On the basis of Lorentz's theory, if we limit ourselves to a single spectral line, it suffices to assume that each atom (or molecule) contains a single moving electron.
Pieter ZeemanThe rotation of the polarization plane is extraordinarily small in all gases, thus also in sodium vapour.
Pieter ZeemanAccording to well-known electrodynamic laws, an electron moving in a magnetic field is acted upon by a force which runs perpendicular to the direction of motion of the electron and to the direction of the magnetic field, and whose magnitude is easily determined.
Pieter ZeemanMoreover, photography has made it possible to fix these images and now provides us with a permanent record of each observed spectrum, which can be measured out at any time.
Pieter Zeeman