the emanation.
In further experiments, Curie and Debierne13 found that many substances were phosphorescent under the action of the emanation and the excited activity produced by it. In their experiments, two glass bulbs A and B (Fig. 54) were connected with a glass tube. The active material was placed in the bulb A and the substance to be examined in the other.
They found that, in general, substances that were phosphorescent in ordinary light became luminous. The sulphide of zinc was especially brilliant and became as luminous as if exposed to a strong light. After sufficient time had elapsed the luminosity reached a constant value. The phosphorescence is partly due to the excited activity produced by the emanation on its surface, and partly to the direct radiation from the emanation.
Phosphorescence was also produced in glass. Thuringian glass showed the most marked effects. The luminosity of the glass was found to be about the same in the two bulbs, but was more marked in the connecting tube. The effect in the two bulbs was the same even if connected by a very narrow tube.
Some experiments were also made with a series of phosphorescent plates placed in the vessel at varying distances apart. With the plates 1 mm. apart the effect was very feeble, but increased directly as the distance and was large for a distance of 3 cms.
These effects receive a general explanation on the