ever the same twice?

  3. An open notebook and a magnifier under an oil lamp

    In 1936 the physicist Ukichiro Nakaya grew the first snow crystal ever made in a laboratory, on a single rabbit hair.

  4. Snow crystals resting on a dark wool sleeve

    Every crystal is shaped by the air it falls through. He called them letters sent from the sky.

  5. A bundle of old letters by lamplight

    People still write to this room. Six letters are unanswered.

    From tonight, the chamber is yours.

The correspondence

Six letters, six crystals

Each writer saw something fall. None knows the temperature or the humidity, only what they noticed. Work out the air, grow the crystal, and they write back.

The keeper's desk from above: six sealed envelopes, a brass microscope, an open notebook and a specimen box

  1. Letter one Free

    Aya, aged eight, Asahikawa

    My snowflake has six flat sides and my uncle says it is wrong.

  2. Letter two Free

    Mara, ski patrol, north ridge hut

    Crystals on my sleeve at the storm's edge: stars, but solid.

  3. Letter three

    Old Ishii, keeper of the pass tea house

    A guest left a sketch in my ledger and no name to thank.

  4. Letter four

    Dr. Okabe, meteorologist, the col station

    One crystal in the log I cannot bring myself to name.

  5. Letter five

    Captain Holt, of the strait ferry

    The squall buried my deck in feathers before we made the far shore.

  6. Letter six

    Dr. Enda Sol, glaciologist, the high plateau camp

    The plainest crystals I have ever seen, and the hardest earned.

Two letters free. One purchase opens the rest and the ending.

Two dials, one map

The air decides the shape

Two dials, temperature and vapour: the axes of Nakaya’s diagram. Choose a region to see what grows there.

−12 °C · 109 % of cloud

Stellar Dendrite

Branching into the air

Near −15 °C the sky has the most vapour to spare, and the arms run away with it.

The dashed cloud line is the wettest air an ordinary cloud holds. It peaks near −12 °C, where the most branched crystals grow.

A simplified map

The model grows flat crystals only, so the columns and needles real clouds make between −3 and −10 °C are missing. Its settings are fitted by hand, and the vapour scale is a display choice, not a measurement.

Real crystals, not drawings

Grown, never drawn

Every crystal is grown cell by cell on your phone by the Gravner–Griffeath model, a published simulation of snow growth. Same air, same form, never quite the same crystal.

The crystal at the top of this page is the same model, running in your browser.

The museum

Nine forms, and the gaps between them

Keep what you grow. The shelf shows every form the chamber can make, including the ones you have not found yet.

Made with care

Quiet by design

A snowflake is not a decoration. It is a measurement.

No instrument was up in that cloud. The crystal was.

Coming soon to the App Store