  Analytic energy bounds for N-boson systems governed by semirelativistic
Hamiltonians of the form H=\sum_{i=1}^N(p_i^2 + m^2)^{1/2} - sum_{1=i<j}^N
v/r_{ij}, with v>0, are derived by use of Jacobi relative coordinates. For
gravity v=c/N, these bounds are substantially tighter than earlier bounds and
they are shown to coincide with known results in the nonrelativistic limit.
