Storm Cloud, 13cm
Aboard HMS Beagle during the Darwin Expeditions of 1831-36, Captain Robert Fitzroy developed and refined the 18th century storm bottle. This involved much testing and observation of crystal formations, and resulted in him being able to make a number of weather predictions with a fair(ish) degree of accuracy. Then, as now, no one is quite sure how the storm bottle works. Is it atmospheric pressure, temperature, electrical disturbances…? Keep your own records and see if you can confirm or improve upon Fitzroy’s observations.