  The third period is taken up by the papers Boltzmann wrote during the 1880's have attracted much less attention. During this period, he abandoned the combinatorial argument, and went back to an approach that relied on a combination of the ergodic hypothesis and the use of ensembles. For a while Boltzmann worked on an application of this approach to Helmholtz's concept of monocyclic systems. However, after finding that concept did not always provide the desired thermodynamical analogies, he abandoned this topic again.