  We obtain the equations that define the equilibrium of a homogeneous
relativistic gas of neutrons, protons and electrons in a constant magnetic
field as applied to the conditions that probably occur near the center of
neutron stars. We compute the relative densities of the particles at
equilibrium and the Fermi momentum of electrons in the strong magnetic field as
function of the density of neutrons and the magnetic field induction. Novel
features are revealed as to the ratio of the number of protons to the number of
neutrons at equilibrium in the presence of large magnetic fields.
