Subject: Did Boltzmann use discrete energy levels in statistical thermodynamics?

I was recently given an introductory course on Statistical Thermodynamics
as part of my degree studies. In it we were told that Boltzmann
did much of the early work in the field. However, the material we were
taught (partition functions, etc.) appeared to rest entirely on the
assumption that atoms and molecules possessed discrete energy levels. It
was my understanding that this assumption only came in with quantum theory
at the beginning of the twentieth century. However, Boltzmann did his work
in the nineteenth century. So my question is: did he assume discrete
energy levels in his theories? If so, how did he know that this was the
right assumption to make, and if not, how does his work relate to what we
are taught today?

Re: Did Boltzmann use discrete energy levels in statistical thermodynamics?