Fitzroys Storm Glass, 28cm.
The storm glass or chemical weather glass was an instrument which was proposed as a method for predicting weather. It consisted of a special liquid placed inside a sealed transparent glass. The state of crystallization within the liquid was believed to be related to the weather. The inventor is unknown but the device became popular in the 1860s after being promoted by Admiral Robert Fittzroy who claimed that
“if fixed, undisturbed, in free air, not exposed to radiation, fire, or sun, but in the ordinary light of a well-ventilated room or outer air, the chemical mixture in a so-called storm-glass varies in character with the direction of the wind, not its force, specially (though it may so vary in appearance only) from another cause, electrical tension.”
The compositions of the liquid in a storm glass varied but usually contained “camphor, nitrate of potassium and sal-ammoniac, dissolved by alcohol, with water and some air.” These devices are now known to have little value in weather prediction but continue to be a curiosity.
FitzRoy carefully documented how the storm glass would predict the weather:
- 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.