Existence of Positive Ions of Abnormally High Mobilities in Air.—Contrary to the conclusions of other observers, Nolan has reported what he believes to be indications of the presence in ionized moist air of ions of eight different mobilities ranging from one to seven times the normal value. A repetition of Nolan's experiment, however, with duplicate apparatus, has led to an explanation of his anomalous results. In his experiment, ions generated in a small shielded space next the lower plate of a long condenser, are carried by an air current into the electric field where the mobility is determined by a blast method. At first curves similar to Nolan's were obtained, but the irregularities interpreted as due to different groups of ions were removed when precautions were taken to insure a uniform blast of air. Then it was discovered by the author that in spite of a lead shield between the emanation tubes emitting the ionizing rays and the measuring chamber, there was, contrary to Nolan's assumption, a volume ionization in that chamber, due probably to secondary x-rays from the lead, which accounted for his results. When these secondary rays were eliminated by substituting polonium as the source of ionization the mobility came out normal.