What is Thermometry?

Thermometry

A branch of science which deals with the measurement of temperature of a substance is known as thermometry.

The linear variation in some physical properties of a substance with change of temperature is the basic principle of thermometry and these properties are defined as thermometric property (x) of the substance.

Thermometric properties (x) may be as follows

• Length of liquid in capillary
  
• Pressure of gas at constant volume.
  
• Volume of gas at constant pressure.
  
• Resistance of a given platinum wire.
  

In old thermometry, freezing point (0°C) and steam point (100°C) are taken to define the temperature scale. So if the thermometric property at temperature 0°C, 100°C and t°C are x₀, x₁₀₀ and x respectively then

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In modern thermometry instead of two fixed points only one reference point is chosen (triple point of water 273.16 K) the other is itself 0 K where the value of thermometric property is assumed to be zero.

So if the value of thermometric property at 0 K, 273.16 K and TK are 0, x_Tr and x respectively then

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