Stability of infinite active lines

A postulational approach is presented to the stability of infinite active lines in the complex frequency-complex wavenumber domain. It is shown that the discrimination between stability and instability together with the verification of instabilities can be made at sight upon examination of a plot in the
\sigma-{\alpha}
plane, where a is the real part of complex frequency p and a is the real part of the complex wavenumber
\gamma
.