What is A thermometer?

an instrument for measuring and indicating temperature, typically one consisting of a narrow, hermetically sealed glass tube marked with graduations and having at one end a bulb containing mercury or alcohol that expands and contracts in the tube with heating and cooling.

A thermometer is an instrument we can use to measure temperature. Analog thermometers consist of a sealed tube with markings on it which are increasing temperatures in Celsius or Fahrenheit. The markings on a clinical and weather thermometer are different but they work in the same way.

The glass tube of a thermometer usually contains mercury. Mercury is perfect to test temperature because it changes from a solid to liquid very easily. When the metal tip of the thermometer comes into contact with the material it is testing, it conducts heat energy to the mercury. The mercury turns into liquid and begins to rise up the tube. When it stops is where you can take the temperature reading on the scale.

an instrument for measuring temperature, often a sealed glass tube that contains a column of liquid, as mercury, that expands and contracts, or rises and falls, with temperature changes, the temperature being read where the top of the column coincides with a calibrated scale marked on the tube or its frame.