Galileo thermometer

It is named after Galileo Galilei because he discovered the principle on which this thermometer is based—that the density of a liquid changes in proportion to its temperature.

[5] The outer vessel was filled with 'rectified spirits of wine' (a concentrated solution of ethanol in water); the weights of the glass bubbles were adjusted by grinding a small amount of glass from the sealed end; and a small air space was left at the top of the main vessel to allow 'for the Liquor to rarefie' (i.e. expand).

The device now called the Galileo thermometer was revived in the modern era by the Natural History Museum, London, which started selling a version in the 1990s.

Once the hand-blown bulbs have been sealed, their effective densities are adjusted using the metal tags hanging from beneath them.

Eventually all the bulbs may be at the base of the tube depending on the temperature of the surroundings and therefore that of the clear holding fluid.