storm glass barometer is a type of weather forecasting device, composed of a sealed glass container filled with liquid. The appearance of the liquid purportedly predicts the weather, but most modern experiments have failed to confirm this.
One type of barometer used by Fitzroy was a storm glass. Observing the liquid in the storm glass was supposed to indicate changes in the weather. If the liquid in the glass was clear, the weather would be bright and clear. If the liquid was cloudy, the weather would be cloudy as well, perhaps with precipitation.
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.
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