We study the spectrum of the spinless-Salpeter Hamiltonian H = \beta
\sqrt{m^2 + p^2} + V(r), where V(r) is an attractive central potential in three
dimensions. If V(r) is a convex transformation of the Coulomb potential -1/r
and a concave transformation of the harmonic-oscillator potential r^2, then
upper and lower bounds on the discrete eigenvalues of H can be constructed,
which may all be expressed in the form E = min_{r>0} [ \beta \sqrt{m^2 +
P^2/r^2} + V(r) ] for suitable values of P here provided. At the critical point
the relative growth to the Coulomb potential h(r)=-1/r must be bounded by dV/dh
< 2\beta/\pi.Comment: 11 pages, 1 figur