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Name:  Justin
Status: student
Grade: 9-12
Location: CA 
Country: USA
Date: N/A 


Question:
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 crystals?


Replies:
Hi Justin!

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 and clear.

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)


Justin,

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

http://en.wikipedia.org/wiki/Storm_glass.

David Cook


Justin

From the following on-line article:

http://en.wikipedia.org/wiki/Storm_glass

Accuracy:

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.

AND

Description:

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.

Sincere regards,
Mike Stewart


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