ABSTRACT
This chapter considers the perturbations of a stationary uniform medium. Propagation of waves in such a medium is anisotropic because of the uniform magnetic field. The wave speed is a function of the angle between the wave normal and the magnetic field. The simplest wave equation describes waves in a uniform non-dispersive medium. Wave propagation in an elastic medium, initially in equilibrium, occurs when the medium is perturbed. The simplest illustration is a wave on a stretched string. A great deal can be deduced about the properties of harmonic waves by studying the dispersion relation between the frequency and the wavevector. The slow-wave surface is an open surface and the wave is strongly anisotropic. There are two surfaces, roughly planar so that its properties are qualitatively similar to those of the transverse Alfven wave.
