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.
Experiments also on differently-coloured lights. Summary of results. The photo-electrically active metals arrange themselves in the following order—Pure K, alloys of K and Na, pure Na. Amalgams of Rb, K, Na, Li, Mg (Tl, Zn); the same as their voltaic order. With the most sensitive term of the series a candle six metres off can be detected, and the region of spectral red is not inactive. The later terms of the series demand smaller waves, and even for potassium blue light gives a much greater effect than red. No discharge of positive electricity is observable with these substances.
Wied. Ann. 44, p. 722.—On the Dissipation of Electric Charge
from Mineral Surfaces by Sunlight.
Hitherto only Balmain’s paint powder has been observed to be active among non-metallic substances. Now they try other phosphorescent bodies, and arrive at the following results:—
Fluorspar is conspicuously photo-electric, both in sunlight and daylight, especially the variety of fluorite called stinkfluss.
Freshly-broken surfaces discharge much more rapidly than old surfaces.
Blue waves, and not alone the ultra-violet, have a perceptible effect on fluorspar.
In a vacuum the mineral loses its photo-electric sensibility and its conductivity too. Contact with damp air restores its sensibility. Moistening with water weakens but does not destroy the sensitiveness. On the other hand, igniting the mineral destroys both its photo-electric power and its exceptional phosphorescent property.