Z Zeeman effect Discovered by P. Zeeman in 1896 who observed the broadening of spectral lines in the presence of a magnetic field. It was later shown that the lines were split into doublets, triplets and higher order. The effect was explained by Lorentz in his classical theory of the electron: If vo is the electronic frequency at zero field, then in a magnetic field H , it is split into components vo ± ∆v, where ∆v = eBm , where e = electronic charge, m = electronic mass and c = velocity of light.