This is a note originally distributed in 1983. I am re-releasing it now, with a couple of words changed, so that it can be used for test problems, distributed more openly, and so forth. One could argue that it should be published, but I do not have time to reshape it into something I would regard as suitable for journal publication. A different derivation of the same result is being published in an appendix in D.W. Phillion and S.M. Pollaine, ``Dynamical Compensation of Irradiation Nonuniformities in a Spherical Hohlraum Illuminated with Tetrahedral Symmetry by Laser Beams,`` submitted to Phys. Plasmas.