Microcanonical Thermodynamics: Phase Transitions in "small" Systems - Dieter H. E. Gross - Google Books

http://books.google.de/books?id=qcgtEpL8O3sC&pg=PA141&dq=%22negative+heat+capacity%22

Boltzmann''s formula S = In[ W (E) ] defines the microcanonical ensemble. The usual textbooks on statistical mechanics start with the microensemble but rather quickly switch to the canonical ensemble introduced by Gibbs. This has the main advantage of…