[38] Corresponding to the activity of this gas as found by Wiedemann and Ebert (_Wied. Ann._, XXXIII., p. 258), in their researches on the influence of light on ease of sparking. [Illustration: FIG. 61. _Explanation of Fig. 61._--P is the plate of amalgamated zinc, and R is the earth ring, as before. Ultra-violet light is introduced through a quartz window Q from a spark gap _r_. The vessel has a joint at the middle, so that the sensitive plate can be got at and changed. Magnet poles are applied outside this vessel in various positions.] The authors then discuss the meaning of the result, and its bearing on the opposition hypotheses of Lenard and Wolf and of Righi. Lenard and Wolf’s view is that the loss of negative electricity is due to dust disintegrated from the surface by the action of light, but whose existence they consider is established by an observed effect on steam jets. Righi, on the other hand, believes that gas molecules themselves act the part of electric carriers. Elster and Geitel consider that the magnetic effect observed by them supports this latter view, it being known that a magnet acts on currents through gases; and they surmise that the impact of light vibrations may directly assist electric interchange between a gas molecule and the surface, by setting up in them syntonic stationary vibrations, something like resonant Leyden jars. It is to be remembered that phosphorescent substances, such as Balmain’s paint powder, exhibit marked photo-electric effect in daylight. [Illustration: FIG. 62. _Explanation of Fig. 62._--A simpler arrangement, like the one above (Fig. 61), whereby clean liquid alkali metals can be introduced into the experimental chamber B, from the preliminary chamber A, through a cleansing funnel, F, which dips its beak into the interior.] The unilateral character of the electric motion, and the charging of neutral surfaces by light, require special hypotheses, concerning an E.M.F. at the boundary of gases and conductors, such as Schuster and Lehmann have made. _Weid. Ann. 42, p. 564.--Note on a New Form of Apparatus for Demonstrating the Photo-electric Discharging Action of Daylight._ A vacuum tube suitable for experiments with sodium-amalgam or pure sodium, or the liquid sodium-potassium alloy, is described, with the aid of which a current (shown by the charge of an electroscope) can be maintained by a dry pile through the rarefied gas above the metal when it is illuminated from ordinary windows. _Wied. Ann. 43, p. 225.--On the Dependence of the Discharging Action of Light on the Nature of the Illuminated Surface._