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



In the following investigations I shall employ specially the two last 

 methods, and hope to demonstrate the fundamendal unity of effects of 

 visible and invisible radiation on matter. The subject is very exten- 

 sive, and I propose to deal with it, as briefly as is compatible with 

 clearness, in the three accompanying papers : — 



I. " On the Continuity of Effect of Light and Electric Eadiation on 

 Matter." In this paper various experiments will be described and 

 results given, which can only be explained on the supposition that the 

 observed effects are due to strain. 



II. "On the Similarities between Mechanical and Radiation 

 Strains." If the effects as described in (1.) are really due to strain,, 

 then similar results might be brought about by artificially producing 

 strain regarding which there can be no possibility of doubt, for 

 instance, strain by mechanical means. In this paper I shall show the 

 remarkable parallelism between those two classes of phenomena through- 

 out an extensive range. 



III. " On the Strain Theory of Photographic Action." Having 

 shown the strain effect due to light, I will show how some of the 

 most obscure phenomena in photography receive a simple explanation 

 on the above theory. 



Effect of Electric Eadiation. 



1, Method of Conductivity Variation. 



This method is specially well suited for studying the effect of 

 electric radiation on discontinuous particles. For the action of radia- 

 tion being one of surface, the larger the area of this the greater is the 

 result, and in loose particles the effective surface is very much 

 enlarged. In this case, again, the effective total resistance of the mass 

 of particles being due to resistances of surface contacts, any change in 

 the property of surface layers will greatly modify the total resistance. 

 In a continuous solid, on the other hand, only a comparatively thin 

 molecular layer on the surface is acted upon ; but this has little effect 

 on the conductivity of the mass in the interior, protected by the outer 

 conducting sheet. A slight conductivity variation can, however, be 

 detected if the continuous solid takes the form of an extremely thin 

 layer. I shall presently show that for the detection of molecular strain 

 in a continuous solid the electromotive variation is the more suitable. 



I have before said that in the positive class there is produced a 

 diminution, and in the negative an increase of resistance. These 

 opposite properties at first seem difficult to understand, but about 

 their reality there can be no doubt. In another paper to be shortly 

 communicated, I shall give an account of an independent inquiry in 

 which the positive, the neutral, and the negative classes of substances 

 are differentiated by their characteristic curves. In the paramagnetic 



