174 



Prof. J. C. Bose. On the Similarities [Apr. 18, 



a tendency towards reversal had already taken place after an exposure 

 of about 9 seconds. In the third, response is feebler still. In the fourth, 

 during illumination, the normal response is extremely weak, and lasts 

 for only 3 seconds ; there is then a reversal in the response which is 

 fairly strong. On the stoppage of light the effect continues for some 

 time. Hitherto the recovery commenced immediately on the cessation 

 of light. After the fourth, the responses are of opposite signs. They 

 also get feebler and feebler. 



It will thus be seen that both electric radiation and light pro- 

 duce similar conductivity and electromotive variations. In both, two 

 opposite effects are observed. The curves of effect in both are similar. 

 Under the action of continued radiation both exhibit a limiting 

 effect. Under too long continued action, both exhibit a tendency 

 towards or an actual reversal. 



In the next paper I shall adduce further evidence tending to show 

 that these effects are due to molecular strain. 



* On the Similarities between Eadiation and Mechanical Strains." 

 By Jagadis Chunder Bose. Communicated by Lord Eay- 

 leigh, F.B.S. Received April 18 —Bead June 20, 1901. 



I have in the previous paper described the various interesting effects 

 •due to visible and electric radiation. 



Different considerations were adduced which tended to show that 

 these effects were due to molecular strain, produced in the substance 

 by the action of radiation. The whole history of the change pro- 

 duced by radiation — both the direct and after-effects — was graphically 

 recorded in the various curves given. It was supposed that the strain 

 effect on a substance was attended with conductivity or electromo- 

 tive variation. This supposition can be further verified by observing 

 whether undoubted strain, which can be produced by mechanical 

 means, does give rise to a conductivity or electromotive variation. 



As regards the conductivity variation due to mechanical strain, it is 

 well known that in the construction of standard resistance coils the 

 effect of winding the wire on a spool is to produce a distinct variation 

 of resistance, and that this strain effect can only be removed by 

 annealing. The difference between the resistance of a substance when 

 strained and after it is annealed is sometimes very considerable. 



The effect of electric radiation is very great in changing the con- 

 ductivity of a mass of discontinuous particles. It is to be borne in 

 mind that the effect of electric radiation is only skin-deep. As the 

 .action is one of surface, the larger the surface the greater is the effect 

 produced. We see that in loose particles the effective surface acces- 



