(a) Of the allotropic transformation being attended with changes in the conductivity of the substance.
(b) Of the existence (and, if possible, the production by chemical means) of an allotropic modification analogous to the radiation product or B variety, whose reaction should be opposite to that of the substance in a normal condition (A variety).
(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.
Allotropic Modification produced by Visible Radiation.
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 amorphous 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 not known is not because such effects are not more numerous, but because we are unable to detect such 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.
Variation of Conductivity produced by Allotropic Changes.
There is one method of detecting these molecular variations to which little attention has hitherto been given, but which appears to be of great interest, and promises to yield important results in investigations of this class. It is evident that changes in molecular structure must be attended with changes of physical properties, electric conductivity being one of them. Among other instances of allotropic changes attended with changes in electric conductivity may be mentioned the wide difference of conducting power between graphite and diamond. The same great differences of conductivity is seen between the crystalline and amorphous varieties of silicon, and between the "metallic"
