A '''thermometer''' is a device for measuring [[temperature]]. The two simplest ways to do this both rely on the principle that hot things expand and cold things contract. A liquid such as colored alcohol or mercury can be placed in an evacuated glass tube. The expansion and contraction of the liquid indicates the temperature. A helical spring can also be used, is in the common refrigerator thermometer. | A '''thermometer''' is a device for measuring [[temperature]]. The two simplest ways to do this both rely on the principle that hot things expand and cold things contract. A liquid such as colored alcohol or mercury can be placed in an evacuated glass tube. The expansion and contraction of the liquid indicates the temperature. A helical spring can also be used, is in the common refrigerator thermometer. |