k was already in use as Boltzmann's constant by that time, I think: https://en.wikipedia.org/wiki/Boltzmann_constant https://en.wikipedia.org/wiki/Boltzmann_co

k was already in use as Boltzmann's constant by that time, I think: https://en.wikipedia.org/wiki/Boltzmann_constant https://en.wikipedia.org/wiki/Boltzmann_constant