From the very beginning, man has been interested in measurements. Even money is a means for measuring the worth of tangible as well as intangible things. Therefore man has also been inquisitive to measure the degree of “hotness” or “coldness” (temperature) of his surroundings.

The thermometer is obtained from two Greek works; thermo (heat) and meter (to measure). The history of thermometers starts from early 11th century, when Avicenna invented an air thermometer. Italian inventor Santorio Santorio was the first person to assign a numerical scale to the thermometer to give meaning to the readings (for clinical use). The first liquid thermometer was invented by the Italian scientist Galileo Galilei, in 1592, after he discovered that when air is contracted in a tube, liquids are drawn up. The initial mercury thermometer was created by the German scientist Daniel Gabriel Fahrenheit in 1714. Nowadays, mercury thermometers have been largely replaced with digital thermometers (also known as electronic thermometers), which are more accurate and easy to read. Numerous measurement scales, like the Fahrenheit (by Daniel Gabriel Fahrenheit) and Celsius scales (by Anders Celsius), have been proposed over the course of its history to measure the extent of heat. Other related equipments like thermistor, thermocouple and silicon band gap temperature sensor, are also used to measure temperature.

A thermometer has various applications. Some are as following:

• Clinical use
  
• Laboratory use
  
• Domestic use (for example, using room thermometer to measure the temperature inside the house)
  
• Cooking use (for example, using candy or meat thermometer to measures the internal temperature and therefore stages of cooking the item).
  

Different types of thermometers are:

• Alcohol thermometer (consists of a glass tube marked with measurement scale and containing alcohol which rises or falls based on the temperature).
  
• Basal thermometer (used to measure the lowest normal body temperature, which occurs during sleep; so the temperature is mostly measured immediately upon waking up).
  
• Mercury thermometer (consists of mercury in a glass tube; used most frequently over the years for measuring human body temperature).
  
• Bi-metal mechanical thermometer (uses a bi-metallic strip wrapped into a coil; as the two metals expand at different rates, the strip bends depending on the degree of temperature; used to help measure and therefore convert a temperature change into mechanical displacement).
  
• Electrical resistance thermometer (exploits the change in electrical resistance of some materials with changing temperature; provides high accuracy, low drift and a wide operating range).
  
• Galileo thermometer (made of a packed glass cylinder making a clear liquid with a number of suspended weights which rise and fall, when temperature chamges, to stay at the position where their density is equal to that of the surrounding liquid).
  
• Infrared thermometer (measures temperature using blackbody radiation, generally infrared, emitted from objects; applications range from checking for hot spots in fire fighting situations to detecting clouds for remote telescope operation).
  
• Liquid crystal thermometer (consists of heat-sensitive liquid crystals in a plastic strip that change color to indicate different temperatures; nomally uses for clinical purposes).
  
• Reversing thermometer (able to record a given temperature to be examined later on; when flipped upside down, the current temperature will be shown until it is turned upright again; used in the past by oceanographers to determine water temperatures below the surface of the ocean).
  
• Silicon bandgap temperature sensor (commonly used in electronic devices; can be included in a silicon integrated circuit at very low cost).
  
• Six's thermometer (can measure the maximum and minimum temperature during a given time; commonly used wherever to measure the extremes of temperature at a location).
  
• Thermistor (a kind of resistor; measures and records temperature by relying on the changes in its resistance with changing temperature).
  
• Thermocouple (kind of temperature sensor; can be utilized as a means to convert thermal potential difference into electric potential difference).
  
• Coulomb blockade thermometer (made from an array of metallic islands, linked to one another with the help of a thin insulating layer; electrons might tunnel across the junction between these islands when voltage is supplied; temperature is gauged based on the tunneling rates and the conductance).
  
• Oral thermometer (used to measure the human body temperature by pacing the thermometer under the patient’s tongue)