  In order to explain the empirical integer multiple rule for the stable mesons
and baryons presented in the preceding paper we assume that the particles are
held together in a cubic nuclear lattice. This is a novel approach to the
particles, based on the fact that the range of the weak nuclear force is only a
thousandth of the diameter of the nucleon, and that the crystals are the
best-known macroscopic bodies held together by a microscopic force. We
investigate the standing waves in a cubic nuclear lattice. From the frequency
distribution of the waves follows that the masses of the $\gamma$-branch
particles are integer multiples of $m(\pi^0)$. We show that each particle has
automatically an antiparticle. Assuming that the energy of the oscillations is
determined by Planck's formula for the energy of a linear oscillator, it turns
out that the $\pi^0$ meson and the other members of the $\gamma$-branch are
like cubic black bodies filled with plane, standing electromagnetic waves. Our
standing wave model explains the integer multiple rule of the masses of the
neutral mesons and baryons of the $\gamma$-branch and uses nothing else but
photons. Our results justify the cubic lattice assumption.
