Thermometers
Touch gives a rough idea of how hot something is, but it is not accurate and gives no number, so it is no way to measure temperature. Scientists long ago needed an instrument.
Thermometer
The instrument used to measure temperature is the thermometer. The first was made by Galileo Galilei in about 1600 AD.
Figure to be added
The glass–mercury thermometer
It is a glass tube with a very fine bore (a capillary), joined to a bulb of mercury at one end. As the temperature rises the mercury expands and moves along the bore, and the temperature is read from the scale against the length of the mercury column. Because the bore is so narrow, a small change in volume moves the mercury a clearly visible distance.
Figure to be added
Why mercury
- It expands evenly over a wide range of temperature.
- It conducts heat well.
- It stays liquid from −39 °C to 357 °C.
Mercury is poisonous
A broken mercury thermometer can cause serious environmental pollution, so mercury thermometers are being used less and less.