The reappearance of the residual charge is promoted by tapping the glass.
Analogous changes are observed in the residual magnetization which remains after the wire has been subjected to fields of different strength.
Both observers noticed analogous effects in the residual magnetization.
Was whether the mechanical impulsion was a direct effect of the light, or whether the radiation only set up internal stresses, acting in and through the residual air, between the vanes and the walls of the enclosure.
If the light exerted direct impulsion on the vanes, their motion would gradually drag the case round after them, by reason of the friction of the residual air in the bulb and of the pivot.