Page:On the Continuity of Effect of Light and Electric Radiation on Matter.djvu/3

156 In the following investigations I shall employ specially the two last methods, and hope to demonstrate the fundamendalfundamental [sic] unity of effects of visible and invisible radiation on matter. The subject is very extensive, 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 Radiation 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 throughout 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.

1. Method of Conudctivity Variation. This method is specially well suited for studying the effect of electric radiation on discontinuous particles. For the action of radiation 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