Comments on paper by E. Leer and T. E. Holzer, 'Collisionless solar wind protons: a comparison of kinetic and hydrodynamic descriptions'
Recently, Leer and Holzer (1972) presented a comparison of kinetic and hydrodynamic solar-wind models. Since both their models produced the same solar- wind properties at Earth, and since the hydrodynamic description did not include viscosity, they concluded that viscosity is not important in the solar wind. The present authors disagree that this conclusion applies to the real solar wind. Also it is felt that they did not demonstrate any general applicability for their conclusion that the kinetic and hydrodynamic approaches are equivalent in the solar wind. (WDM)