Wiedemann's Annalen der Physik nnd Cheniie, No. 9.—Effect of light on spark discharges, by E. Warburg. This effect is not a direct action, but is the consequence of the shortening of a process preceding the spark discharge, and this shortening is brought about by illumination. The author studied the shortening by applying the difference of potential more or less rapidly, and finding the lowest difference of potential capable of producing discharge within five minutes, this being the greatest delay observed. The discharge potential thus found he calls the statical discharge potential, to distinguish it from the dynamic discharge potential producing sparks when the current surges to and fro. The experiments made by the author show that the statical discharge potential is not materially influenced by illumination.