Discussion Following the Reports by Weaver and Field

Abstract

This long, very intensive, and partially very confused discussion, has been rearranged in six sections: (1) Direct and Indirect Evidence of X-rays and Low-Energy Cosmic Rays; (2) The Boundary Layer between the Stable Gas Phases; (3) Theoretical Aspects of Interstellar Gas Dynamics and the Formation of Clouds; (4) Observational Aspects of Interstellar Gas Dynamics and the Formation of Clouds; (5) Observations of the Rarefied, Neutral Intercloud Medium and of the Interstellar Electron Density; (6) The Dynamical Theory of HII Regions. Section 2 has been transferred from the Discussion on Monday, September 8 (Chapter 2). To Section 6 have been added remarks made during various discussions. A couple of remarks have been transferred to other Discussions. Part of the Discussion (in Section 5) was very confused; an attempt has been made to condense and to make as much sense as possible out of what was said. For the convenience of the reader I recapitulate a few concepts, the (mis)-use of which lead partially to the confusion:

• i. The hydrogen surface density or column density $N_\text H = \int {n_\text H \text dl}$ (N_H is sometimes called the hydrogen measure HM).

• ii. The dispersion measure DM = $\text D\text M = \int {n_e \text dl}$ (DM is often called the electron surface density N _e ).

• iii. The rotation measure $\text R\text M = c_1 \int {n_e B_{||} \,\text dl}$.

• iv. The emission measure $\text E\text M = \int {n_e^2 \text dl}$.