Experimental observation of transitions between discrete longitudinal
wave modes in a de neon glow discharge is reported. Experimental findi
ngs concerning the pattern selecting instability agree with observatio
ns of the Eckhaus instability in fluid systems. This is supported by t
heoretical considerations of a model equation (Complex Ginzburg-Landau
equation) based on a fluid model. (C) 1998 American Institute of Phys
ics.