The behavior of an ionized gas in cosmical observations and laboratory experiments is examined by means of dimensionless parameters. The deviations of experimental from theoretical calculations on electric neutrality and "creep diffusion" are estimated. The coupling between plasma and neutral gas is investigated by the basic equations for a partially ionized gas, This was found to give a dispersion relation for plane disturbances of small amplitudes. The effective electrical conductivity can be deduced from the corresponding damplng distance. Agreement was obtained with the conclusions of Piddington and Cowling regarding the increased dissipation of magneto-hydrodynamic waves in the solar chromosphere and of magnetic fields in cool interstellar clouds. It was determined that magnetohydrodynamic oscillations with wave lengths comparable to the thickness of the ionospheric F/sub 1/ region and with periods comparable to those of "giant pulsations" are damped moderately only if the ionization degree is about a hundred times greater inside than outside of the auroral zones. As an experimental illustration of the theory, torsional oscillations in a cylindrical "magnetohydrodynamic wave guide" are discussed. It was found that Alfvon waves will exist In an ionized gas in the laboratory only in a high-current discharge of relatively large dimensions. The dlffusion processesmore » which take place in a plasma column situated in a longitudinal magnetic field are discussed, Experimental data on the electric potential drop were found to agree well with the collision diffusion theory in a range of magnetic fields up to a centain critical value. Above this value a marked change occurs which can be interpreted as a sudden and rapid increase in the diffusion coefficient with a simultaneous rise in the noise level, These results support the "drain" diffusion mechanism proposed by Bohm, Burhop, Massey, and Williams-particle dlffusion across the magnetic field is accelerated by the action of transverse electric fields.« less