![A typical 19th century thermometer.](http://static.sciencelearn.org.nz/images/images/000/003/528/full/ITV_V_TIMELINE_Weather_1714_Thermometer_Lanscape.jpg?1674171076)
The first reliable thermometers were composed of calibrated glass tubes filled with mercury. This is a typical 19th century thermometer.
The first reliable thermometers were composed of calibrated glass tubes filled with mercury. This is a typical 19th century thermometer.