Radiating and Ionizing Potentials of Hydrogen.—To detect and distinguish between radiation and ionization, the Lenard method, modified by the introduction of a receiving electrode of variable area, was used. Both radiation and ionization were obtained at about 10.8 volts, probable radiation at about 13.4 volts, and strong ionization at 15.9 volts. These experimental results are compared with those of other investigators; and as an explanation of apparent discrepancies it is pointed out that the following effects may occur together: radiation from free atoms near 10.8 volts and ionization near 13.5 volts; ionization without dissociation of molecules near 10.8 volts, dissociation plus radiation from one of the atoms near 13.4 volts and dissociation plus ionization of one atom near 15.9 volts.