The Temperature Handbook

In 1848, Sir William Thomson (Lord Kelvin) stated the zero principle of dynamics. This principle enabled him to define thermodynamic temperature and to establish an objective method of measuring it.

When two systems are each in thermal equilibrium with a third, they are in thermal equilibrium with each other. This equilibrium is expressed by their equal temperatures. If a conventional value is ascribed to the temperature of a system in a given physical state, other temperatures can be determined by thermodynamic measures.

Temperature-Handbook