This beautiful conversation piece combines two ancient technologies - the Admiral Fitzroy Storm Glass and the Galileo Thermometer.
The Admiral Fitzroy Storm Glass:
How this storm glass really works is a mystery, but it is believed that electromagnetic changes in weather patterns activate crystals inside (sealed-glass chamber fills with crystals when air pressure decreases). Famed meteorologist Admiral Fitzroy used a storm glass in 1750 on a historic voyage with Charles Darwin.
A storm glass works on the premise that temperature and pressure affect solubility, sometimes resulting in clear liquid; other times causing precipitants to form. However, the method by which this works is not fully understood. Although it is well-established that temperature affects solubility, some studies have simultaneously observed several different storm glasses forming similar crystal patterns at different temperatures. In addition, sealed glasses are not exposed to atmospheric pressure changes and do not react to the pressure variations associated with weather systems.
Some people have proposed that surface interactions between the glass wall of the storm glass and the liquid contents account for the crystals. Explanations sometimes include effects of electricity or quantum tunneling across the glass.
The Galileo Thermometer:
The Galileo thermometer consists of a sealed glass tube that is filled with fluid (paraffin oil) and several floating bubbles. The bubbles are glass spheres filled with a colored liquid mixture.
Attached to each bubble is a little metal tag that indicates a temperature. These metal tags are calibrated counterweights. The weight of each tag is slightly different from the others. Since the bubbles are all hand-blown glass, they aren't exactly the same size and shape.
The bubbles are calibrated by adding a certain amount of fluid to them so that they have the exact same density. So, after the weighted tags are attached to the bubbles, each differs very slightly in density (the ratio of mass to volume) from the other bubbles, and the density of all of them is very close to the density of the surrounding water.
As the temperature of the air outside the thermometer changes, so does the temperature of the fluid surrounding the bubbles. As the temperature of the fluid changes, it either expands or contracts, thereby changing its density. So, at any given density, some of the bubbles will float and others will sink. The bubble that sinks the most indicates the approximate current temperature.