Wavelength as a function of wave frequency for n₀ = 10⁶ and a grain size a = 3 × 10⁻⁶ cm as stated by Eq. (24). In the top panel, the red and black lines represent the two solutions with grain inertia accounted for whereas on bottom panel the cyan and purple lines (which cannot be distinguished in this particular case) represent the solutions without grain inertia. For ease of comparison, the solutions of top panel have been reported (thin lines) on bottom panel.