  The strength distributions of the giant monopole resonance (GMR) have been
measured in the even-A Sn isotopes (A=112--124) with inelastic scattering of
400-MeV $\alpha$ particles in the angular range
  $0^\circ$--$8.5^\circ$. We find that the experimentally-observed GMR energies
of the Sn isotopes are lower than the values predicted by theoretical
calculations that reproduce the GMR energies in $^{208}$Pb and $^{90}$Zr very
well. From the GMR data, a value of $K_{\tau} = -550 \pm 100$ MeV is obtained
for the asymmetry-term in the nuclear incompressibility.
