We have learned from Lindsey Smith's talk how useful it would be for our understanding of Wolf-Rayet stars to have reliable effective temperatures and bolometric corrections. The ring nebulae surrounding a few WN stars provide one method for estimating the stellar temperatures. I have assumed each nebula is a normal H ii region excited primarily by the Lyman continuum radiation of the central star. Then, if the nebula is optically thick shortward of 912 Å, each stellar photon with more energy than 13.6 eV is absorbed by the nebula and re-radiated in a predictable way as hydrogen lines and free-free radio emission. Consequently, nebular radio measures such as those recently obtained by Hugh Johnson (1971) provide a direct indication of the number of Lymancontinuum photons emitted by the central star. The exact equations have been described in the Astrophysical Journal (Morton, 1969; Morton, 1970).