Equations of motion and Ohm's law for an ionized gas in a stellar atmosphere are presented. Ambiguities in plasma physics relative to the solar atmosphere, sunspots, the heating mechanism of the chromosphere and the corona, and the state of ionization of the solar corona are discussed, The hydromagnetic ambiguities of interplanetary space are discussed relative to isorotation, force- free fields, densities, velocities, transport of angular momentum, magnetic fields, and comet tails. (C.J.G.)