Page:Collected Physical Papers.djvu/194

receiver showed the usual increase of resistance with a tendency to self-recovery. In about half an hour it began to exhibit the most perfect self-recovery, and for the next 3 hours of continuous work it went on giving an extraordinary consistency of response.

The intensity of incident radiation was varied by changing the distance of the radiator. In fig. 35 are given responses to individual flashes at distances of 40 and 15 cm. It will be seen that the effects are very

Fig. 35. Transient increase of resistance in an Ag′ receiver due to single flashes of radiation. In (a) the radiator was at a distance of 40 cm.; in (b) the distance was reduced to 15 cm. Thick lines represent the effect of radiation, thin lines represent the recovery.

consistent, the occasional variation being probably due to some of the oscillatory sparks not having been as efficient as the others.

Certain analogies with the phenomena of Phosphorescence and Thermo-luminescence.—A remarkable phenomenon will be noticed in the recovery curve. It will be seen that the complete recovery is effected after a series of minor oscillations. In other words, there seems to be an after-vibration which persists for a time in substances subjected to radiation. This is very