The many lined visible spectrum from the striae in the positive column of a discharge through hydrogen must arise from electronic transitions between excited states having energy levels differing by only about 3 volts for the violet lines. The assumption made by others that the light arises from transitions to the ground level from the lowest excited state of 11.5 volts cannot hold because such transitions would give light in the extreme ultra-violet region only. It is necessary to produce excited states at least 3 volts above the lowest excited level. This requires an energy not far below the ionization potential of 16.1 volts. A process is described by which both excitation of molecules to the required levels and ionization might occur at equal intervals throughout the positive column, but a difficulty arises in the fact that the voltage drop between striae under certain conditions is found to be several volts below the ionization potential. It is assumed that the electrons acquire enough energy for ionization in these cases from collisions of the second kind with molecules of some impurity which are in excited states of comparatively low energy levels. Reasons are given for believing that the impurities involved come from the walls of the discharge tube, and that the walls play a very important role otherwise, as well.

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