The Galileo thermometer (named after the famous Italian physicist Galileo Galilei) is a thermometer made of a sealed glass cylinder containing a clear liquid (usually paraffin or ethanol) and a series of sealed glass bulbs with different densities.
It’s named after Galileo because he discovered the principle on which this thermometer is based – that the density of a liquid changes in proportion to its temperature. As the temperature increases, the density of the clear liquid decreases causing the bulbs to sink; and vice versa. Tags attached to the bulbs then allow you to determine the temperature.
The temperature is typically read from an engraved metal disc on each bulb. Usually a gap separates the top group of bulbs from the bottom group of bulbs, lowest ball of the top cluster determines the temperature. If a bulb is free-floating in the gap, then its tag reading would be closest to the ambient temperature.
Warning: This product is not a toy. Keep away from children. Contains Paraffin oil/Light wax oil. In case of breakage: If liquid becomes in contact with skin, rinse with plenty of water and ensure the room is well ventilated as the oil has a strong odour. Use gloves to clean up spills. Do not ingest. If ingested call your nearest poison line and wash out mouth with water.