Fitzroy's Storm Glass
I was reading about Darwin's voyages, and saw several
references to a weather instrument that Admiral Fitzroy built. I
tried looking up how the instrument works, but am confused. In the
sealed container, how do you get the different types of crystals and
then match it to the kind of weather expected? Just what are those
It is an interesting instrument and it is said to work fine...you
can try yourself and see! A storm glass is composed of a sealed
glass container, filled with liquid, that allows the user to
forecast the weather by observing the appearance of the liquid in
the glass. The liquid within the glass is a mixture of several
ingredients, most commonly distilled water plus ethanol, and with
some potassium nitrate, ammonium chloride, and camphor all dissolved
to begin the experiment. This specific mixture was developed by
Admiral Robert FitzRoy and used on his voyage with Charles Darwin on
the HMS Beagle. According to Admiral Fitzroy:
1. If there are large flakes throughout the liquid, it will be
overcast in temperate seasons or snowy in the winter.
2. If there are threads near the top, it will be warming or windy.
3. If the liquid contains small stars on sunny winter days, then
snow is coming.
4.If there are crystals at the bottom, this indicates frost.
5. A cloudy glass with small stars indicates thunderstorms.
6. If the liquid in the glass is clear, the weather will be bright
Since I live in the south hemisphere (Brazil) and the weather
usually is warm/quite hot (no snow!) it does not work around here...
Maybe in some places of California!
Mabel (Dr. Mabel Rodrigues)
The crystals that you are speaking of are in the "hygrometer"
(a misnomer) within the Fitzroy Storm Glass. The predictive
capability of the Storm Glass is questionable and changes
within it may only occur as it reacts to the temperature of the
glass chamber. The crystals and precipitant that form inside the
glass are salts within the liquid.
A good reference for learning more about the salt glass is Wikipedia
From the following on-line article:
Cecil Adams performed informal experiments with a storm glass and found that
the success of prediction was no better than random probability. However,
there have been few published studies in peer-reviewed journals testing the
instrument's accuracy; one example is an article in the Journal of Crystal
Growth, whose conclusion was that temperature change is the sole cause of
crystal growth in storm glasses.
The liquid within the glass is a mixture of several ingredients, most
commonly distilled water, ethanol, potassium nitrate, ammonium chloride, and
camphor. This specific mixture was developed by Admiral Robert FitzRoy and
used on his voyage with Charles Darwin on the HMS Beagle.
Click here to return to the Weather Archives
Update: June 2012