  We have determined theoretically the rest mass of the muon neutrino at 50
milli-eV and the rest mass of the electron neutrino at 5 meV, as well as, to 1%
accuracy, the ratio of the masses of the stable elementary particles which
decay by weak decays. We assume that the particles of the neutrino branch
consist of a cubic, isotropic nuclear lattice, held together by the weak
nuclear force. The eigenfrequencies of the lattice are calculated with Born's
theory of cubic lattices. Only neutrinos are required to explain the so-called
stable particles of the neutrino branch.
