What is Thermometer?
[[File:St-Germain Auxerrois thermometre.jpg|thumb|Outdoor thermometer]] A '''thermometer''' is an instrument for measuring or showing [[temperature]] (how hot or cold something is). One type of thermometer is a narrow, concealed glass tube containing [[mercury (element)|mercury]] or [[alcohol]] which extends along the tube as it expands. Another type is a [[digital thermometer]], which uses electronics to measure temperature. Early thermometers from the time of [[Galileo]] measured the expansion and contraction of air. After the middle 17th century many used alcohol or mercury. In the 19th century a mechanical thermometer was invented that used a bimetallic strip to move a pointer. This kind is still popular where people like to read temperature from a distance. == Laboratory thermometers (Lab Thermometer) == A laboratory thermometer is a tool used in [[laboratories]], places where [[scientists]] and [[science]] techs perform experiments and measure things. A [[laboratory]] thermometer can measure temperature very closely. A laboratory thermometer can be put into the liquid or other thing that the scientist wants to measure. A laboratory thermometer has a long stem with a silver bulb at the end. The silver color in the bulb usually means there is mercury in it. Mercury becomes bigger as the temperature becomes hotter. But mercury is a [[poison]] to humans. [[Mercury-in-glass thermometer]]s are less used in the 21st century because people want digital, alcohol-filled, and organic-based thermometers instead. == Medical thermometers == [[File:Kwikthermometers.jpg|thumb|Medical thermometers.]] In the 20th century, the traditional [[clinical thermometer]] was a [[mercury (element)|mercury]]-in-glass thermometer. People put the end of this in their mouth (''oral'' temperature), under their arm, or in their [[rectum]] (''rectal'' temperature). It is only possible to find oral temperatures on patients who can hold the thermometer correctly in their mouth. So small children cannot use this method. It is also a p