This is an image of a mercury bulb thermometer. The temperature is measured by reading the number next to the thin black line that goes partly up the yellow tube.
Click on image for full size
Image courtesy of Wikipedia Creative Commons
Thermometer
Thermometers measure temperature. "Thermo" means heat and "meter" means to measure. You can use a thermometer to measure the temperature of many things, including the temperature of the air, the temperature of our bodies, and the temperature of the food when we cook. Temperature is a measure of the hotness and coldness of an object.
Thermometers usually have a bulb at the base and a long glass tube that extends to the top. The glass tube of a thermometer is filled with alcohol or mercury. Both mercury and alcohol grow bigger when heated and smaller when cooled. Inside the glass tube of a thermometer, the liquid has no place to go but up when the temperature is hot and down when the temperature is cold. Numbers are placed alongside the glass tube that mark the temperature when the line is at that point.
Other types of thermometers include dial thermometers and electronic thermometers. Electronic thermometers measure temperature much more quickly than mercury and dial thermometers.
The thermometer measures temperatures in Fahrenheit, Celsius and another scale called Kelvin. Fahrenheit is used mostly in the United States, and most of the rest of the world uses Celsius. Kelvin is used by some scientists.
You might also be interested in:

The Kelvin scale is a temperature scale that is often used in astronomy and space science. You are probably more familiar with the Celsius (or Centigrade) scale, which is part of the metric system of measures,
...more
Rainbows appear in the sky when there is bright sunlight and rain. Sunlight is known as visible or white light and is actually a mixture of colors. Rainbows result from the refraction and reflection of
...more
The Earth travels around the sun one full time per year. During this year, the seasons change depending on the amount of sunlight reaching the surface and the Earth's tilt as it revolves around the sun.
...more
Scientists sometimes travel in specially outfitted airplanes in order to gather data about atmospheric conditions. These research aircraft have special inlet ports that bring air from the outside into
...more
An anemometer is a weather instrument used to measure the wind (it can also be called a wind gauge). Anemometers can measure wind speed, wind direction, and other information like the largest gust of wind
...more
Thermometers measure temperature. "Thermo" means heat and "meter" means to measure. You can use a thermometer to measure the temperature of many things, including the temperature of
...more
Weather balloons are used to carry weather instruments that measure temperature, pressure, humidity, and winds in the atmosphere. The balloons are made of rubber and weigh up to one kilogram (2.2 pounds).
...more