Page:Collected Physical Papers.djvu/191

Rh exhibited by various substances in regard to self-recovery is one merely of degree. I give below typical cases which exhibit the gradual transition from so-called non-recovery to complete self-recovery.

The galvanometer used is a dead-beat D'Arsonval of moderate sensitiveness. The receiver was appropriately fixed on a heavy base. This was supported on one or two sets of pneumatic tyres so as to protect the sensitive receiver from mechanical vibration.

Positive Type.—In fig. 33 (a) is shown the effect of radiation on Fe3O4 when cold. Only the upper portion of the curve is given; the flash of radiation produced a deflection of the galvanometer of sixty-four divisions.

It will be observed that it had recovered to the extent of three divisions in the course of 60 seconds; if the rate