Clapeyron, Benoit Paul Emile
26 Jan 1799 - 28 Jan 1864
French
Educated at École Polytechnique he went to Russia in 1810, remaining there for 21 years. He expressed Sadi Carnot's ideas on heat analytically, with the help of graphical representations, in 1834. This work had important influences on Thomson and Clausius. He also was interested in railway engineering and designed steam locomotives. The Clapeyron relation, a differential equation which determines the heat of vaporisation of a liquid, is named after him.

Clausius, Rudolf Julius Emmanuel

2 Jan 1822 - 24 Aug 1888
German
He was professor of physics in Berlin, then in Zurich, then at Würzburg and finally at Bonn. Essentially a theoretical physicist, he did important work in thermodynamics. In a paper of 1865 he stated the First and Second laws of thermodynamics in the following form.
1. The energy of the universe is constant.
2. The entropy of the universe tends to a maximum.
In all he wrote eight important papers on the topic.
He restated Sadi Carnot's principle of the efficiency of heat engines. The Clausius-Clapeyron equation expresses the relation between the pressure and temperature at which two phases of a substance are in equilibrium.



JOC/EFR February 1995