The spectra of the stars P Cygni and 3' Cassiopeiae can be explained in terms of electrical discharges in one or more localized cometary nebulae, similar to that photographed in Hubble's Variable Nebula associated with the star R Monocerotis, and in the planetary nebulae generally (Sd). 2 An explanation is offered on this basis for the variation in the spectrum of P Cygni of the velocities and of the emission/absorption ratios of the ions with their levels of excitation. In that star the conditions in the discharge channels are shown to be somewhat analogous to those in laboratory plasma-jet tubes, and in hyperthermal wind tunnels. The'theory accounts for the gas velocities associated with the highest levels of excitation in these stars, and for the variation of the Doppler-shift velocities along the lines of the Balmer series. It is suggested that in P Cygni, one such cometary nebula lies in the line of sight on the near side of the star, while in 3, Cassiopeiae four equally spaced nebulae lie in a plane containing the line of sight and revolve in a period of about four years. This latter conclusion derives from a study of Baldwin's spectroscopic study of the 1935 outburst, in which two diametrically opposed arms were involved, in association with Holborn's light curve of the star from 1938 to 1960.
Zanstra's method of determining the temperatures of the central stars of planetary nebulae is shown to lead to a determination of the temperature of the gas excited by the discharges and not to that of the central star itself.