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 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, people more often used alcohol or mercury thermometers. In the 19th century, a mechanical thermometer was invented that used a bimetallic strip to move a pointer. This type of thermometer is still popular where people like to read temperature from a distance.

A laboratory thermometer is a tool used in laboratories, places where scientists and science technicians perform experiments and measure things. A laboratory thermometer can measure temperature very closely. A laboratory thermometer can be put into what 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 expands as the temperature becomes hotter. Mercury is a poison to humans if touched, inhaled, or swallowed, which makes it dangerous to use when taking people's temperatures. Mercury-in-glass thermometers are less used in the 21st century. This is because digital thermometers are more accurate, and alcohol-filled and organic-based thermometers are safer to use than mercury thermometers.

In the 20th century, the traditional clinical thermometer was a 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. Mercury thermometers need a long time to measure the temperature, so it would be difficult to get the temperature of small children, people with a cough, or people who are vomiting. Today's digital thermometers are much faster and more accurate. If a person drinks something hot or cold, a person needs to wait before testing their oral temperature.

Rectal thermometers are usually more reliable since they aren't as much influenced by other factors.^[1]

There are other kinds of medical thermometers: tympanic thermometers test the temperature of the tympanic membrane (the eardrum) with infrared; band thermometers test a person's temperature on the front of their head.

• Liquid-in-glass thermometer
• Mercury-in-glass thermometer
• Alcohol-in-glass thermometer
• Clinical thermometer
• Digital thermometer
• Rotary thermometer
• Resistance thermometer
• Liquid crystal thermometer
• Infra-red thermometer