Galileo Galilei was an Italian physicist, mathematician, astronomer and philosopher who had a major role in the scientific revolution of the sixteenth century. He was the first to discover that the density of liquid changes as a result of increasing or decreasing temperatures.
The thermometer named after him is made up of a sealed glass cylinder. Inside there is a clear liquid and a series of bulbs. Each bulb has a weight attached to it. As the temperature changes, they rise and fall depending of a number of mathematical principles. Yet the Galileo Thermometers has an aesthetic that goes beyond its function – it is a beautiful object in its own right.
Although he did not invent the Galileo Thermometer, it was named in his honor because without his discoveries it would have not been possible to invent it. These devices have been manufactured since the end of the seventeenth century.
On each of the bulbs the weight is also tagged. A number and a degree symbol are engraved on each one. The weights are finely regulated counterweights. Each of the weights is a little different from the others. The colored water in the bubbles is added so that each one will have the same density – but it certainly adds to the overall attraction of this special thermometer.
The mathematical principles applied to the Galileo thermometer are straightforward. Each bulb in the thermometer has the same volume and therefore exactly the same density. This means that each bulb has the same magnitude of both gravitational and buoyant forces. Gravity pushes down, buoyancy upwards.
Each bulb is defined by the mass that is suspended from its base. This mass increases the relative weight of the bulb as well as the effect of gravity on it. The weight means that each of the bulbs has a slightly different density to the others. The bottom most floating bulb is the one that indicates the correct temperature. Take a look at a time-lapse video of a Galileo Thermometer in action.
As the density of the fluid outside of the bulb changes the force of gravity overcomes the buoyant force, so making the bulb sink. As the temperature increases then the density of the fluid increases. As the density decreases the buoyant force also decreases. Each bulb remains constant so as the temperature as the fluid increases the buoyant force decreases due to proportionality with the fluid density and the bulb will sink.
The inverse is true if the density of the water increase. Each bulb is weighted so that it will fall or rise at a certain surrounding density dependent on a specific temperature. In terms of design, it has an elegant and graceful form. The Galileo Thermometer is truly a thing of scientific beauty.