Magnetic influence on classical dispersion

We discuss the Lorentz model for dispersion and absorption of radiation in dilute, linear and isotropic materials. Initially, with the purpose of making the paper as self-contained as possible, we reproduce the usual calculations concerning the interaction between the charged material oscillators and the electric field of the incident radiation, obtaining the main behavior of the reactive and dissipative electromagnetic properties of the materials. Thereafter, we also include the magnetic contribution of the Lorentz force to the equation of motion of the oscillators up to first order in $v/c$, which leads to some interesting results, like the approximately linear dependence of the refraction index with the radiation intensity and the appearance of a second region of anomalous dispersion around half the natural frequencies of the material.