Dipole resonance of a cold plasma column can be predicted quite simply and observed experimentally. It is normally accompanied, however, by a series of subsidiary resonances. These have recently been explained phenomenologically as depending on nonuniform electron density and nonzero electron temperature for their existence. Numerical results of an analysis of the resonances by Nickel, Parker, and Gould are compared to the recently published experimental work on which the phenomenological description was founded, and it is shown that there is very good agreement. These observations and the theory have considerable relevance to the pressure waves described by Bohm and Gross, and to the effectiveness of Landau damping under conditions of nonuniform electron density. It is also possible to use the computed data to estimate the error in dipole resonance measurements of electron density.