  The infrared Hall angle in optimally doped single crystal $\rm Bi_2 Sr_2 Ca
Cu_2 O_{8+x}$ was measured from 3.05 to 21.75 meV as a continuous function of
temperature from 25 to 300\,K. In the normal state, the temperature dependence
of the real part of the cotangent of the infrared Hall angle obeys the same
power law as dc measurements. The measured Hall frequency $\rm \omega_H$ is
significantly larger than the expected value based upon ARPES data analyzed in
terms of the relaxation time approximation. This discrepancy as well as the
temperature dependence of $\rm Re(\cot{\theta_H})$ and $\omega_H$ is well
described by a Fermi liquid theory in which current vertex corrections produced
by electron-magnon scattering are included.
