Barometers Realm

A storm glass is a small bottle containing a chemical solution, supposedly capable of predicting the weather. Inside is an alcohol-based solution with camphor, ammonium chloride, potassium nitrate, and distilled water. While storm glasses are an integral part of FitzRoy’s barometers, they can also be found as standalone devices. According to FitzRoy himself, they were sold in London as early as the 18th century. The lore suggests that by observing the behavior of camphor crystals inside the solution, one could predict upcoming weather. The crystals may precipitate or dissolve, rise and fall within the liquid, appearing as both large and small flakes, leading to various weather interpretations.

Here are some predictions linked to the behavior of the crystals:

• Clear liquid — good weather.
• Crystals at the bottom — frost in winter.
• Cloudy liquid — rain.
• Cloudy liquid with small crystals — a thunderstorm.
• Large flakes — overcast weather, snow in winter.
• Thread-like formations above the liquid — windy weather.
• Small dots — humid weather, fog.
• Rising flakes that linger — wind in higher altitudes.

As was often the case, instruments for Robert FitzRoy were manufactured by the company Negretti & Zambra, and this also included the storm glass. In 1861, Negretti & Zambra described the recipe for this concoction as: "The storm glass consists of a mixture of camphor, alcohol, potassium nitrate, ammonium chloride, and water, although the proportions of these ingredients and the method of preparation are kept secret by all who make it."

Negretti & Zambra also warned their clients about inferior-quality storm glasses, stating: “Each person who prepares it has their own preferred method, and the mixture improves with age.”

Typically, storm glasses are sealed at the top with a cork or wax, or sometimes completely sealed, leading to the logical assumption that the storm glass does not respond to changes in air pressure, only to temperature fluctuations.

The Admiral Fitzroy Storm Glass presented here, from the mid-20th century, is crafted in an oak case and features a flat protective glass. The interior of the device is lined with a paper scale displaying temperature values in both Fahrenheit and Celsius, along with instructions for using the instrument. Inside the elongated glass vial, sealed with wax, is a chemical solution, which supposedly allows for weather predictions based on its behavior.