The Mysterious Weather Predicting Storm Glass

I first saw a storm glass at a friends house. When I inquired about it she explained that the storm glass can predict the weather, but I wondered “Do storm glasses work?”, if so “How does a storm glass work?”.  The storm

It is claimed to predict weather by measuring atmospheric pressure, but current research concludes that the storm glass is merely a weather-thermometer.  Although, I don’t exactly agree with the testing protocols used in these.

Regardless, the mystical weather predicting storm glass to find that it has quite a rich history and involvement with the Darwin Expedition.  First we’ll start with the basics, then go into history, and finally review scientific studies about the storm glass.

Storm Glass Basics

What is a storm glass? Well, it is a sealed glass tube with a mixture of the following components: potassium nitrate (NH4Cl), ammonium chloride (KNO3), water, ethanol (vodka), and most importantly natural camphor. These compounds form crystals based on environmental changes, such as temperature.

You can make one, but they’re pretty cheap to buy. Here is an Amazon affiliate link to my favorite storm glass

Storm Glass History

One of the storm glasses famous debuts was it’s mention in the novel Twenty Thousand Leagues Under the Sea by Jules Verne as he described the instruments hanging on Captain Nemo’s wall.

“the storm-glass, the contents of which, by decomposing, announce the approach of tempests” –  Twenty Leagues Under the Sea by Jules Verne

Although FitzRoy Admiral is often associated with the storm glass, he did not invent it. FitzRoy was responsible for the rise after the a huge storm hit the British Isles leading to the mass distribution of “FitzRoys Storm Barometers” by the Royal British Court.

Mysteriously, the inventor of the storm glass is still unknown!

Fitzroy Admiral claimed that in the early 1800’s some Italian guy, Malcredi, popped by the British Kingdom with some of these weather predicting glasses claiming the contents changed based on the weather, especially wind direction. Being a curious cat, FitzRoy had to have a couple and became the biggest storm glass fan girl.

During the Darwin Expedition, FitzRoy Admiral observed and researched the how the storm glass predicted weather and compared it with other barometers, such as the Galileo Thermometer. This research is still used today to correlate the crystallization appearances to storm glass weather predictions. In FitzRoy’s observations he extrapolated that not only air (wind) pressure, but wind direction also affected the type of crystal formation!

“When the main air-currents meet, and turn towards the west, making easterly winds, stars are more or less numerous, and the liquid dull, or less clear. When, and while they combine by the west, making westerly wind, the liquid is clear, and the crystallisation well defined, without loose stars.” – The weather book.

How Accurate are Storm Glasses at Predicting Weather?

There have been multiple studies on the storm glass determining correlation between crystal formation and temperature or precipitation. These studies found that the crystal formation was correlated to temperature changes, but not verifiably correlated to precipitation. The storm glass has been concluded to be most useful as a weather-thermometer.

I reviewed these studies closely using my scientific training background I felt that many of the testing protocols used were too rigid to make conclusive results.

One simple based their results on crystal formation means rain and no crystals means no rain, which is ridiculous since the air and clouds carry different amounts of moisture but don’t always rain on you.

Many just heated and cooled the storm glass to determine its relationship with temperature, providing zero means to correlate with weather prediction. They also wrote off the difference in crystal formation when heated in a water bath vs the an incubator, assuming these differences were due to the rapidness of thermal equilibrium. An assumption that should have been tested.

Also, I haven’t found any that explored the correlation with wind and wind direction. Therefore, I’ll do an experiment on my own and report back promptly.

How to Read a Storm Glass?

Crystal Formation Correlated with Weather Prediction of Storm Glass
Clear liquid – bright and clear
Cloudy liquid – cloudy, possible precipitation
Small dots – humid or foggy (expected
Cloudy liquid with small stars – thunderstorms
Clear Liquid with small stars – snow is coming
Large flakes throughout liquid – overcast in temperate seasons or snowy in the winter.
Crystals at the bottom – frost.
Threads near the top – windy.

Get your Admiral Fitzroy Storm Glass today!


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