Elster and Geitel1 have shown that normal air contains positive and negative ions in nearly equal quantities and that these ions are free to move in ordinarily pure air. In damp air their mobility is not so marked. The ionic condition of gases first investigated by W. Geise2 in 1882, has been used by Elster and Geitel as a basis of the theory explaining the origin of the electrification of the atmosphere. Zeleny3 showed that the negative ions as a rule have the greater mobility.