What Is a Storm Glass and Can It Accurately Predict the Weather?

Throughout history, scientists have been inventing devices to help predict the weather. Some of the best-known names in history have dabbled in the science of weather forecasting — Leonardo da Vinci invented an early anemometer and hygrometer, for example, and Galileo created an accurate and beautiful thermometer. Storm glasses are among those early inventions that still hold a fascination for modern weather watchers. What is a storm glass, and what makes it work? Perhaps most importantly, does a storm glass accurately predict the weather? Here’s what we know.

What Is a Storm Glass?

There are two very different historical meteorological devices that share the name “storm glass” or “weather glass.” Both became popular at about the same time — the late 1700s — and both were widely used to predict changes in weather using liquid in a glass container. But that’s where the similarities end. Here’s a quick look at both devices and how they work.

The Fitzroy Storm Glass

While no one is sure exactly who invented the Fitzroy storm glass, it was popularized by Admiral Robert Fitzroy. He famously captained the HMS Beagle that carried Charles Darwin on his voyage of exploration. Fitzroy was also hugely influential in the history of meteorology, spearheading efforts to collect weather data and make it more accessible to fishermen and others who relied on it. Under his command, the British crown distributed storm glasses to small fishing communities throughout the British Isles.

How the Fitzroy Storm Glass Works

The Fitzroy storm glass is a closed glass container, often shaped like a raindrop, holding a supersaturated mixture of alcohol, water, and various chemicals. There are a number of different recipes for making the solution, but most include camphor, ammonium nitrate, and sodium nitrate. As the weather changes, the chemicals in the glass crystallize in various patterns that are said to predict the weather. The patterns can range from cloudy liquid to intricate crystals resembling snowflakes, stars, spirals, and threads. While scientists aren’t certain exactly what influences the formation of crystals — and the shape they take — most have concluded that temperature changes seem to be the most important.

How To Predict Weather With a Fitzroy Storm Glass

These storm glasses generally come with a chart based on Fitzroy’s original observations:

Is the Fitzroy Storm Glass Accurate?

Since Fitzroy’s time, weather scientists have repeatedly tried to gauge the accuracy of the storm glass and found that, at best, its predictions are accurate about 50% of the time.

The Goethe Storm Glass

Unlike the closed Fitzroy glass, the Goethe storm glass — also called a Cape Cod storm glass, thunder glass, or water barometer — is a glass container with a narrow spout that’s open to the air. It’s filled with colored water, which reacts to changes in barometric pressure in the atmosphere outside the glass. The Goethe barometer is generally believed to be the oldest type of barometer in the world, with examples dating back thousands of years. Its modern iteration is attributable to the German statesman, scientist, and philosopher Johann Wolfgang von Goethe, who built on work by Evangelista Torricelli — a 17th-century student and contemporary of Galileo — to create his own version of a water barometer.

How Does the Goethe Storm Glass Work?

A Goethe storm glass is a type of water barometer, which uses a glass bulb filled with colored water to show changes in atmospheric air pressure. The glass is shaped somewhat like a sealed teapot — a rounded globe or cylinder with a long spout starting near the base of the main body and extending upward. The body is filled with colored liquid to a level above the inner mouth of the spout, trapping an air bubble inside the body, which exerts pressure on the liquid, forcing it up into the spout.

How To Predict Weather With a Goethe Storm Glass

As long as the air pressure inside and outside the bottle is the same as they were when the bottle was filled, the liquid remains at the same level in the spout. When the atmospheric air pressure changes, so does the level of liquid in the spout. If the pressure is lower than it was when the air bubble was trapped, the water in the spout will rise above the level of the water in the body. If it’s higher, the water level in the spout will drop lower. In general, high barometric pressure suggests clear skies and uneventful weather, whereas low pressure implies incoming clouds and stormy weather.

Is a Goethe Storm Glass Accurate?

While a Goethe storm glass generally doesn’t give numeric readings like modern barometers, it does record changes in barometric pressure, which can give you a rough idea of incoming weather events. There is, however, a small catch — the air bubble will also react to changes in temperature, expanding when it’s warmer and contracting when it’s cooler. That can affect the accuracy of the readings you get, although they’re considerably more useful than ones from a Fitzroy storm glass. In fact, while it’s not particularly precise, the Goethe storm glass is still considered reasonably accurate at reflecting changes in barometric pressure.

Fun Activities With a Storm Glass

Rudimentary weather instruments like the storm glass offer lots of fun ways to get kids active, engaged, and interested in the weather. Here are just a few suggestions for weather activities related to storm glasses to do with your kids.

Measure the Instrument’s Accuracy

Why take our word for it when simple observations can lead your kids to form their own conclusions? Start with the absolute simplest exercise — measure the accuracy of the storm glass against the readings from your weather station. Does the water level in the spout go up when the barometer on your weather station reflects low or falling pressure? Does it go down when the barometric pressure on the display shows it rising or high pressure?

Use the Storm Glass To Predict the Weather

Download a daily weather journal from our Junior Weather Watchers page. Each day, write down your measurements from the storm glass and predict upcoming weather based on them. Check the accuracy against the actual weather in the next few days or weeks.

Build Your Own Water Barometer

Our blog post about fun weather activities for kids includes a link to instructions to build your own water barometer, along with other weather activities to keep your kids engaged and spark a lifelong interest in weather and science.

Predict the Weather With Storm Glass

Want to do your own observations without having to build your own storm glass? Consider the AcuRite version of a glass Galileo thermometer with an attached globe storm glass. The accent piece combines style and functionality and is the perfect gift for any weather enthusiast in your life.