Boltzmann's Constant, k
Index
Boltzmann developed a statistical understanding of the concept of entropy, stating that the entropy of a system was proportional to the natural logarithm of the thermodynamic probability of the system: S = k ln W. The constant of proportionality, k, is known as Boltzmann's constant.

k = 8.6 x 10-5 eV/atom-K 
k = 1.38 x 10-23joules/atom-K

Ludwig Eduard Boltzmann Austria (1844 - 1906)