How do weather globes work?

What’s the deal with a storm glass? Hammacher Schlemmer sells one and says, “Although how it functions remains a mystery, the ability of the stormglass to predict atmospheric change is well documented.” Does it work? If so, how? Or is it just a crappy lava lamp? —Dan

Hey, don’t knock lava lamps. For $179.95, a storm glass from Hammacher Schlemmer gets you a weather forecast of dubious accuracy. Whereas a 25-buck lava lamp, aided by the right combination of tunes and substances, will let you see God.

A storm glass, also called a weather glass or camphor glass, is a glass tube containing a mixture of ammonium chloride, potassium nitrate, camphor, water, and alcohol, making a normally clear liquid in which different types of white crystals periodically grow and dissolve. The idea is that the mixture is so finely balanced that minor fluctuations in atmospheric conditions will change the solubility of the chemicals and produce a wide variety of crystal shapes, from tiny floating flakes to large masses of feathery fans. Each supposedly predicts a certain type of weather.

The inventor of the storm glass is unknown, but descriptions date to the late 18th century. Early theories held that the chemical blend inside was sensitive to light, heat, wind, atmospheric pressure, or even electrical charge. In some glasses the contents were exposed to atmospheric pressure via a flexible rubber cap, but other models were hermetically sealed. (The sealed version is standard nowadays, mainly because a whiff of the contents can bowl you over.)

Interest in storm glasses crested in the 1860s, when such scientific notables as Michael Faraday, Robert Fitzroy, and Charles Tomlinson investigated their properties. Fitzroy, meteorologist and captain of HMS Beagle (of Charles Darwin fame), touted the glasses’ accuracy in his Weather Book of 1863. Tomlinson, on the other hand, tested a glass for several months and found it was sensitive only to heat, calling it a “rude thermoscope.” Japanese research from 2008 backs this up, pointing to temperature change as the sole cause of crystal growth.

I decided we should check this out. However, no way was I shelling out $179.95. No problem, said my assistants Una and Fierra. We’ll make some storm glasses of our own.

They researched storm glass recipes and ordered the appropriate chemicals and laboratory equipment. A hitch: initially no scientific supply house would ship the goods to a private residence, doubtless seeing in the ominous-sounding chemicals the ingredients of a terrorist plot. Una eventually convinced one supplier to send the chemicals after producing her engineering license.

Toiling late one night at Straight Dope Labs, Una and Fierra made six storm glasses. Each consisted of a big test tube filled with the precisely measured chemical mixture, then capped. At first the experiment looked like a bust—the storm glasses became opaque with massed crystals. But after a few days the initial crystal growth settled to the bottom of the tubes, leaving the liquid above clear. Thereafter new crystals would grow or diminish in response to ...well, that’s what we meant to find out.

Every day for 12 weeks, Una and Fierra recorded local weather conditions plus their observations of the crystals in each glass. Problems emerged. First, how do you read crystals? Previous researchers’ descriptions were vague, but this much seemed plain: clear liquid meant clear skies, while crystals or cloudiness meant precipitation, which we defined as rain. This gave us a couple simple tests: the storm glass was clear or it wasn’t; rain fell or it didn’t.

In the end, accuracy for individual glasses ranged from 45 to 54 percent, for an average of 49 percent. I’ve got a penny that can do as well as that.

Defenders of the storm glass may blame this on our simplistic scoring method. Suppose a storm glass develops crystals, indicating rain, and subsequently the weather is overcast and threatening—but no rain actually falls. Was the storm glass wrong?

To avoid such ambiguities, I had Una look strictly at days when it rained: did the storm glasses show crystals or not? Result: 53 percent accuracy, with a range of 38 to 62 percent.

Personally, I’m sticking with the lava lamp.

Proposed meteorological instrument

The storm glass or chemical weather glass was an instrument claimed to help predict weather. It consists of a special liquid placed inside a sealed transparent glass. The state of crystallization within the liquid was believed to be related to the weather. The inventor is unknown but the device became popular in the 1860s after being promoted by Royal Navy Admiral Robert FitzRoy who claimed that

if fixed, undisturbed, in free air, not exposed to radiation, fire, or sun, but in the ordinary light of a well-ventilated room or outer air, the chemical mixture in a so-called storm-glass varies in character with the direction of the wind, not its force, specially (though it may so vary in appearance only) from another cause, electrical tension.

The compositions of the liquid in a storm glass varies but usually contains "camphor, nitrate of potassium and sal-ammoniac, dissolved by alcohol, with water and some air." These devices are now known to have little value in weather prediction but continue to be a curiosity.[1]

Description

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The liquid within the glass is a mixture of several ingredients, most commonly distilled water, ethanol, potassium nitrate, ammonium chloride, and camphor. This specific mixture was promoted by Admiral Robert FitzRoy although similar devices existed even two decades earlier with variants in Italy, France and Germany.[2][3][4][5]

FitzRoy carefully documented his claims on how the storm glass would predict the weather:[2][failed verification]

• A catalogue of storm glasses c. 1863If the liquid in the glass is clear, the weather will be bright and clear.
• If the liquid is cloudy, the weather will be cloudy as well, perhaps with precipitation.
• If there are small dots in the liquid, humid or foggy weather can be expected.
• A cloudy glass with small stars indicates thunderstorms.
• If the liquid contains small stars on sunny winter days, then snow is coming.
• If there are large flakes throughout the liquid, it will be overcast in temperate seasons or snowy in the winter.
• If there are crystals at the bottom, this indicates frost.
• If there are threads near the top, it will be windy.

A version of the device was available in the 18th century in France and the inventor is unknown.[5] In 1859, violent storms struck the British Isles. In response, the British Crown distributed storm glasses, then known as "FitzRoy's storm barometers," to many small fishing communities around the British Isles for consultation by ships in port before setting sail.

Accuracy

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In 1863 Charles Tomlinson published an analysis in The Philosophical Magazine concluding that while attractive, "I think it may fairly be concluded from these experiments and observations that the storm-glass acts as a crude kind of thermoscope, inferior, for most of the purposes of observation, to the thermometer."[1] In 2008 an article in the Journal of Crystal Growth similarly concluded that temperature change is the sole cause of crystal growth in storm glasses.[6]

See also

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• Tempest Prognosticator – an alternative to the storm glass that the British government investigated

References

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