Page:Collected Physical Papers.djvu/161

Rh (c) Of the assumption that after the maximum transformation of A into B, the further action of radiation is to reconvert, to a more or less extent, the form B into A, such transformations giving rise to electric reversals.

(d) Of the existence of the radiation product in a fatigued specimen.

The above mentioned hypotheses will obtain still stronger support if further deductions from the above theory are borne out by confirmatory experiments.

I will now describe investigations on the lines sketched above.

As regards the action of radiation in producing allotropic modification, several such instances are known in the case of visible radiation. In the familiar example, of the conversion of yellow phosphorus into the red variety, the effect is quite apparent. But this is not the case in the transformation of the soluble sulphur into an insoluble variety by the action of light; here the transformation is not apparent, and has to be indirectly inferred from the insolubility of the solarised product in carbon bisulphide. The reason why a far larger number of instances of allotropic transformation produced by light is unknown, is not because such effects are not more numerous, but because we are unable to detect such minute changes. It must be admitted that our knowledge of molecular changes, specially in a solid, and the means of their detection, is at present extremely limited.