Page:Collected Physical Papers.djvu/271

Rh substances the conductivity distortion varies with the intensity of radiation. Under the continued action of radiation, the distortion attains a maximum, balanced by a force of restitution, and on the cessation of radiation there is an elastic self-recovery.

2. The three classes of substances, positive, negative and neutral, may be distinguished by their characteristic curves.

3. The change produced in the sensitive substance by the action of radiation is not, normally speaking, chemical.

4. The conductivity change is produced, not only by very rapid, but also by comparatively slow electric variation. Generally speaking, all the conductivity variation effects produced by electric radiation can be reproduced by comparatively slow cyclic electromotive variation.

5. These conductivity changes under cyclic E. M. variation can be continuously recorded by means of the Conductivity Recorder.

6. Electric conduction in metallic particles sensitive to electric radiation does not obey Ohm's law. The conductivity is not constant and independent of the E. M. F., but varies with it. In the positive class the characteristic curve, in which the ordinates represent the currents, and the abscissa the E. M. F., is concave to the axis of the current. The conductivity increases continuously with the increasing E. M. F. The variation of the conductivity in the lower portion of the curve is small, but increases with great rapidity in the upper portion. In the negative class of substance the characteristic curve is convex to the axis of the current.