  We report on neutron-scattering results on the impact of a magnetic field on
stripe order in the cuprate La$_{1.875}$Ba$_{0.125}$CuO$_4$. It is found that a
7 T magnetic field applied along the {\it c} axis causes a small but finite
enhancement of the spin-order peak intensity and has no observable effect on
the peak width. Inelastic neutron-scattering measurements indicate that the
low-energy magnetic excitations are not affected by the field, within
experimental error. In particular, the small energy gap that was recently
reported is still present at low temperature in the applied field. In addition,
we find that the spin-correlation length along the antiferromagnetic stripes is
greater than that perpendicular to them.
