The device used to measure temperature is called a thermometer. Thermometers can be found in various forms, including digital, mercury, and alcohol types, each serving specific applications. Digital thermometers provide quick and precise readings, often used in homes or medical settings, while traditional mercury thermometers measure temperature through the expansion of liquid mercury in a sealed glass tube. Thermometers are essential in numerous fields, from medicine for monitoring body temperature to meteorology for tracking atmospheric conditions. The invention of thermometers has greatly enhanced our ability to understand and measure temperature variations in both scientific research and daily life.