Galileo Galilei discovered that the density of fluids varies with temperature variation, and here is the basic operating principle of one of the first meteorological instruments.
It consists of a glass tube closed on both sides, filled with water and inside it contains some spheres submerged one below the other but with different amounts of liquid and air, which is why they have different densities.
When the temperature rises, the liquid in the glass tube becomes less dense, causing the glass spheres to sink. In conclusion, as the temperature rises, the spheres at the top fall towards the bottom and as the temperature decreases, the spheres at the bottom rise towards the top. The temperature is indicated by the sphere that floats at a lower height within the upper group.
Each sphere has an insert where the temperature is recorded.
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