The Fitzroy Storm Glass is a sealed glass container filled with a liquid which responds to changes in the weather, which was designed to allow the observer to forecast the possibility of storms, snow, wind, rain or clear skies. While it was later found to only react to current temperature rather than be an effective tool for forecasting the weather, its visually beautiful changes make the storm glass an extremely attractive and conversational room ornament.
This specific mixture was developed by Admiral Robert FitzRoy and was used on his voyage with Charles Darwin on the HMS Beagle. FitzRoy documented the use of his storm glass as a tool for measuring the weather, claiming that:
- If 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.
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 that were to be consulted by ships at port before setting sail.