[Lewis Thomson (OP)]

Peter emailed this question to The Naked Scientists.

"Can you explain if Admiral Fitzroy’s weather predicting storm glass actually works or is it pseudoscience? What are the known facts?"

Can you help them find answers? Leave them in the comments below...

[Bored chemist]

It is pseudoscience.
But they do sometimes make pretty patterns.

[alancalverd]

True, but what makes the patterns? The only possible influences are temperature and pressure, which are, I'm told, something to do with the weather. And what really intrigues me is how Fitzroy or whoever actually invented it, stumbled upon the particular formulation.

Wikipedia also offers a link to Merryweather's Tempest Prognosticator, whose weirdness  knows no bounds, but also rests on a very odd observation by a poet. Give them credit, the Victorians were surprisingly observant and curious compared with their great-grandchildren!

[chris]

What is Admiral Fitzroy's storm glass?

[Bored chemist]

What is Admiral Fitzroy's storm glass?

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

The only possible influences are temperature and pressure,

Air pressure isn't going to do much to  a sealed system.

The same Admiral Fitzroy did much to popularise the use of the barometer.

[alancalverd]

...and even got a sea area named after himself.

The oddity is the number of different appearances of the device. If it were completely filled with liquid then the flexibility of the glass would transfer barometric pressure to the liquid, but  the presence of gas above the liquid means that temperature fluctuations will dominate, so the habit and dispersion of the crystals may depend not only on temperature but also on the rate of change of temperature. Still not a good storm prognosticator but a fun piece of kit!