We argue that the relativistic correction δRc.m. to the
center-of-mass vector can lead to the approximate equality of the proton and
neutron electric polarizabilities in the quark model. The explicit form of
δRc.m. depends only on the non-relativistic potential between
quarks. In particular, this correction is the same for the potential generated
by Lorentz-vector and -scalar interactions.Comment: 8 pages, LaTeX, conclusion extende