3 Part One. The Predicate

The Kelvin Temperature Scaleand Modern Means of Measuring the Temperature
About 200 years ago scientists noticed that a sample of gas that is cooled decreases in volume in a regular way, and they saw that if the volume were to continue to decrease in the same way, it would become zero at about -273°C. The concept was developed that this temperature -273°C (more accurately -273.15°C) is the minimum temperature, the absolute zero.A new temperature scale was then devised by Lord Kelvin, a great British physicist (1824-1907). The Kelvin scale is defined in such a way as to permit the laws of thermodynamics to be expressed in a simple form.

The International Standard temperature scale is the Kelvin scale with a new definition of the degree. The absolute zero is taken to be OK and the triple point of water is taken to be 273.15K. (The triple point of water, the temperature at which pure liquid water, icc and water vapour are in equilibrium, will be discusscd later.) With this definition of the degree, the boiling point of water at onc-atmosphcrc pressure is 373.15K and the freezing point of water saturated with air at onc-atmosphcrc pressure is 273.15K. Hence the SI Kelvin temperature is 273.15K greater than the centigrade temperature.