168 



Prof. J. C. Bose. On the Continuity of [Apr. 18, 



will also be found characteristic of other receivers responding to the 

 stimulus of light or of mechanical vibration. 

















r 













































































75" 







Time of exposure. 



Fig-. 7. — Tendency towards reversal under the continued action of radiation on 

 Fe 3 4 receiver. Thick line shows the immediate effect, the thin line the 

 continued effect of radiation. In other cases the reversal is complete. 



7. Physical Nature of the Change. 



From the fact that the conductivity variation above described takes 

 place in platinum and other noble metals, and the further fact that the 

 action goes on even when the substance is kept immersed in a protect- 

 ing medium such as naphtha, it would appear that the observed effect 

 is primarily due to physical strain. By chemical action we generally 

 understand an irreversible operation. But in the cases of complete 

 self -recovery exhibited by various substances, we have an automatic 

 return to the original condition. It should, however, be borne in mind 

 that, as a result of the strain, the chemical activity of the substance 

 may be changed, and if the strained substance happen to be immersed 

 in a medium for which under strain it has a relatively stronger attrac- 

 tion, there may then be a chemical action. But this would be merely 

 a, secondary effect. 



8. Electromotive Variation produced by Electric Radiation. 



I said that if radiation causes molecular strain, there might be pro- 

 duced a difference of potential between the acted and unacted portions 

 of a substance. A voltaic cell could be made with two plates of 

 similar substance; there would then be no P.D. between the two. 

 But on exposing one to the effect of radiation, a difference of potential 

 may be established between the acted and unacted plates. The 

 differential effect, if it exists, could then be detected by a galvanometer 



